[bolger] Re: mj knockdowns/hydrogen jukebox
Yes Chris, excellent idea. Hydrogen is cheap and readily accessible
to anyone. We could put the floatation tanks right next to the propane
tank and the barbeque grill. then relax and enjoy our cigars.
hmmm? maybe we could just use propane tanks! but we would have to
anchor offshore in the quarantine area.
chris crandall <crandal-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3622
to anyone. We could put the floatation tanks right next to the propane
tank and the barbeque grill. then relax and enjoy our cigars.
hmmm? maybe we could just use propane tanks! but we would have to
anchor offshore in the quarantine area.
chris crandall <crandal-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3622
>[snip]
> I agree. We use hydrogen. Cheaper, and a lot more exciting than the
> pantywaist voice you get from inhaling it.
>
On Sat, 11 Mar 2000, David Jost wrote:
pantywaist voice you get from inhaling it.
> Helium is expensive. We just had a birthday party with helium balloonsI agree. We use hydrogen. Cheaper, and a lot more exciting than the
> that nearly broke the bank.
pantywaist voice you get from inhaling it.
Helium is expensive. We just had a birthday party with helium balloons
that nearly broke the bank.
"clyde s. wisner" <clydewi-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3584
that nearly broke the bank.
"clyde s. wisner" <clydewi-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3584
> What about boyancy? 400 lbs of helium is a lot more boyant than 400lbs of
> cookies in air. It doesn't take much boyancy to float 400 lbs ofwater in
> water but it does take some to float sand. I thought this was part ofthe
> charm of water boyancy, when part of it goes under in healing of theboat,
> that part is almost neutral. Clydemass.
>
> Chris Crandall wrote:
>
> > On Wed, 8 Mar 2000, GHC wrote:
> > > Not again...there's nothing wrong with sand - mass is mass is
> > > 400 pounds of water, 400 pounds of sand, 400 pounds of cookies.shift,
> >
> > So good to see this. I posted the "rose poem" corruption on the
> > boatdesign list, and got little or no support.
> >
> > But this is very true. If the sand bags were fixed and did not
> > then they would be *better* than water, for their presumed lowercenter of
> > gravity. But they'd be PITAs in their own right, for other reasons.66045
> >
> > Chris Crandallcrandall@...(785) 864-4131
> > Department of Psychology University of Kansas Lawrence, KS
> > I have data convincingly disconfirming the Duhem-Quine hypothesis.
> >
Hi Gregg - as usual you're perfectly right...
ghc <ghart-@...> wrote:
beautiful sailing wind. Well, 25 kts is force 6 Beaufort (gale is force
8), and a normail sailboat is supposed to put two reefs in the main. If
I remember well, before being annihilated by the aliens, Luna Rossa
raced in similar conditions against America One (oh, memories), and it
was a lively race!
Best, Pippo
ghc <ghart-@...> wrote:
> On the general topic of stability, there's a price to pay to get 10"draft
> in a 20' vessel. While you get a high initial stability due to thehard
> corners (square), you also get a short range of positive stability(i.e. in
> degrees from vertical).Exact! I wrote just about that a few days ago. Trade offs!
> And, 25 knots? That's one heck of a LOT of wind.Right again! A gung-ho sailor in the list wrote that 25 knots are a
beautiful sailing wind. Well, 25 kts is force 6 Beaufort (gale is force
8), and a normail sailboat is supposed to put two reefs in the main. If
I remember well, before being annihilated by the aliens, Luna Rossa
raced in similar conditions against America One (oh, memories), and it
was a lively race!
Best, Pippo
No, it isn't.
Archimedes discovered 2200 years ago that a body immersed in a fluid is
bouyed by the WEIGHT OF THE FLUID DISPLACED - only that and nothing. That's
why boats and balloons float and monkey wrenches feel light underwater
(they are).
Once you know the volume of the fluid you displace, subtract the weight of
your machine.
So, take a light bulb underwater and measure the bouyancy. Then, break the
bulb's vacuum and insert your helium - the light bulb is heavier, less
bouyant! The laws of physics hold up - only ideas have no mass.
I can guarantee you, if balloonists could find a lighter way to hold the
envelope open than filling it up, they would.
All gases are compressable. A cup of helium can certainly weigh LOTS more
than a cup of lead (less bouyant?).
However, if you insist on exchanging the air in his sand with helium,
you'll will make the boat LESS HEAVY by an ounce (water-64 lb/ft3 air-.08
lb/ft3 helium-.01 lb/ft3 @ 0 C. & 760 mmHg).
Lastly, the water outside the boat would unlikely be aware what's inside
the boat. Water is poor ballst because it's light; the only reason you use
it is to leave it on the ramp.
- - -
On the general topic of stability, there's a price to pay to get 10" draft
in a 20' vessel. While you get a high initial stability due to the hard
corners (square), you also get a short range of positive stability (i.e. in
degrees from vertical).
These boats, especially lightly ballasted with water, are not going to
stand up with deeper vessels. This shouldn't be a surprise; drawing 6.5
feet, my sailboat is still required to have floor boards secured to race
offshore.
And, 25 knots? That's one heck of a LOT of wind.
Gregg Carlson
At 08:34 AM 3/11/2000 -0500, you wrote:
Archimedes discovered 2200 years ago that a body immersed in a fluid is
bouyed by the WEIGHT OF THE FLUID DISPLACED - only that and nothing. That's
why boats and balloons float and monkey wrenches feel light underwater
(they are).
Once you know the volume of the fluid you displace, subtract the weight of
your machine.
So, take a light bulb underwater and measure the bouyancy. Then, break the
bulb's vacuum and insert your helium - the light bulb is heavier, less
bouyant! The laws of physics hold up - only ideas have no mass.
I can guarantee you, if balloonists could find a lighter way to hold the
envelope open than filling it up, they would.
All gases are compressable. A cup of helium can certainly weigh LOTS more
than a cup of lead (less bouyant?).
However, if you insist on exchanging the air in his sand with helium,
you'll will make the boat LESS HEAVY by an ounce (water-64 lb/ft3 air-.08
lb/ft3 helium-.01 lb/ft3 @ 0 C. & 760 mmHg).
Lastly, the water outside the boat would unlikely be aware what's inside
the boat. Water is poor ballst because it's light; the only reason you use
it is to leave it on the ramp.
- - -
On the general topic of stability, there's a price to pay to get 10" draft
in a 20' vessel. While you get a high initial stability due to the hard
corners (square), you also get a short range of positive stability (i.e. in
degrees from vertical).
These boats, especially lightly ballasted with water, are not going to
stand up with deeper vessels. This shouldn't be a surprise; drawing 6.5
feet, my sailboat is still required to have floor boards secured to race
offshore.
And, 25 knots? That's one heck of a LOT of wind.
Gregg Carlson
At 08:34 AM 3/11/2000 -0500, you wrote:
> What about boyancy? 400 lbs of helium is a lot more boyant than 400 lbs
>of cookies in air. It doesn't take much boyancy to float 400 lbs of water
>in water but it does take some to float sand. I thought this was part of
>the charm of water boyancy, when part of it goes under in healing of the
>boat, that part is almost neutral. Clyde
I bow to the voice of experience, but I still think that sailing along at,
say, 30 degrees of heel is too far past the point of maximum power and too
close to the danger point.
PHV
say, 30 degrees of heel is too far past the point of maximum power and too
close to the danger point.
PHV
>I offer the observation that it is
>>very important to keep the boat upright. This is not a boat in which it
>>is good practice to lope along at a big angle of heel.
>
>Hi Peter,
>
>Here I beg to disagree. I have put my Martha Jane through many paces, sail
>combos, lying to, heaving to, sailing backwards, sailing with no rudder. I
>have capsized repeatedly (I usually back up in 30 secs, don't even get wet
>unless I chose to swim around and check things), have capsized and swamped
>once, have never allowed my ship to turtle.
Assume the water entirely fills the tanks. It may be that 400 lbs of
water has more buoyancy than 400 lbs of sand, but you also have enough
air in those tanks around the sand to make up EXACTLY (except for the
weight of the air) the difference. If the center of gravity is the
same, and the weight is the same, if it can't move, and if it's inside
the hull, it doesn't affect the stability if the ballast is helium or
uranium.
Of course if the tanks or the hull leak it's another story.
There is no magic. Think about it.
"clyde s. wisner" <clydewi-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3584
water has more buoyancy than 400 lbs of sand, but you also have enough
air in those tanks around the sand to make up EXACTLY (except for the
weight of the air) the difference. If the center of gravity is the
same, and the weight is the same, if it can't move, and if it's inside
the hull, it doesn't affect the stability if the ballast is helium or
uranium.
Of course if the tanks or the hull leak it's another story.
There is no magic. Think about it.
"clyde s. wisner" <clydewi-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3584
> What about boyancy? 400 lbs of helium is a lot more boyant than 400lbs of
> cookies in air. It doesn't take much boyancy to float 400 lbs ofwater in
> water but it does take some to float sand. I thought this was part ofthe
> charm of water boyancy, when part of it goes under in healing of theboat,
> that part is almost neutral. Clyde
>
> Chsnip
What about boyancy? 400 lbs of helium is a lot more boyant than 400 lbs
of cookies in air. It doesn't take much boyancy to float 400 lbs of water
in water but it does take some to float sand. I thought this was part of
the charm of water boyancy, when part of it goes under in healing of the
boat, that part is almost neutral. Clyde
Chris Crandall wrote:
On Wed, 8 Mar 2000, GHC wrote:
> Not again...there's nothing wrong with sand - mass is mass is mass.
> 400 pounds of water, 400 pounds of sand, 400 pounds of cookies.
So good to see this. I posted the "rose poem" corruption on the
boatdesign list, and got little or no support.
But this is very true. If the sand bags were fixed and did not
shift,
then they would be *better* than water, for their presumed lower center
of
gravity. But they'd be PITAs in their own right, for other reasons.
Chris Crandall
crandall@... (785) 864-4131
Department of Psychology University of Kansas
Lawrence, KS 66045
I have data convincingly disconfirming the Duhem-Quine hypothesis.
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As a teenager we raced and played with a Rainbow Skimmer (14' x4'
hardchine plywood scow with a small footwell that did not fill) and a
Coronado 15 (moderately responsive daysailing sloop with a self
draining cockpit and no ballast). Being teenagers, we pushed the boats
frequently to the brink of capsizing and obviously capsized often. We
even "practiced" recovery because "we might need to be able to get
under way and stay in the race." This was a small lake in southern
California -- the lake was long and narrow with many two story homes on
the shore, so we prepared (played) in gusty-wind shadow conditions.
Since we spent so much time on the brink of capsize, capsized, and
turtled, we discovered a few things. Unless you were quick enough to
throw your leg over the side of the boat as she went over so that you
could sit astride the hull and stand on the centerboard, your weight
hanging on the inside of the boat at 90 degrees would most assuredly
pull the mast underwater (both hollow aluminum), and the boat would
turn turtle, and the scow would fill its mid-section if it went more
than 90 with someone hanging on. The rule was if you didn't get on top
as she went over, you had to drop into the water and quit trying to
climb into the boat. When you are past the point of no return, the
crew weight would pull the boat turtle. I think it was Peter V. who
mentioned this in his explanation.
The Coronado 15 would sail over on its ear farther, before capsize,
than the scow (if you can call this sailing). The Rainbow Skimmer went
sooner (from less of an angle) and faster.
We knew from racing hard on the wind that in a strong gust we had to
round up into the wind. This permitted the sails to spill wind and
help gain ground to windward with boat speed. We would never drop off
downwind in a gust -- both the sloop and the scow sails would fill
more, stand the boat on its ear or capsize -- and you lose ground to
the mark. However, if you were driving hard to windward, sailing on
the brink of capsize (teenagers playing here) and then rounded up hard,
the centrifugal force of the mast and rig (lots of force out farther
from the rotation of the boat) and our weight high over the center of
buoyancy, could pull the boat over too quickly - in fact with enough
force that those on the high rail could be thrown onto the boom, now in
the water. The first time this happened to us it was quite a surprise,
the expectation was that the boat would go back flat.
Death roll ??
If all things are the same for two boats, i.e., if the sheeting angle
is the same, and if the boats orientation to the wind the same, except
that one is moving and one is still, then the boat that is moving will
feel less of a heeling force because the apparent wind is farther
forward, i.e., there is a less effective angle for a heeling effect.
With the MJ on the brink of capsize, movable ballast (crew) on the
inside of the boat or in the cockpit (not yet in the water) and the
boat rounding up (and being forced over) from a full mizzen (main is
luffing) there can be some strong dynamic forces pulling her over to
capsize and turtle - centrifugal forces of rig and crew -- and movable
ballast (crew) on the lee side. And never forget an inopportune gust
of wind.
Phil Lea
Russellville, Arkansas
hardchine plywood scow with a small footwell that did not fill) and a
Coronado 15 (moderately responsive daysailing sloop with a self
draining cockpit and no ballast). Being teenagers, we pushed the boats
frequently to the brink of capsizing and obviously capsized often. We
even "practiced" recovery because "we might need to be able to get
under way and stay in the race." This was a small lake in southern
California -- the lake was long and narrow with many two story homes on
the shore, so we prepared (played) in gusty-wind shadow conditions.
Since we spent so much time on the brink of capsize, capsized, and
turtled, we discovered a few things. Unless you were quick enough to
throw your leg over the side of the boat as she went over so that you
could sit astride the hull and stand on the centerboard, your weight
hanging on the inside of the boat at 90 degrees would most assuredly
pull the mast underwater (both hollow aluminum), and the boat would
turn turtle, and the scow would fill its mid-section if it went more
than 90 with someone hanging on. The rule was if you didn't get on top
as she went over, you had to drop into the water and quit trying to
climb into the boat. When you are past the point of no return, the
crew weight would pull the boat turtle. I think it was Peter V. who
mentioned this in his explanation.
The Coronado 15 would sail over on its ear farther, before capsize,
than the scow (if you can call this sailing). The Rainbow Skimmer went
sooner (from less of an angle) and faster.
We knew from racing hard on the wind that in a strong gust we had to
round up into the wind. This permitted the sails to spill wind and
help gain ground to windward with boat speed. We would never drop off
downwind in a gust -- both the sloop and the scow sails would fill
more, stand the boat on its ear or capsize -- and you lose ground to
the mark. However, if you were driving hard to windward, sailing on
the brink of capsize (teenagers playing here) and then rounded up hard,
the centrifugal force of the mast and rig (lots of force out farther
from the rotation of the boat) and our weight high over the center of
buoyancy, could pull the boat over too quickly - in fact with enough
force that those on the high rail could be thrown onto the boom, now in
the water. The first time this happened to us it was quite a surprise,
the expectation was that the boat would go back flat.
Death roll ??
If all things are the same for two boats, i.e., if the sheeting angle
is the same, and if the boats orientation to the wind the same, except
that one is moving and one is still, then the boat that is moving will
feel less of a heeling force because the apparent wind is farther
forward, i.e., there is a less effective angle for a heeling effect.
With the MJ on the brink of capsize, movable ballast (crew) on the
inside of the boat or in the cockpit (not yet in the water) and the
boat rounding up (and being forced over) from a full mizzen (main is
luffing) there can be some strong dynamic forces pulling her over to
capsize and turtle - centrifugal forces of rig and crew -- and movable
ballast (crew) on the lee side. And never forget an inopportune gust
of wind.
Phil Lea
Russellville, Arkansas
I offer the observation that it is
Here I beg to disagree. I have put my Martha Jane through many paces, sail
combos, lying to, heaving to, sailing backwards, sailing with no rudder. I
have capsized repeatedly (I usually back up in 30 secs, don't even get wet
unless I chose to swim around and check things), have capsized and swamped
once, have never allowed my ship to turtle.
Downwind, no problem. Sail her flat. Upwind, this boat wants to lie right on
15%, max 30%. Beyond that she softens and is no good. Might capsize even.
She talks to me and she has told me this. I can feel the surge and the power
and the parting of the sea on that beautiful chine. I am taking some small
steps to stiffen my Martha a little, but she is built regulation Bolger.
If one more word can be said... Re sand ballast. Steve, once your hull is
down flat, if the mast begin to sink, then the boat is now more than 90, she
is 91 plus & the shortest distance to gravity on that up-tank is to roll
further. Ideally, if the water were over 20' deep, she would do a 360, that
is, 269o back to swamped upright.
At least if you had enough sand in her. PCB says a lot of waterballast boats
go 180 and hang there.
As for the big lead keel cruiser that blew flat, the answer is simply
momentum.
ED HAILE
Martha Jane "Terrapin"
>very important to keep the boat upright. This is not a boat in which itHi Peter,
>is good practice to lope along at a big angle of heel.
Here I beg to disagree. I have put my Martha Jane through many paces, sail
combos, lying to, heaving to, sailing backwards, sailing with no rudder. I
have capsized repeatedly (I usually back up in 30 secs, don't even get wet
unless I chose to swim around and check things), have capsized and swamped
once, have never allowed my ship to turtle.
Downwind, no problem. Sail her flat. Upwind, this boat wants to lie right on
15%, max 30%. Beyond that she softens and is no good. Might capsize even.
She talks to me and she has told me this. I can feel the surge and the power
and the parting of the sea on that beautiful chine. I am taking some small
steps to stiffen my Martha a little, but she is built regulation Bolger.
If one more word can be said... Re sand ballast. Steve, once your hull is
down flat, if the mast begin to sink, then the boat is now more than 90, she
is 91 plus & the shortest distance to gravity on that up-tank is to roll
further. Ideally, if the water were over 20' deep, she would do a 360, that
is, 269o back to swamped upright.
At least if you had enough sand in her. PCB says a lot of waterballast boats
go 180 and hang there.
As for the big lead keel cruiser that blew flat, the answer is simply
momentum.
ED HAILE
Martha Jane "Terrapin"
>______________________________________________________
>First, the evidence given suggests that if you get to the point where
>water comes over the rail, you are at grave risk for capsize. Any
>shallow boat with internal ballast (of any material) will have a fairly
>early 'point of no return.' MJ is no exception.
>
>Second, the boat will have the most stability at a low angle of heel.
>She will sail best if you can keep her upright.
>
>Third, there is great danger of tripping the boom. The boom at 16 feet
>is far longer than the (2 x beam) recommended as a maximum. Scaling
>some measurements from the drawings in BWAOM, I get the gooseneck at
>4.4 above lwl, and the boom extending 13.2 feet from the gooseneck. If
>the boom is perpendicular to the mast (i.e. horizontal with the boat
>upright), then when it out perpendicular to the centerline (straight
>out to the side over the water) then the boat only has to heel about 20
>degrees to get the boom end in the water.
>
>This is the scenario: The boat is proceeding on a beam reach, wind at
>about 90 degrees. A gust heels the boat. The skipper lets the sheet run
>free, but the boom end is in the water. The forward motion of the boat
>drags the boom aft, so the sail stays full. The skipper pushes the
>tiller to leeward, but the mizzen is out of commission, and the full
>sail up forward does not let the bow swing to windward. The boat heels
>to the point where the live ballast falls out of position, water comes
>over the lee rail and over she goes.
>
>Just glancing at the drawings again, a possible place for some more
>flotation would be between the leeboards and the hull, above the
>leeboard guards. (Another unexamined, crackpot idea!)
>
>Peter
>
>
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"peter vanderwaart" <pvander-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3552
program he uses for analyzing stability (I don't remember its name -
Plyboats maybe). Everything necessary to input is known about the MJ
and someone with a Pee Cee could easily run a stability curve. Amounts
of ballast may be varied.
A thought.
original article:http://www.egroups.com/group/bolger/?start=3552
> > I Made up a couple of rough sketches that can be viewed atwater
> >http://www.ultranet.com/~djost/mj.htm
> > that illustrate my point.
>
> We have another one of those tricky ballast situations here.
>
> Let's assume for the purposes of discussion that the balance point of
> the boat is at about the bottom corner in your diagrams, where the
> arrow says 'ineffective'. Then the 250 lbs of water ballast and the
> 500 lbs of lead ballast have the same righting moment because the
> is twice as far from the balance point. The lead would be slightlyJim Michalak's page has a link to the demo version of the boat CAD
> better than the water because it is lower (when the hull is at rest),
> and but the difference would be small.
program he uses for analyzing stability (I don't remember its name -
Plyboats maybe). Everything necessary to input is known about the MJ
and someone with a Pee Cee could easily run a stability curve. Amounts
of ballast may be varied.
A thought.
In a message dated 3/9/00 5:34:33 PM Eastern Standard Time,
wjochems@...writes:
<< My equation of speed with stability was such that I was most cautious
just after completing a tack into strong wind. To me the boat seemed
vulnerable until she had picked up speed on the new tack. >>
Ah yes! Bill you are right on here. We had just completed a tack somehow (
with a partially out of shape mizzen) and had little way on. In fact I was
eager to get up some speed because standing still in a martha jane in gusty
high winds is like being on a roller coaster - only from side to side. You
are absolutely on target - your peril is greatest in an mj when standing
still or close to it. Therefore the strategy is don't cleat anything -
including the mizzen unless you are moving or hove to directly in the eye of
the wind. Strong wind on the beam needs little - a mizzen is enough - to
knock her over. Steve
wjochems@...writes:
<< My equation of speed with stability was such that I was most cautious
just after completing a tack into strong wind. To me the boat seemed
vulnerable until she had picked up speed on the new tack. >>
Ah yes! Bill you are right on here. We had just completed a tack somehow (
with a partially out of shape mizzen) and had little way on. In fact I was
eager to get up some speed because standing still in a martha jane in gusty
high winds is like being on a roller coaster - only from side to side. You
are absolutely on target - your peril is greatest in an mj when standing
still or close to it. Therefore the strategy is don't cleat anything -
including the mizzen unless you are moving or hove to directly in the eye of
the wind. Strong wind on the beam needs little - a mizzen is enough - to
knock her over. Steve
Hello Guys
My feeling too is that you must never be caught "dead in the water" whatever
the circumstances as this inevitably leads to futher problems. For
instance, rounding up, if taken to far, in any sort of sea leaves one
feeling very vunerable.
In my very limited experience it is necessary to be "tuned" enough to
conditions or changes so that the boat is reefed/reduced in sail area early
OR course/helming style adjustments made. The old motto of "reef when it
first enters your mind" is very relevant. I know that the MJ in question
was already reefed so this leaves us to explore other helm tactics in
discussing solutions to the specific incident.
This has been a very "learning" thread for me and I hope we can continue to
explore these thoughts for a while yet
Regards - Foster
My feeling too is that you must never be caught "dead in the water" whatever
the circumstances as this inevitably leads to futher problems. For
instance, rounding up, if taken to far, in any sort of sea leaves one
feeling very vunerable.
In my very limited experience it is necessary to be "tuned" enough to
conditions or changes so that the boat is reefed/reduced in sail area early
OR course/helming style adjustments made. The old motto of "reef when it
first enters your mind" is very relevant. I know that the MJ in question
was already reefed so this leaves us to explore other helm tactics in
discussing solutions to the specific incident.
This has been a very "learning" thread for me and I hope we can continue to
explore these thoughts for a while yet
Regards - Foster
>Previous comments by Tim and Davis aluding to keeping the boat moving (ienot freeing the sheets - Completly?)and bearing away also refer.
>
> As for boat speed, a stopped boat is a vulnerable boat
> because you have
> no steerage way. If you get caught in irons, then you can be very
> vulnerable indeed.
>
> It does seem like the ability of a boat to move forard helps to
> dissapate a the force of a gust by translating more of it into thrust.
> Maybe this has something to due with stalled vs smooth
> airflow. I don't
> know.
>
>
I looked at these sketches, but I note that the 250 lbs of water is a
lot further away from the center of bouyancy than the 500 lbs of lead.
Of course the 500 lbs of lead is lower, which helps some. If you take
the center of gravity of the two tanks, it's almost in the same place
as the lead, except for the help the lead gets from being just a tad
lower (which helps put the lead further toward the high side when the
boat heels). So you might have a little advantage from making the cg
lower, but not a huge advantage.
"david jost" <djos-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3551
lot further away from the center of bouyancy than the 500 lbs of lead.
Of course the 500 lbs of lead is lower, which helps some. If you take
the center of gravity of the two tanks, it's almost in the same place
as the lead, except for the help the lead gets from being just a tad
lower (which helps put the lead further toward the high side when the
boat heels). So you might have a little advantage from making the cg
lower, but not a huge advantage.
"david jost" <djos-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3551
> snip
> I made up a couple of rough sketches that can be viewed at
>http://www.ultranet.com/~djost/mj.htm
> that illustrate my point.
> I am not an engineer or a physicist, but I think this might be a good
> solution. (If you can tow the weight, Lead/cookies/beer. It really
> doesn't matter.
> snip
> I Made up a couple of rough sketches that can be viewed atWe have another one of those tricky ballast situations here.
>http://www.ultranet.com/~djost/mj.htm
> that illustrate my point.
Let's assume for the purposes of discussion that the balance point of
the boat is at about the bottom corner in your diagrams, where the
arrow says 'ineffective'. Then the 250 lbs of water ballast and the
500 lbs of lead ballast have the same righting moment because the water
is twice as far from the balance point. The lead would be slightly
better than the water because it is lower (when the hull is at rest),
and but the difference would be small.
As for boat speed, a stopped boat is a vulnerable boat because you have
no steerage way. If you get caught in irons, then you can be very
vulnerable indeed.
It does seem like the ability of a boat to move forard helps to
dissapate a the force of a gust by translating more of it into thrust.
Maybe this has something to due with stalled vs smooth airflow. I don't
know.
I have long felt that there is a phenomenon that happens in a knockdown
that I don't understand and which is not generally understood. I was on
a Burmuda 40 (as big and heavy a blue water boat as you could ever hope
to sail) that was knocked flat, mast parallel to the water, by a gust
of wind in Charlotte Harbor near Punta Gorda, FL. The boat stayed
knocked down for an exciting several seconds before recovering. Waves
were not a factor.
I really don't see how this happens because, one would think, the
heeling force would diminish to zero as the boat heels, and therefore
the boat would stop heeling somewhere before 90 degrees, even in a real
blast. Besides, the gust of wind was maybe 30mph, an amount of wind the
boat could easily sail in if properly trimmed. Whatever the phenomenon
is, it has been attributed in this thread to the wind on the bottom of
the boat. But it is hard to see that as a factor with the Burmuda 40.
So, wind tunnel tests are in order, I think.
Peter
Peter's point is well taken.
With the mizzen out of commission, you essentially have a real large
jib. Most boats that I have sailed will head downwind under jib only
once you have lost steering. The live ballast becomes ineffective and
only half of your ballast is available as a counterweight. If the boat
goes completely over and swamps the boat is done for the day.
I made up a couple of rough sketches that can be viewed at
http://www.ultranet.com/~djost/mj.htm
that illustrate my point.
I am not an engineer or a physicist, but I think this might be a good
solution. (If you can tow the weight, Lead/cookies/beer. It really
doesn't matter.
hwa-@...wrote:
original article:http://www.egroups.com/group/bolger/?start=3548
With the mizzen out of commission, you essentially have a real large
jib. Most boats that I have sailed will head downwind under jib only
once you have lost steering. The live ballast becomes ineffective and
only half of your ballast is available as a counterweight. If the boat
goes completely over and swamps the boat is done for the day.
I made up a couple of rough sketches that can be viewed at
http://www.ultranet.com/~djost/mj.htm
that illustrate my point.
I am not an engineer or a physicist, but I think this might be a good
solution. (If you can tow the weight, Lead/cookies/beer. It really
doesn't matter.
hwa-@...wrote:
original article:http://www.egroups.com/group/bolger/?start=3548
> In a message dated 3/9/2000 12:39:52 PM Eastern Standard Time,20
>pvanderw@...writes:
>
> << If
> the boom is perpendicular to the mast (i.e. horizontal with the boat
> upright), then when it out perpendicular to the centerline (straight
> out to the side over the water) then the boat only has to heel about
> degrees to get the boom end in the water. >>more when
>
> Hi Peter - good analysis - The boom does rake up some - and even
> the sail is filled - I did some measuring and figuring after readingyours -
> ( with some paper cutout squares and doll rods -) I figured about 30degrees
> and the tip of the boom hits the water.hadn''t
>
> I did not see the tip of the boom touch the water. At 45 degrees it
> touched the water and was luffing ( flailing) ( after that I waswatching
> the rail) Again - it happens so fast - but I think we had also lostmost of
> our headway - I don't know exactly what a boom will do to a boat thathas
> become almost stationary - our forward motion was slow at best - Ithink the
> slower the boat is moving the easier it is to knock down - I think -but I'm
> not sure why I think that.luffing
>
> Anyway - we were well on our way down while the mainsail was still
> and clear of the water- but I could be wrong - we might not havereached the
> point of no return as early as I thought. Heck - while it was layingflat I
> thought she was going to right - and she stayed right there longenough for
> me to ask her if she was coming up again or not. Not. The windagainst her
> backside was pretty strong right about then. I have no doubt that ifthe wind
> had stopped completely at that moment she would have popped rightback onto
> her feet. I like to think so. Knock downs don't happen in calmconditions
> tho do they? Perhaps with full sail and mizzen up - it would takeless wind
> to be knocked down and the wind on the bottom would be less of afactor - It
> was a strong wind. Steve
Bolgeristas,
The Martha Jane which I sailed for two years (now owned by Ed Haile) was
definitely more stable when she was moving fast. And she seemed to react to
a gust by tending to head up-which was comforting. Phil Bolger wrote
somewhere that when a boat heels sharply to a gust, the helmsman should
resist his inclination to let the sheets go and instead should head up.
My equation of speed with stability was such that I was most cautious
just after completing a tack into strong wind. To me the boat seemed
vulnerable until she had picked up speed on the new tack.
But bear in mind that at this point I've spent more hours building boats
than sailing.
Bill Jochems
-----Original Message-----
From:Hwal@...<Hwal@...>
To:bolger@egroups.com<bolger@egroups.com>
Date: Thursday, March 09, 2000 11:24 AM
Subject: [bolger] Re: mj knockdowns alternate strategies
The Martha Jane which I sailed for two years (now owned by Ed Haile) was
definitely more stable when she was moving fast. And she seemed to react to
a gust by tending to head up-which was comforting. Phil Bolger wrote
somewhere that when a boat heels sharply to a gust, the helmsman should
resist his inclination to let the sheets go and instead should head up.
My equation of speed with stability was such that I was most cautious
just after completing a tack into strong wind. To me the boat seemed
vulnerable until she had picked up speed on the new tack.
But bear in mind that at this point I've spent more hours building boats
than sailing.
Bill Jochems
-----Original Message-----
From:Hwal@...<Hwal@...>
To:bolger@egroups.com<bolger@egroups.com>
Date: Thursday, March 09, 2000 11:24 AM
Subject: [bolger] Re: mj knockdowns alternate strategies
>In a message dated 3/9/2000 12:39:52 PM Eastern Standard Time,yours -
>pvanderw@...writes:
>
><< If
> the boom is perpendicular to the mast (i.e. horizontal with the boat
> upright), then when it out perpendicular to the centerline (straight
> out to the side over the water) then the boat only has to heel about 20
> degrees to get the boom end in the water. >>
>
>Hi Peter - good analysis - The boom does rake up some - and even more when
>the sail is filled - I did some measuring and figuring after reading
>( with some paper cutout squares and doll rods -) I figured about 30degrees
>and the tip of the boom hits the water.hadn''t
>
>I did not see the tip of the boom touch the water. At 45 degrees it
>touched the water and was luffing ( flailing) ( after that I was watchingthe
>the rail) Again - it happens so fast - but I think we had also lost most of
>our headway - I don't know exactly what a boom will do to a boat that has
>become almost stationary - our forward motion was slow at best - I think
>slower the boat is moving the easier it is to knock down - I think - butI'm
>not sure why I think that.the
>
>Anyway - we were well on our way down while the mainsail was still luffing
>and clear of the water- but I could be wrong - we might not have reached
>point of no return as early as I thought. Heck - while it was laying flat Iwind
>thought she was going to right - and she stayed right there long enough for
>me to ask her if she was coming up again or not. Not. The wind against her
>backside was pretty strong right about then. I have no doubt that if the
>had stopped completely at that moment she would have popped right back ontowind
>her feet. I like to think so. Knock downs don't happen in calm conditions
>tho do they? Perhaps with full sail and mizzen up - it would take less
>to be knocked down and the wind on the bottom would be less of a factor -It
>was a strong wind. Steve
>
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In a message dated 3/9/2000 12:39:52 PM Eastern Standard Time,
pvanderw@...writes:
<< If
the boom is perpendicular to the mast (i.e. horizontal with the boat
upright), then when it out perpendicular to the centerline (straight
out to the side over the water) then the boat only has to heel about 20
degrees to get the boom end in the water. >>
Hi Peter - good analysis - The boom does rake up some - and even more when
the sail is filled - I did some measuring and figuring after reading yours -
( with some paper cutout squares and doll rods -) I figured about 30 degrees
and the tip of the boom hits the water.
I did not see the tip of the boom touch the water. At 45 degrees it hadn''t
touched the water and was luffing ( flailing) ( after that I was watching
the rail) Again - it happens so fast - but I think we had also lost most of
our headway - I don't know exactly what a boom will do to a boat that has
become almost stationary - our forward motion was slow at best - I think the
slower the boat is moving the easier it is to knock down - I think - but I'm
not sure why I think that.
Anyway - we were well on our way down while the mainsail was still luffing
and clear of the water- but I could be wrong - we might not have reached the
point of no return as early as I thought. Heck - while it was laying flat I
thought she was going to right - and she stayed right there long enough for
me to ask her if she was coming up again or not. Not. The wind against her
backside was pretty strong right about then. I have no doubt that if the wind
had stopped completely at that moment she would have popped right back onto
her feet. I like to think so. Knock downs don't happen in calm conditions
tho do they? Perhaps with full sail and mizzen up - it would take less wind
to be knocked down and the wind on the bottom would be less of a factor - It
was a strong wind. Steve
pvanderw@...writes:
<< If
the boom is perpendicular to the mast (i.e. horizontal with the boat
upright), then when it out perpendicular to the centerline (straight
out to the side over the water) then the boat only has to heel about 20
degrees to get the boom end in the water. >>
Hi Peter - good analysis - The boom does rake up some - and even more when
the sail is filled - I did some measuring and figuring after reading yours -
( with some paper cutout squares and doll rods -) I figured about 30 degrees
and the tip of the boom hits the water.
I did not see the tip of the boom touch the water. At 45 degrees it hadn''t
touched the water and was luffing ( flailing) ( after that I was watching
the rail) Again - it happens so fast - but I think we had also lost most of
our headway - I don't know exactly what a boom will do to a boat that has
become almost stationary - our forward motion was slow at best - I think the
slower the boat is moving the easier it is to knock down - I think - but I'm
not sure why I think that.
Anyway - we were well on our way down while the mainsail was still luffing
and clear of the water- but I could be wrong - we might not have reached the
point of no return as early as I thought. Heck - while it was laying flat I
thought she was going to right - and she stayed right there long enough for
me to ask her if she was coming up again or not. Not. The wind against her
backside was pretty strong right about then. I have no doubt that if the wind
had stopped completely at that moment she would have popped right back onto
her feet. I like to think so. Knock downs don't happen in calm conditions
tho do they? Perhaps with full sail and mizzen up - it would take less wind
to be knocked down and the wind on the bottom would be less of a factor - It
was a strong wind. Steve
Y'all feel free to check my caculations on this.
One area of discussion about the MJ knockdown problem that can stand
further elaboration is question of seamanship and the best way to
handle the boat in breezy weather. I offer the observation that it is
very important to keep the boat upright. This is not a boat in which it
is good practice to lope along at a big angle of heel.
First, the evidence given suggests that if you get to the point where
water comes over the rail, you are at grave risk for capsize. Any
shallow boat with internal ballast (of any material) will have a fairly
early 'point of no return.' MJ is no exception.
Second, the boat will have the most stability at a low angle of heel.
She will sail best if you can keep her upright.
Third, there is great danger of tripping the boom. The boom at 16 feet
is far longer than the (2 x beam) recommended as a maximum. Scaling
some measurements from the drawings in BWAOM, I get the gooseneck at
4.4 above lwl, and the boom extending 13.2 feet from the gooseneck. If
the boom is perpendicular to the mast (i.e. horizontal with the boat
upright), then when it out perpendicular to the centerline (straight
out to the side over the water) then the boat only has to heel about 20
degrees to get the boom end in the water.
This is the scenario: The boat is proceeding on a beam reach, wind at
about 90 degrees. A gust heels the boat. The skipper lets the sheet run
free, but the boom end is in the water. The forward motion of the boat
drags the boom aft, so the sail stays full. The skipper pushes the
tiller to leeward, but the mizzen is out of commission, and the full
sail up forward does not let the bow swing to windward. The boat heels
to the point where the live ballast falls out of position, water comes
over the lee rail and over she goes.
Just glancing at the drawings again, a possible place for some more
flotation would be between the leeboards and the hull, above the
leeboard guards. (Another unexamined, crackpot idea!)
Peter
One area of discussion about the MJ knockdown problem that can stand
further elaboration is question of seamanship and the best way to
handle the boat in breezy weather. I offer the observation that it is
very important to keep the boat upright. This is not a boat in which it
is good practice to lope along at a big angle of heel.
First, the evidence given suggests that if you get to the point where
water comes over the rail, you are at grave risk for capsize. Any
shallow boat with internal ballast (of any material) will have a fairly
early 'point of no return.' MJ is no exception.
Second, the boat will have the most stability at a low angle of heel.
She will sail best if you can keep her upright.
Third, there is great danger of tripping the boom. The boom at 16 feet
is far longer than the (2 x beam) recommended as a maximum. Scaling
some measurements from the drawings in BWAOM, I get the gooseneck at
4.4 above lwl, and the boom extending 13.2 feet from the gooseneck. If
the boom is perpendicular to the mast (i.e. horizontal with the boat
upright), then when it out perpendicular to the centerline (straight
out to the side over the water) then the boat only has to heel about 20
degrees to get the boom end in the water.
This is the scenario: The boat is proceeding on a beam reach, wind at
about 90 degrees. A gust heels the boat. The skipper lets the sheet run
free, but the boom end is in the water. The forward motion of the boat
drags the boom aft, so the sail stays full. The skipper pushes the
tiller to leeward, but the mizzen is out of commission, and the full
sail up forward does not let the bow swing to windward. The boat heels
to the point where the live ballast falls out of position, water comes
over the lee rail and over she goes.
Just glancing at the drawings again, a possible place for some more
flotation would be between the leeboards and the hull, above the
leeboard guards. (Another unexamined, crackpot idea!)
Peter
I forgot that I needed to convert the pict files to jpeg or gifs for PC
users. I will try again in a couple of days. I am kind of busy at
work this week to go any further with this for now.
hwa-@...wrote:
original article:http://www.egroups.com/group/bolger/?start=3542
users. I will try again in a couple of days. I am kind of busy at
work this week to go any further with this for now.
hwa-@...wrote:
original article:http://www.egroups.com/group/bolger/?start=3542
> In a message dated 3/8/2000 9:55:33 PM Eastern Standard Time,missing
>djost@...writes:
>
> << I placed a small diagram of the keel idea/ drawing in the vault.
> see Marthjane.htm document in the vault. >>
> I checked again this AM and don't find this in the vault. Am I
> something? Steve
I have an idea that would produce interesting results, but it would be
work to carry out.
Would you be willing to set up the boat in a slip in such a way as to
fasten the bow from straigt ahead, and the stern from straight behind.
Then from the side, pull the mast until the boat heels 45 degrees and
then 90 degrees in order to measure the amount of weight is pulling
against you at the tip of the mast?
MacGregor does this in his video for the 26X - on that boat, it takes
200 lbs of pressuure to hold the boat over at close to 90 degrees.
Just a suggestion that seems to be in context.
Mike
hwa-@...wrote:
original article:http://www.egroups.com/group/bolger/?start=3542
work to carry out.
Would you be willing to set up the boat in a slip in such a way as to
fasten the bow from straigt ahead, and the stern from straight behind.
Then from the side, pull the mast until the boat heels 45 degrees and
then 90 degrees in order to measure the amount of weight is pulling
against you at the tip of the mast?
MacGregor does this in his video for the 26X - on that boat, it takes
200 lbs of pressuure to hold the boat over at close to 90 degrees.
Just a suggestion that seems to be in context.
Mike
hwa-@...wrote:
original article:http://www.egroups.com/group/bolger/?start=3542
> In a message dated 3/8/2000 9:55:33 PM Eastern Standard Time,missing
>djost@...writes:
>
> << I placed a small diagram of the keel idea/ drawing in the vault.
> see Marthjane.htm document in the vault. >>
> I checked again this AM and don't find this in the vault. Am I
> something? Steve
In a message dated 3/8/2000 9:55:33 PM Eastern Standard Time,
djost@...writes:
<< I placed a small diagram of the keel idea/ drawing in the vault.
see Marthjane.htm document in the vault. >>
I checked again this AM and don't find this in the vault. Am I missing
something? Steve
djost@...writes:
<< I placed a small diagram of the keel idea/ drawing in the vault.
see Marthjane.htm document in the vault. >>
I checked again this AM and don't find this in the vault. Am I missing
something? Steve
> In a message dated 3/8/2000 6:19:40 PM Eastern Standard Time,Lets see... if I tied it in the rafters of the pilot house and my boat
>ghartc@...writes:
>
> << Ahuh, if you inflated an inner tube and carried it on board, would
> the boat
> would float higher...;-} >>
turned turtle on its startled little head... then maybe....?
djb
> --SOME CLICKS THAT COUNT!!
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Here's my latest boat:
http://members.tripod.com/simplicityboats/featherwind.html
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Quasi esoteric musical instruments
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In a message dated 3/8/2000 9:55:33 PM Eastern Standard Time,
djost@...writes:
Hi David - I just checked the vault and didn't see it listed there - maybe it
has some turn around time?? Steve
djost@...writes:
Hi David - I just checked the vault and didn't see it listed there - maybe it
has some turn around time?? Steve
In a message dated 3/8/2000 8:05:36 PM Eastern Standard Time,
djost@...writes:
<< It is
certainly easy enough to cast and install. It is just not removable,
and makes trailering a wee bit more difficult. >>
So David - this ( a lead shoe keel) doesn't sound easy to cast and install -
it sounds like you have experience here - ? How do you do this? Steve
djost@...writes:
<< It is
certainly easy enough to cast and install. It is just not removable,
and makes trailering a wee bit more difficult. >>
So David - this ( a lead shoe keel) doesn't sound easy to cast and install -
it sounds like you have experience here - ? How do you do this? Steve
In a message dated 3/8/2000 8:05:36 PM Eastern Standard Time,
djost@...writes:
<< I get your point about the cookies, roses, etc... no one mentioned
beer. >>
I would be afraid to use beer - if the other members of our sailing club
caught wind of it my boat would be full of holes and there they'd be along
side with straws.
Sorry - I do take this seriously but I have gotten extremely punchy.
Steve
djost@...writes:
<< I get your point about the cookies, roses, etc... no one mentioned
beer. >>
I would be afraid to use beer - if the other members of our sailing club
caught wind of it my boat would be full of holes and there they'd be along
side with straws.
Sorry - I do take this seriously but I have gotten extremely punchy.
Steve
In a message dated 3/8/2000 6:19:40 PM Eastern Standard Time,
ghartc@...writes:
<< Ahuh, if you inflated an inner tube and carried it on board, would the boat
would float higher...;-} >>
It would depend on if it was on the leeside or the high side - above or below
the waterline.
I guess I can be the one to make light - since it was my boat that sank.
Steve
ghartc@...writes:
<< Ahuh, if you inflated an inner tube and carried it on board, would the boat
would float higher...;-} >>
It would depend on if it was on the leeside or the high side - above or below
the waterline.
I guess I can be the one to make light - since it was my boat that sank.
Steve
In a message dated 3/8/2000 6:11:34 PM Eastern Standard Time,
mmccracken@...writes:
<< Wouldn't the air around the sand/sand bags add bouyancy, thus reducing the
effective weight of the ballast?
so tightly that they squeeze together and you can actually squeeze all of the
air out of them and your resulting ballast is extremely dense. Dense is good
- in ballast. Steve
mmccracken@...writes:
<< Wouldn't the air around the sand/sand bags add bouyancy, thus reducing the
effective weight of the ballast?
>>Actually this is the real benefit of using rose pedals - you can stack them
so tightly that they squeeze together and you can actually squeeze all of the
air out of them and your resulting ballast is extremely dense. Dense is good
- in ballast. Steve
Ahuh, if you inflated an inner tube and carried it on board, would the boat
would float higher...;-}
Gregg Carlson
At 01:49 PM 3/8/2000 -0800, you wrote:
would float higher...;-}
Gregg Carlson
At 01:49 PM 3/8/2000 -0800, you wrote:
>Wouldn't the air around the sand/sand bags add bouyancy, thus reducing the
>effective weight of the ballast?
>
>GHC wrote:
>
>> Not again...there's nothing wrong with sand - mass is mass is mass. 400
>> pounds of water, 400 pounds of sand, 400 pounds of cookies.
>>
>> Water is 64 lbs/ft3, while sand is 90-100 lbs/ft3. So, you'll even get a
>> very slightly lower c.g. with the sand (until it moves).
>>
>> Gregg Carlson
>>
>> At 05:35 AM 3/8/2000 -0800, you wrote:
>> > I must be missing something here. Martha Jane was designed for
>> >water ballast. Sand in place of water ballast doesn't appear to be the
>> >solution. The sand on the leeward side becomes a liability in this
>> >situation by making the leeward side of the boat sink lower in the
>> >water than the designers plan. If water comes in through the hatch or
>> >ventilator, you are 'sunk". The leeward sand in effect counteracts the
>> >sand on the windward side which when heeled and also drives the hull
>> >further down. I am assuming that this design has a starboard and port
>> >tank. Water ballast is negated somewhat on the leeward side when
>> >heeling, and the windward side ballast will be effective through about
>> >70 degrees of knockdown.
>>
>> ------------------------------------------------------------------------
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>
Wouldn't the air around the sand/sand bags add bouyancy, thus reducing the
effective weight of the ballast?
GHC wrote:
effective weight of the ballast?
GHC wrote:
> Not again...there's nothing wrong with sand - mass is mass is mass. 400
> pounds of water, 400 pounds of sand, 400 pounds of cookies.
>
> Water is 64 lbs/ft3, while sand is 90-100 lbs/ft3. So, you'll even get a
> very slightly lower c.g. with the sand (until it moves).
>
> Gregg Carlson
>
> At 05:35 AM 3/8/2000 -0800, you wrote:
> > I must be missing something here. Martha Jane was designed for
> >water ballast. Sand in place of water ballast doesn't appear to be the
> >solution. The sand on the leeward side becomes a liability in this
> >situation by making the leeward side of the boat sink lower in the
> >water than the designers plan. If water comes in through the hatch or
> >ventilator, you are 'sunk". The leeward sand in effect counteracts the
> >sand on the windward side which when heeled and also drives the hull
> >further down. I am assuming that this design has a starboard and port
> >tank. Water ballast is negated somewhat on the leeward side when
> >heeling, and the windward side ballast will be effective through about
> >70 degrees of knockdown.
>
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In a message dated 3/8/2000 1:15:10 PM Eastern Standard Time,
crandall@...writes:
<< So good to see this. I posted the "rose poem" corruption on the
boatdesign list, and got little or no support.
But this is very true. If the sand bags were fixed and did not shift,
then they would be *better* than water, for their presumed lower center of
gravity. >>
Actually Chris - 500 lbs of rose pedals were my second choice - but the boat
just wasn't big enough. Steve
crandall@...writes:
<< So good to see this. I posted the "rose poem" corruption on the
boatdesign list, and got little or no support.
But this is very true. If the sand bags were fixed and did not shift,
then they would be *better* than water, for their presumed lower center of
gravity. >>
Actually Chris - 500 lbs of rose pedals were my second choice - but the boat
just wasn't big enough. Steve
I think my perference is to have a boat round up as it heels - if that can't
happen - then I don't want it to heel as far - I can't see any solution for
that other than more ballast - because with the mainsail double reefed and
still going over - lowering the sail plan profile obviously isn't the
solution.
Thinking some more about placement of extra floatation - it occured to me
that some floatation could be placed on the outside of the boat between the
sliding hatch rails and glassed in. Do it right and it would look very
natural. steve
happen - then I don't want it to heel as far - I can't see any solution for
that other than more ballast - because with the mainsail double reefed and
still going over - lowering the sail plan profile obviously isn't the
solution.
Thinking some more about placement of extra floatation - it occured to me
that some floatation could be placed on the outside of the boat between the
sliding hatch rails and glassed in. Do it right and it would look very
natural. steve
On Wed, 8 Mar 2000, GHC wrote:
boatdesign list, and got little or no support.
But this is very true. If the sand bags were fixed and did not shift,
then they would be *better* than water, for their presumed lower center of
gravity. But they'd be PITAs in their own right, for other reasons.
Chris Crandallcrandall@...(785) 864-4131
Department of Psychology University of Kansas Lawrence, KS 66045
I have data convincingly disconfirming the Duhem-Quine hypothesis.
> Not again...there's nothing wrong with sand - mass is mass is mass.So good to see this. I posted the "rose poem" corruption on the
> 400 pounds of water, 400 pounds of sand, 400 pounds of cookies.
boatdesign list, and got little or no support.
But this is very true. If the sand bags were fixed and did not shift,
then they would be *better* than water, for their presumed lower center of
gravity. But they'd be PITAs in their own right, for other reasons.
Chris Crandallcrandall@...(785) 864-4131
Department of Psychology University of Kansas Lawrence, KS 66045
I have data convincingly disconfirming the Duhem-Quine hypothesis.
In a message dated 3/8/2000 9:25:54 AM Eastern Standard Time,
lincolnr@...writes:
<< Having said that, I wonder if the weight of the sand is as much as
water completely filling the ballast tanks. Anyone have a a good
measurement on the volume of the tanks? If the tanks are much more than
8 cubic feet (500 lbs of water), then we have at least a partial answer
to the knockdown.
slightly less that 8 cubic feet - The tanks are pretty much on target there -
tho' there is a little room for interpretation as you put them in - and
whether or not your boat is perfectly symetrical. steve
lincolnr@...writes:
<< Having said that, I wonder if the weight of the sand is as much as
water completely filling the ballast tanks. Anyone have a a good
measurement on the volume of the tanks? If the tanks are much more than
8 cubic feet (500 lbs of water), then we have at least a partial answer
to the knockdown.
>>When I measured my tanks and figured the volume - I came up with a figure
slightly less that 8 cubic feet - The tanks are pretty much on target there -
tho' there is a little room for interpretation as you put them in - and
whether or not your boat is perfectly symetrical. steve
Not again...there's nothing wrong with sand - mass is mass is mass. 400
pounds of water, 400 pounds of sand, 400 pounds of cookies.
Water is 64 lbs/ft3, while sand is 90-100 lbs/ft3. So, you'll even get a
very slightly lower c.g. with the sand (until it moves).
Gregg Carlson
At 05:35 AM 3/8/2000 -0800, you wrote:
pounds of water, 400 pounds of sand, 400 pounds of cookies.
Water is 64 lbs/ft3, while sand is 90-100 lbs/ft3. So, you'll even get a
very slightly lower c.g. with the sand (until it moves).
Gregg Carlson
At 05:35 AM 3/8/2000 -0800, you wrote:
> I must be missing something here. Martha Jane was designed for
>water ballast. Sand in place of water ballast doesn't appear to be the
>solution. The sand on the leeward side becomes a liability in this
>situation by making the leeward side of the boat sink lower in the
>water than the designers plan. If water comes in through the hatch or
>ventilator, you are 'sunk". The leeward sand in effect counteracts the
>sand on the windward side which when heeled and also drives the hull
>further down. I am assuming that this design has a starboard and port
>tank. Water ballast is negated somewhat on the leeward side when
>heeling, and the windward side ballast will be effective through about
>70 degrees of knockdown.
There's nothing magic about water vs sand. If the weight distribution
is the same and the water has no free surface (i.e. can't over around),
then the effects on stability should be the same. THe water outside
can't tell what you've got inside, and gravity only responds to mass.
It's true that you can approximate the effects of water ballast by
saying the boat acts like the part full of water isn't there until some
of it gets above the waterline, but these results will be the same as
the ones you get by calculations using the weight distribution of the
hull. There is no magic effect.
Having said that, I wonder if the weight of the sand is as much as
water completely filling the ballast tanks. Anyone have a a good
measurement on the volume of the tanks? If the tanks are much more than
8 cubic feet (500 lbs of water), then we have at least a partial answer
to the knockdown.
As far as weight placement, if the center of mass of the ballast is the
same, it doesn't matter if it's two chunks port and starboard or one
big chunk in the middle. Lower is better, of course.
"david jost" <djos-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3501
is the same and the water has no free surface (i.e. can't over around),
then the effects on stability should be the same. THe water outside
can't tell what you've got inside, and gravity only responds to mass.
It's true that you can approximate the effects of water ballast by
saying the boat acts like the part full of water isn't there until some
of it gets above the waterline, but these results will be the same as
the ones you get by calculations using the weight distribution of the
hull. There is no magic effect.
Having said that, I wonder if the weight of the sand is as much as
water completely filling the ballast tanks. Anyone have a a good
measurement on the volume of the tanks? If the tanks are much more than
8 cubic feet (500 lbs of water), then we have at least a partial answer
to the knockdown.
As far as weight placement, if the center of mass of the ballast is the
same, it doesn't matter if it's two chunks port and starboard or one
big chunk in the middle. Lower is better, of course.
"david jost" <djos-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3501
>snipthe
> I must be missing something here. Martha Jane was designed for
> water ballast. Sand in place of water ballast doesn't appear to be
> solution. The sand on the leeward side becomes a liability in thisthe
> situation by making the leeward side of the boat sink lower in the
> water than the designers plan. If water comes in through the hatch or
> ventilator, you are 'sunk". The leeward sand in effect counteracts
> sand on the windward side which when heeled and also drives the hull
> further down. I am assuming that this design has a starboard and port
> tank. Water ballast is negated somewhat on the leeward side when
> heeling, and the windward side ballast will be effective through about
> 70 degrees of knockdown. The crew weight is positioned too far inside
> of this boat to be very effective to counteract the knockdown.
> snip
random thoughts on knockdowns.
Any time I have capsized any boat and it has failed to respond, two
things have happened.
1. The hull was breached allowing it to swamp. We always close the
main hatch on all racing boats in winds over 20kts. Just in case. A
J24 is a pain in the neck to bail!
2. The rig was driven under and filled up with water not allowing the
boat to come back up. (in one case the mast tip was driven into the
sand/muck. No answer to this except to get a tow!
I must be missing something here. Martha Jane was designed for
water ballast. Sand in place of water ballast doesn't appear to be the
solution. The sand on the leeward side becomes a liability in this
situation by making the leeward side of the boat sink lower in the
water than the designers plan. If water comes in through the hatch or
ventilator, you are 'sunk". The leeward sand in effect counteracts the
sand on the windward side which when heeled and also drives the hull
further down. I am assuming that this design has a starboard and port
tank. Water ballast is negated somewhat on the leeward side when
heeling, and the windward side ballast will be effective through about
70 degrees of knockdown. The crew weight is positioned too far inside
of this boat to be very effective to counteract the knockdown.
Without the mizzen's effectiveness and the rudder being in limited
contact with the water the boat will go to leeward with the sails set
this way. All cats do at this point. What brings them back up is
releasing the main and allowing the beam to do its thing. If the boat
has swamped during the process, the beam of the boat is not able to do
what it was designed to do.
How about pouring a shallow 1X4 plank keel about 6 feet long for the
bottom in place of the sand. It would put the weight where you want
it. It would not increase the draft much, and help protect the hull in
groundings.
Good luck with what appears to be an interesting problem.
David Jost
hwa-@...wrote:
original article:http://www.egroups.com/group/bolger/?start=3499
Any time I have capsized any boat and it has failed to respond, two
things have happened.
1. The hull was breached allowing it to swamp. We always close the
main hatch on all racing boats in winds over 20kts. Just in case. A
J24 is a pain in the neck to bail!
2. The rig was driven under and filled up with water not allowing the
boat to come back up. (in one case the mast tip was driven into the
sand/muck. No answer to this except to get a tow!
I must be missing something here. Martha Jane was designed for
water ballast. Sand in place of water ballast doesn't appear to be the
solution. The sand on the leeward side becomes a liability in this
situation by making the leeward side of the boat sink lower in the
water than the designers plan. If water comes in through the hatch or
ventilator, you are 'sunk". The leeward sand in effect counteracts the
sand on the windward side which when heeled and also drives the hull
further down. I am assuming that this design has a starboard and port
tank. Water ballast is negated somewhat on the leeward side when
heeling, and the windward side ballast will be effective through about
70 degrees of knockdown. The crew weight is positioned too far inside
of this boat to be very effective to counteract the knockdown.
Without the mizzen's effectiveness and the rudder being in limited
contact with the water the boat will go to leeward with the sails set
this way. All cats do at this point. What brings them back up is
releasing the main and allowing the beam to do its thing. If the boat
has swamped during the process, the beam of the boat is not able to do
what it was designed to do.
How about pouring a shallow 1X4 plank keel about 6 feet long for the
bottom in place of the sand. It would put the weight where you want
it. It would not increase the draft much, and help protect the hull in
groundings.
Good luck with what appears to be an interesting problem.
David Jost
hwa-@...wrote:
original article:http://www.egroups.com/group/bolger/?start=3499
> So - a better line of discussion now might be - what might haveworked
> better. I started the outboard and left the mizzen cleated thinkingI would
> round up - didn't happen.uncleat the
>
> If doing it all again - ( which I hope not to do) I think I would
> mizzen, drop the weather board - and if still standing at that pointI would
> raise the leeboard half way and then ease in the mizzen to see if shewould
> slowly round up - The situation is unusual in that the mizzen wasnot
> completely laced to the mast anymore. But I think that perhaps thatis the
> course of action for any mj which has lost headway in strong windsand needs
> to heave to.and
>
> Also - I think a larger outboard is called for.
>
> The other question is - should more ballast be added - if so how much
> should foam floatation then also be added and where. I'm thinking ofadding
> another hundred pounds of sand - which will fit in the tanks insmaller bags.
> Foam under the bow well and back in the quarterberth area - way inthe back
> near the transom
>
> Steve
>
So - a better line of discussion now might be - what might have worked
better. I started the outboard and left the mizzen cleated thinking I would
round up - didn't happen.
If doing it all again - ( which I hope not to do) I think I would uncleat the
mizzen, drop the weather board - and if still standing at that point I would
raise the leeboard half way and then ease in the mizzen to see if she would
slowly round up - The situation is unusual in that the mizzen was not
completely laced to the mast anymore. But I think that perhaps that is the
course of action for any mj which has lost headway in strong winds and needs
to heave to.
Also - I think a larger outboard is called for.
The other question is - should more ballast be added - if so how much and
should foam floatation then also be added and where. I'm thinking of adding
another hundred pounds of sand - which will fit in the tanks in smaller bags.
Foam under the bow well and back in the quarterberth area - way in the back
near the transom
Steve
better. I started the outboard and left the mizzen cleated thinking I would
round up - didn't happen.
If doing it all again - ( which I hope not to do) I think I would uncleat the
mizzen, drop the weather board - and if still standing at that point I would
raise the leeboard half way and then ease in the mizzen to see if she would
slowly round up - The situation is unusual in that the mizzen was not
completely laced to the mast anymore. But I think that perhaps that is the
course of action for any mj which has lost headway in strong winds and needs
to heave to.
Also - I think a larger outboard is called for.
The other question is - should more ballast be added - if so how much and
should foam floatation then also be added and where. I'm thinking of adding
another hundred pounds of sand - which will fit in the tanks in smaller bags.
Foam under the bow well and back in the quarterberth area - way in the back
near the transom
Steve