Re: software help
Rick,
The classic formula for pure displacement speed, or "hull speed" is,
hs=1.34 xWL^2, where WL in feet
But, that's pretty conservative. Even heavy vessels with very fair
lines reach SL ratios of 1.4 or 1.45.
And, light vessels (i.e. a low displ to length ratio, DL) will
operate between 1.34 and 2.5 to 3.0 without actually planing. "Semi-
displacement" performance covers a whole range of characteristics,
though generally including 1. flat run aft (when at rest), 2. light
weight, and 3. high power.
1. For instance,
<2 degree aft run produces an SL of 2.5 or higher
4 deg run an SL around 2
7 deg run and SL around 1.5
2. Formulas for semi-displacement are,
DL = DisplLongTons(.01*WL)^3, where long ton is 2240 lbs, WL in feet
SL = 8.26/ (DL)^.311
So, a DL of 60-100 produces a an SL ratio of about 2, a DL of 200
about 1.6, and a heavy 300 about 1.4.
3. Bear in mind the SL is all potential without sufficient power.
(Once you know your SL, you can estimate the power required to reach
it - see Gerr's Propeller Handbook).
So, a light, flat skiff may be driven very fast with very little
power, but is dangerous in rough water. A deep, full, heavy, hull
like a sailboat may be very safe and comfortable, but no amount of
power will cause her to exceed a certain SL. And, even very heavy
vessel can achieve exceed the SL predictions with flat runs and huge
powerplants (but may be unseaworthy or unseakindly).
Keeps it pretty interesting. Obviously why guys like Bolger make all
the big bucks ;-}
Gregg Carlson
The classic formula for pure displacement speed, or "hull speed" is,
hs=1.34 xWL^2, where WL in feet
But, that's pretty conservative. Even heavy vessels with very fair
lines reach SL ratios of 1.4 or 1.45.
And, light vessels (i.e. a low displ to length ratio, DL) will
operate between 1.34 and 2.5 to 3.0 without actually planing. "Semi-
displacement" performance covers a whole range of characteristics,
though generally including 1. flat run aft (when at rest), 2. light
weight, and 3. high power.
1. For instance,
<2 degree aft run produces an SL of 2.5 or higher
4 deg run an SL around 2
7 deg run and SL around 1.5
2. Formulas for semi-displacement are,
DL = DisplLongTons(.01*WL)^3, where long ton is 2240 lbs, WL in feet
SL = 8.26/ (DL)^.311
So, a DL of 60-100 produces a an SL ratio of about 2, a DL of 200
about 1.6, and a heavy 300 about 1.4.
3. Bear in mind the SL is all potential without sufficient power.
(Once you know your SL, you can estimate the power required to reach
it - see Gerr's Propeller Handbook).
So, a light, flat skiff may be driven very fast with very little
power, but is dangerous in rough water. A deep, full, heavy, hull
like a sailboat may be very safe and comfortable, but no amount of
power will cause her to exceed a certain SL. And, even very heavy
vessel can achieve exceed the SL predictions with flat runs and huge
powerplants (but may be unseaworthy or unseakindly).
Keeps it pretty interesting. Obviously why guys like Bolger make all
the big bucks ;-}
Gregg Carlson
--- In bolger@y..., rickc10ny@y... wrote:
> I have been doodling with diffrent hull shapes using hull designer.
> I have seen the software mentioned here in this forum.It gives a
> value for "D/L limited speed" Anyone know what that means?
PB&F's v. 2 Martha Jane improved about a 3 to 1 ballast
ratio by
one or both of adding ballast and a higher side. MJ's tanks
are port and starboard,
for'n'aft inside the cabin. I don't know if they have baffles.
Anhinga weighs about a third of the basic MJ dry, half as
much tanked up.
They carry about the same amount of water.
People who have water ballast seem happy. I have heard about
them dribbling water from the higher side. Need good plugs on
top and bottom.
Have you found Chuck Merrell's piece on square boat stability?
http://www.boatdesign.com/postings/pages/knockdown.htm
Whatever weakness you gather for your own conditions may be helped
by the 484 type stern. If you want to run the ST on your own boat,
its an evening's messabout with the demo at
http://www.plyboats.com
if you haven't already had it.
I did think of a couple larger water ballast yachts. Both
from Bolger, of course.
The first is a 45' triangular looking three piece take-apart
sailing shantyboat. ( I can't remember the name. ) In the
chapter that's in he says, "Perhaps one day we'll give her a
different pair of ends."
The other is a 2 page spread in an old CSD catalog. A
slightly flared sharpie.
'Break Down Schooner'
46' 11" x 7' 8"
Displacement 13,000 lb.
Ballast 4100 lb.
all half inch ply.
3 segments, largest 19' 6" x 7' 8",
Bernie Wolfard called it, "Big, very fast, trailerable
cruiser." Bill McKibben built, with tyvek sails, for sailing
in Vancouver Sound.
Really quite wonderful. Has a center cockpit, with a
doghouse aft of that.
Mark
thomas dalzell wrote:
ratio by
one or both of adding ballast and a higher side. MJ's tanks
are port and starboard,
for'n'aft inside the cabin. I don't know if they have baffles.
Anhinga weighs about a third of the basic MJ dry, half as
much tanked up.
They carry about the same amount of water.
People who have water ballast seem happy. I have heard about
them dribbling water from the higher side. Need good plugs on
top and bottom.
Have you found Chuck Merrell's piece on square boat stability?
http://www.boatdesign.com/postings/pages/knockdown.htm
Whatever weakness you gather for your own conditions may be helped
by the 484 type stern. If you want to run the ST on your own boat,
its an evening's messabout with the demo at
http://www.plyboats.com
if you haven't already had it.
I did think of a couple larger water ballast yachts. Both
from Bolger, of course.
The first is a 45' triangular looking three piece take-apart
sailing shantyboat. ( I can't remember the name. ) In the
chapter that's in he says, "Perhaps one day we'll give her a
different pair of ends."
The other is a 2 page spread in an old CSD catalog. A
slightly flared sharpie.
'Break Down Schooner'
46' 11" x 7' 8"
Displacement 13,000 lb.
Ballast 4100 lb.
all half inch ply.
3 segments, largest 19' 6" x 7' 8",
Bernie Wolfard called it, "Big, very fast, trailerable
cruiser." Bill McKibben built, with tyvek sails, for sailing
in Vancouver Sound.
Really quite wonderful. Has a center cockpit, with a
doghouse aft of that.
Mark
thomas dalzell wrote:
>
> I have been looking at the Anhinga plans closely. One
> of PCB's objectives in making this style of boat was
> to be able to carry extra ballast aft. In the case of
> Eeek, we have the positioning of the lead pigs behind
> the recumbant sailor, and in Anhinga we have the water
> ballast aft.
>
> The possibility exists that some of these water
> ballasted sharpies have the approximate stability of a
> tumbleweed. There are the Anhinga problems of serial
> capsise, and there is the Martha Jane debacle. We
> know that at that time stability curves were not so
> much calculated as sized up.
>
> With Anhinga there is one special problem. The water
> ballast is carried aft, as mentioned above. At the
> rearmost point in the boat the ballast is only @ 1.25'
> from the CL. The average distance is 1.875' on a beam
> of 5'. In the nockdown position this isn't all that
> critical, but at other times it isn't all that great.
>
> The water tank is 3.5" deep, the boat is designed to
> operate at a draft of 7" and a displacement of 2400#.
> The question I have is given that the main structure
> of the boat probably weighs in the Sneakeasy range
> (400-500#?) and that the water ballast will only fill
> if the boat is sunk to the level of 4 inches first,
> what is the chance that the water ballast isn't
> filling, and that as a result it is sloshing back and
> forth in there? There aren't any longitudinal
> stringers, they are transverse, so the water ballast
> can move to the lowest level as the boat heels, unless
> the tank is full. With MJs does the tank fill all the
> way?
>
> If we take the "Sandy Bottoms" Anhinga example, this
> boat had serious problems, but it also didn't have the
> specified boards or rig. It also had a little more
> sail than intended, though that sail was reefable. It
> can't be the design's fault that she didn't sail, but
> she shouldn't have nocked down so easily.
>
> If we consider three better known boats than Anhinga
> (1/2" bottom), Birdwatcher (1" bottom), Black Skimmer
> (500# of ballast and beefy scantlings), and Martha
> Jane (beefier scantlings and water ballasted, though
> enough problems with nock down that the design has an
> optional form and ballast revision). It is only the
> water ballasted ones that have the problems of
> unexpected nock down.
>
> _______________________________________________________
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>
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>
>
> Bolger rules!!!
> - no cursing, flaming, trolling, spamming, or flogging
> dead horses
> - pls take "personals" off-list, stay on topic, and
> punctuate
> - add your comments at the TOP and SIGN your posts, snip
> all you like
> - To order plans: Mr. Philip C. Bolger, P.O. Box 1209,
> Gloucester, MA, 01930, Fax: (978) 282-1349
> - Unsubscribe:bolger-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to the Yahoo! Terms
> of Service.
I have been looking at the Anhinga plans closely. One
of PCB's objectives in making this style of boat was
to be able to carry extra ballast aft. In the case of
Eeek, we have the positioning of the lead pigs behind
the recumbant sailor, and in Anhinga we have the water
ballast aft.
The possibility exists that some of these water
ballasted sharpies have the approximate stability of a
tumbleweed. There are the Anhinga problems of serial
capsise, and there is the Martha Jane debacle. We
know that at that time stability curves were not so
much calculated as sized up.
With Anhinga there is one special problem. The water
ballast is carried aft, as mentioned above. At the
rearmost point in the boat the ballast is only @ 1.25'
from the CL. The average distance is 1.875' on a beam
of 5'. In the nockdown position this isn't all that
critical, but at other times it isn't all that great.
The water tank is 3.5" deep, the boat is designed to
operate at a draft of 7" and a displacement of 2400#.
The question I have is given that the main structure
of the boat probably weighs in the Sneakeasy range
(400-500#?) and that the water ballast will only fill
if the boat is sunk to the level of 4 inches first,
what is the chance that the water ballast isn't
filling, and that as a result it is sloshing back and
forth in there? There aren't any longitudinal
stringers, they are transverse, so the water ballast
can move to the lowest level as the boat heels, unless
the tank is full. With MJs does the tank fill all the
way?
If we take the "Sandy Bottoms" Anhinga example, this
boat had serious problems, but it also didn't have the
specified boards or rig. It also had a little more
sail than intended, though that sail was reefable. It
can't be the design's fault that she didn't sail, but
she shouldn't have nocked down so easily.
If we consider three better known boats than Anhinga
(1/2" bottom), Birdwatcher (1" bottom), Black Skimmer
(500# of ballast and beefy scantlings), and Martha
Jane (beefier scantlings and water ballasted, though
enough problems with nock down that the design has an
optional form and ballast revision). It is only the
water ballasted ones that have the problems of
unexpected nock down.
_______________________________________________________
Build your own website in minutes and for free athttp://ca.geocities.com
of PCB's objectives in making this style of boat was
to be able to carry extra ballast aft. In the case of
Eeek, we have the positioning of the lead pigs behind
the recumbant sailor, and in Anhinga we have the water
ballast aft.
The possibility exists that some of these water
ballasted sharpies have the approximate stability of a
tumbleweed. There are the Anhinga problems of serial
capsise, and there is the Martha Jane debacle. We
know that at that time stability curves were not so
much calculated as sized up.
With Anhinga there is one special problem. The water
ballast is carried aft, as mentioned above. At the
rearmost point in the boat the ballast is only @ 1.25'
from the CL. The average distance is 1.875' on a beam
of 5'. In the nockdown position this isn't all that
critical, but at other times it isn't all that great.
The water tank is 3.5" deep, the boat is designed to
operate at a draft of 7" and a displacement of 2400#.
The question I have is given that the main structure
of the boat probably weighs in the Sneakeasy range
(400-500#?) and that the water ballast will only fill
if the boat is sunk to the level of 4 inches first,
what is the chance that the water ballast isn't
filling, and that as a result it is sloshing back and
forth in there? There aren't any longitudinal
stringers, they are transverse, so the water ballast
can move to the lowest level as the boat heels, unless
the tank is full. With MJs does the tank fill all the
way?
If we take the "Sandy Bottoms" Anhinga example, this
boat had serious problems, but it also didn't have the
specified boards or rig. It also had a little more
sail than intended, though that sail was reefable. It
can't be the design's fault that she didn't sail, but
she shouldn't have nocked down so easily.
If we consider three better known boats than Anhinga
(1/2" bottom), Birdwatcher (1" bottom), Black Skimmer
(500# of ballast and beefy scantlings), and Martha
Jane (beefier scantlings and water ballasted, though
enough problems with nock down that the design has an
optional form and ballast revision). It is only the
water ballasted ones that have the problems of
unexpected nock down.
_______________________________________________________
Build your own website in minutes and for free athttp://ca.geocities.com
Rick,
A boat's Displacement / Length ratio will limit speed as you
move to the heavy side.
More to it than this, but d/l = 50 is an ultralight; 380+
is a pretty "heavy".
When I "Calculate Displacement," Hulls gives a value for
the D/L, but I don't see, "Limited speed." Can you name one
of the boats in the standard set that return this?
Is your doodle short and beamy? What's the D/L ?
Mark
rickc10ny@...wrote:
snips>
A boat's Displacement / Length ratio will limit speed as you
move to the heavy side.
More to it than this, but d/l = 50 is an ultralight; 380+
is a pretty "heavy".
When I "Calculate Displacement," Hulls gives a value for
the D/L, but I don't see, "Limited speed." Can you name one
of the boats in the standard set that return this?
Is your doodle short and beamy? What's the D/L ?
Mark
rickc10ny@...wrote:
snips>
> I have been doodling with diffrent hull shapes using hull designer.
> It gives a
> value for "D/L limited speed" Anyone know what that means?
Hi Rick
"D/L LIMITED SPEED"
I think means "down / load limited speed "
WillO
WillO
will@...
503-805-8421
-----Original Message-----
From:rickc10ny@...[mailto:rickc10ny@...]
Sent: Thursday, November 22, 2001 12:57 PM
To:bolger@yahoogroups.com
Subject: [bolger] software help
I have been doodling with diffrent hull shapes using hull designer.
I have seen the software mentioned here in this forum.It gives a
value for "D/L limited speed" Anyone know what that means?
Thanks in Advance
Rick
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Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- pls take "personals" off-list, stay on topic, and punctuate
- add your comments at the TOP and SIGN your posts, snip all you like
- To order plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA,
01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to the Yahoo!
<http://docs.yahoo.com/info/terms/> Terms of Service.
[Non-text portions of this message have been removed]
"D/L LIMITED SPEED"
I think means "down / load limited speed "
WillO
WillO
will@...
503-805-8421
-----Original Message-----
From:rickc10ny@...[mailto:rickc10ny@...]
Sent: Thursday, November 22, 2001 12:57 PM
To:bolger@yahoogroups.com
Subject: [bolger] software help
I have been doodling with diffrent hull shapes using hull designer.
I have seen the software mentioned here in this forum.It gives a
value for "D/L limited speed" Anyone know what that means?
Thanks in Advance
Rick
Yahoo! Groups Sponsor
ADVERTISEMENT
<http://rd.yahoo.com/M=213858.1737107.3257770.1261774/D=egroupweb/S=1705
065791:HM/A=763352/R=0/*http:/www..classmates.com/index.tf?s=5085>
<http://us.adserver.yahoo.com/l?M=213858.1737107.3257770.1261774/D=egrou
pmail/S=1705065791:HM/A=763352/rand=269747169>
Bolger rules!!!
- no cursing, flaming, trolling, spamming, or flogging dead horses
- pls take "personals" off-list, stay on topic, and punctuate
- add your comments at the TOP and SIGN your posts, snip all you like
- To order plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA,
01930, Fax: (978) 282-1349
- Unsubscribe:bolger-unsubscribe@yahoogroups.com
Your use of Yahoo! Groups is subject to the Yahoo!
<http://docs.yahoo.com/info/terms/> Terms of Service.
[Non-text portions of this message have been removed]
I have been doodling with diffrent hull shapes using hull designer.
I have seen the software mentioned here in this forum.It gives a
value for "D/L limited speed" Anyone know what that means?
Thanks in Advance
Rick
I have seen the software mentioned here in this forum.It gives a
value for "D/L limited speed" Anyone know what that means?
Thanks in Advance
Rick