Re: [bolger] mizzen sizing formula
Richard,
have you tried hooking the small mizzen up to the tiller?
Sounds possible with your setup.
Only design example I can think of right now
is Charlie Walshs Barges by Wolstenholme, (not even sure if
its launched yet) but its also
been done on smaller yachts.
http://www.sailingnow.com/boat_tests/bargyacht/bargyacht.html
Jeff Gilbert
have you tried hooking the small mizzen up to the tiller?
Sounds possible with your setup.
Only design example I can think of right now
is Charlie Walshs Barges by Wolstenholme, (not even sure if
its launched yet) but its also
been done on smaller yachts.
http://www.sailingnow.com/boat_tests/bargyacht/bargyacht.html
Jeff Gilbert
----- Original Message -----
From: Richard Spelling <richard@...>
To: <bolger@egroups.com>
Sent: Friday, June 23, 2000 7:02 AM
Subject: Re: [bolger] mizzen sizing formula
Also, my mizzen mast is on the transom, canted back, so the center of effort
is quite far back. This is why I'm starting with such a small one, I don't
particulary want to have to move the main.
Richard Spelling,http://www.spellingbusiness.com/boats
From the muddy waters of Oklahoma
Where the locals ask "Catch anything?" when you come back from sailing...
Mine generates lee helm in light to moderate airs. In puffs and heavy air,
she has light weather helm. Of course, reefing exacerbates the lee helm, and
pretty much eliminates the weather helm.
Also, my mizzen mast is on the transom, canted back, so the center of effort
is quite far back. This is why I'm starting with such a small one, I don't
particulary want to have to move the main.
Richard Spelling,http://www.spellingbusiness.com/boats
From the muddy waters of Oklahoma
Where the locals ask "Catch anything?" when you come back from sailing...
she has light weather helm. Of course, reefing exacerbates the lee helm, and
pretty much eliminates the weather helm.
Also, my mizzen mast is on the transom, canted back, so the center of effort
is quite far back. This is why I'm starting with such a small one, I don't
particulary want to have to move the main.
Richard Spelling,http://www.spellingbusiness.com/boats
From the muddy waters of Oklahoma
Where the locals ask "Catch anything?" when you come back from sailing...
----- Original Message -----
From: "T Webber" <tbertw@...>
To: <bolger@egroups.com>
Sent: Thursday, June 22, 2000 3:23 PM
Subject: Re: [bolger] mizzen sizing formula
> If a boat does not generate lee helm, a mizzen probably should not be
used.
> If it is used, it can be used at anchor or during sail changes. Otherwise,
> I fear the boat will spend the sailing time locked in "irons".
>
List,
The main / mizzen sail relationship is very similar to the main wing / tail
of an small airplane. the main difference is the mizzen cannot develop
negative lift and an airplane tail can. when sailing aboard Charles Fulk's
Micro, It became appearant that the mizzen was an "air rudder". The main
when trimmed properly developed a small amount of "lee helm" the mizzen was
trimmed in to nuetralize the lee helm. When the main became unwieldly in
higher winds and would over power the mizzen's ability to correct the helm,
it was time to reef the main.
The size calculations and location of the mizzen are closely related in
concept to "weight and balance" of an airplane. Assuming the main alone
will develop lee helm, the further aft the mizzen is the less area it
needs. I have not bothered to check GHK's math, his reputation would cause
me to accept it!! I always used a weighted average approach. The amount of
lee helm of the main must be offset by the weather helm generated by the
mizzen. The summation of the weather and lee helms must occur very close to
the center of lateral resistance. In Michalak's boats, somewhere near the
lee board.
If a boat does not generate lee helm, a mizzen probably should not be used.
If it is used, it can be used at anchor or during sail changes. Otherwise,
I fear the boat will spend the sailing time locked in "irons".
Tim - Houston - where advice is seldom worth what is paid for it!!!!
The main / mizzen sail relationship is very similar to the main wing / tail
of an small airplane. the main difference is the mizzen cannot develop
negative lift and an airplane tail can. when sailing aboard Charles Fulk's
Micro, It became appearant that the mizzen was an "air rudder". The main
when trimmed properly developed a small amount of "lee helm" the mizzen was
trimmed in to nuetralize the lee helm. When the main became unwieldly in
higher winds and would over power the mizzen's ability to correct the helm,
it was time to reef the main.
The size calculations and location of the mizzen are closely related in
concept to "weight and balance" of an airplane. Assuming the main alone
will develop lee helm, the further aft the mizzen is the less area it
needs. I have not bothered to check GHK's math, his reputation would cause
me to accept it!! I always used a weighted average approach. The amount of
lee helm of the main must be offset by the weather helm generated by the
mizzen. The summation of the weather and lee helms must occur very close to
the center of lateral resistance. In Michalak's boats, somewhere near the
lee board.
If a boat does not generate lee helm, a mizzen probably should not be used.
If it is used, it can be used at anchor or during sail changes. Otherwise,
I fear the boat will spend the sailing time locked in "irons".
Tim - Houston - where advice is seldom worth what is paid for it!!!!
It's a high peaked gaff main, no roach. The CE of
the main moves forward when reefed.
The main is vertical, but the mizzen mast cants
back at about 25 degrees...
I'm sure a formula could be created to give an
exact answer, but by calculating the various C.E.'s of the combined rig (thanks
Gregg) for various mizzen sizes, for the three reef conditions, I've come up
with some numbers.
Using best guesses for the various CE's, 28sq ft
works out pretty good. Of course, this has the effect of moving the CE of the
boat back 1.7 ft, assuming you are using the mizzen for propulsion.
If you keep the mizzen slacked off on a beat for
steering, this shouldn't be a big problem. On a reach and a run it shouldn't
matter to much...
We'll see how the 15 does in different wind
conditions, and make it bigger if needed.
----- Original Message -----From:Jeff GilbertSent:Wednesday, September 03, 1997 8:03 PMSubject:Re: [bolger] mizzen sizing formulaRichard,do you mean the combined (or effective overall) C of E?Its impossible to figure do a formula without knowing how heavily roached the main is, & relative angle of the masts if they cant back.. The only way to keep it the same is ifreefing pulls the main C E forrd (little or no roach in the main.) to compensate for the more effective mizzen.
ok. This let's me figure the C.E. in each configuration.
C.E.(1) = ((5?' x 126) +(13' x 15)) / (126 + 15) = 5.8' (new C.E.)
C.E.(2) = ((4.5?' x 105) +(13' x 15)) / (105 + 15) = 5.6' (new C.E.)
C.E.(3) = ((4?' x 85) +(13' x 15)) / (85 + 15) = 5.4' (new C.E.)
So, I would need to adjust the mizzen size up till ce1=ce2=ce3....
There is probably a formula, but brute force and excel gives 43 as the best
fit.
33 get's me a movement of less than 1 inch.
Interesting. I'll do some more testing with the one I've got, if it isn't
big enough, I may go with the 33 and see how that works. (good thing
polytarp is cheap!)
Thanks Gregg
- Richard
C.E.(1) = ((5?' x 126) +(13' x 15)) / (126 + 15) = 5.8' (new C.E.)
C.E.(2) = ((4.5?' x 105) +(13' x 15)) / (105 + 15) = 5.6' (new C.E.)
C.E.(3) = ((4?' x 85) +(13' x 15)) / (85 + 15) = 5.4' (new C.E.)
So, I would need to adjust the mizzen size up till ce1=ce2=ce3....
There is probably a formula, but brute force and excel gives 43 as the best
fit.
33 get's me a movement of less than 1 inch.
Interesting. I'll do some more testing with the one I've got, if it isn't
big enough, I may go with the 33 and see how that works. (good thing
polytarp is cheap!)
Thanks Gregg
- Richard
----- Original Message -----
From: "GHC" <ghartc@...>
To: <bolger@egroups.com>
Sent: Thursday, June 22, 2000 12:51 PM
Subject: Re: [bolger] mizzen sizing formula
> Take any datum line, the bow, for instance. Multiply the distance to the
> main center of effort by the main area. Multiply the distance to the
> mizzen C.E. by the mizzen area. Sum the two (or more for more sails) and
> divide by the total sail area.
>
> For instance,
>
> ((MainC.E. x Main Area) + (MizzenC.E. x MizzenArea)) /
(MainArea+MizzenArea)
>
> your example (guessing C.E.'s):
>
> ((5?' x 126) +(13' x 15)) / (126 + 15) = 5.8' (new C.E.)
>
> Of course, you need to estimate the C.E. of each sail in each (reefed)
> case. (You could similarly estimate the combined vertical C.E. if you want
> to know that.)
>
> Undoubtedly, there would be fudge factors considering the shadowing of the
> mizzen and its relatively flatter shape.
>
> Gregg Carlson
>
>
> At 10:42 AM 6/22/2000 -0500, you wrote:
> > I'm experimenting with a small mizzen on Entropy. The main purpose
> >being to hold the boat into the wind when reefing/unreefing
singlehanded.
> >Some helm balancing/self steering would be a bonus. Not concerned with
> >drive from the sail. Bolger writes that if the mizzen on your cat-yawl
> >is "sized correctly", then when you reef the main the center of area of
> >both sails stays pretty much the same. Any of you mathmaticaly
inclined
> >people care to take a stab at figuring out the formula? Example:
with
> >one reef, and ~85sqft with two reefs. Mizzen mast is aproximatly 13ft
from
> >the main mast.... Current, experimental, mizzen is ~15sqft. Went out
> >last night in light winds, 0-5, and it seemed to turn the boat into the
> >wind,when the wind was actualy blowing at all. Of course, with such light
> >winds, inertia would cause the boat to turn into the wind and keep on
> >going...have to try with more air. Also, seemed to be some
selfsteering
> >effect, but again, need to test in more wind. Any thoughts?
> >
> > Bolger rules:
> > - no cursing
> > - stay on topic
> > - use punctuation
> > - add your comments at the TOP and SIGN your posts
> >"""" posts off-list.
> >
>
>
> ------------------------------------------------------------------------
> SALESFORCE.COM MAKES SOFTWARE OBSOLETE
> Secure, online sales force automation with 5 users FREE for 1 year!
>http://click.egroups.com/1/2658/13/_/3457/_/961696411/
> ------------------------------------------------------------------------
>
> Bolger rules:
> - no cursing
> - stay on topic
> - use punctuation
> - add your comments at the TOP and SIGN your posts
> - add content: send "thanks!" and "ditto!" posts off-list.
>
Take any datum line, the bow, for instance. Multiply the distance to the
main center of effort by the main area. Multiply the distance to the
mizzen C.E. by the mizzen area. Sum the two (or more for more sails) and
divide by the total sail area.
For instance,
((MainC.E. x Main Area) + (MizzenC.E. x MizzenArea)) / (MainArea+MizzenArea)
your example (guessing C.E.'s):
((5?' x 126) +(13' x 15)) / (126 + 15) = 5.8' (new C.E.)
Of course, you need to estimate the C.E. of each sail in each (reefed)
case. (You could similarly estimate the combined vertical C.E. if you want
to know that.)
Undoubtedly, there would be fudge factors considering the shadowing of the
mizzen and its relatively flatter shape.
Gregg Carlson
At 10:42 AM 6/22/2000 -0500, you wrote:
main center of effort by the main area. Multiply the distance to the
mizzen C.E. by the mizzen area. Sum the two (or more for more sails) and
divide by the total sail area.
For instance,
((MainC.E. x Main Area) + (MizzenC.E. x MizzenArea)) / (MainArea+MizzenArea)
your example (guessing C.E.'s):
((5?' x 126) +(13' x 15)) / (126 + 15) = 5.8' (new C.E.)
Of course, you need to estimate the C.E. of each sail in each (reefed)
case. (You could similarly estimate the combined vertical C.E. if you want
to know that.)
Undoubtedly, there would be fudge factors considering the shadowing of the
mizzen and its relatively flatter shape.
Gregg Carlson
At 10:42 AM 6/22/2000 -0500, you wrote:
> I'm experimenting with a small mizzen on Entropy. The main purpose
>being to hold the boat into the wind when reefing/unreefing singlehanded.
>Some helm balancing/self steering would be a bonus. Not concerned with
>drive from the sail. Bolger writes that if the mizzen on your cat-yawl
>is "sized correctly", then when you reef the main the center of area of
>both sails stays pretty much the same. Any of you mathmaticaly inclined
>people care to take a stab at figuring out the formula? Example: with
>one reef, and ~85sqft with two reefs. Mizzen mast is aproximatly 13ft from
>the main mast.... Current, experimental, mizzen is ~15sqft. Went out
>last night in light winds, 0-5, and it seemed to turn the boat into the
>wind,when the wind was actualy blowing at all. Of course, with such light
>winds, inertia would cause the boat to turn into the wind and keep on
>going...have to try with more air. Also, seemed to be some selfsteering
>effect, but again, need to test in more wind. Any thoughts?
>
> Bolger rules:
> - no cursing
> - stay on topic
> - use punctuation
> - add your comments at the TOP and SIGN your posts
>"""" posts off-list.
>
I'm experimenting with a small mizzen on Entropy.
The main purpose being to hold the boat into the wind when reefing/unreefing
singlehanded. Some helm balancing/self steering would be a bonus. Not concerned
with drive from the sail.
Bolger writes that if the mizzen on your cat-yawl
is "sized correctly", then when you reef the main the center of area of both
sails stays pretty much the same.
Any of you mathmaticaly inclined people care to
take a stab at figuring out the formula?
Example:
Entropy's main is 126sqft full, ~105sqft with
one reef, and ~85sqft with two reefs. Mizzen mast is aproximatly 13ft from the
main mast....
Current, experimental, mizzen is ~15sqft. Went out
last night in light winds, 0-5, and it seemed to turn the boat into the
wind,when the wind was actualy blowing at all. Of course, with such light winds,
inertia would cause the boat to turn into the wind and keep on going...have to
try with more air.
Also, seemed to be some selfsteering effect, but
again, need to test in more wind.
Any thoughts?
----- Original Message -----From:Richard SpellingSent:Friday, June 23, 2000 6:06 AMSubject:Re: [bolger] mizzen sizing formulaIt's a high peaked gaff main, no roach. The CE of the main moves forward when reefed.The main is vertical, but the mizzen mast cants back at about 25 degrees...I'm sure a formula could be created to give an exact answer, but by calculating the various C.E.'s of the combined rig (thanks Gregg) for various mizzen sizes, for the three reef conditions, I've come up with some numbers.Using best guesses for the various CE's, 28sq ft works out pretty good. Of course, this has the effect of moving the CE of the boat back 1.7 ft, assuming you are using the mizzen for propulsion.If you keep the mizzen slacked off on a beat for steering, this shouldn't be a big problem. On a reach and a run it shouldn't matter to much...We'll see how the 15 does in different wind conditions, and make it bigger if needed.Bolger rules:----- Original Message -----From:Jeff GilbertSent:Wednesday, September 03, 1997 8:03 PMSubject:Re: [bolger] mizzen sizing formulaRichard,do you mean the combined (or effective overall) C of E?Its impossible to figure do a formula without knowing how heavily roached the main is, & relative angle of the masts if they cant back.. The only way to keep it the same is ifreefing pulls the main C E forrd (little or no roach in the main.) to compensate for the more effective mizzen.
- no cursing
- stay on topic
- use punctuation
- add your comments at the TOP and SIGN your posts
- add content: send "thanks!" and "ditto!" posts off-list.
IAssuming you reef to the boom the combined CE
will drop.
Where it goes laterally will depend a fair bit on
how roachy the main is.
Jeff Gilbert
----- Original Message -----From:Richard SpellingSent:Friday, June 23, 2000 1:42 AMSubject:[bolger] mizzen sizing formulaBolger writes that if the mizzen on your cat-yawl is "sized correctly", then when you reef the main the center of area of both sails stays pretty much the same.
Richard,
do you mean the combined (or
effective overall) C of E?
Its impossible to figure do a formula without
knowing how heavily roached the main is, & relative angle of the masts if
they cant back.. The only way to keep it the same is if
reefing pulls the main C E forrd (little or no
roach in the main.) to compensate for the more effective mizzen.
Unless you reef to the mast the combined CE will
drop, which I guess is good in a narrow boat.
Jeff Gilbert.
ps
Think of it as a seesaw with Laurel & Hardy on
the ends!
From:Richard SpellingSent:Friday, June 23, 2000 1:42 AMSubject:[bolger] mizzen sizing formulaBolger writes that if the mizzen on your cat-yawl is "sized correctly", then when you reef the main the center of area of both sails stays pretty much the same.