design for light airs

Ok, I'm not blind. I'm dumb. V-3 is displacement in tons.

So that leaves sail area.

 

I doubt the modern Wauquiez (post Beneteau purchase) are the same quality as the 1980s boats. I haven't seen the modern ones; just guessing. Which is not to say the Elan isn't a fine boat. But the modern design objective is to go lightweight when in doubt. It saves $$ (unless high tech) and helps performance. It's obvious that the 1980s Wauquiez didn't have this built-in bias for lightweight.

Lightweight is good in almost every argument about sailboats (assuming equal strength) until you start talking about impact on rocks.

I figured out the tonnage just as you were posting.

THANK YOU for your help. We will see three boats tomorrow, and a fourth is waiting in the wings. My, my, this IS fun.

 

Yes I agree, that's why I have said "a modern Wauquiez"

 

I have emailed Koopmans for the SA/D of design No. 263, as it closely resembles this boat.

 

Short stick

Well, the Koopmans had a very short stick. Ironically, a sistership of our old boat was a few slips away, so we could compare. Stick is about 20% shorter, despite about 60% more displacement. I don't this boat is gonna work for us. Bummer.

Haven't hear from Koopmans Jr. yet.

None of the measurements as advertised were correct. Boat is about a foot longer, more narrow, etc., etc.

 

The broker measured the spars, etc., for me on the Koopmans.
P = 37'
E = 13'
I = 40.5'
J = 16.5'

I get a main and 100% jib area of 577 square feet.

Using a dry displacement of 18,300 pound, SA/D computes to 13.3 (not using staysail area).

I get a feeling this boat was designed for Antartica.

 

Any way to determine the righting moment at 30 degrees of heel? One nice thing about measuring in feet and pounds: if you assume a pressure of one pound per square foot of sail area

• Pounds Pressure * Heeling Arm = Heeling Moment
• You can increase sail area until heeling moment = righting moment at 30 degrees

This is a simplification, of course, but it'll get you in the ballpark of how much sail you have the stability to carry.

 

hiracer,
With data taken from Koopman's design 263, Bwl as 0.9*Bmax, the sail area you calculated, the engine's 30 HP at YachWorld, asuming a ballast/disp ratio of 0.35 and guessing a body draught of 0.68 m, I get the following:

Lh =10,5 m
Lwl = 8,8 m
Bmax = 3,44 m
Bwl = 3,1 m
Draught = 1,5 m
HD = 0,68 m
Disp = 8508 kg
Ballast = 2978 kg
Sail area = 53,6 m2
Power = 30 HP

Ballast/Disp Ratio W/Disp =0,35
Displacement/Length Ratio D/L = 348,21
Sail Area/Disp. Ratio SA/D = 13,07
Power/ Disp. Ratio HP/D = 1,6HP/ton
Hull speed HSPD = 7,2Kn
Potential Maximum Speed PMS = 7,17Kn
Velocity Ratio VR =1
Comfort Safety Factor CSF = 1,7
Motion Comfort Ratio MCR = 37,35
Screening Stability Value SSV = 42,33
Angle of Vanishing Stability AVS = 122,37º
Heft Ratio HF =1,34
Roll Period T =3,56Sec
Roll Acceleration Acc =0,07G's
Stability Index SI = 1,03

Based in estimated Roll Period:

Righting Arm 20º RA20 =0,17m
Righting Arm 30º RA30 =0,23m
Righting Arm 10º RA10 =0,09m
Initial Metacentric height GMo =0,53m



Cheers.

 

I really like this boat, but I can't live with a SA/D of 13.

I had hoped that the staysail area is included in the SA/D calculation, but I've learned that is is not.

Thanks for all the help but I gotta have a SA/D of at least 15.5.

 

Stephen,

If we know Roll Period T, we can estimate (roughly) GZ30 = (Bwl/T)^2/11

If we'd know the heeling arm HA, we could easily also calculate the Dellenbaugh's angle, which also gives an idea of the boat's ability to carry sail. For a medium sized boat it should be less than 14º, following Kasten and others.

We could also work with the Wind Pressure Coefficent WPC = RM20/HM20
Where HM20 = SA*HA*0.883
(For 1 pound/sqft wind pressure)
Following Skene, this coefficient should be around 1.01 for keel boats; above this value the boat is stiff.
Following Gerr it should be between 1.2 to 1.5 for heavy cruising boats and 1.3 to 1.7 for ocean voyagers.

Just for some hours at home, I'll be back on boating tomorrow (great!), so I'll come back on the semiplanning power prediction thing by the end of next week.

Cheers

 

If Guillermo's and I are both right, there's enough information here to establish what we think the sail area should be. Should we do the calculation? Any chance you want to buy the boat and spend some money to give it a bigger rig?

 

That's very, very kind, but the boat is bumping against our budget as is.

New rig, sails, etc., is beyond our means.

Although I might live to regret this decision.

I have an offer on the boat right now, and I'm going to fax a termination.

Thanks.

 

I have seen the photo of the boat and the rig seems alright to me.

Koopmans was a very good designer, and if you are in the market for a 34ft, 20 year old oceangoing steel boat I doubt you will find a better one. They all will have small rigs by modern standards.

As Milan has said to you, if you want a marginally faster boat you should look for a Van de Stadt design, or similar...but then the boat will not be the kind you like...I mean narrow, nor as beautiful

 

hiracer,
You are the one with the decission in your hands, but with a Velocity Ratio of 1, and taking into account that staysail wil add extra power, I'd say the boat is quite well balanced. She seems to be a very nice all around cruising boat, in my opinion.
The only doubt I have is if displacement is in light or loaded condition. Maybe is loaded (using the D/L ratio of around 350 as a clue).
If loaded displacement would be, let's say, the 22000 pounds you mentioned before, then we'd have D/L = 409 and SA/D = 11.73 which seem values pretty high and low, respectively, for what the boat seems to be. So maybe 18770 pounds (8508 kg) is the displacement in loaded condition...

 

Yes, I agree with Guillermo. In a cutter rig you sail to winward with the three sails, so you should count the staysail area. The boat seems alright to me.