mainsail design for a 42ft burmuda sloop

[bigbear69]

Hi, just wondering about a few aspects of mainsail design for a 42 ft steel sloop.
have found a design program on the web called 'sailcut' so had a play with it. iT looks ok pretty basic.
You can enter sail camber depth in a percentage for lower middle and upper. can anyone help with ideal numbers are for a 42ft cruising yacht burmuda sloop rig. luff 13.6, foot 4.9. mast is pretty much straight, marginal bend and rake.
Also should i have a straight leech or a small bit of roach? Any curve on the foot( iguess it depends if it is fixed ot floating?) or curve in the luff?
Any help would be much appreciated.
cheers

[TeddyDiver]

You got to give more info, like masthead or fractional, sideview to know how the backstay restricts sail & CE, what kind of mast other sails etc, where and which conditions you intend to use it, cruising, racing...

[bigbear69]

cheers for reply ,
just a cruising sail no racing. general purpose main around 8.5 oz cloth. winds ranging from not much up to 30 knots +.it is a masthead rig. boom is 5.2m, max sail foot is 5.1m, backstays are 6.2m from mast at boom level. I can have a little bit of roach without interferring with the backstays but not much. maybe 200 - 250 mm max. wondering if It is better to have a bit of roach or just a straight triangular sail. more importantly depth of camber and how it varies from the foot/middle/head of the sail.
Also do I need any curve in the luff to give a fuller camber depth or is it all in the broadseams.
I'm just thinking about making a sail. I have confidence of my ability in the actual making and machining of the sail but would love some advice on the design/shape.
cheers

[Gilbert]

Get a copy of "Make Your Own Sails: A Handbook for the Amatuer and Professional Sailmaker" by R. M. Bowker and S. A. Budd. They never led me astray on the sails I made following their methods.
My own suggestion is to have the leach straight just to avoid the nuisance of battens. Otherwise just consult the book. I see there are currently 3 used copies at Amazon.com for $6.95 US.

[iznogoud]

You can go with a leech roach of 2% without troubles. If you do it straight you still need battens and it will look negative while sailing.
Foot, just put a bit of roach so it look good. Go for a free edge, less work to do and performs as well.
Luff roach is important, as the mast bend is. Measure the min and max value you can get out of your mast. You should be able to flatten you sail, so remove all the luff roach.

good luck

[bigbear69]

cheers for reply. Was thinking along those lines. one thing I don't know anything about is the depth of camber required in the sail? At different heights up the sail also. What would be the ideal depth of camber in the bottom/ middle/ top sections of the sail for a cruising sail?
cheers

[bigbear69]

Originally Posted by Gilbert

Get a copy of "Make Your Own Sails: A Handbook for the Amatuer and Professional Sailmaker" by R. M. Bowker and S. A. Budd. They never led me astray on the sails I made following their methods.
My own suggestion is to have the leach straight just to avoid the nuisance of battens. Otherwise just consult the book. I see there are currently 3 used copies at Amazon.com for $6.95 US.

thanks for reply I'll check amazon and buy a copy.

[iznogoud]

You can start with arround 6%, go up to 10/11% and finish arroud 9%
The curve have to look fair.

Start wit a fixed camber position arrounf 42% for all your profiles. That should give you a good result.

The most important thing is to have all your curve parameter fair.
I don't know your program so i wont be a big help. sorry

Luff curve, you rather have to much (easy to recut) then not enough... max at 50% and be symetric is a good start.

good luck

[Gilbert]

A flatter sail is better than one with too much draft if you are not going to replace the sail if the wind comes up.
Uffa Fox said he never lost a race through using a sail that was too flat.

[gonzo]

Uffa Fox raced with cotton sails that were cut flat and then strectched to shape by the user.

[Crag Cay]

Uffa Fox raced with cotton sails that were cut flat and then strectched to shape by the user.

Well . . he perhaps started with cotton sails but there was plenty of time in his life to do an awful lot of sailing with terylene sails. He took a keen interest in the prototype sails Gowens produced in 1950.

To when is that quote attributed?

[gonzo]

Terylene is very strechy compared to moder polyesters.

[Crag Cay]

Terylene is the trade name of ICI who invented the stuff.
Dacron is the IDENTICAL stuff made by Dupont under licence from ICI.

[Gilbert]

Mr. Fox's comment was made while discussing how much draft your mainsail should should have. The material is not relevant. His inference was that he certainly had lost races through having a mainsail with too much draft.

[gonzo]

I guess the sails I've used that were terylene were old. The fabric was very strechy