A lot of “Build Log” for Hulls of any kind, few “Build Log” for sails and none dedicated to “Sail drawing”. I decided therefore to presents a 7 pages paper (PDF) describing the method I use to DRAW my Class M Sails.
Why Class M ?
Because is more complicated then others.
Frank Russel, kindly enough, issued on the Net a set of Class M Sail forms with data ready to be copied and built.
Myself, I’m just explaining what happen before the drawing paper template is ready.
The document can be free downloaded, see below.
Hope will not be not too complicate to read it, drawings are reporting major data and text try to explain how it is done step by step.
Only Rig A is presented in the paper since Rig B and C follow the same drawing technique.
Any questions ? Do not hesitate

Here below a useful Guide Table to select the Class M Rigs and Sail Surfaces.

Another paper about general Data used to design a Class M Sail and description of the ‘surface transfer’ method to move part of the surface from Lower side of the Main sail to Upper side of the Main sail.
Plans for standard Rig Type B and C ongoing.

Thanks Claudio!!

I have been trying to find info on this everywhere.
I will download the PDF in the morning (on my phone now) and I’m sure I will have many questions.

PS - Happy Christmas everyone.

Hi guys :slight_smile:

I was hoping that someone could answer these questions for me.

  1. Main sail shape - what are the gains from different designs - eg. the flat topped mainsails on the IACC120 boats and the “triangular” shaped versions like the free Goth RG plans.
  2. Battens - how do you decide where and how long they should be, do you run them parallel to the water line or perpendicular to the leech etc?

I know that different classes are very strict on sail plans and battens (IOM seems particularly strict) but it’s quite difficult to get info on a basic starting point that is acceptable if you just want to play around with sails for fun.


let start with the principle that higher the mast is better fresh air you get.
Now the IOM, 10R, class M and many others classes, have their own rules where the sail shape including top main sail is defined .
Generally battens are oriented orthogonal to the leech.
The wide top main sail is a recent America Cup concept aiming to catch as much as possible air power .
This solution imply various techniques in order to keep the shape in place. Particular reinforcements and special battens are used similar to the ones used on sail surfs.
Of course wide top offer more sail power

Thanks Claudio,

With regards to the battens - is there a generally accepted procedure to determine the length of the battens?
Is it determined by something like the roach on the sails or the max camber position?

Am I correct in thinking that the reason the sails get a lower, wider profile as the wind increases is to reduce the levering force the sails exert on the rest of the boat (In my mind you are moving the fulcrum)?

I have just found this through a google image link and thought it might help out some others.

http://www.iacc120.it/Media/media.html you may observe here sail pictures of the AC120 models.
The Sail making, aside the Rules, is something personal where you can try to find a “solution”.
I suppose that the Bermuda Rig was responding to the double criteria to increase sailing power: aspect ratio where the taller mast and sails are offering the best efficiency and the simplicity of rigging.
More recently in the history with the America Cup, the technology and Rules allowed to build “squared Main sails” that of course are producing more power. At the begin the roach was rather rounded and full of battens.
Battens, when allowed by the Rules, should be put in the most appropriated places to insure the sail keeping shape including their length.
The point is that models shall race withing the Rules frames, and an AC120 cannot race officially with a Class M although having similar sail area. The Main top of a class M is normally limited to 20mm while on the AC120 can vary from 60 to 200mm.