Roach - What Size ?

Hi - I’ve learn’t a lot from these pages and run many searches - thanks to all the people who share their knowledge.

But I still have a question I can’t find an answer to : how do I decide what area of the main sail should be in the roach ?

I came across a small trimaran at a car boot sale and I am planning to make a smaller set of sails to hopefully help reduce pitch poling in stronger winds

Details of the trimaran :

Length = 65 cm, Beam = 58 cm, Mast = 92 cm, AUW = 1.1 Kg
Total sail area jib + main = 387 sq in, Jib : Main sail area = 1: 2
Estimated main sail roach area (ie additional to triangle) is 24% of main sail area

The only “facts” that I have managed to glean so far are :

  • the roach is about 2.5 inch on a Marblehead
  • about 15% max on a 1.3 metre mast
  • with a longer boom and less roach you can get better sail control and less twist as the wind picks up.

I hope one of you can help as I am keen to learn by doing - thanks in anticipation.

You are in an area of personal opinion… in my opinion :cool:

Much akin to asking who was the greatest ball player, if there was a definitive answer it would be obvious. Since you are seeing (and correctly so) so many different shapes and applications, you can see that no one single source has cracked the code on it either.