When our club started sailing J class to avoid the weed we used an IOM B rig to keep the cost down. Now we have some J’s with proper J class rigs I would like to chart the differences. I.E. when the fleet is on an IOM B rig should I be on a J class A or B rig?

A simple solution is the school maths area of a right angled triangle, 1/2 base x height... Won't be entirely accurate as it doesn't account for roach, but will give you a simple baseline....

For a bit more accuracy the roach area is roughly 2/3 * leech length * maximum roach width.   You measure the roach width at right angles to a line joining the tack to the clew.  Same formula can be used for luff round and foot round.

For more accuracy still, look at how 10R sails are measured.

For mathematicians - use Simpson's Rule.

Using Larry's triangle method I came up with the following in square metres :-

     J Class   IOM

A   0.552   0.538

B   0.466   0.378

C   0.433   0.253

Assuming I've got this right the closest seems to be the J Class C rig versus the IOM B rig.

I am surprised at the relatively small range in the J rigs and the bigger range in IOM rigs.

Some side by side testing based on these results seems to be indicated.

Cheers

Trevor