Measuring sails

I’ve got a simple question on measuring sails. But I’ve gotten two different answers when I’ve asked people.

Attached is modified pic from the Marblehead rules, but it serves as a guide.

When laying out the quarter, half, three-quarter widths, do you do:



Hi Guzz


Please see attachments for any help !

I was afraid of that.

I guess I have to remake my last set of sails. Sigh… Some aspects of the rules just aren’t logical (to me), this was one of them.

I though the quarter points were found by folding the sails in half, then in half again on the leach, not the luff? I guess I need to go back and read the rules. I do know folding in half was the preferred method and can give slightly different dimensions.


Take another look at your diagram. The quarter width measurements are based on the R dimension, not Q. The “a” dimension has nothing to do with sail area calculations.

I wasn’t concerned with the quarter WIDTHS, those I understand.

It was the quarter POINTS, where along the luff do you measure the quarter widths, that had me confused.

I shouldn’t have use the word, WIDTHS in the original post, sorry.
Shows how to find quarter leech points. Note that they are leech, not luff, which will make them slightly higher and the sail larger than when measured by using the luff.

Folding the sails, as described previously, is a perfectly good method of locating the leach points. In fact, one of the previous Marblehead Class Rules pictured a method of draping the sails over a stick of sufficient diameter to avoid creasing the sail material and/or any luff wires.

For sails already on spars, however, folding or draping them won’t work. To find the mid point, I use a tape measure, a pencil, and an assistant to mark off equal length distances along the leach from the head and clew points until they meet at a single point. Then measure from the mid point to the head and clew points to get the quarter point locations.

It’s trial and eror, but with a little patience you will accurately locate the three leach quarter points.