Measuring Sails

Using I, P J and E  , the sailmaker is able to  determine the size of the sails for your boat.

Genoa jibs are described as a percentage of the J measurement. A 150% genoa jib  has an LPG that is 150% of J. LPG is the measurement from the clew of the sail to a point perpendicular to the luff. To find the sail area you multiply LPG times the Luff  length and divide by 2.

Mainsail Luff length shouldn’t be greater then the P measurement when fully stretched, and the foot length shouldn’t exceed the E measurement when fully stretched.  Given a P and E measurement the largest main you can make for that boat will have a 90 degree tack angle. The area of the main is calculated by multiplying P time E and dividing by 2.

Symetrical spinnakers have an SL or luff length equal to .95 times the square root of  I squared plus J squared. This number usually comes out close to the I measurement of the boat. The  SMW  or spinnaker width is 180% of the J measurement.  Th calculate the area of a spinnaker multiply the sl times the SMW.