What Are I, J, P and E?
I, J, P and E are dimensions used in measuring the rigging and sail area.
I is measured along the front of mast from the jib halyard to the main deck. The main deck is where the deck would be if there were no deckhouse.
J is the base of the foretriangle measured along the deck from the headstay pin to the front of the mast.
P is the luff length of the mainsail, measured along the aft face of the mast from the top of the boom to the highest point that the mainsail can be hoisted or black band.
E is the foot length of the mainsail, measured along the boom from the aft face of the mast to the outermost point on the boom to which the main can be pulled or to the black band.
How to Calculate Sail Areas
The following formulas will give you approximately areas for:
- Mainsail = (P x E) / 2 (add 10% for racing mains)
- 155% Genoa = (( J x I ) / 2) x 1.65
- 135% Genoa = (( J x I ) / 2) x 1.44
- 100% Jib = ( I x J ) / 2
- Racing Symmetrical Spinnaker = 1.8 x J x I
- Racing Asymmetrical Spinnaker = 1.8 x J x I
- Cruising Asymmetrical Spinnaker = 1.65 x J x I