SAIL DATA (please use feet/decimal feet; i.e. 66.24') I - A dimension from the headsail halyard hoist to the sidestay termination (chainplate) or sheer line of the boat. J - Distance between the headstay termination (chainplate) at the deck to the forward surface of the mast at the sheer line. P - Distance from the top surface of the boom to the maximum mainsail halyard hoist, or the distance between black bands on the mast. E - Distance from the aft surface of the boom to your desired clew position, or the distance between black bands on the boom.
Foretriangle: