Sail Dimensions and Details

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Sail Dimensions and Details

Sailmakers require specific measurements in order to make up a sail. These are known as the p, e, i, j, figures and can be useful to find the lengths of the mast and boom.

p is the length of the luff of the mainsail from the top of the boom to the highest point a sail can be hoisted.

e is the length of the foot of the mainsail from the goose neck at the mast to the furthest point along the boom a sail can be fixed.

i is the length from the genoa/jib haliard at the top of the mast to the deck level, not the coach-house roof.

j is the length from the fixing point of the foot of the foresail to the mast at deck level, not the coach-house roof.

py and ey respectively apply to ketches and yawls and are the luff lengths and foot lengths of the mizzen sail.

iy and jy apply to staysails and are the halyard to deck, and staysail foot to the base of the mast measurements respectively.

Racing Boats will have a black band on the mast and boom to signify the measuring points for these figures.


Foresails that reach up to the mast (J = less than 100%) are called Jibs. Foresails that extend past the mast (J = greater than 100%) are called Genoas.

Jibs usually come in 3 sizes, No1 Jib or Working Jib, No 2 Jib, and No 3 Jib also called a Storm Jib. Their names developed from the old sailing ships.

Genoas usually come in 2 sizes. 155%J Genoa or 135%J Genoa although these sizes tend to get blurred. A Genoa larger than 155% becomes over-powerful and the nose of the boat will be blown away from the wind.

Cruising Chutes and Spinakers tend to be around 165%J

Formula for Working Out Sail Area knowing only the lengths of the sides of the sail

Area = SQRT(s*(s-a)*(s-b)*(s-c))   where s = (side a + side b + side c)/2