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Calculate The Size Of A Sail

To calculate the square area of a rectangle, you multiply the base by the height. (in other words, the length of the short end multiplied by the long side).

Calculating the square area of a right triangle is very easy because it is half of a rectangle. You multiply the base times the height, then divide in half. But that only works for right triangles where the base and height are perpendicular (at 90 degrees).

When it comes to calculating the area of non-right triangles and 4 sided polygons that don't have right angles, there is a simple trick, all you need to do is split the shape up into multiple right triangles and rectangles. Calculate those seperately, add them all together and presto, you have the total sail size.

Lets calculate an example using the dimensions of my red sail, the dimensions are listed on the Super Awsome Leg O Mutton page.

Upper Triangle:
A = 8.25 feet (8'3")
B = 10.58 feet (10'7")
A * B / 2 = 43.6 sqft


Lower Triangle:
A = 8.25 feet (8'3")
C = 3.41 feet (3'5")
A * C / 2 = 14.0 sqft

43.6 sqft for upper triangle
14.0 sqft for lower triangle
-------
57.6 total square feet

Here is a sketch of a balanced lug sail. It can be broken into a couple of triangles, simply calculate the area of those trangles plus the main rectangle, add them all together and presto you have the square area of the entire sail.