The Four Elements of Sail Trim

Before we go into the individual adjustments made to your headsail and mainsail for proper sail trim we need to understand the 4 main elements of sail trim. Here is a brief description of each element along with how to control it.

I. Draft Depth- belly of the sail.
A) Controlled by backstay (upper 1/3), outhaul (lower 2/3) and mainsheet.
B) If you increase the tension on any of the above, you flatten the sail.
1. Flat for heavy winds and close hauled sailing
2. Belly for light air, reaching or running

II. Draft Position – 50% along the boom.
A) Controlled by the backstay, outhaul, Cunningham and
mainsheet
B) If you increase the tension on any of the above, you
will be moving the draft forward
1. Draft forward – less power in heavy air
2. Draft aft – more power in light to medium air

III. Twist – angle of the leech as viewed from below
A) Controlled by the mainsheet and the boom vang
B) If you ease the above, you will get more leeward twist
1. More twist is good for speed and acceleration
2. Less twist is for better pointing

IV. Angle of Attack – angle between the boom and the apparent wind
A) Controlled by the mainsheet and the traveler
B) If you trim in the above, you increase the power and lift by creating a larger difference between low pressure on leeward side and high pressure on the windward side.