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Goals of Sail Trim

The goal of trimming the sails is to go as fast as possible in a given set of conditions. The amount of wind available determines how much power we have available to move the boat forward. The waves determine how much power we need to move forward. Until the boat reaches maximum potential speed, we basically try to make use as much as possible of the available power. After that, we decrease using power, and 'depower', so that we aren't overpowered.

Trim Guidelines

A large chunk of this stuff is adapted from "Illustrated Sail & Rig Tuning" by Ivar Dedekam, a truly phenomenal book. If you are at all interested in sail trim, go and buy it - well worth the $$.

Sail-shape Overview

Basically, a sail functions like a wing of an airplane. That is, it produces lift to move us forward into the wind. There are a few simple rules that govern how a sail works:

	A sail only works well if there is air moving over both sides of it (telltales streaming aft tell us if that's the case)
	A deep sail (with a lot of curvature) produces a lot of power, and more drag than a flat sail
	A flat sail produces little drag at the cost of less power

So, how do we use this knowledge to trim our sails? A couple of resulting rules:

	In light air, we need power, hence deep sails
	In heavy air, we have power, so can go faster with flat sails and less drag

Now if we are still overpowered after we have flattened the sails, we can do one of two things

	Reduce the amount of sail up there (e.g. reef, change to a smaller jib)
	Reduce the amount of working area of the sail. In other words, have parts of the sail point directly into the wind, so it doesn't generate power. This is called twist.

Sail Controls

There are a bunch of controls that we can use to adjust our sails to the wind conditions, the goal being to be as powered up as we can, while not being over powered (e.g. too much weather helm or too much heeling).

In general, think of the sail as being a big triangular napkin. Now imagine that a bunch of us are holding this napkin up horizontally by the edges and corners. If we all pull really hard, we'll pull the horizontal napkin pretty flat. If we all take a step towards each other, it'll hang down with a big curve in it.

Sail controls basically work the same way. Depending on where we pull or ease on the sail, we'll get a flatter or deeper sail.

Jib Sail Controls:

	Headstay tension (depth of draft)
	Halyard tension (location of draft)
	Sheet tension (angle of attack)
	Fairlead location (twist)

Mainsail Controls:

	Mast Bend (backstay & checkstay tension) - depth & location of draft
	Halyard tension (location of draft)
	Outhaul tension (depth of draft bottom half/3rd of sail)
	Traveller location (angle of attack)
	Sheet tension (angle of attack & twist)
	Vang (twist)