Adjustable outhauls allow you to take advantage of the incredible range that today’s sails have, and they save time and effort because you don’t have to go back to the beach and re-rig every time the wind changes velocity.
You’ll discover that tweaking your outhaul on the fly allows your sail to respond differently at various angles of attack. A sail is more efficient while sailing upwind, for example, if more downhaul is added to make it more flat. On the other hand, while sailing deep off the wind, the sail should be full with very little to no outhaul. In fact, when sailing off the wind, it’s okay for your sail to touch the body of the boom. On a beam reach, the sail should be adjusted with marginal outhaul so it’s not too flat or too full; this will make it both controllable and fast.
To determine boom length, there are a couple of rules to follow: First, if conditions are such that your sail is perfectly powered, during puffs and lulls, your boom should be extended only as long as the manufacturer’s recommended specs. In the lulls, when you’re underpowered, simply release outhaul tension. This increases the sail’s depth and adds power. When you get overpowered in the puffs, just pull more outhaul.
Second, if you’re sailing in overpowered conditions, leave a minimum of 2 inches past the manufacturer’s recommended specs. With maximum outhaul, the sail can look extremely flat, and when your sail is flat, it will sail dead and twitchy in the light spots. To remedy the situation, just release outhaul tension.