On most boats, the mainsail is by far the biggest sail, and this means the mainsail trimmer has the most important speed-producing job in the whole crew.

Because there are so many ways to adjust the shape of your mainsail, trimming it can be pretty challenging. However, if you follow a few basic guidelines, even an inexperienced trimmer can make this sail go fast. Whether you race a one-design or a one-tonner, here’s a list of fool-proof mainsail trimming ideas and rules of thumb.


Before you start racing

Almost every crewing job requires a good deal of practice and preparation to optimize performance, and the main trimmer is no exception. Here are some things you can, and should, do before the race begins.

· Get familiar with all the sail controls such as vang, outhaul, cunningham, backstay and traveler. Know where each one leads and how to tighten and ease it.

· Attach telltales on the upper leech near the top two batten pockets. I recommend brightly colored yarn about 6-8 inches in length.

· Make sure your battens are inserted securely in their pockets, with the more flexible end forward. If you have a choice of battens, use bendier ones in light air and stiffer ones in heavier air.


You don’t usually need tension on the boom vang when sailing upwind in light or moderate air. As you get overpowered, however, you will start easing the boom below centerline. That’s when, in most boats, you should pull the vang on hard to keep the boom from rising up as you ease the sheet.   © Barry Hyman


· Hoist the main halyard so the head of the sail is all the way up to the black band at the top of the mast (you may have to ask someone on another boat to help you judge this). After sailing for a while, check the halyard again for possible stretch and slippage.

· In general, keep mainsail flogging to a minimum. This will prolong the life of your main and reduce the chance of pre-race damage to your sail or battens. If you have a leech cord, set it just tight enough to eliminate flutter.

· Be sure your mast is straight athwartships while sailing in a moderate breeze. To judge this, eyeball the groove on the aft side of the mast with your head as close to the gooseneck as possible.

· Adjust your main cam cleat so the jaws are just below the main- sheet when you’re holding it from a hiked-out position. You want the cam low enough so the sheet won’t cleat itself automatically, but high enough so you can use your hand or foot to get the sheet in the cam temporarily if you need to (I never cleat the mainsheet on a one-design).

·Ask your helmsperson to spend some time sailing upwind before the race, with another boat if possible. Trim your main to a good setting and use a magic marker to put a ref- erence mark on the sheet where it’s easy to see. This will serve as a quick guide for getting your main trim in the ballpark after tacks, ducks, mark roundings, etc.

· Set up all your control lines so they are clear, out of the way and even on each side.


The basics of fast trim

Once you start racing, follow these basic guidelines to get and keep yourself in the ballpark:

· Set sheet tension and traveler position so the boom is roughly on centerline. This is a good all-around position until you start to get over- powered, when you should drop the boom to leeward to reduce helm.

· Trim the mainsheet so the upper batten is parallel to the boom. To see this, crouch under the boom and sight upward, lining up the top batten with the boom.

· When the main is trimmed correctly, the telltale on the top batten should be streaming aft most of the time and stalling (curling behind the main) once in a while. In flat water and medium air – ideal pointing conditions – you can trim the mainsheet harder so the top telltale is stalled most of the time (and the top batten pokes a bit to windward). ■


This article originally appeared in David Dellenbaugh’s Speed & Smarts, The newsletter of how-to tips for racing sailors. If you want to sail faster and smarter, log onto SpeedandSmarts.com.