Five Tips for Better Mainsail Trim
Article of the Month April 2008Get the best from your Mainsail and Sail plan
On most modern cruising boats, the mainsail plays the leading role in the sail plan. Even on boats with in-mast roller furling mains, you have to use the big sail to balance the helm and create or decrease power.
Here are five tips to help you get the best from your mainsail and sail plan while striving to achieve a balanced helm and optimum boat speed:
ONE: The mainsail and the rudder work closely together so make sure you use them in synch. In other words, as you turn up to sail closer to the wind, trim in the main as you turn. This will make the boat “weathercock” into the wind. More important, when heading off the wind –particularly if you need to turn quickly—ease the mainsail so the bow can fall off without having to battle the power of the big sail.
TWO: Use the telltales to trim the sail. There should be telltales streaming from the ends of the battens on conventional mainsails or from the leech of the roller furling sails. When the sail is well trimmed, the telltales will stream straight aft. If the telltales flutter onto the windward side of the sail, you need to pull in on the mainsheet. If the telltales are fluttering on the leeward side, you need to let the sail out a bit.
THREE: Often the telltales will be out of synch because the sail has too much or too little twist. In light airs, you want more shape and twist to the sail than in stronger breezes so you need to haul the traveler to windward a bit, ease the boom vang and ease off on the outhaul to release the foot. In stronger airs, tighten the outhaul, haul down on the vang and ease the traveler to leeward.
FOUR: Reefing the sail should be an easy job for everyone who sails with you regularly so you can steer and trim while your crew hauls in a reef. The key to reefing the mainsail is the old adage, “reef early, reef often.” Most modern cruising boats will need to be reefed when the apparent wind—wind over the deck—reaches 18 to 20 knots. Sailing up wind, that’s six knots of boat speed into 15 or so knots of wind speed.
The point is to get the boat back to sailing more upright and to relieve weather helm. Sailing with the rail buried and the helm hard to windward is slow, uncomfortable and a sure sign of a mainsail that needs to be reefed.
On roller mainsails, all you have to do is roll in enough sail to balance the helm to the point that you have about five degrees of weather helm. On slab reefed mains, the furling adjustment is less precise since the first reef will remove roughly 30 percent of the sail area, which may be more than you want. Still, you may be surprised after reefing to find that the boat’s easy, upright motion and light helm has you sailing faster and higher than you were before you reefed.
FIVE: Preventers, vangs and boombreaks will help you control the most dangerous piece of gear on the boat—the boom. Preventers are lines that run from the end of the boom to the foredeck or bow when you are running downwind to keep the sail from accidentally jibing across the boat. Vangs are the rigid, adjustable struts that run from the boom to the base of the mast; but, vangs are also block and tackle rigs that run from the middle of the boom to the middle of the side decks, which in turn help “prevent” jibes and allow you to flatten and control the sail. Loose vangs work really well in lumpy conditions when the boom is bouncing around.
Boombrakes are devices that attach to the middle of the boom and allow you to control the side-to-side movement of the boom from the cockpit. As a jibe preventer or jibe controller, a boombrake can be a really useful tool.
The mainsail is your big work horse, so you need to get it under control and hauling in the direction you want…or you may find yourself struggling to get the best from your boat.
