A trysail is a small, triangular shaped sail used on a sailboat, most often during storms or high wind conditions. Rather than provide a sail with which to derive power or the ability to move forward, trysails instead provide balance. In high winds or storms, a trysail provides control over how the boat lies in direct relation to the surrounding waves. Sailors can control which way a boat lists by adjusting the boat's trysail and using it to catch the wind to list the boat back one way or another.
For safety reasons, trysails and associated components must possess the ability to withstand gale force winds. As such, the material a trysail is cut from must be more rugged and stronger than typical mainsails. Trysails require more reinforcements at the corners and at each slide, as well as heavier fabric weight. There are no battens or batten pockets on a trysail, since its only job is to balance the boat during high winds and rough waters.
The most common sailboats to use a trysail are those with fore and aft rigging. That is to say, sailboats whose sails run in line with the boat's fore and aft lines, as opposed to athwart or across the ship's lines, are considered to have a fore-and-aft rigged sail. On such boats, the trysail sits behind the mainmast and mainsail. When used, such a trysail faces slightly athwart or across the boat, just behind the mainmast, to provide balance.
Some sailors prefer to use only storm jibs, rather than trysails, in harsh weather conditions. Storm jibs, small triangular sails to the front of the mainmast, much like trysails, assist with maintaining balance. On boats with a mast far forward, however, a storm jib alone does not provide adequate balance. Trysails offer the second sail needed to maintain balance, especially for shorter keels.
Experts recommend that trysails encompass an area no more than 30 percent of a boat's mainsail to prevent the sail providing momentum, rather than balance. Both the storm jib and trysails, according to experts, should be bright orange in color, for better visibility by rescue ships, coast guard crews, and other seamen. Additionally, many experts recommend a separate track specifically for use with a trysail, rather than sharing tracks with the mainsail.
Separate tracks for mainsails and trysails are recommended for nearly all sailing vessels, especially larger sailboats. The primary goal of a separate track is to prevent the need for removing the mainsail to use or set a trysail. On very small vessels, removing the mainsail, even in rough conditions, may not be a difficult procedure, although it is still not a recommended rigging option. Boats built for racing must consider weight and other factors, so a separate track may not prove beneficial, although for safety concerns a separate track is still considered the safest option.