is used for preventer lines. To reduce the shock loads on the tackles, for example in an unexpected jibe, three-strand nylon line may be preferred over braided cored line. Boom Brake Another form of preventer is the boom brake, which, when sailing downwind, can also be used to jibe the mainsail in a slow, measured action. The brake usually rides on a line running perpendicular to, and below the boom. When the boom brake is actuated, friction on the line either works as a preventer (stops the boom from moving in the direction that would slacken the main sheet), or slows the boom’s speed while jibing. The brake is actuated by either tensioning the line upon which it rides or by using a second line to adjust the brake itself. Jibing When jibing a fully loaded mainsail in a following sea, the following procedure may be used. Using the steering, the stern of the boat is carefully brought up into the wind. Then the leeward, working preventer is released little by little, while the mainsheet is shortened to bring in the boom. It is important to maintain at least a turn or two around the preventer's cleat the whole time ready to catch an early jibe during this stage of the manoeuvre. The mainsheet should pull the preventer around its cleat, without it being offered any slack. All the while it is also necessary to take in slack on the lazy preventer to keep it under control (i.e. prevent it getting tangled around something) until it is needed. When the boom is as near as possible to midships (near to running fore-and-aft along the boat's centreline), the working preventer is slackened, the lazy one tightened, and the mainsheet made very secure. It is important that all crew are safe from where the boom may swing, and a call of "Jibe-ho" is a traditional last warning for this. At this point, a slight steering adjustment will actually jibe the sail. The course of the boat may slew further than expected, which can be ignored as it gives a shorthanded crew time to do the next three things: Run out the mainsheet as fast as possible without burning the hands, ensuring that the newly-lazy preventer runs free, then tighten in and secure the newly working preventer. External links Photo-sequence of a yachtsman single-handedly jibing during an ocean passage and setting a preventer