Mainsail Boom Preventer


In order to prevent the boom from swinging wildly in the case of an accidental jibe, we use a boom preventer. We prefer the single block setup with both ends of the line accessible without leaving the cockpit. When the wind is aft of the beam (broad reach or run) or there are heavy seas rocking the boat significantly, using the preventer is recommended.


Setup

  1. Install a turning block at the bow. Make sure the attachment point is strong.


2. Run the continuous preventer line thru the block until midpoint and take each

end back to the cockpit on either side of the boat.



3. Install a soft shackle or other dyneema loop/strap on the boom (2-3 ft from the end of the boom if possible). 



Preparation

1. Before bearing away to a broach reach, connect the leeward end of the preventer to the lanyard on the boom.


2. As the mainsheet is eased out and the boom goes back towards the shrouds, take up the slack on the windward end of the preventer.

3. Once the mainsail is trimmed to the desired wide angle, snug up the preventer line and cleat it off on the windward side. 

Use 4 wraps on the winch in case you have to ease the preventer is a controlled fashion after an accidental jibe.


Jibing


1. Take the windward end of the preventer off the cleat.


2. Center the boom as you normally would before the jibe.


3. Disconnect the preventer from the boom lanyard and connect the end that was on the cleat.


4. Jibe the mainsail and ease out the mainsheet while taking up the slack on the new windward end of the preventer line.


5. Once the mainsail is trimmed to the desired wide angle, snug up the preventer line and cleat it off on the windward side.


Accidental Jibe


1, If you experience an accidental jibe stopped by the preventer, the main will be backed. Steer the boat up towards the 

wind until the main is no longer backed. Do NOT release the preventer suddenly until the main is drawing correctly. 

Unlike a mainsheet easing out and away from the cockpit, the preventer ease would allow the boom to come towards

the cockpit. It may be possible or even necessary to ease it in a controlled fashion with the winch.