Rigging a Boom Brake

Before I left Sydney for Hamilton Island in May, I rigged a boom brake to control the boom during gybing. I knew I was going to be short-handed some of the time and a recent fatality on the coast where a man was killed when struck on the head by the boom during an accidental gybe was fresh in my mind.

My boom brake is very simple – a Figure 8 “rescue descender” used for rock climbing, which I got off EBay for $45, and 20ft of 1/2in polyester braid line. The line is shackled to the starboard toe-rail and runs through the Figure 8 to a block shackled to the port toe-rail and then back up to the cabin top jammers via a free sheave in the line organiser. I use a winch to grind it on. Because of the set-up, it effectively has a 2:1 purchase.

When the line through the Figure 8 is slack, there is virtually no friction and thus no resistance. Wind the boom brake line on tight though, and quite a bit of braking effect is generated. The tighter the line, the higher the friction. I had to play around a bit with the attachment points on the toe-rail and boom to even out the friction through the boom’s swinging arc, but as the boom attachment lug can be moved anywhere between the vang attachment and the boom end, this was not an issue. I’ve opted for higher friction at the end-of-arc, with less friction on the centreline. This way I know the boom will be gradually slowed down as it reached the end of its travel.

A boom brake has a number advantages:

  • The forces on the boom are controlled by friction, so it won’t over-stress the boom when dragging the boom in the water.
  • The boom brake acts as a second vang, pulling down on the boom towards the toe-rail. This is beneficial side-effect is most noticable when running with the main let off. Under these conditions I’ve found the vang to be a bit under-powered; the boom brake significantly reduces the strain on the vang.
  • If you managed to break the traveller or otherwise stuff up the main sheet, the boom brake could be used as an emergency main-sheet.

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