Boom Preventer

Prevent us, O Lord, we beseech thee, by thy most gracious favour... No, this time, the word prevent is in the modern meaning – to impede, to stop something from happening.

Sailing boats are notorious for people being hit over the head by the boom when it swings across the boat. This happens by tacking, when the bow is brought through the wind and sails in a close haul on the opposite tack. It also happens with a much more violent movement when running before the wind – the wind is astern of the boat, and the stern is brought through the wind. This is gybing, which should be a carefully controlled manoeuvre. If gybing is uncontrolled or accidental, it has catastrophic consequences on a yacht and causes a dinghy to capsize. It is the most frequent cause of capsizing.

Accidental gybing usually happens when sailing by the lee, with the jib opposite the mainsail in a scissors or butterfly configuration, the wind almost directly behind the boat and the mainsail is on the point of gybing. I often run before the wind in this manner, but avoid taking the boat to the utmost limit. The gybe is caused by the helmsman steering over, by a sudden change in the wind direction or a wave that pushes the stern over too violently to be compensated by the rudder.

The solution to this problem is to be able to control the movement of the mainsail, to bring it through the gybe slowly and gently. An alternative is preventing this from happening until the helmsman and crew are ready for the gybe. There are two devices: a boom brake and a boom preventer. The boom brake is set up when the boat is rigged, and is engaged when the line is pulled tight and cleated. The boom preventer has to be taken by a crew member forward, past the outside of the standing rigging and threaded through a mooring cleat or fairlead at the boat’s bow or a forward mooring cleat. The line is brought back to the cockpit. After the gybe, the line is pulled in and the process is repeated on the other side of the boat. This is nerve-racking on a yacht on a heavy sea and quite impractical on a dinghy.

Here is a presentation of several devices on a yacht and how they work:

With the exception of the boom preventer, which is simply a piece of rope or a warp, the braking devices are bought from the ship chandler’s shop and are quite expensive. The cost is justified by the saving of major repair costs to a broken rig, not to speak of an emergency at sea. That is for yachts with their enormous areas of sail.

A dinghy is that much more reactive and the simpler they are, the better they work, especially for racing. Dinghy cruisers tend to modify their boats and make them into “mini yachts”. An uncontrolled gybe, unlike on a large yacht, does not bear the consequences of breaking the rig. However, the boat rolls over suddenly and the boom end digs into the water, the hull lurches towards the wind, the stern and rudder lift up out of the water and no control is possible. The broached boat capsizes. A highly skilled skipper is able to anticipate the movement from the moment of the gybe, and gets up onto the uppermost side of the boat and clambers onto the centreboard, saving himself a swim. From sailing school, I have always been nervous about gybing, especially in a fresh breeze.

It is possible to avoid gybing altogether. You bring the boat up to the wind gently by hauling in the main and jib, and then you tack, and then ease off both sails after the tack. You always anticipate for the whims of the wind and waves by not going further away from the wind than a full reach. That is possible, but “chicken gybing” is laborious and complex.

I decided to install a boom brake on Sarum. Here it is:

The line is tied with a bowline to a chain plate on the starboard side, through the braking device, through a fairlead on the port side and back along the gunwale of the boat.

I have used a simple nickle-plated brass swivel, which I have attached to the boom vang (kicker or downhaul if you prefer) fitting. Friction is increased when the (red) line is tightened.

It is then taken back along the port side and tied to a pulley. Another line tied to the aft mooring cleat is taken through the pulley and back to a cleat. This second line gives a 2 to 1 force on the brake line. Because the braking device is not attached directly to the boom, there is a bit of shock absorbing, which is ideal.Before doing a gybe, I can take the line off the cleat and ease it out. I can slow the gybing of the mainsail and keep better control of the boat. When I am running before the wind and “on the lee”, I can prevent the boom from going over. The sail might start flapping and wind might start to hit the opposite surface, and this will warn me to correct my helm. Another trick is sailing in such a way as the jib is only just not collapsing, and this will tell me that the main is firmly on the right tack. But there are still those rogue winds and waves, and even the most experienced sailor cannot anticipate them.

The boom brake also works as a boom preventer. Another use for this device is when there is very little wind and the boat is “ghosting”. You can either sit on the lee side of the boat and let gravity keep the boom from falling to the other side and spilling the wind out of the sail, but that might be risky in the event of a sudden gust. You can use a whisker pole (the boat’s gaff) on the boom like on the jib, or this device.

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