Using a Boom Preventer

[magicol]

Recent helpful threads here have caused me to look at the way I rig a preventer on my boat. I raced dinghies for many years and have the bruises to show the effects of an uncontrolled gybe so I have always understood that this is a critical safety issue. Now however, I’m wondering how a preventer actually works in practice and what risks there are if it is ever needed.
I use a preventer but tend to be ultra cautious and usually end up ‘tacking’ downwind. I’ve never been in a situation where the wind has caught the ‘wrong’ side of the main so calling the preventer into action.
I completely understand the theory of using a preventer and how it aims to protect the rig but I wonder what stresses are created on rig, rudder, steering and boat generally if ever a helming error or wind shift causes the boat to try to gybe but is stopped from doing so by the preventer.
Is this an issue? Or am I worrying needlessly?

 

[FairweatherDave]

Others will come along but I can describe my experience of backwinding the main with preventer on. One situation is when goosewinging in very benign conditions. Easy to helm back on the water right downwind course. The second situation has been in more rolly seas. After an accidental gybe my priority has simply to release the preventer quickly but under control, and so complete the gybe. The rudder forces and heeling can then be brought back under control.

 

[Supertramp]

There are numerous threads on this with much discussion and different view points. There is no single yes/no answer! I think stopping or controlling the boom in a gybe situation is an important safety measure, with the boom and mainsheet creating serious injury and damage potential. And perhaps even more so if cruising or singlehanded when your attention can easily be elsewhere.

A boom brake is one option which will slip under high load and slow the boom movement in a full gybe. Often attached to the kicker attachment.

A preventer is rigged to stop a gybe developing, often from the boom end to the bow. It may stop the boom in a full gybe or it may stretch/break. Depends how it's set up.

I also use one in lighter winds and rolly seas on all points of sailing to stop the boom moving and slamming.

My advice is to research the threads, read some of the published articles and then experiment with what works for your boat and the way you sail.

 

[Steamkettle]

This is one of a series of articles discussing boom preventers & brakes where the forces you were querying are calculated and applied to potential solutions. It's a paywall site but IMO very much worth the money for anyone venturing beyond the confines of a harbour.

Building A Safer Boom Preventer, Part 1—Forces and Angles

 

[Sea Change]

I'm a big fan of preventers, and always rig one when sailing deep downwind for more than a few miles.
I have a line permanently attached to the boom end, and clipped on near the gooseneck. I then extend this with another line outside of the shrouds, round a fairlead at the bow, and back to the cockpit. This saves all the messing about wrestling to tie a line on to the end of an uncooperative boom. If I anticipate frequent gybes, I'll prepare an extension line on each side.

There seem to be two schools of thought on the best way for a preventer to behave- some favour a bit of elasticity, others think it should be as tight and unyielding as possible. I'm in the latter camp, because I would rather the boat round up under the pressure on the main, than have the preventer stretch to the point where it places pressure on the shrouds. But I can see arguments both ways.

 

[Stemar]

I'm a big fan of preventers, and always rig one when sailing deep downwind for more than a few miles.

Same, but not in crowded waters, as you can't change course in a hurry if someone ignores colregs (that "I'm racing" guy, for instance). I reckon that, with a preventer on the main and a pole on the genny, a boat almost qualified for a D flag, but That Guy wouldn't know what it meant anyway

I haven't sorted how to do it on Jazzcat yet, but on Jissel, I had a line that clipped onto the pushpit, went outside everything to a block at the bow and back to a cleat on the pushpit. To use it, I just unclipped from the pushpit, clipped to the end of the boom and took up the slack. If I needed to gybe, I'd take the preventer in hand and control the boom's movement with it, using a turn around a cleat, if necessary. If the wind was too strong for me to do that, I'd generally just be under poled out genny, anyway. The preventer set up like that was also useful when picking up a mooring in a blow, as I could attach it by the cockpit and pull it in at leisure.

 

[flaming]

I'm a big fan of preventers, and always rig one when sailing deep downwind for more than a few miles.
I have a line permanently attached to the boom end, and clipped on near the gooseneck. I then extend this with another line outside of the shrouds, round a fairlead at the bow, and back to the cockpit. This saves all the messing about wrestling to tie a line on to the end of an uncooperative boom. If I anticipate frequent gybes, I'll prepare an extension line on each side.

There seem to be two schools of thought on the best way for a preventer to behave- some favour a bit of elasticity, others think it should be as tight and unyielding as possible. I'm in the latter camp, because I would rather the boat round up under the pressure on the main, than have the preventer stretch to the point where it places pressure on the shrouds. But I can see arguments both ways.

Exactly my favoured setup. The only modification I've made to suit my current steed is that when I rig one I tie it round the boom and through the clew of the main. In this way I hope to avoid any excessive unwanted loads on the boom.

I'm also in the "take the slack out of the preventer" camp. I have found that if the gybe is the result of a bit of inattention by the helm you can generally steer the boat back through without any issues if you react reasonably promptly to the gybe. If it's more of the "oh poo" round down broach type, then you will need to ease the preventer line and let the boom across gently once you're sure that everyone is clear.

 

[dansaskip]

I rig two preventers, one each side. One end is clipped (with a Wichard clip) to a short rope loop permanently tied to the boom end and led forward to a turning block far forward then back to one of the winches on the coachroof so within easy reach of the helm. I wrap this line around the winch and depending on the number of turns holds it securely but is quickly releasable or would slip in an extreme case. In an intentional gybe as I centre the boom I can unclip the preventer from the boom loop and clip in the one from the other side. So all done from the cockpit. The unused preventer or preventer's are clipped to the guardrail wires agin in easy reach.
It took me a while and may different tries to come up with this way to do it but it seems to work well - at least for me and my boat and single handing.

 

[Sandy]

Like @dansaskip I rig two lines, they happen to be my mooring lines, loop goes round the end of the boom led forward to the bow cleats then back to a cockpit winch.

 

[westhinder]

Exactly my favoured setup. The only modification I've made to suit my current steed is that when I rig one I tie it round the boom and through the clew of the main. In this way I hope to avoid any excessive unwanted loads on the boom.

I'm also in the "take the slack out of the preventer" camp. I have found that if the gybe is the result of a bit of inattention by the helm you can generally steer the boat back through without any issues if you react reasonably promptly to the gybe. If it's more of the "oh poo" round down broach type, then you will need to ease the preventer line and let the boom across gently once you're sure that everyone is clear.

Good thinking. My approach has been to clip the preventer to the attachment point for the mainsheet on the boom, which is approximately 25 cm from the end of the boom. Your system enables this point on the boom to move with the reefs, on the other hand it would involve untying and re-tying as you take in or shake out reefs.

 

[RunAgroundHard]

... a preventer and how it aims to protect the rig but I wonder what stresses are created on rig, rudder, steering and boat generally if ever a helming error or wind shift causes the boat to try to gybe but is stopped from doing so by the preventer.
Is this an issue? Or am I worrying needlessly?

No it is not an issue in itself. Most accidental gybes will be managed by the vessel without stressing everything to failure. There are quite a few videos on YouTube that show this with all sorts of rig types accidentally gybing and the vessel recovering. Of course there are always exceptions and booms do brake, masts snap and steering fails.

Are you worrying needlessly? I think that depends on the type of boat you sail, the age of the rig, the state of wear and tear, your ability to reef down wind. For example, you rig your gybe preventer correctly for your boat type, mainsail is reefed for the wind strength, everything is marinated, all should be fine. You gybe accidentally, the mainsail is backed, the gybe preventer snaps and the boom moves rapidly across the boat and snaps. Force on steering should be manageable but a weak steering cable or a rotted tiller or cracked quadrant could see loss of steering and you entering SNAFU land.

For those who leave their gybe preventers premenantly rigged, UV radiation significantly degrades the strength of the line. I used to leave mine permanently rigged, but now I don't, it does not have to be there all the time and takes seconds to rig.

I don't know if carbon fibre masts and booms are more susceptible than alloy.

 

[Sea Change]

The only instances I'm aware of where a boom was broken by a preventer were when it wasn't attached at the end.