Mainsail preventer line

[jbweston]

I'm in the camp that uses a preventer for stopping the boom from swinging in light airs as the boat rolls. That is, preventing it from swinging to a point where the main is back-winded and will cause an accidental gybe. I don't want a preventer that is strong enough to hold the boom once the main is back-winded, certainly not if the wind is above a light one.

Therefore some polyester codline would do the job for me from the point of view of strength, but it would be tough on the hands and wouldn't withstand chafe. So I use 10 mm braid on braid. That's on a 38 foot boat with a dipslacement probably around 9 tons.

In moderate to stronger wind I find the wind direction is more constant (except when blowing offshore round buildings, trees and other obstructions) so an accidental gybe is less likely. It's when the wind's light and variable that I have trouble to prevent.

The key to preventing accidental gybes, in my opinion, is not accidentally gybing, which is down to the helmsman (or often in my case, the autopilot) and how close to dead astern the skipper expects him/it to steer. Of course I make mistakes but my aim is not to gybe accidentally. I wouldn't like to ask a preventer and the associated anchorages to hold if I gybed in a blow.

I have one length of line permananetly attached to the boom and the longer length on deck ready to rig. I join them with a heavy duty alloy Inglefield clip, one half of which is permanently in place on each end to be joined. I've tried to remember who made it but can't. I thought it was Wichard but can't find it on their site.

 

[ip485]

Inevitably, I am going to say a boom brake has many advantages, and may be worth considering, if you havent yet rigged a preventer.

 

[Refueler]

Maybe I'm strange - but I dislike trying to stay direct in line of wind and prefer to sail off direct wind direction ... and purposely gybe every so often to make my destination... I accept in strong winds this can be a risk ... but if its that strong - then I'm on foresail only anyway ..
The odd time I do rig a preventer is if the boat is rolling in swell as you get sometimes ... that sickening lurch type of roll ... but then mines just a simple line clipped to boom and then down to cleat near bow. Basically because I don't use preventers in strong wind ... there's not the real need for line led back to winch etc.

But as I said - that's me.

 

[gregcope]

I have a 12mm line under the boom, with two eye splices and soft shackles. The length is from the aft end of the boom to the kicker location. The idea is that the kicker attachment will always be inboard/accessible.

I then have two lines that run from the cockpit forward to a snap shackle near the bow back down each deck and attached to the kicker end via a bowline, outside of anything.

To deploy, unhitch the kicker attachment and sheet in the side you want to prevent. On Gybing release and sheet in other side.

This is all in 10 to 12mm nylon. I want stretch as it is easy to damage a boom by dragging it in the water or having really strong attachment points in the wrong place. A little stretch will absorb energy and hopefully stop damage, but be enough to stop the boom coming inboard enough to hit anyone/anything.

Works for me. YMMV. Used so far in winds upto F7.

 

[jdc]

...I don't want a preventer that is strong enough to hold the boom once the main is back-winded, certainly not if the wind is above a light one...

The odd time I do rig a preventer is if the boat is rolling in swell as you get sometimes ... that sickening lurch type of roll ... but then mines just a simple line clipped to boom and then down to cleat near bow. Basically because I don't use preventers in strong wind ... there's not the real need for line led back to winch etc...

I think the thing which I take away from these posts is that we all do different sailing. Short or single-handing oceanic passages puts a different perspective on things. Especially in the ITCZs where one may be in a gentle broad reach with full sail up and then 5 mins later - and it's pitch black so you won't really see it coming, a 90 degree shift and gusts to 40 knots. I tell you, you want a preventer, a strong one, to a point well forward, led back to a winch in the cockpit via a set of (possibly snatch) blocks! I think ever specifying a preventer which would snap in a back-wind is downright dangerous. Unexpected gybes are what kills ocean sailors.

 

[RupertW]

I think the thing which I take away from these posts is that we all do different sailing. Short or single-handing oceanic passages puts a different perspective on things. Especially in the ITCZs where one may be in a gentle broad reach with full sail up and then 5 mins later - and it's pitch black so you won't really see it coming, a 90 degree shift and gusts to 40 knots. I tell you, you want a preventer, a strong one, to a point well forward, led back to a winch in the cockpit via a set of (possibly snatch) blocks! I think ever specifying a preventer which would snap in a back-wind is downright dangerous. Unexpected gybes are what kills ocean sailors.

That’s where I’m coming from too. I was really surprised to see suggestions about the vang being part of the setup. I want only the end of boom and a forward cleat used.

 

[RJJ]

I believe the preventer should go to the same point on the boom as the mainsheet. In my case, the boom end. On many cruisers, mid-boom. Never the vang take-off.

 

[dunedin]

I think the thing which I take away from these posts is that we all do different sailing. Short or single-handing oceanic passages puts a different perspective on things. Especially in the ITCZs where one may be in a gentle broad reach with full sail up and then 5 mins later - and it's pitch black so you won't really see it coming, a 90 degree shift and gusts to 40 knots. I tell you, you want a preventer, a strong one, to a point well forward, led back to a winch in the cockpit via a set of (possibly snatch) blocks! I think ever specifying a preventer which would snap in a back-wind is downright dangerous. Unexpected gybes are what kills ocean sailors.

I agree. For sailing at night and/or in waves I would definitely want
- preventer rigged to the boom end (not mid boom mainsheet point)
- strong enough to hold the boom when aback in 30 knots
- able to be eased under control from the the cockpit
Why do I say that? Well been there done it when confused in the dark in the middle of the night mid ocean after change of watch we gybe accidentally. Going on deck in the dark and waves to release a gybe preventer at a mid cleat would be near suicidal, particularly as likely to be (as in our case) crew leaping on deck direct from bunks with no life jackets or harnesses on.
Boom preventer suddenly breaking would have been hugely dangerous to crew and or rig.

And seen so many broken booms due to gybe preventers tied to middle of the boom. Fine for sailing in flat water and daylight, but boom can break in an instant if broach to windward and boom end goes in water at speed. That is when a preventer with a bit of give (ie not dyneema) but still with strength to restrain the boom is needed.

 

[jbweston]

I think the thing which I take away from these posts is that we all do different sailing. Short or single-handing oceanic passages puts a different perspective on things. Especially in the ITCZs where one may be in a gentle broad reach with full sail up and then 5 mins later - and it's pitch black so you won't really see it coming, a 90 degree shift and gusts to 40 knots. I tell you, you want a preventer, a strong one, to a point well forward, led back to a winch in the cockpit via a set of (possibly snatch) blocks! I think ever specifying a preventer which would snap in a back-wind is downright dangerous. Unexpected gybes are what kills ocean sailors.

I'm sure you're right. Different sailing, different requirements. I'm in the Baltic, long light days, mainly predictable wind conditions in the short term. No need for a preventer at all much of the time. It's slatting I'm trying to prevent, as uneccesary rattles and bangs offend my aesthetic sense , and in light airs the danger of roll swinging the boom across far enough for the wind to get behind the mainsail is a problem. It would disturb my reading of Wallander and spill my mug of coffee.

 

[tudorsailor]

I agree. For sailing at night and/or in waves I would definitely want
- preventer rigged to the boom end (not mid boom mainsheet point)
- strong enough to hold the boom when aback in 30 knots
- able to be eased under control from the the cockpit
Why do I say that? Well been there done it when confused in the dark in the middle of the night mid ocean after change of watch we gybe accidentally. Going on deck in the dark and waves to release a gybe preventer at a mid cleat would be near suicidal, particularly as likely to be (as in our case) crew leaping on deck direct from bunks with no life jackets or harnesses on.
Boom preventer suddenly breaking would have been hugely dangerous to crew and or rig.

And seen so many broken booms due to gybe preventers tied to middle of the boom. Fine for sailing in flat water and daylight, but boom can break in an instant if broach to windward and boom end goes in water at speed. That is when a preventer with a bit of give (ie not dyneema) but still with strength to restrain the boom is needed.

Just a comment or two.......... When I was on a trip at night across Biscay downwind on autopilot, we had an accidental gybe. The preventer was on the winch and quite tight. The preventer did not stop the boom reaching the midline, but only just. The only damage was a bent stanchion. The guy on watch reacted appropriately buy switching off the autopilot and staying on the new tack. Had he gone back to the original tack, the boom would have swung without restraint as far as the mainsheet would allow.

So my learning points are firstly that the stretch in the 12 braid on braid that runs from from the end of the boom to the bow fairlead and then back to the winch at the cockpit (so about 25metres) is enough to allow the boom to reach the midline. Secondly, whoever is on watch if/when there is an accidental gybe should not immediately correct to go back to the original tack without taking in the main!

And yes, I was told off for trying to go on deck without my lifejacket having been woken by the loud bang!

TudorSailor

 

[Refueler]

I'm sure you're right. Different sailing, different requirements. I'm in the Baltic, long light days, mainly predictable wind conditions in the short term. No need for a preventer at all much of the time. It's slatting I'm trying to prevent, as uneccesary rattles and bangs offend my aesthetic sense , and in light airs the danger of roll swinging the boom across far enough for the wind to get behind the mainsail is a problem. It would disturb my reading of Wallander and spill my mug of coffee.

I am Baltic as well and agree.

As another says earlier - the sailing area and style affects what you do.

If I was sailing oceans - then of course a preventer controlled from cockpit is the answer ... but given my post earlier explaining that I use it mostly to prevent the boom swinging about in those horrible following seas ... its a different game.

 

[temptress]

Will fit one imminently but wondered what size of line I should look at. Yacht is 39’ will fully battened main. Would 10mm line be ok?

i would go for 14mm with some stretch. Maybe braid on braid or in your case anchorplat?

you want some give to absorbs shock loads. IMO Dyneema would be too rigid. 1 is certainly strong enough.

On out boat we use 14mm braid on braid. we have done over 60k mile sqith this setup including a fe wunint3need gybes in Squall's.

 

[Stemar]

When I use the preventer, the boom positioning is tensioned between the sheet and the preventer. In such a case, a little elasticity is advantageous, but not too much. If things are bumpy enough for there to be any risk of the boom getting in the water on a Snapdragon, the Admiral will have instructed me in no uncertain terms to reduce sail well before. In fact, I'll probably be under orders to get into the nearest port with all haste.

 

[lw395]

I'm in the camp that uses a preventer for stopping the boom from swinging in light airs as the boat rolls. That is, preventing it from swinging to a point where the main is back-winded and will cause an accidental gybe. I don't want a preventer that is strong enough to hold the boom once the main is back-winded, certainly not if the wind is above a light one.

Therefore some polyester codline would do the job for me from the point of view of strength, but it would be tough on the hands and wouldn't withstand chafe. So I use 10 mm braid on braid. That's on a 38 foot boat with a dipslacement probably around 9 tons.

In moderate to stronger wind I find the wind direction is more constant (except when blowing offshore round buildings, trees and other obstructions) so an accidental gybe is less likely. It's when the wind's light and variable that I have trouble to prevent.

The key to preventing accidental gybes, in my opinion, is not accidentally gybing, which is down to the helmsman (or often in my case, the autopilot) and how close to dead astern the skipper expects him/it to steer. Of course I make mistakes but my aim is not to gybe accidentally. I wouldn't like to ask a preventer and the associated anchorages to hold if I gybed in a blow.

I have one length of line permananetly attached to the boom and the longer length on deck ready to rig. I join them with a heavy duty alloy Inglefield clip, one half of which is permanently in place on each end to be joined. I've tried to remember who made it but can't. I thought it was Wichard but can't find it on their site.

Completely agree with that, we rig a preventer far more often in light air, to stop the chop or powerboat wash shaking the sails, than we do in strong winds.
In light air, anything would do.
But we have a permanently rigged line from the clew end of the boom which we take forwards. It's 10mm dyneema I think.
In strong wins if we really feel the need for a preventer, we clip the pole downhaul/foreguy to the preventer line, so it's 2:1 and led back to the cockpit.
It is handy to use a preventer when you're goosewinging the jib, or running down a narrow channel perhaps.

But in any weather, you have to think for a moment about what loads it's going to put on the rig if you dip the clew in the waves.
Better to reef the main and use more genoa?
Generally, head up a few degrees until you're sure of not accidentally gybing. It's a lot more pleasant and rarely slower.
Use the windshifts perhaps?
Sail the boat. Take charge of it and get good at gybing, then you will never feel the need to push your luck running too broad or by the lee.
(I sail my Laser by the lee sometimes, it can be fast, but swimming is always on the menu if it's breezy.....)

 

[thinwater]

At what wind angles are people experiencing accidental jibes? For me, only if running wing-and-wing (which cats can do without poles).

When you I use one?

• Wing and wing.
• Any time the boom is bouncing too much.

I don't use one with the chute because I don't fly a chute below ~ 110 degrees apparent. Few cats do. With the genoa the AWA will be <80 degrees. In both cases, no gybe risk (cats don't roll downwind either).

Because few cats have a vang, I I typically take it to the midships cleat. This will seem wrong, but remember that on a cat, we don't ease the boom all the way forward (the shrouds are in the way) and the midships cleats actually give a very good, strong angle with the line from the boom end. This is different from monos and I don't suggest you try it.

As for boom brakes, I'm listening. I've used them, didn't really like them... but a cat can do the same thing, to a large extent, with a beam-width traveler. We seldom have that much sheet out (remember the shroud problem?). I'm trying to understand the use of brakes better. There have been a few high-profile cases of big boats gybing, resulting in fatalities in part because after the preventer failed, they could not regain control of the boom. It seems to me a boom brake could be really handy in this case, even if it was not used all the time.

I have seen at least two reports of boom brakes causing boom failure. Poor attachment point and overly agressive use, perhaps. But failure nonetheless. That's concerning too. Most booms really are not designed for side loads.

 

[Caladh]

Thanks for all the really informative replies.

 

[lw395]

Just a comment or two.......... When I was on a trip at night across Biscay downwind on autopilot, we had an accidental gybe. The preventer was on the winch and quite tight. The preventer did not stop the boom reaching the midline, but only just. The only damage was a bent stanchion. The guy on watch reacted appropriately buy switching off the autopilot and staying on the new tack. Had he gone back to the original tack, the boom would have swung without restraint as far as the mainsheet would allow.

So my learning points are firstly that the stretch in the 12 braid on braid that runs from from the end of the boom to the bow fairlead and then back to the winch at the cockpit (so about 25metres) is enough to allow the boom to reach the midline. Secondly, whoever is on watch if/when there is an accidental gybe should not immediately correct to go back to the original tack without taking in the main!

And yes, I was told off for trying to go on deck without my lifejacket having been woken by the loud bang!

TudorSailor

Looking at that, it seems to me that it takes a lot of stretch for the boom to go from fully out to centreline? Must be more than 1m of stretch, even if the boom was only out say 80 degrees?
1m in 20m is something like 1/3 the breaking load typically for polyester?
So more than 1500kgf in that rope?Seems a lot, just how windy was it? Or was the rope old and weak?
Or did all that force pull the rig out of shape? I think you have a pretty big boat?

Quite right not to gybe back, that is serious energy stored in that rope.

But when things start getting out of shape, isn't that when we should be wearing LJs? (Just saying, as I can see myself doing exactly the same!)

 

[jdc]

At what wind angles are people experiencing accidental jibes?...

Well, they're not frequent you understand, maybe once every other Atlantic crossing, but the angle can be anything aft of about 135 aparent. The reasons are (a) shifts happen and will not be seen in time if after dark and sudden (or you're asleep), and (b) wind-vane steering is occasionally pushed outside its ability to cope, and the boat either rounds up to a close reach or gybes unbidden. This happens whenever the boat's heading is pushed more than about 30 degrees off by a breaking wave (which, as often as not, is so friendly and joins you in the cockpit). On some passages this has been every 50 minutes, but mostly much rarer, thankfully!

While I quite agree with those who sail in the Baltic, or indeed in the English Channel, that in light winds one mostly uses a preventer to stop slamming, the OP' was asking what one should use and imho it's as well to specify what will do the job even if the conditions are a little worse!

It's also true that one could reduce sail, or just use foresails, which I do as a matter of course when I know it's really going to blow, but it's frustrating to go at 5 knots when one could do 8 just because one hasn't bothered to rig an appropriate boom preventer. Think about 2000 miles like that: about a week's difference in crossing time. Besides, the last time it really counted for me to have had good preventer was while racing (AZAB).

 

[thinwater]

^^ Thanks!

I can see how that would be more of a problem with a wind vane.

A multihull problem is that if you are going hard and jibe accidentally, with a preventer on hard, that can cause a capsize. When cruising, with the exception of a chute, it is a bad Idea to carry more sail than you can carry upwind, hauled in tight. This is one of the reasons.

 

[Finbar]

Agree with most of the above. I use a 12 mm line with eyed carbiniers at each end. Runs through centre of aft cleat clipped back on to itself to a block at the bow and back to the other aft cleat outside everything when stowed. In use release both ends, clip one to end of boom and winch other end. To gybe, release boom end when boom is hauled in, clip on other end and gybe. Very simple, easy to use, strong enough and stows well.