DIY boom brake. What do you think of this?

[Oscarpop]

A couple of years ago, following a thread on here about diy boom brakes, I purchased a climbing figure of 8.

It's about 6 inches long in old money.

I was going to rig it to use as a boom brake. Hang it just aft of the rigid kicker. One line from the chain plate, through the figure of 8 ( as shown in the picture), then through a block by the other chainplate, led back to a clutch in the cockpit. I figure that this is the same tensioner as some of the other devices on the market, works on friction , however it cost a damn site less.

Is this a dumb idea? I don't want to be reliant on someone that is dangerous.

Ideas and suggestions please.

Yacht is 40ft and med displacement

 

[lw395]

Boom brake rigged near the kicker might break the boom if you use it in strong winds and the boom catches a wave.
If you want it for light airs and sloppy seas, fair enough, but if you need a preventer, rig it to the clew end of the boom.

If you just want to control the boom as it crosses the boat in a gybe, you won't regret sorting your mainsheet and buying a ratchet block.

 

[Sniper]

It is working on the same principle and at the same point on the boom as at least one of the commercial ones. I imagine that as long as you use it only as a brake during gybes it will work fine and improve safety. It might be more questionable to use it as a preventer as this might have the potential to damage the boom. I agree that a preventer is better rigged nearer the clew.

 

[johnphilip]

I have the overpriced Gyb Easy and on a 33' boat I need to use the second level rig so the rope has rather more friction than on your suggestion. It may work however as the other parameter is the tension in rope, if set pretty tight it may have a reasonable performance.
I don't know if you realise that the Gyb Easy you are mimicing uses a special rope which feels somewhat waxy and I am told is like a climbing rope. Mine has definitely lost its effectiveness over a few years and I probably need to replace the rope to regain efficacy, as instructed by the manufacturers.

 

[William_H]

The figure 8 device depends on the total rope tension to provide the frition where the rope turnsd around the shaft. I would think it would require some experiment to get the total tension correct to give the effect you want. ie enough friction to slow down the boom swing while not so much as to impeded the boom from gybing. Something like a high field lever on one end could ensure that you get a repeatable tension once you know what is needed. Or perhaps yu could just just the tension each time you fit it. good luck olewill

 

[Oscarpop]

I think that if I run the line back to the cockpit and through a clutch, I should be able to tension it easily to apply friction as the rope slides.
This is not meant to replace a preventer in strong winds, just slow the boom

 

[Len Ingalls]

Similar item http://dreamgreen.org/order2/boat-parts

 

[Venus1]

Howdy Oscarpop,
Good question. I have been down a similar path on my similar sized boat, with the same logic (and have also used the gyb easy on other boats). I use a climbing figure 8. I am still not totally happy, but gybes are controlled to some extent.
Some points:
You will need more turns than your pic shows.
Tension is critical. Both sides need tension.
Rope needs to be rough surface. Consider nylon for shock absorption (climbing rope)
Preferably use winch(es) at cockpit: 1) to get enough tension, and 2) for controlled release if needed.
Good luck,

 

[Gryphon2]

Old climbing rope. Invaluable for preventers, mooring in surging harbours and for anchor snubbers!

 

[Oscarpop]

Howdy Oscarpop,
Good question. I have been down a similar path on my similar sized boat, with the same logic (and have also used the gyb easy on other boats). I use a climbing figure 8. I am still not totally happy, but gybes are controlled to some extent.
Some points:
You will need more turns than your pic shows.
Tension is critical. Both sides need tension.
Rope needs to be rough surface. Consider nylon for shock absorption (climbing rope)
Preferably use winch(es) at cockpit: 1) to get enough tension, and 2) for controlled release if needed.
Good luck,

Ok, so the yanks sell something very similar.

So, how would I get more turns on a figure of 8 ?

As I see it, the rope can only be rigged this way?

 

[maby]

An acquaintance of mine who was both a sailor and climber experimented with rappelling eights as boom brakes on my suggestion. He came to the conclusion based on the specification of the available devices and some crude maths that they should work fine on boats up to a little over 30 feet, but the normal sail area on larger boats is likely to overload them. The are designed to support an average adult human with a significant safety margin, but we are still talking a couple of hundred kilos. I think you'll find that the force on the main sail of a forty foot cruiser can get a lot more than that. It's not so much a question of the eight physically failing as of the friction that you can set up on the brake line. It is also difficult to rig a brake line on most boats that gives the correct run through the eight - further reducing the available friction.

 

[Blue_mischief]

I have a 28 foot heavy displacement boat (Twister) and have a figure of eight rigged as a boom brake. It works, but not sure if it would for a 40 foot boat. The amount of tension is crucial and the sheet winch is used to apply this.
With a following wind I find using just the Genoa is much less stressful than involving the main, which invariably blankets the Genoa and renders it pretty useless. The Twisters Genoa is big, so maybe not so good for other boats.

Just spent two weeks in the far northwest of Scotland, South winds for the first week so went north, north winds for the second week so went south. Main used hardly at all, but averaged 5-5.5 knots all fortnight, some of it tide assisted.

 

[lw395]

How can the tension be remotely constant when the total distance chainplate-boom-chainplate will vary significantly through a gybe?
Also don't forget that you will need at least four times as much friction working at the kicker as you would working at the clew or mainsheet.
And that friction works against you while you are pulling the main towards the centreline, unlike surging the sheet through a ratchet block.

I think there can be an issue with these things that if the rope goes completely slack, it can get out of place and lock?

The sheet tension on our 40ft boat could easily be 40 kg, with a 6:1 sheet. With the mechanical disadvantage of working at the kicker you would be looking at over a ton?

 

[maby]

How can the tension be remotely constant when the total distance chainplate-boom-chainplate will vary significantly through a gybe?
Also don't forget that you will need at least four times as much friction working at the kicker as you would working at the clew or mainsheet.
And that friction works against you while you are pulling the main towards the centreline, unlike surging the sheet through a ratchet block.

I think there can be an issue with these things that if the rope goes completely slack, it can get out of place and lock?

The sheet tension on our 40ft boat could easily be 40 kg, with a 6:1 sheet. With the mechanical disadvantage of working at the kicker you would be looking at over a ton?

Exactly - the sums don't work out on big boats. It is possible to get the geometry right to maintain adequate tension on the line - there are commercial solutions available that work in exactly the same way - but it needs to be carefully set up. The bottom line is that climbing rappelling gear is only designed to support the weight of an adult man - the mainsail of a moderate size boat in a decent blow exerts far more force.

 

[savageseadog]

Figure of eight descenders are enormously strong, they are designed to be worn away at least 50% (as I've done with one of mine)

 

[maby]

Figure of eight descenders are enormously strong, they are designed to be worn away at least 50% (as I've done with one of mine)

It's not the strength, it's the braking force. Most climbers are relatively fit and slim - but even a seriously overweight man is only going to be a couple of hundred kilos. The main on a forty foot boat could be applying far more than that to the brake.

 

[Blue_mischief]

I think you'll find climbing gear has breaking loads measured in the tonnes. It's not the weight of the climber, but the dynamic force applied by a falling body which has to be catered for. Still not sure about using it on a 40 boat though, the maths is beyond me to work out.

 

[Daydream believer]

Boom brake rigged near the kicker might break the boom if you use it in strong winds and the boom catches a wave.
.

And how often has your boom hit the water ?- assuming you have something bigger than a 14 ft dinghy

 

[lw395]

And how often has your boom hit the water ?- assuming you have something bigger than a 14 ft dinghy

A couple of times running down the Solent with a preventer rigged. It does get very lumpy sometimes!

 

[Daydream believer]

It's not the strength, it's the braking force. Most climbers are relatively fit and slim - but even a seriously overweight man is only going to be a couple of hundred kilos. The main on a forty foot boat could be applying far more than that to the brake.

But is it to be used to prevent a gybe or to allow the boom to go over in a controlled manner even in the event of an accidental gybe
In that case it is applying friction rather than taking the full load & slowing down the speed of the boom --giving everyone time to duck & wake the helm up

As for comments about it being at or near boom end I would have thought risk of lassoing the crew would be quite high also in a gybe the angle from the chain plates to point on boom would be very acute & then the leverage would be very high. If it was nearer the kicking strap the angles would be wider.

I really think comments about boom hitting the water are pretty remote. In 20 years of mad racing (when much younger)in my own & others boats in all conditions i do not recall ever dipping the boom although i admit we did put the spinnaker pole in a couple of times.
In those sort of situations we would not have bothered with a preventer as we were racing.
I doubt if the Solent is any worse than the North sea, but others may disagree