Stemar
Well-known member
No problem. Next time I'm around Go Outdoors or similar, I'll pick up a carabiner and have a play.
Boom brake
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geem
Well-known member
Boom brake was fitted at the kicker. It wasn't 'on'. Lines were slack and not made off. Wind went from 5kts to 40kts around a headland. We healed over, I dumped the mainsheet and the friction in the boom brake, even though it wasn't supposed to be on, snapped a very substantial boom. We don't use one anymore!
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We learn by our experiences, I’m sticking with a preventer then!
goeasy123
Active member
With the main sheet at the end of the boom and the brake in the middle your heading for disaster. Basic O level maths tells you the force of the couple acting on the point where the boom brake is fixed is huge.... and the boom is not designed to take such high side-on forces.
We saw 3 trans-Atlantic yachts come into A Coruna with in a couple of weeks with broken booms.
They're called boom brakes because they 'break' booms. They're for people that have everything they need, but want to spend more money.
I did see a much better idea on a big custom yacht in NL. It acted directly on the main sheet gathering it in and letting it out controlled by an clutch.... still it looked like a solution looking for a problem.
We saw 3 trans-Atlantic yachts come into A Coruna with in a couple of weeks with broken booms.
They're called boom brakes because they 'break' booms. They're for people that have everything they need, but want to spend more money.
I did see a much better idea on a big custom yacht in NL. It acted directly on the main sheet gathering it in and letting it out controlled by an clutch.... still it looked like a solution looking for a problem.
geem
Well-known member
Not possible to install a boom break to the end of our boom. We use twin preventers now and it works fine. No risk of boom damage.
Jimmy Cornell swears by them. Fixed to the kicker location. Totally opposite of what you are saying, but I am with you. Not worth the trouble, cost or breakages when two lines work more safely?
goeasy123
Active member
Jimmy Cornell probably didn't do O level maths
In fact I'm pretty sure he was too busy avoiding bullets from the police... according to his amazing (highly recommended) book.
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Which book? Passion for the sea?Jimmy Cornell probably didn't do O level maths
In fact I'm pretty sure he was too busy avoiding bullets from the police... according to his amazing (highly recommended) book.
goeasy123
Active member
I can't remember. If not Passion.... maybe 200,000 miles.
geem
Well-known member
A big Ben came and anchored next to us this morning in Cascais. Boom brake fixed to kicker location. Do you think I should tell him ?
goeasy123
Active member
To be clear.... the boom brake needs to be fixed to the boom at the same point as the main sheet.... Otherwise you induce a bending couple in a direction the boom cross-section is not designed to take. Big Ben risks breaking his boom.
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Th
That seems logical but it’s the first time I’ve seen that recommended. Most of the boom brake retailers seem to suggest attaching at the kicker point. Just schoolboy physics can see the massive load that will fall upon boom and gooseneck with a brake attached to the kicker attach point. I’m surprised not to have heard the gooseneck fittings have been broken in this manner.
Elemental
Well-known member
The closer to the gooseneck that the brake is fitted the less effective it will be for two reasons (this may go some way to 'protecting' the book from sideways bends).
- Leverage - the end of the boom has a greater leverage against the brake if the brake is fitted further inboard
- Speed and gearing. Brakes work on tension/friction. During an uncontrolled gybe, the end of the boom will describe a much larger arc (compared with the kicker position), consuming a longer length of brake line. Equivalent to a higher gearing . The same longer arc is also at a higher speed and AIUI these friction devices are more effective at higher rope speeds.
goeasy123
Active member
A boom brake might be a useful tool to execute a controlled gybe without sheeting in and out the main. That's maybe what the inventor/sellers intended. To prevent damage from an accidental gybe one might consider a preventer as a better solution... for all sorts of reasons. But if you where designing a device to mitigate the effects of an accidental gybe would some sort of shock absorber of decelerator be a much better idea?
mjcoon
Well-known member
I don't understand that assertion. Surely when the boom brake is exerting its braking effect is when the boom is swinging freely and not influenced by the mainsheet?
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I think the discussion about fixing point is about the optimum position to minimise the lever effects on the boom. In a crash gybe the mainsheet is likely to be very loose as the boom swings overhead and therefore applying zero forceto the boom albeit momentarily.
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Yes maybe that is what Brake designers intend, a substitute for sheeting the main through the gybe. Seen in that context a Brake is a lot of expense and additional rigging (trip ropes) for little gain.
Chae_73
Active member
how do boats with "german" type main sheet systems which are mounted on the coach roof and attached mid boom avoid the risk of the boom breaking in a situation such as described by @geem ?
Seems that they could / would exert similar forces to a boom brake unless the sheet was running freely, in which case the boom will presumably meet the shrouds and / or the sea in a bit of hurry which isn't ideal either.
Seems that they could / would exert similar forces to a boom brake unless the sheet was running freely, in which case the boom will presumably meet the shrouds and / or the sea in a bit of hurry which isn't ideal either.
Stemar
Well-known member
Presumably, those booms with the sheet in the middle are designed to handle the forces involved. They certainly tend to be meatier than similar length booms on older boats where the sheet is at the end.
My feeling is that a boom brake should be attached where the mainsheet is attached. The brake isn't designed to hold the boom, only slow it down. A preventer is another matter. It's going to take the full force of a wave in the mainsail if the boat heels that far, and not yield significantly, though I quite like the idea of a bit of elasticity in a preventer to reduce shock loads.
My feeling is that a boom brake should be attached where the mainsheet is attached. The brake isn't designed to hold the boom, only slow it down. A preventer is another matter. It's going to take the full force of a wave in the mainsail if the boat heels that far, and not yield significantly, though I quite like the idea of a bit of elasticity in a preventer to reduce shock loads.
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Strikes me that any mainsheet configuration where the mainsheet is attached in front of or above the spray hood won‘t allow a brake to be fitted unless it is fitted at the kicker attachment fitting. And as discussed above it seems fitting a brake so close to the mast is asking for trouble. On my boat I can’t fit a brake at the mainsheet fitting as the lines would foul the windshield.
Chae_73
Active member
Although I can't see how a brake fitted at the end of the boom would work.
The stern of the boat isn't wide enough to form a sensible shaped triangle with the boom out on a downwind position. It would just replicate what the mainsheet does as far as I can envisage.
The stern of the boat isn't wide enough to form a sensible shaped triangle with the boom out on a downwind position. It would just replicate what the mainsheet does as far as I can envisage.
