Boom Preventor/Brake on a catamaran

[Scaramanga F25]

A preventer is a fixed line to the boom from a fixed point on deck.
A boom brake or a snubber lets the boom jibe but slowly.

[44'cruisingcat]

Originally Posted by UNCIVILIZED

Thoughts regarding a Preventer (as in fixes the boom in place) contributing to a capsize?

It's probably only caused around 50% of our capsizes. It's no big deal, (as I've learned on CF) we capsize so often we hardly even notice it these days. In fact we really don't notice it at all....

Getting back to reality, I always carry an amount of mainsail such that if I need to I can turn round and sail back upwind. If you have to reef or drop the main before you can turn around and recover a MOB, the MOB is probably a goner.

And the occasions you're using a preventer, you're sailing DDW or close to it right? so even if the main gets back winded, it's in not much apparent wind.

So no, the preventer isn't going to cause us to capsize. Well no more than a couple of hundred times a day...

[D&D]

We use a preventer on the main anytime wind's >150AWA, typically about the same time we go to wing-on-wing. We fix the main preventer to a forward cleat, both because a good friend with hundreds of thousands of sea miles reckoned it should be fixed well forward...and comforted by the large backing plates there. It works a treat. Like others already noted, we find it both prevents/dampens wild gybes and holds the boom down/steady; the latter also assists passengers comfort in light winds as it reduces the noise from the boom moving about with wind puffs.

Hard to imagine a capsize risk from a back-winded mainsail running downwind and there's no hint of it in our experience, but hey...according to some, cruising cats just capsize a lot...

[StuM]

Originally Posted by 44'cruisingcat

Getting back to reality, I always carry an amount of mainsail such that if I need to I can turn round and sail back upwind. If you have to reef or drop the main before you can turn around and recover a MOB, the MOB is probably a goner.

+100

[mark_morwood]

Originally Posted by UNCIVILIZED

Thoughts regarding a Preventer (as in fixes the boom in place) contributing to a capsize?

In a cruising catamaran? Not at all. The sail just doesn't load up the same way it does when you are heading on a reach or upwind (not that that will lead to a capsize either). Sheesh, enough with the fixation on catamarans capsizing. Worry about something more likely.

I personally never saw the need for a preventer with a long traveller on a cat. Deep downwind, which is when a preventer is typically used, the traveller was dropped all the way to leeward and the main sheet was in relatively tight to keep the main flat enough to not chafe or invert on the shrouds. An accidental gybe left the main still sheeted in relatively tight with the traveller now all the way up on the new windward side with the sail over sheeted for the point of sail so not driving much at all. Assuming you had a reasonable balance with main and jib, the cat doesn't round up the same way a mono-hull might as it doesn't heel enough. So you get a bang as the battens pop over and the boom swings a short distance, but very controlled. Similar for a twin main sheet rig.

We would occasionally put a snubbing line out to the leeward rail slightly forward to lock the boom in position, so it wouldn't slap with waves if for some reason we had the main up downwind. The triangle of the main sheet, snubber and topping lift would hold the boom exactly where you wanted it, still with some sail shape.

However if we were sailing any distance deep downwind, we usually had the main down, and just being pulled along by headsails, for a nice, easy, quiet, controlled ride.

Mark.

[AD28]

Originally Posted by mark_morwood

we usually had the main down, and just being pulled along by headsails, for a nice, easy, quiet, controlled ride.

What then happens if the breeze picks up, and you have no main up to blanket the spinnaker for takedown?

[mark_morwood]

We had a big 200sqm asym in a sock that we flew quite a lot. Certainly more than most of our firends flew their's. (2 transatlantics, 18 months in the med, 1 pacific crossing). I never had trouble getting it down even if we had left it up a bit long while we were using a sock (different story when we briefly had it set up with a top down furler). I'm guessing the strongest wind I took it down in would have been around 25 true (15 to 20 apparent) or maybe a bit more. The method we used, which I picked up from others, was:
- head deep down wind
- ease the windward tack line (we normally flew it with a tack line from each bow that ran back to the cockpit)
- sheet in hard to bring the clew back towards mid ships on the leeward side
- blow the remaining tack line (spinnaker is now streaming forwards from the clew and head) but located over the trampoline
- pull down the sock while someone eases the sheet near the end
- drop the furled spinnaker into the deck locker
- roll out the jib or code 0 (we used it as a heavier weather down wind sail, though not really designed for that)
If worried, I have heard of others putting the engines on to maintain speed to keep the apparent wind down, but we never needed to.

As the wind picked up we would progress from asymmetric spinnaker 200sqm, to code 0/screacher 100sqm on continuous line furler, to jib on roller furler.

Mark.

[UNCIVILIZED]

Man, ya'll are touchy on that capsize thing. You'd think I was over on SA.
Just mentioning the word alone, kicks off a hair trigger, knee jerk response. Have a couple of cold ones, & chill guys.

[44'cruisingcat]

You asked a question, (IMO a pretty stupid one, but there you go) it was answered.

[UNCIVILIZED]

Originally Posted by 44'cruisingcat

You asked a question, (IMO a pretty stupid one, but there you go) it was answered.

Thanks for that. Consider your keg access privledges, Revoked, under my roof.

[D&D]

Originally Posted by 44'cruisingcat

always carry an amount of mainsail such that if I need to I can turn round and sail back upwind. If you have to reef or drop the main before you can turn around and recover a MOB, the MOB is probably a goner.

Agree with that, altho (happily!) we'v never needed to recover a MOB.

We also need a bit of mainsail if we want to hove to; that's only happened once, but it was (again happily!) easy...and made for a much-needed spell of rest for the crew.

Pardon the...

[DRS]

I have in boom furling and a moster boom. There is no way I want this thing flailing about so I run a brake. Love the thing. Has a tensioner that I can run loose for upwind easy tacking and tighten up for down wind. It will allow the boom to come over but in a nice civilized manner
Picture attached

[Factor]

Originally Posted by UNCIVILIZED

Thanks for that. Consider your keg access privledges, Revoked, under my roof.

Mate, add me to your list .

[arsenelupiga]

i plan to use 5 mm dyneema rope for preventer. I also find that main can be trimmed considerably better under some reaching conditions resulting is some decent speeds.

As dyneema is slippery should enable controlled jybe in SHTF conditions, subject to appropriate knot used on cleat (not too many turns and extra free rope so it slides to the other side)

Anyone else uses that method?