Boom Preventer

[Firehoser75]

Landonshaw,
Yes the lazy preventer is slack, but not too slack and no I have never had them tangle (with other lines or anything else for that matter). I currently do not leave them "fully deployed" unless I anticipate requiring them on an off the wind point of sail, then I rig them prior to getting under way. I agree with Euro about if possible leaving them "rigged" so you will use them, but I would use a system similar to what is shown in the book that Steve references, because in that way, the lines are not always in the way or under foot (safety first). I personally do not like the idea of using a vang, as the vang is meant to control the main on a downwind point of sail and you would have to release it to move it to the other side during a gybe (not a good idea IMHO). The advice in the book is excellent.
Good luck,
Tom

[hpeer]

Legal or not, it just sold a book.

[Euro Cruiser]

Bill's book is indeed a gem of a resource for those thinking of heading offshore. However, his description of using a vang/preventer - if memory serves - was given in the context of a boat with end boom sheeting. There really is no way to avoid the obstruction of the lifelines, and therefore the limitation on how far out you can position the boom, when using the vang/preventer option. OTOH this will keep the main from experiencing any chafe against the aft shrouds and spreaders as the sail won't be able to reach that far forward.

Jack

[Andrew Troup]

Originally Posted by hpeer

Legal or not, it just sold a book.

Make that two books

[Andrew Troup]

FWIW, I'm a big fan of tackles run from the chainplate region on either side-deck to midboom, for routine use in lieu of a preventer, and to control the boom during gybes.

Tails led to the cockpit winches means the system can be used whenever the course is deeper than a beam reach. The benefit in alleviating chafe of the sail, by preventing the boom pumping up and down while sailcloth is being pinched against the standing rigging at the battens, is sufficient on its own, IMO, to make this method well worthwhile, but the safety and peace of mind are also considerable. I recommend dedicated clutches for these tails.

If the boom is sized as it should be for a modern cruising yacht, the downforce if an inattentive helmsman or massive windshift throws the sail hard aback should not be a problem in any conditions short of the supremely challenging combinations mentioned below. (Caveat: If you've got a really shallow boom with endboom sheeting, clearly not designed for a powerful vang, it would pay to seek expert advice)

Remember the tackle cannot pull the boom anywhere near horizontally; the force it applies will be in line with the ropes of the tackle in tension; the boom will pivot on the gooseneck to line up its maximum depth in this direction.

Similarly the sail will not pull the end of the boom horizontally, or anywhere near it; if it's loose footed, the force vector will lie in the plane of the clew patch; if not, there's so little tension in the foot shelf that the force distribution is effectively the same. So all the apparently "sideways" forces line up pretty close to the plane in which the boom is deepest.

Surging the tail around a winch with a 2:1 tackle on small to medium mainsails (block on the boom, single sheave block with becket at the chainplate) and a 3:1 (2 sheave block at the chainplates, becket single block on the boom) on monsters, will give fingertip control throughout the dangerous sector of the gybe.

I disagree that the tackle should lead to the boom end for end-sheeted booms; you just have to make sure everybody understands they must not crank in the mainsheet while the vang tackle remains cleated.

However I fully agree that this is not a good preventer option in conditions where the boom might dip, although even then (as I hope to explain later) it remains a good gybe controller.

For a proper preventer in challenging situations (long boom vs beam, and/or big seas and/or heavy rolling possible), I recommend the 'gold standard' installation.

By this I mean a permanent line living on each side of the boom (Seifert points out in the excellent Tip linked to from post #15, one line is sufficient for end boom sheeting> This is true even with a permanent vang/kicker (which he doesn't mention), because it's easy to pass it around behind a kicker, but not so for the mainsheet)
This line runs from a stout padeye near the boom end, REGARDLESS of whether your sheeting is mid boom or end-of-boom, to a cleat near the gooseneck

Again, I realise I am contradicting an earlier post in this thread, which I am sorry to do, but I say this because, when the boom dips, it's the end of the boom, and the clew patch area of the sail, which will apply major aftwards loading, and the preventer needs to be out as near as can be in line with that load vector to relieve the bending moment on the boom.

However I would stress that the other system will still earn its keep in these conditions: leave it slack and uncleated, but with a couple of turns of the tail around a winch when the preventer is set up, so that you can control a gybe with it after throwing the heavy-duty preventer off the cleat.

Another benefit of this system is found in sloppy seas with light winds: the boom can be immobilised wherever it might be (using the topping lift for triangulation to keep the leech open)> The hardest knock I ever had from a boom was in just such conditions, from quite a small boom which had almost no sideways freedom, sailing on the wind. My head was right alongside it, using binos, when the foot of the sail slopped aback just as the boat jerk-rolled hard in the opposite direction... even without the binos, or the benefit of darkness, I've never seen so many stars.

Sorry to be so longwinded, and to seem perhaps a little dogmatic. The seriousness of the topic justifies the first, I hope.
Most of the people who were killed by a piece of sailing equipment meet their maker with the assistance of either the boom or the mainsheet.

Nothing justifies the second ... but curmudgeonliness and lots of unhappy miles on vessels with badly set up booms (and even more happy miles on vessels of the 'other' persuasion) explains, if not excuses it.

[sesmith]

Since this thread is out of mothballs...here's a link to a preventer similar to one I rigged on our boat. Simple and effective.

Sail-World.com : Permanently installed preventer: Another view

[Andrew Troup]

There's a post relevant to this topic here, with a photo

http://www.cruisersforum.com/forums/...ml#post1241774

[estarzinger]

On Hawk, we have always used dual preventors - we have a tang welded thru the aft end of the boom (pad eyes would also work). On each I have splices prot and starboard spectra lines that reach about to the front of the boom, and stow on cleats there, with eyes on their front end. On each toe rail I have dacron lines with snap shackles, that go to toe rail blocks about where the chain plates are and then run back to the cockpit, thru a toerail mounted clutch within reach of the cockpit.

We can connect the specta line to the Dacron line either inside (for close reaching) or outside the life lines (for deep running).

The block on the toe rail is positioned to both "prevent" (eg hold out) and vang (eg hold down) the boom.

We have port and starboard ones, so in a gybe we can release one side, gybe and immediately have the other side on, without any fussing.

One question: anyone know a well designed boom brake that will work with 760 sq ft of mainsail? Most of the ones I have seen look like they would not stand up to our use/loads.

[model 10]

If you check the angle of the dangle, only leading the preventers back to even with the chain plates and the goose neck, you would see that the boom would fail under a severe load. The arc of the preventer needs to be longer than the arc of the boom.

[tartansail]

Originally Posted by estarzinger

One question: anyone know a well designed boom brake that will work with 760 sq ft of mainsail? Most of the ones I have seen look like they would not stand up to our use/loads.

I crewed on a Tartan 4600 from NE to St. Thomas that had a Dutchman boom brake. It was easy to rig and tension. We tested it, but never had a serious unintentional jibe. It seemed to work fine and handled the main on a similar sized boat to yours. I can't give you the exact mainsail area.

[estarzinger]

Originally Posted by Guy

If you check the angle of the dangle, only leading the preventers back to even with the chain plates and the goose neck, you would see that the boom would fail under a severe load. The arc of the preventer needs to be longer than the arc of the boom.

Can you explain further why do you say that? Note the load comes on the tang welded thru the end of the boom.

My vang certainly has a smaller arc than the boom.

And I have had these preventers since 1989 and have not broken the boom yet, and I will admit that I have made some helming mistakes over the years and they have handled some pretty strong accidental gybes.

Originally Posted by tartansail

I crewed on a Tartan 4600 from NE to St. Thomas that had a Dutchman boom brake. It was easy to rig and tension. We tested it, but never had a serious unintentional jibe. It seemed to work fine and handled the main on a similar sized boat to yours. I can't give you the exact mainsail area.

Thanks. I just looked and their biggest model appears to be rated 'up to 750 sq ft', which I suspect means its too small for Hawk, since we have a particularly high righting moment (and thus higher than average sail loads), but I will ask them.

So, does anyone know of a brake rather higher than the biggest Dutchman one?

[Andrew Troup]

Evans

Unless your boom is shorter in relation to your beam than I recollect, it seems to me the preventer alignment you describe (from near the end of the boom to chainplates) would create a fair bit of thrust into the gooseneck and mast if the main were caught aback?

(forgive me if I misunderstand : for instance, the tang you refer to may be well forward from the clew....)

- - - - -

New topic: for those who are fans of the traditional end-boom to bow preventer, this "endless loop" idea seemed to me like an ingenious way of setting it up, although I have not tried it. I'm presuming the lee (return) side is diverted around the midships docking cleat purely to prevent it rubbing along the cabin side .... it's not entirely clear from the description...

http://www.cruisersforum.com/forums/...tml#post993225

- - - - - --

My personal preference tends towards reinforcing the boom midsection and fitting beefy tangs each side for a multipart purchase to the toerail immediately aft of the chainplates, permanently rigged (doesn't have to be swapped around the lifelines when bearing away from a close to a broad reach, for example)

On small boats where the cockpit gets filled with rope tails, I have found it useful to use the 'endless line' concept in reverse: the port tackle tail travels around outside the aft mooring cleats and becomes the starboard tail.

This is not great though if you tend to have lots of guests: at some point in the circuit, someone will be sitting or standing on the tail: no safety issue, but inconvenient, as the tail has to be able to render through every time the boom angle changes, not just when you gybe....

So it's a good layout for short handing, and it does provide a useful 'automatic brake' backup function; the friction of all the combined blocks and corners will definitely slow the boom down in an uncontrolled gybe.

[Paul Elliott]

I think he means that the "short arc" preventer won't let the boom rise if you start dragging it through the water.

In my case, the vang and the main sheet limit the boom rise, and they're both mid-boom attached anyway. I have port and starboard preventers attached mid-boom and to my midships cleats, using a 2:1 block arrangement. The 2:1 boom-attachments are spread out a few feet, which should at least reduce the point-loading under stress. These preventers lead up the boom to the gooseneck, then down to the deck and aft to two clutches under the dodger. They are useful and easy. And yes, potential boom-breakers.

I also have a typical end-boom preventer let up to a block at the bow, that I use when we're doing stupid things with the spinnaker.

[Capt.Don]

I read somewhere that you should add a light breaking link to the preventer to that would fail before sufficient loads are placed on the boom, gooseneck.... As I recall, this was 4 or 5 lashings of light 1/8" line formed into a loop, connected between the deak/cleat and boom.

[Andrew Troup]

I think there's some confusion - not on this thread, but in general sailing conversation - about the loading to a boom arising from a mid-boom toerail vang.

There are two entirely different scenarios:

1) Dipping the boom while running at speed (due to rolling)*

2) Getting a full mainsail caught aback

These differ markedly in the direction of load on the boom.

Situation 2), contrary to intuition, loads the boom up and down, in the strong direction. **


If the boom could handle mid boom sheeting, (whether or not in your case it does) it should be able to handle situation 2 without reinforcement further to what would be required for a mainsheet tang or bail.

Situation 1) is much less common on modern boats than the conventional wisdom seems to assume.

Much of the feeling on this probably entered that consolidated and slow-to-adapt body of wisdom from the era of low-freeboard, narrow beamed boats with long, spindly booms.

Or from IOR-era boats which rolled through 100 degrees with minimal provocation - for instance, the Whitbread boats from that era would occasionally dig deep, green V-shaped trenches through the ocean with their mainsail clew ...

(or, more often, through their own rather generously proportioned bow-wave ....

The latter situation is more exciting visually than in terms of imminent breakage, because the bow-wave is travelling in the same direction as the boat, at the same speed).

One I sailed on had a Navtec control on each side of the cockpit which not only dumped the hydraulic vang on command, but a custom-intensified nitrogen pre-charge at the 'lazy' end of the cylinder instantly sent the boom end skywards, out of harm's way, by 6'. A crewman would be stationed at this control when things got interesting.

Naturally the preventers were led to the bow ....


* or more exotic possibilities to do with presenting the prevented boom into a wave coming, improbably, from ahead (after a ~ 180 broach, or a savage ~ 180 windshift - both of which I can vouch for as possibilities, but never - touch wood, so far - offshore!)

** provided it has the usual universal gooseneck joint, ie horizontal axis swivel as well as vertical: I've never seen a cruising boom which didn't, except in patent applications....

Another thing about mainsails going aback: if the boom has no leeway, and the leech is tight BEFORE it goes aback (which can only be arranged with a powerful vang) there is actually not a huge shock, unless the main is bagged and shagged-out, or has a huge roach....

The boom having no leeway to swing is important: think of a door slamming in a breeze. A child could hold it, provided they were already holding it before the pressure reversal. However, if they try to stop it after even a few inches ..... forget it!