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.