[Amel Yacht Owners] Re: Slowing down in increasing winds
Bill,toggle quoted messageShow quoted text
Your comment about a real preventer needing to run to the end of a boom raises some interesting questions. Namely what are some factors that determine the shock loading that the boom and the rig receives in an uncontrolled gybe? Here a a few things that I believe are significant:
1. The elasticity of the mainsheet. A modern super low stretch fiber as opposed to using conventional Dacron for instance will greatly increase the shock load.
2. Because our mainsheet attaches to the bottom of the boom and the mass of the boom is I assume above the centreline of the boom with the sail attached, the ability of the boom to rotate longitudinally should absorb some of the shock since that rotation would occur in opposition to the membrane of the sail. A fixed/ non rotating gooseneck on the other hand would receive a large torsional load by comparison. I would very much be interested in your input on the rotating gooseneck design of our boats because I had not thought much about it until this discussion came up, but I am starting to like it.
I would like to add that compared to what I am used to on other boats, the weldements on the boom for the attachment of the mainsheet seem to be incredibly strong. The boom itself also seems to be a heavier extrusion than what I would expect for a boat the size of mine. Being a Ketch of course shortens both the main and the mizzen booms and thereby reduces the risks of a jibe causing damage. While all measures to prevent an accidental jibe are important, it seems to me that Amel may have done a lot to help reduce the risk of damage to the rig due to an uncontrolled gybe.
Does anyone know of an instance where the main or mizzen boom or rig of a SM, SN or Maramu was damaged in an uncontrolled gybe? That could be an interesting data point given the Ocean miles that some of these boats have accumulated over the years.
I didn’t intend to open a big discussion like that. I always gybe the usual way like Danny describes. But I did leave the knob across once and there was an accidental gybe. There was no impact shock load as the whole car system slowed the final arrest of the boom, so no sudden full load on the traveller or boom attachments.
Just for the record I wasn’t advocating this as a method of gybing. The main sheet is so easy to pull in by hand on the winch that control is simple.
In my early days of ownership the mainsheet did catch the midships centre knob a couple of times (sometimes the mainsheet gets jammed against its own top pulley leaving one strand hanging loose). Since then I removed that knob and only use the outer one to hold the window down. Never had a problem since, nor any leaks.
Happy gybing everyone
Off back to UK tomorrow from. Antigua and it looks like there might be some long downwind days............
Ocean Hobo SN96
I'll have to think about the gooseneck, and how it changes things... a good thought... And I agree the elasticity of the mainsheet can help... but only to a point. If the mainsheet stretches enough to allow the boom to hit the shrouds, more problems can occur than are solved.
There is another really important piece of the puzzle, that someone else mentioned earlier in this discussion. The position of the traveler has a huge impact on the amount of damage that can happen in a gybe.
If the traveler is centered, and the boom is eased out only with the mainsheet, a gybe can be really dangerous. With that much mainsheet out, the boom can rise when it crosses, when the mainsail goose-wings around the mast. It can rise enough to actually hit the backstay as it comes across. If the boom was out touching (or very close to touching) the aft lower shroud, when it comes across it can impact the aft lower shroud on the other side. Both of these scenarios are potentially disastrous both to the boom--and the rig itself.
If the traveler is all the way over to the leeward side, then these problems can't happen, or at least are minimized, because the mainsheet is so much shorter, and the boom is stopped halfway across, before it can get really moving.
One of the things I really love about the Amel set up is that the traveler is long enough to actually be really useful as a sail trim tool. When sailing anything upwind of a beam reach, we adjust the traveler far more often than we do the mainsheet. If we are sailing downwind, the traveler is always (no exceptions--ever) eased down to the leeward side.
There are aways two parts to preventing damage in an accidental gybe. First is avoid the gybe in the first place. A nice idea, but it will happen to everybody. The second part is to be sure the boat is set up so damage is avoided or minimized.
Deltaville, VA, USA