SD, Robert,
Interesting to read your observations on twin headstay / backstay rigs. Apropos the point about balancing tension in the wires, here's how it's done:
http://www.swainsons.com/gallery/dis...lbum=13&pos=10
click the picture to see a larger version. The stays are about 2 inches apart, so even if the hanks do hook both stays at once, it's not a problem to pull the sail down far enough to unhook them. This has only ever happened to me once, and only with the snap-hanks on my genoa, never with piston hanks (I don't even begin to see how piston hanks could snag both stays if they're properly closed in the first place).
In terms of sag, it helps that my boat's built like a brick outhouse ( approx 3/8" minimum skin thickness) and so I'm able to dial up the tension on the (3/16" stainless wire) stays a little more than the vintage of the boat might suggest is necessary.
The twin backstays, bolted to big, fully-glassed-in hanging knees either side of the transom, also act as running backstays, taking some of the sideways load of the rig when we're chopping along at 35 degrees of heel - a not unusual occurrence going to windward under full sail in a fresh breeze. I don't believe that this induces a significant degree of torsion, even assuming that the leeward stay goes slack (which it doesn't): The boat is roughly 10m long, so say the mast is 6m from the stern. The stays are about 1.5m apart at the stern, so the tangent of the maximum angle of deflection (when the mast is twisted in line with the windward backstay) would be 0.75/6, making the angle 7.12 degrees. That degree of twist over a length of 11m or so (approx. mast height above deck) just isn't enough to matter.
Again, that's the maximum twist - assuming no tension in the forestay. Also, I'd disagree with the shock-loading argument for a couple of reasons: 1) I don't know how fast anyone else tacks, but even on a good day, I take a finite 10 seconds or so to tack. That's not a quick enough transfer of load to qualify as a shock. 2) Say I run the headsail up the starboard headstay (as I usually do - my snap-hanks open to starboard). I'm romping along on port tack, with the sail tight in and the starboard headstay sagging a little to starboard. The port headstay then is a little less tense perhaps, but balanced by the triangular tension-balancer I have fitted between the stays and the stemhead fitting. Now I decide to tack. I head up to port, the sail begins to luff and the tension unloads. The boat stands up again, and as the bow comes through the wind I hold my starboard sheet for maybe a second to help the bow around. I then drop the starboard sheet, come onto starboard tack, and sheet in hard and fast on the port genoa sheet, finishing up with a couple of strokes of winch handle if I haven't managed to trim it before the wind load comes on. The wind fills the sail and tensions... the starboard stay, because the sail is still hanked onto the same headstay! No shock loading there.
By contrast, when I hit a steep wake or fall off a wave, I have double the amount of metal resisting the mast's efforts to fall forwards and then backwards - now that
is shock loading.
sorry, I'm a crusty, but at least I know it
BE
I love roller furlers, don't get me wrong... just not on my boat, and not when they're treated with the "fit and forget" mentality. I have enough maintenance tasks to do, without having to refurb a roller furler every season!
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