Quote:
Originally Posted by thinwater
A little cat experience might help. You may not be understanding the point.
One of the functions of the backstay, in addition to keeping the mast up, is providing forestay tension. Angled shrouds are not good at this, the forestay tends to sag if the main is not tight, and the jib becomes full and draft-aft. Racers pay a LOT of attention to keeping the forestay tight with mainsheet tension. This is a really big deal on beach cats and some dinghies.
Off they wind this does not matter. No main needed (but still a good idea).
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OK, I thought it would be obvious what I meant, apparently not. I do understand, I come from a
racing background. The point was that the leech tension is NOT required to 'support' the
mast. Obviously leech tension pulls the mast backwards and tensions the forestay. In my mind that's not 'supporting' the mast, it's tuning the rig.
And anyway, the point made by the poster:
Quote:
Originally Posted by foufou
I believe there is another reason for travelers that has not been mentioned. The sail, with main sheet attached to the traveler act as a back stay. While catamarans have swept back shrouds that take loads from astern the leech of the main and the main sheet also take those loads. It is all part of the mast support system.
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was that a 'traveller' is necessary to allow the main to act as that 'backstay'. That is evidently not true, the leech tension only provides the pull on the forestay when roughly upwind, in which case the mainsheet attachment point doesn't require a traveller to be in the right place.
The whole point of the traveller is to move the mainsheet attachment point
outboard, when sailing more downwind, in order to maintain twist control if you have no other way of controlling twist; the point of my initial post about vangs. At these angles the leech tension is neither sufficient nor in the right direction to provide forestay tension and 'support' the mast, and the rig tune doesn't need it anyway
And finally, rigs with swept back shrouds, as long as mounted on correctly built and braced hulls, absolutely can provide sufficient forestay tension. Your point is true once the
boat gets big/heavy enough, hence bigger
boats having perpendicular shrouds and back stays.
As a side point, one of the problems of building a swept back stayed rig with no backstay and then mounting it on a poorly built
hull (I'm looking at you Lagoon) oddly enough seems to cause structural issues with the bulkheads, I wonder why...
Quote:
Originally Posted by Sos
I believe that Lagoon advice that you don't sail with just the jib in higher wind strengths so the mainsheet/topping lift are working hard. Also applies to flying just a spinnaker.
Not a problem on our cat since we have backstays but then we have no roach in the mainsail!
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It seems that the
Lagoon engineers understand this and, rather than fix the fundamental design problem, ask you as the owner to sail a particular way to protect them from the consequences of choices prioritising internal space over good structural design/build quality.
Any well-built
boat with no backstay that wants to maintain good forestay tension created by the shrouds, has angled bulkheads along the line of the forces. Look at literally any
racing boat with that style rig that needs rig tension to perform. I've only seen one production cruising cat that does that. A good job that most cruising cats owners never want to
race and improve their rig setup. I think there would be many more problems as the structures are fighting the physics.
To be clear, this is a different rig from a beach cat style that uses mainsheet tension to create luff tension upwind and lets the rig flop forward downwind.