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| Aussie jib halyard http://www.hobie.com/au/en/forums/viewtopic.php?f=14&t=4126 |
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| Author: | 747pilot [ Sat Jul 08, 2006 10:14 pm ] |
| Post subject: | Aussie jib halyard |
I just the other day saw for the first time a Aussie jib halyard. Question I have is 2 fold. 1) Why the piece of 3/16" steel cable at the top end that attaches to the mast tang instead of a piece of high tech line? The line would be plenty strong and lighter. 2) The sales info on it says that it reduces mast compression by 66%. I don't see how that is possible. Thanks 
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| Author: | yoh [ Sun Jul 09, 2006 6:42 am ] |
| Post subject: | |
1 - You need something to extend a few inches from the tang. In this case it is that pig stay made from stainless steel cable. On my boat I use a 7 hole chain plate in that spot. Sure you could use amsteel or some other fancier rope. It would be lighter. But the high tech lines do not enjoy being tortured over sharp edged nor do they like to be smoked in sunlight. Lifespan is a lot shorter compared to stainless steel. The stiffness factor of the pig stay might play a role in this application as well. Considering the old school constructions we cruise around on - what difference does it make if we have 2.3 oz more weight hanging from a monster (non tapered) aluminum mast?! 2 - The aussie halyard is essentially a block and tackle - like the mainsheet system on your boat. I assume that you do not argue that there is no mechanical advantage of the block and tackle design. Because if you do I am sure Archimedes will haunt you in your sleep or at least sink your boat the next time you hit out. Think in this direction - Assuming proper sail trim with the conventional system or the aussie halyard the tension on the leech is the same with both systems. The reduction in force would be achieved between mast tang and where you cleat the halyards - theoretically 2/3 the force - resulting in 66% less mast compression. You could achieve even less compression by using even more pulleys - and a lot of low stretch high tech line. I am not so sure about the other “benefits†|
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| Author: | 747pilot [ Sun Jul 09, 2006 8:31 am ] |
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Ah, OK they're just talking about the force of the halyard as it goes from the mast tang to the cleat. They're not talking about the downward force caused by the tension of the combined jib luff and shrouds. I'd be willing to bet that if you were able to measure the total downward force on the mast base (thus compression) it would be no where near 66% less. Probably more like 0%. I suppose there would be a little less bending moment on the mast from the halyard. It's just hard to believe that the difference between 300# and 100# or so (and only between the tang and the cleat) is very significant compared to the total downward force provided by the standing rigging. Back to the first question. Unless someone can tell me that the stiffness of the steel cable is needed for some reason, I think I'll go with Amsteel spliced and a couple of thimbles. I don't mind replacing it once a year and the splices are easy enough to make. 
Thanks for the help |
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