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Gnav Loads |
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tgruitt
Really should get out more Joined: 02 Dec 04 Online Status: Offline Posts: 2479 |
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Topic: Gnav Loads Posted: 07 Dec 07 at 6:20pm |
I reckon they must be fairly similar? The thing is with a GNAV is that it does strange things to the bend in the mast, maybe there is a way of making it better that way too? Just an idea. Good luck, Cherub 'Shiny Beast' the bright green one has a pretty simple gnav system which works really well. See pic.
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Needs to sail more...
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Merlinboy
Really should get out more Joined: 03 Jul 06 Location: United Kingdom Online Status: Offline Posts: 3169 |
Post Options Quote Reply Posted: 07 Dec 07 at 6:20pm |
Hang on a minute mate! Someone posted earlier about bearings and tracks on Gnav systems i was just explaining how ours works! Therefore explaing a simple but effective system! Why do you need to know the loads? i hould imagine thats quite a complexed calculation but i'm sure Jimc should be able to give you the calculation to work it out! |
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mike ellis
Really should get out more Joined: 30 Dec 05 Location: United Kingdom Online Status: Offline Posts: 2339 |
Post Options Quote Reply Posted: 07 Dec 07 at 6:22pm |
i would geuss the loads would be similar on a gnav as in a kicker but in different directions, hence contributing to weird mast bend. Edited by mike ellis |
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600 732, will call it Sticks and Stones when i get round to it.
Also International 14, 1318 |
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CurlyBen
Really should get out more Joined: 17 Aug 05 Location: Southampton Online Status: Offline Posts: 539 |
Post Options Quote Reply Posted: 07 Dec 07 at 7:50pm |
It depends on how accurate you need the numbers. Are you looking for something within a factor of 10 (i.e. 1N, 10N, 100N) or do you need more accuracy than that? What kind of boat are you looking at? What's the geometry of the setup? How is the boat being sailed (stabbing or flapping) and in what wind strength? I suspect there are too many variables to make a particularly accurate guess so you may be better off trying to do some measurements (not that this will be easy)
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RS800 GBR848
Weston SC |
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redback
Really should get out more Joined: 16 Mar 04 Location: Tunbridge Wells Online Status: Offline Posts: 1502 |
Post Options Quote Reply Posted: 07 Dec 07 at 10:28pm |
I wouldn't have thought measuring the loads would be that difficult. What about putting a spring balance in the control lines? Once you've got the tension on the control line it would require only simple trigonometry to calculate the forces and directions in the metalwork (or carbon). Give me some data and I'll work it out. No on second thoughts get the data and I'll explian what to do with it. |
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JimC
Really should get out more Joined: 17 May 04 Location: United Kingdom Online Status: Offline Posts: 6649 |
Post Options Quote Reply Posted: 08 Dec 07 at 1:56am |
I've no idea what the loads might be - never measured them. Depends hugely on the boat. Granite's idea of starting by how hard you can pull a line and then working up through purchases and levers should get you an order of magnitude figure which I should have thought would be adequate for the project.
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Ross
Really should get out more Joined: 02 May 07 Online Status: Offline Posts: 1163 |
Post Options Quote Reply Posted: 08 Dec 07 at 9:10am |
Shiney's GNAV snapped in septemeber in france!
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Ross
If you can't carry it, don't sail it! |
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tgruitt
Really should get out more Joined: 02 Dec 04 Online Status: Offline Posts: 2479 |
Post Options Quote Reply Posted: 08 Dec 07 at 10:40am |
Quite a lot of things have broken since Andy sold it. Nothing ever broke when he had it! |
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Needs to sail more...
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Ian99
Posting king Joined: 07 Apr 05 Online Status: Offline Posts: 138 |
Post Options Quote Reply Posted: 08 Dec 07 at 10:59am |
If you had large amounts of research money, you could custom build a carbon mast and boom with fibre optic strain gauges embedded and take the thing sailing with several thousand worth of analysis kit in the bottom of the boat! However, as I suspect your money won't stretch to that, I'd get a few cheap strain gauges from RS (the electronics distributor not the sailing company!) and superglue them on at strategic points and angles on the gnav itself, boom, mast and gooseneck and wind the gnav on as hard as you would upwind in a force 7 on land and measure it there.
Simpler still, but probably reasonably accurate would be to measure how much the boom bends when the gnav is on, and then recreate this on land away from the boat by supporting the boom at each end and hanging a load of lead off the point where the gnav attaches. Once the bend is the same, the weight of the lead will be somewhere near the force on the connection between the boom and the gnav. You'd need a fair bit of lead though ...a stack of gym weights might be fairly good. I reckon the force is probably somewhere in the region of 2-3000N. To get that figure, my fag packet maths was: 16:1 kicker, but at approx 45 degrees, it effectively is only 8:1 worth of downwards purchase. I pull the kicker on as hard as I can with one arm when its windy which I reckon would be able to pull about 40 kilos = 400N. 400x8 = 3200 and then there's a bit of loss in the system so somewhere between 2-3000 Newtons force. |
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djdhi
Groupie Joined: 06 Oct 07 Online Status: Offline Posts: 44 |
Post Options Quote Reply Posted: 08 Dec 07 at 11:43am |
GNAV FORCES hI, surely the maximum a GNAV should exert is the force required to bend a particular mast above the stay attachment point. So in practice you could bend a mast tip in a bench with a spring balance till you got near the theoretical breaking point. That would be the practical limit. djdhi |
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