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A WORKING CAPSTAN |
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Moderators: Winston, aew
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aew |
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aew![]() ![]() ![]() Registered Member #1929 Joined: Wed Nov 30 2011, 03:05pmPosts: 2924 | Clare: I take back what I said about the efficiency having to be better than 50%. The friction depends on the cable tension so if you release the capstan, the cable goes slack and the friction drops to next to nothing (compared to the weight of anchor and cable).
The coefficient of friction for hemp on dry wood is given as 0.5 and at that value the cable tension more than doubles, going up by just over 120% and making the overall efficiency around 45%. The cable would obviously be wet but I don't know how much effect that would have. | ||
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aew |
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aew![]() ![]() ![]() Registered Member #1929 Joined: Wed Nov 30 2011, 03:05pmPosts: 2924 | OK, One final version and I'll stop cluttering up Gene's build log:
I've assumed that the friction with a wet rope is slightly less than a dry one, but even then the power required has nearly doubled. I've also set it to assume that the cable is buoyed up by the water, but even so the men couldn't sustain that power requirement. Surprisingly, putting more men on each bar doesn't make much difference. They're too close to the centre to contribute much power. Things obviously get easier as the cable shortens but even when the anchor is almost fully raised it still requires 10HP.
Maybe it turned more slowly than I've assumed, but even then I can only assume that the men were changed regularly. | ||
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Gene Bodnar |
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![]() ![]() Registered Member #126 Joined: Tue Jul 21 2009, 11:20amPosts: 1778 | Arthur, It's not clutter; instead, it's very interesting stuff. Thanks for all the information and time you've put into this. Gene | ||
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Gene Bodnar |
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![]() ![]() Registered Member #126 Joined: Tue Jul 21 2009, 11:20amPosts: 1778 | Fourteen figures have been completed. I've increased the size of the messenger cable. I once again changed the size of the pawls. The anchor and the triple block hanging from the cathead are the only new items added. The project is now finished! ![]() ![]() ![]() ![]() ![]() ![]() ![]() | ||
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donfarr |
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![]() Registered Member #2001 Joined: Fri Dec 23 2011, 09:51pmPosts: 1755 | Fantasitc as usual Gene but the speed of your work is unbelvable also Don | ||
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aew |
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aew![]() ![]() ![]() Registered Member #1929 Joined: Wed Nov 30 2011, 03:05pmPosts: 2924 | That's a great model Gene. I'd seen Glenn Grieco's model before and although I could understand the principle, following the construction of your model has raised and answered lots of questions. As an example, Claire was speculating about the friction of the cables dragging along the deck. In your latest pictures, you can see they're clear of the deck at both the capstan and hawse hole ends.
The figures are a great success at showing how it operated. I'd choose to be the one at the bow looking to see how things are progressing! | ||
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Gene Bodnar |
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![]() ![]() Registered Member #126 Joined: Tue Jul 21 2009, 11:20amPosts: 1778 | Thank you, Don and Arthur. I thank everyone for a really great discussion that taught me a lot that I never even considered before. It's been a very interesting build. Now what do I do with it? Gene | ||
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Winston |
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winston![]() ![]() ![]() Registered Member #1 Joined: Sat Jun 13 2009, 02:08pmPosts: 2513 | Definitely an interesting build to follow Gene. Builds always seem to be more interesting when such discussions pop up. Just goes to show how long we can build something and not even take into consideration how it actually operated. Always a learning process. ![]() | ||
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Kishmul |
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![]() Registered Member #4822 Joined: Sun Aug 21 2016, 03:38pmPosts: 8 | Great model and interesting discussion. The manpower to turn the capstan comes from the legs, passing that power through the back and arms diminishes the power delivered. It is easier to deliver the maximum power by turning your back to the direction of motion and hooking your arms over the bars. This solution can be seen today on manually operated canal locks | ||
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