Gin Pole

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Paul
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Gin Pole

Postby Paul » Sat Apr 21, 2012 11:23 am

OK you engineering types, here's the problem:
You have a pole about 26' long weighing 80 pounds. One end is the fulcrum point. The gin pole is located at the fulcrum point and is 8' long. A line will be attached from the top of the pole to the gin pole and from there to a winch to erect the pole.

What is the compression pressure downward on the gin pole?

Obviously you recognize I'm erecting the mast. While making the gin pole I want to make sure it is strong enough in compression.

Thanks
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Postby Rivercruiser » Sat Apr 21, 2012 9:01 pm

:?: use boom for gin pole :?:
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Postby Banshi » Sun Apr 22, 2012 5:42 am

Compression is not really the problem, it is going to be lateral stiffness. It will want to bend under the load long before compression becomes an issue (the compression is of coarse causing the pole to bend). Set your pole on two saw horses and sit on it, if it holds you should be good to go.

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Postby Paul » Sun Apr 22, 2012 11:53 am

Thanks, I've been using the boom but am adding lazy jacks. This places multiple lines on the boom making a gin pole much easier to manage when getting the mast up.

As for bending moment, there should be little lateral pressure because the line from the gin pole forward equals in tension the line from the gin pole aft. The lateral pressure is minimal since all you are doing is keeping the pole centered and again have equal pressure from each side. So, the compression is really the only significant pressure placed on the pole. At least this is my understanding.

Just for fun I gave the problem to an engineering student at our local college. We'll see what happens.

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Postby Banshi » Mon Apr 23, 2012 3:18 am

Take a spaghetti noodle stand it vertical and push down on it, it will bend and break long before it compresses. Same principle.

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Postby Paul » Mon Apr 23, 2012 5:55 pm

Thanks! I think we're saying the same thing with different words. It's the downward force that makes it bend like a spaghetti noodle that I'm looking for. Thanks for making it more clear.

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Postby Paul » Fri Apr 27, 2012 9:22 pm

My young engineering friend has an answer. The greatest force downward on the pole is when the pole is vertical and the mast is just being picked up from the horizontal postion. I have the equation, though I doubt anyone cares so I won't reproduce it here.

The answer, however is that 144 pounds of downward pressure is exerted. That should make my 1 1/4" EMT conduit strong enough to handle it. Finished the project tonight. Pictures coming to my photobucket account soon.

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Postby cs3079 » Sat Apr 28, 2012 12:31 pm

Interesting, when I'm using the muscle method of raising the mast on the C-20, that's also the position that accounts for the greatest stress on my back and ticker. After it gets past about the 60 degree point it's actually a piece of cake. I've got a make shift crutch I use to raise the mast up a bit before I start heave-hoing, which helps a immensely.
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Postby lecker68 » Sat Oct 20, 2012 6:15 pm

I used 1" pipe with a cap and a 5/8" hole drilled for the pin. Gives me 10' and I use a 4:1 purchase and my winch I can stop and cleat it off at any point.
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Postby Dallasbob » Sun Nov 11, 2012 10:32 pm

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