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Old 20-01-2021, 14:14   #1
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Pulley Advantage?

HI All

My boat came the the rig pictured. Not sure of it's intended purpose, but I want to use it to hoist my dinghy. I googled this and it should be giving me a 4-1 advantage over simply lifting the dinghy. The dinghy weighs 60-lbs - I can easily lift it with two hands. I thought that I should be able to use just one hand to pull it up with the pulleys - nope. Seems to take the same effort as lifting it. All pulleys involved are free wheeling and the rope is not in the clamp. What's wrong?
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Old 20-01-2021, 15:48   #2
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Re: Pulley Advantage?

The line looks too big and if it is old it may not be as flexible as a new line. I switched to a much smaller line to reduce friction and also from 4:1 to 6:1 to lift my dingy, about 150 lb. Roller bearing pulleys will also help a lot.
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Old 20-01-2021, 16:54   #3
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Re: Pulley Advantage?

Quote:
Originally Posted by dmksails View Post
HI All

My boat came the the rig pictured. Not sure of it's intended purpose, but I want to use it to hoist my dinghy. I googled this and it should be giving me a 4-1 advantage over simply lifting the dinghy. The dinghy weighs 60-lbs - I can easily lift it with two hands. I thought that I should be able to use just one hand to pull it up with the pulleys - nope. Seems to take the same effort as lifting it. All pulleys involved are free wheeling and the rope is not in the clamp. What's wrong?
I absolutely guarantee that if every sheave is freely turning and the line is not too stiff or too big pulling down on the free end with 15 lbs force will result a lifting force of 60lbs.

However there is always some loss due to friction. Double check that. And it's unlikely but those sheaves might turn freely when not loaded but become sticky when a load is on them due to wear.

Mostly, on boats, the friction losses add up quickly. A 6:1 system for a mainsheet, going around several cheek blocks to get to a cabin top winch, will often feel like worse than 1:1 due to all the friction.

Small diameter lines and good, new, small line will help.

However, I'd make a suggestion: For raising a dingy if you can use a masthead halyard led to a winch (with very few blocks) it will probably be easier than rigging that 4:1 block and tackle you have every time.
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Old 20-01-2021, 17:04   #4
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Re: Pulley Advantage?

Well the actual purpose of this is either main sheet or possibly a vang
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Old 20-01-2021, 17:36   #5
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Re: Pulley Advantage?

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Well the actual purpose of this is either main sheet or possibly a vang
My first guess was a vang.
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Old 20-01-2021, 18:19   #6
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Re: Pulley Advantage?

It appears to be virtually the same block and tackle as the Boom Vang on our Bristol 29.9, itís always handy to have a block and tackle for hoisting a dinghy or any thing else that is heavy.

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