Extreme Block and Tackle: Building Manual Winch with 4:1 to 500:1 Ratios

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The discussion revolves around the user's plan to lift a 1500lb boat using a manual block and tackle system due to the absence of a winch. They explore the theoretical strength requirements for various block and tackle ratios, concluding that a higher ratio would significantly reduce the necessary rope strength. However, concerns about friction in the system are raised, suggesting that it could negate the advantages of using many pulleys. A recommendation is made to use a comealong as a practical solution for lifting the boat effectively. The conversation also touches on the importance of designing a cradle that properly supports and balances the boat during the lift.
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[ backstory ]
Yesterday I finally, and sadly, put my Matilda http://davesbrain.livejournal.com/315479.html" to bed for the winter.

I want to lift her off her trailer so I can work on her hull. She's 1500lbs. The barn she's sleeping in has a massive traveling lift system (18" steel I-beam on a track) but no winch.

I can't afford to rent a winch for the whole time I have it hanging. (Yes, I know I can build a cradle to sit her on, but...) So I've been thinking about building a manual winch using block & tackle.
[ /backstory ]

So I started wondering how big a block & tackle system I'd need. A rope with 1500lb test?

Question 1 : Correct me if I'm wrong: for a block & tackle with, say 4:1, my line's strength need only be 1500/4=375lbs, right?

What if my block & tackle were 100:1? I'd only need a line that could support 15lbs.
I know that 100 pulleys may sound like a lot but each wheel would only have to support 15lbs. so they could be compact.

What if I had 500:1? 3lb test line. I could lift my boat off its trailer with sewing thread tied to my pinkie!

(Of course, to lift it a mere foot, I'd have to run a tenth of a mile away!)

Question 2 : Is there a flaw in my logic?

I'm thinking the friction might do me in, but I'm also thinking that the friction would be distributed among the 500 strands so it shouldn't be a problem. Or is the friction cumulative?
 
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Bob S said:
Get a comealong:
http://www.cvfsupplycompany.com/hanpowpulcom.html
Really. :bugeye:

That little <$100 device will allow me to hand winch my boat into the air. Wow.

Thank you.

Then my next question is going to be how to design the cradle so that it supports and balances the boat.
 
Unless you can get a cradle that has the pivot point above the boat's center of gravity, I suggest two comealongs, or two straps lifting the boat tied to a crossbeam.
Bob S
 
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