# Floating boat lift

## Main Question or Discussion Point

I am trying to build my own boat lift that uses plastic tanks submerged to lift the boat when they become filled with air. My problem is that I need to lift about 10,000 lbs and i dont know how large the tanks need to be ( how much water they need to displace ) to lift that amount of weight. I am going to be using two tanks. please help!

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AlephZero
Homework Helper
What you need is Archimedes Principle, but there's an easy way to do it for this application.

When the boat is afloat, it displaces a certain volume of water. If you want to "float" it above the water on top of a tank, the tank needs to be the same volume as the part of the boat that was below the waterline - plus a bit more volume, to float the weight of the tanks themselves.

why not use (2) 610 gallon tanks or One 1220 gallon tank to lift the 10,000 pounds. Water weighs 8.33 lbs per gal. at 70 degrees F. We usually use an electric motor with a reduction gearbox driven tooth gear , (a sprocket), which operates a chain that drives a sprocketed shaft that have cables that go through pulleys that lift a cradle that the boat sits in. The motor is able to operate clockwise and counterclockwise for up and down movement. very reliable and durable. These motors are easily found for outdoor environment..much cheaper than using an aircompressor or water pumps with large volume tanks.

AlephZero
Homework Helper
why not use (2) 610 gallon tanks or One 1220 gallon tank to lift the 10,000 pounds. Water weighs 8.33 lbs per gal. at 70 degrees F.
Or 10 lbs per gal, if your boat happens to be in the UK

The Boat probably weighs more overthere also, so it's all probably relative, ha, ha.

AlephZero
Homework Helper
Nope, the boat weighs the same number of pounds, but UK pints and gallons are 20% bigger than US.

Which was not so funny, when somebody refuelled an aircraft using the wrong size of gallon...

FredGarvin
Nope, the boat weighs the same number of pounds, but UK pints and gallons are 20% bigger than US.

Which was not so funny, when somebody refuelled an aircraft using the wrong size of gallon...
Been there. Thank goodness it was stopped before it happened.

I was joking about the weight of the boat. Doesn't an aircraft have fuel guages that are represented in lbs of fuel rather than gallons? Does the sensor in the fuel tank need re-calibration when the aircraft operates in a country with a different standard?