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Old 23-03-2014, 05:47   #16
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Re: Cruising Weight

You can have the boat lifted by a travel lift that has load cells, and get an approximate answer that way. If you want more accuracy, you need a crane with a scale.

The Erie Canal used to weigh barges to calculate fees by putting them in a lock and measuring the water that ran out an using the volume calculation.

I'm not kidding about the acceleration measurement. You need a fixed dock with a piling 10 feet above the water, about 10 feet of space for the boat to move, a 50 pound weight, two pulleys and a line. The line goes from the bow to a pulley at bow height, up to a pulley at the top of the piling, then down to the weight. Put a stick with distance markings on the piling so you can see how far the weight falls. Let the weight pull the boat forward for 10 seconds, and record where the weight is each second. For a 15 ton boat, the weight should have moved about 2.7 feet after 10 seconds, and should be going about 0.5 ft/sec. Stopping it is your problem, but I'd recommend a stern line. Needless to say, you need flat water and a windless day with no surge for best results.

The weight of the boat = W*2*g*t^2/d where
W is the pulling weight
g is the acceleration of gravity
t is the time
d is the distance traveled

You pick the units you are used to, and I'd probably reduce the results by 5% due to friction in the pulleys and drag on the boat.

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Old 23-03-2014, 14:58   #17
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Re: Cruising Weight

Originally Posted by Factor View Post
Actually its exactly like that. Multihull Yacht Club of Queensland for example regularly has days where they weigh boats - even very large - 16 metre cats etc, necessary for OMR Handicap processes.
Well, I don't want to have to sail my yacht to Brisbane to put it on some scales and I've phoned around and no one locally has scales for doing this. So it looks like I'll be going with the arithmatic way of doing it.

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Old 17-06-2014, 00:13   #18
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Re: Cruising Weight

FP should have very accurate calculator for boat weight - their Finite Element guys will have models of the boats volumetric displacement. So all you need to know is the water line position.. and they will have a look up table to show you the exact weight.
FP can you get this LUT from your CAD guys?

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