Big Boat

[CMARSHALL]

I am looking at a steel hulled trawler 45'x20' that needs hull repairs and painting. I am planning on contracting a crane to lift the boat out of the water but to do so they need to know how much it weights. Is there any way to determine/estimate this by displacement, draft or otherwise.

Thanks

[FranklinRatliff]

Water weighs 8 lbs per gallon.

In order to float the boat has to displace a volume of water equal to its weight.

Look for the water line on the hull.

Then measure the width, length and depth of the hull below the water line.

That will give you the volume of water the boat displaces.

[DanishBagger]

Assuming it is box-shaped, of course, and with no deeeep fin keel ;-)


Franklin is right though, you have to figure out how many litres of water it displaces (1ltr=1kgs).

[SamSam]

A cubic foot of fresh water weighs about 62 lbs., a cubic foot of salt water weighs about 65 lbs. If you can figure out how many cubic feet of volume there is below the waterline, multiply that by 62 for fresh water or 65 for salt water, that will tell you how many pounds it weighs. How to determine how many cubic feet of volume you have below the waterline is a little involved. As Franklin says, l x w x d = volume, but then as Bagger says that's the volume of a box shaped hull. If the hull is fairly boxxy like, l x w x d will be close enough for a crane and will give you a margin of error in that your boat cannot weigh more than your calculations. If there is a lot of shape to the hull and/or the l x w x d calculation is too vague, you can take the measurements of a series of cross sections of the below waterline hull, say every 5', figure out the square footage of each, add them all up and divide to find the average, and then multiply that by the length to find the volume. Not exactly but close enough for a crane. Sam

[fiberglass jack]

find a crane company that does marine work your the one paying the bill let the work out the wieght .what happens if some thing goes wrong they will say its your fault find a good crane company