Does anyone on here know how much weight an empty sealed 55 gallon drum will hold buoyancy wise? I am trying to figure out how many would be needed to make a floating dock that will need about a 5000 lb weight capacity. I also will be needing some drums. Hey Waterboy I remember seeing a post you made about have a bunch of them. Send me a PM if you can hook me up.

Thanks,
Chuck

Assuming your using aluminum drums:
55 gallons converts to about 7.35 cubic feet. ( Gallons/7.48 )

Then using Archimedes Theory, we get the following info:

The internal volume of the cylinder is 7.35 / 15 * 14.7 = 7.2 cu ft

The cylinder is made of 50 lb of aluminium, (which has a density of 170 lb/cu ft).

The aluminium therefore has a volume of 50 / 170 = 0.29 cu ft, so the total volume is 7.2 + 0.29 = 7.49 cu ft.

The density of fresh water is 62.4 lb/cu ft, giving 7.49 x 62.4 = 467.4 lb

Air has a density of 0.075 lb/cu ft.
The air in a full cylinder weighs 0.075 x 7.35 cu ft = 0.6 lb.

The cylinder when full has a buoyancy of 467.4 lb - 50 lb = 417.4 lb


12 Drums

Thank you sir for that info. I actually planned on using the plastic drums because I think they will last longer and be a bit more puncture proof. I imagine the overall capacity would be a little higher due to less weight of the plastic vs. the aluminum. Correct?

When we built our dock at our cottage I used steel drums and had them filled with urethane foam. I thought if a puncture were to happen it would't be a problem . It would work great with plastic drums too . You will loose a little lifting capacity by filling the drums . Don't know how much . Just weigh the drum before and after and subtract the difference .I used the company that spray foams my houses so I never got billed but I can't see it costing more than 50 bucks a drum .
Paul

fever is correct... including the part about the weight of the barrel. it really doesn't matter what material the barrel is... just weigh it . the bouyancy will be the interior volume in cubic ft x 64 minus that weight.... just as he says.

Thanks guys. I am just going to go with 12 and that should be enough. I appreciate the help.