"mmc" wrote in message
g.com...

"Dan Listermann" wrote in message
...
I want to build two docks, one permanent and a floating one. The floating
one will be supported by 15 gallon plastic drums. I can get 55 gallon,
but for a 4 x 8 dock, I worry about center of gravity issues.

The permanent one will be built of 55 gallon drums filled with dirt. Any
issues to look out for?

The 55 gallon drums filled with dirt may float because of the air trapped
in the dirt. If soaked after positioning and filling, they still won't
weigh much. Concrete blocks are something like 30-40% thier (in air)
weight when submerged.

The specific gravity of soil starts at 2.6 and goes up to 2.9. Subtracting
1 for the volume of water displaced you get 1.6 * 8.345 * 55 = 734 pounds
submerged.