Water weighs about 64#/CuFt [fresh water slightly less]. Don't forget to subtract the weight of the "tanks" from Your calks, and that You have to allow for people, dock boxes, golf carts or whatever will be on those docks.
As long as ther is more "tank" above the water, You still are safe, but once fully submerged, they will sink like a rock, so allow plenty of additional boyancy above expected loads.
I suggest You put "tanks" on each side with space between them for stability, and EACH side should be able to carry the total expected load, as everybody may be on one side of the dock.
Building floats for docks can be tricky because you want them to support the anticipated loads times a safety factor, but you don't want them to overturn if everyone is standing to one side. That means they can not float too high out of the water thereby placing the center of gravity (think of the all the people standing up on top of the dock) too high above the water line. One way of providing stability is to make sure the dock is rather wide so that it doesn't overturn easily.
The volume of the floats has to equal the (weight of the floats plus the dock structure and the people times a reasonable safety factor / by the density of water) . The dock surface has to be high enough out of the water so that waves are not going to break over the dock or cause it to overturn. The shape of the floats can also influence stability. The floats could have a cross section that is triangular so that the heavier the load, the greater the volume of water displaced. The sketch is just a concept that might work. the actual dimensions, weight of the ballast, etc. would have to be calculated.
You have seen it mentioned here in the Forum a hundred times if you have read it once, a consultation with an engineer, in this case a Marine Engineer, is well worth the money spent.
Best regards - Al
AND, you MUST have a Floating Dock Stamp !!!!!!!!! or a Duck Stamp, I forgot which one it is.
From what I've heard of late, the Ducks haven't fared well. One sank or malfunctioned in Boston and another one was recently steamrolled by a barge in Baltimore. So, I'm not sure about the "Duck Stamp."
Best regards - Al
the docks that are already there have floats made of plastic, the measurements are 24x48x72'', and the customers want to follow those measurements
Make sure you select the right aluminum alloy and filler metal for the type of environment the floats will be in, i.e., salt water or fresh water. Some aluminum alloys (magnesium alloys) will exfoliate when sujected to a salt water environment.
Best regards - Al
One just got hit in Philly, lost power in front of a barge & tug, if I remember right.
I believe you are right. I had the wrong city.
Al
LOL... Now that was funny..!! Dock stamp..!!!!
The duck that was sunk by the barge in Baltimore resulted in two passengers drowning. An unfortunate accident. I haven't heard what the investigation turned up. I understand from the news reports that the tug captain didn't respond to the radio calls made by the duck just before the accident.
Best regards - Al
Al,
From what I understood, the tug captain just thought it was some quack transmitting on the same frequency and didn't pay any attention.
Are you referring to the squawk box?
Al
Yes, that fowl thing.
I bet he flew off the handle after that..!!!!
As long as the floats are air tight they shouldnt sink even if they go below water level. Try and sink a basketball. But extra float is always better.
If You put more weight on them than the water they displace, they sure as hell will sink, even if they are water tight. It isn't that hard to sink a basketball, just put more weight on it.