Floating docks
In certain situations, such as in tidal areas, streams or rivers or reservoirs subject to fluctuating water levels, boat docks need to be built on floats to allow the dock to move up or down as the water level changes. Floats for docks are available commercially, but DIY-minded people can incorporate homemade floats into their own boat docks which will work just as well, and at a significant cost savings.
How Much Flotation
One of the parameters a dock designer needs to consider is the amount of weight the floats will need to support, including the materials used to build the dock, the number of people expected to be on the dock at one time and any permanent structures, furniture or other gear installed on the dock. Once this weight is determined, you can figure the amount of flotation a float will provide by calculating the weight of the amount of water the float will displace. For instance, a 30-gallon drum used as a float will displace 30 gallons of water. Water weighs 8.26 lbs. per gallon, so one drum will float a bit over 245 lbs. If using Styrofoam or some other product not measured in gallons, calculate the cubic feet of the float and multiply that by 62 lbs. of water per cubic foot. A 1-by-2 foot by 8-foot-long billet would be 16 cubic feet and provide flotation for just under a thousand lbs.
Barrel Floats
Used barrels or drums make perfectly serviceable floats for docks. As long as they remain water-tight, they will float. Either 30- or 55-gallon steel barrels will work, but will eventually rust through and need replacing. Using plastic barrels eliminates the problem of rust-out but the plastic is easier to puncture, so the dock design should provide them protection from being hit with boats, paddles or other objects that could penetrate the side of the barrel. Plastic containers come in a variety of sizes with 10, 30 and 50 gallons being the most common.
EPS
Styrofoam is the Dow Chemical brand of expanded polystyrene (EPS) often used for packaging and for inexpensive, foam ice chests. It's also available in large blocks, billets and other shapes for use as insulation in construction or for other needs. Large pieces of EPS can be used as dock floats. It's quite fragile, however, so if you are using it be sure the pieces are well protected. Muskrats will often chew on it as well. Consider wrapping the blocks or billets with aluminum flashing material to boost their longevity.
Tags: float will, blocks billets, boat docks, cubic feet, float will displace, will displace