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Thread: floating dock

  1. #1

    Default floating dock

    I'm thinking about building a 16'x16' floating dock this summer. Does anyone know the calculation for how much floatation I'll need. What's the best source for floats? Someone suggested using plastic barrels to float it, anyone have any experience with that system -- know where you can get them>?

  2. #2
    Member Gerberman's Avatar
    Join Date
    Feb 2008
    Soldotna AK, Eugene, OR

    Default Air in float

    Each cubic foot of air will hold up 62.4 lbs in fresh water and about 64 lbs in salt water. To calculate the air in a drum, take the diameter times the diameter divide by .7854, times the height of the drum, divided by 1,728 multiply by either 62.4 or 64 and you have how much each drum will hold up in the water. If you put closed cell foam inside the barrel it weighs about 2 lbs per cubic foot. so you will loose 2 lbs lift per cubic foot of foam. You just have to weigh all the drums, the wood, the nails, and anything else that will be used to make the float. You should have about a double lift to weight ratio, so the drums will be about 1/2 out of the water. Good luck have fun building Gerberman

  3. #3

    Default floating dock

    I am in the same boat, so to speak. I'm trying to avoid a floating dock if I can. The problem is they tend to sink a bit when you put weight on them. I have an inflatable boat, so when you get out of the boat, and on to the dock, the two trade elevations in a hurry.

    Last summer I accidentally did the splits when getting out at my neighbor's dock. If I were 20 years old or a gymnast, that might have been ok. I'm neither, and all I can say is ouch!

    If I get stuck using floating barrels, I'm not sure if it matters what was in them? Knowing the E.P.A., D.E.C., etc I bet it does. Do you have to use "new" barrels, or can you wash out "used" barrels? I have seen used ones for sale that had car soap in them.

    My current set up is tying the boat to a deadman on the shore.
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  4. #4
    Join Date
    Sep 2008


    Since you usually know the capacity in gallons of a drum instead of it's dimensions, it's easier to go with 8.35 pounds per gallon when figuring how much an empty drum will float. Here's the bouyancy for a few common drum sizes:

    15 gal - 125 lbs

    20 gal - 167 lbs

    30 gal - 250 lbs

    55 gal - 460 lbs

    A very rough guess on what you need to float would be 10 lbs per square foot for the dock itself and 30 lbs per square foot for the people on it. So a 10' x 10' dock (100 square feet) would need 4,000 lbs of floatation (9 55-gal drums). That will vary depending on how you build the dock and how many friends you have.

  5. #5


    Thanks, that's helpful -- much easier for me to use gallons than demensions. I found a website that provided a calculation for determining the a mount of bouyency needed...

    In determining the # of dock floats needed for your project, in general, you can get a good estimate by multiplying the square footage of your floating dock or swim platform by 25 which will give you the total buoyancy weight needed. Then divide this number by the buoyancy rating of the size float you will be using. For example, a 10x10' floating dock = 100 sq ft. 100 sq ft x 25 = 2500 lbs of weight. If you are using 12" floats, the buoyancy of each float is 400 lbs. So 2500 lbs divided by 400 = 6.25 floats, round up to 7.

    Using that formula, I'd need between five and six 55 gallon drums for a 10x10 dock. At first blush that seems like overkill to me, but I guess it's better to know now than when I'm trying to raise it off the bottom!

  6. #6
    Member anonymous1's Avatar
    Join Date
    Apr 2006
    Kodiak Is.

    Smile for us dummies

  7. #7
    Join Date
    Nov 2009

    Default Plastic barrels would be best

    There are a myriad of designs building docks. But what ever you build designe it to be repaired . the biggest mistake is in thinking it will last forever. Ice is nasty stuff. I have seen all kinds of dock configurations working on boats for 18 years . one of my bosses built docks some of the best around.
    Making your dock ridgid as possable is essential,
    an L shape for the simlest designe is the most stable
    Pressure treated wood (coppper sulfate will not allow the wood to rot) in the frame work and considder the angles of stress each portion will endure as you draw out your plan.
    The deck material (TREX)we used is a material recycled from plastic bottles.
    the extrusion shapes varry from 2x4 to hollow oval like but they are impervious to sun and freezing . they add nothing to floating and are not structural but one cannot get splinters from them , shoveling the snow off is easy during the winter, nothing sticks to it . Galvanized dry wall screws hold them well , and they cut easily with a skill saw.
    Think about more things; cleats well anchored, and chaffing of your boat
    on the dock .wave action is mercyless. tying off your boat is very important , but we all know what usually happens . So if only one line is left holding the boat ,make provision so that the serface it will be rubbing against is not abrasive .
    Some people like anchors holding the dock some like poles or pipes.
    If the water is changing levels through the season considder that .
    If you prefir the anchor method make sure it is n ot going to be a prop hazzard for your self or a visiting friend who may not know which direction they are spread.
    Just some food for thought

  8. #8


    20x10 18 30 gal plastic drums. Walkway 20x5 2 55 gal and 2 30 gal drums
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