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Thread: Building a floating boat dock

  1. #1
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    Default Building a floating boat dock

    Hello looking for some insight, I'm going to ramble for a minute:

    Looking at building a 8'x8' floating dock at our cabin in a slow to medium flowing river and anchoring to shore so that we can tie the boat up and fish off of. I searched for info, but was unable to find.

    So my question is what kind of dock did you build, how did you anchor it, and what would you do differently?

    I've ruled out the completely plastic docks because I'm worried about a bear chewing on it and destroying the investment. So that leaves me a wooden deck and sub frame with plastic floats.

    I am looking at the manufactured floats versus using plastic drums and wasn't sure of the trade offs. Manufactured floats have a nice flange/lip for attaching to. Manufactured floats are expensive. Are flat bottomed manufactured floats more stable than rounded drums? etc....

    Looking for any lessons learned from folks who have already gone down this road. Thanks.

  2. #2

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    Our dock is 10x20 and floated with 20 30 gallon plastic drums. Drums are cheap and if you space your joists for the manufactured floats you can always put them in if the drums dont work for you. I have no problems yet with the drums. Would of went with the 55gal to do over, dock would sit higher off the water.

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    We've got 55 gal drums under the docks both at home and at the cabin - they are cheap and work great. Both of ours are on lakes, so not sure on method to attach in a river. I've had good success with the big duckbill anchors from AIH, but will depend on the type of ground you have.

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    Member Rock_skipper's Avatar
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    This is an interesting thread for me, I have 4 pieces of styro foam that are 12"X4'X16' and thought if they were covered with fiberglass they would make a nice dock.

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    It has been many years since I had to deal with a dock in flowing waters and I am thinking on one at the lodge. My first thought on your dimensions 8x8. Think about how much pressure that 8' dam would be creating. If it was me I would go 4x16 in two sections. If the water is moving then ice will flow and it will not be in the water long after that so pulling it and putting it in is a consideration.

    Now you need to find a way to keep it off the shore yet anchor it up stream.

    If you want you can email me with some particular to your site and I can address them at length

    p.s. I had to deal with tide flow changing twice a day....

  6. #6

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    Built a 12x16 floating dock last summer after researching materials for over a year. When all was said and done I ended up buying the floats and hardware from Alaska Dock in Wasilla. It might not the cheapest solution, but in retropsect I'm glad I did it that way. The floats are rugged and structural, with heavy flanges for mounting to the wooden frame I built. I probably put more flotation under it than I needed, but the thing is rock-solid even with a dozen people on it. Don't have much to offer in the way of anchoring advice, mine's on a lake and I just use a mushroom anchor I bought from Westmarine when I float it out from the shore.

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    I don't know about the river you're wanting to put your dock on, but down here in Kansas on the Missouri River alot of people use old pontoon floats for their floats. You can find them in alluminum and steel. And you can find them in lengths of about 20'-30'. Around here they run about $300-$600 per float. I've seen several different ways to anchor them. One was a cable strung over the river with the front of the dock tied to that. You just have to make sure you get the cable high enough that no one will ever run into it, even in high water. Another way is two concrete anchors on the shore at the front and back of the dock. Have a heavy steel bar running from each anchor to the front and back of the dock. Make hinges for the the conection point on the dock and the anchor. On your hinges make it so you can just pull a pin and the dock is free, just in case you ever need to get it moved in a hurry. I attached a pic of a big one nearby me. If you look past the walkway further down stream you'll see one of the anchors I'm talking about. This one's big and fancy but I don't think it would take to much to make one on a small scale.


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    Member KelvinG's Avatar
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    Quote Originally Posted by Rock_skipper View Post
    This is an interesting thread for me, I have 4 pieces of styro foam that are 12"X4'X16' and thought if they were covered with fiberglass they would make a nice dock.
    We tried that combo for floats on a fish wheel. Didn't work too well, the whole thing became water logged. The floats started with the tops about 6" above water level and ended up with the tops being level with the water. When we drilled the fiberglass we found the floats full of water. I'm sure we did something wrong in laying up the glass, but don't have a clue what. If I were to do it again, I'd do a lot of reading up on how they make fiberglass floats for airplanes.

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    So i just built my dock, although I won't know how it floats until spring. I built the frame work and decking with 2x6. Total size 8x10 with 6 30 gallon poly drums for floats. In theory each float should hold about 250 pounds (8.3 pounds per gallon of water x 30 gallons) I built the dock frame work with 8 voids, each void holds a drum. 3 floats along each 10' side with 2 more voids that I left empty so that I could add two more drums later for a total of 8 if I decided to add extra floatation. I used eye bolts on the upstream end of the dock to tie it off to shore. I used some simpson strong tie parts from home depot to reinforce corners and joists. I used cleats from AIH. I'll try to add some photos.

  10. #10

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    You might think about putting the other 2 drums in. Our dock is 10x20 and 20 drums, will put 2 more in this spring. I think we used 2x12 for the stringers and it sits kinda close to the water.

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    jrb,

    First off, what is the flow of the river at the dock location? That is going to determine the extent of support, bracing and anchoring. I have built several floating docks over the years and found that 55gal steel drums work the best (flotation and durability) and cost the least (initial build and future maintenance). There is huge stress to a dock in a flowing body of water, therefore, hurricane straps at every joist are a necessity for longevity. Every corner should be bolted together with 1/4"+ steel angle, inside and outside. Do not lag this bracing to your 2x's. It will fracture and explode over time.

    The very best method for anchoring in a river situation is having a solid ramp from shore attached to the dock utilizing a hinge system. This keeps the dock in a consistent position from the shoreline. The length of ramp depends on the water level fluctuation.

    To keep it laterally secure, run a cable from each of the outside corners (corners furthest from shore) at a 45* angle back to anchors on the shore. I use the outside corners to mitigate the torque on the dock that the flowing river causes. The inside corners can be used if your dock construction allows.

    This will put tension on the ramp and the dock will not want to wander down river. The upriver cable will have a tendancy to collect floating debris unless it's anchored on a high bank, in which case I have floated a delimbed spruce along the same angle as the upriver cable and let it rest just at the outside corner of the dock, again secured to the bank so it doesn't disappear.

    This method has worked for many years and stood up to high water conditions with large floating debris hitting the dock and even an occasional spring break-up ice floe smashing into it.

  13. #13
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    Quote Originally Posted by jrb View Post
    In theory each float should hold about 250 pounds (8.3 pounds per gallon of water x 30 gallons) I built the dock frame work with 8 voids, each void holds a drum.
    Remember, it only supports that much when it is completely submerged. 1/2 way under water each drum will only hold up 125 lbs. Also, if three people are all standing on one side of the dock, all of the weight is on just the drums on that side.

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    Hope its ok to resurrect this thread. My situation is a 4X20 floating dock on a lake. Near shore is slightly over a foot deep. Offshore is about 4'. Rocky bottom makes driving pilings a problem. Current and ice movement are minimal. Im thinking 6 x 1 cu ft. Concrete deadmans with the 4 nearest shore straight down and the 2 on the end criss crossed all on fairly taut chains. im a total novice at this so any and all advice is appreciated. Not sure how to tie it into the shore yet. Im thinking I may just let it float free. Shore has a foot or two of organic soil but then large rocks again making pilings a problem This dock will moore a light 14' skiff. What have others done anchoring a floating dock in a lake?

  15. #15
    Member DRIFTER_016's Avatar
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    Here's some good info on dock building and anchoring I dug up, as I'm looking to build one in the spring if my lease comes through.

    My dock plan is for a 6' to 8' X 16' full floating dock with a 4' X 12' to 16' semi floating ramp which will be attached to the dock on the floating end and be anchored to the bed rock on the other end. I will drill holes into the granite for expansion bolts to hold the hinges in place. I will also drill holes to epoxy a pair of large eye loop connectors or mounting plates with a loop to attach rear chains to the main floating dock. And finally criss crossed anchor chains off the deep end of the dock to concrete deadman's. Hopefully this will make for a good dock, but time will tell.

    http://www.homedepot.com/catalog/pdfImages/7b/7b3ad166-3238-478e-9405-ae8e4ac2666b.pdf


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