Need advice on installing dock floats


I want to add some additional floats to my dock to raise it. I am looking for ideas of how to get the floats under the dock. The dock currently sits about 3-6 inches above the water. I want to add a 4'X6'X24" float to one end of the dock. This float has a buoyancy of 2700 lbs. I need to either raise the current dock or submerge the float to place it under the dock. Some options are:
1) Use a come along to raise the dock. Possible but I would need to raise it about 18". Finding an attachment point could be a problem.
2) Load the float with weight to partially submerge it.
3) Place tempoary floatation (like an inflatable air bag) under the dock to raise it. Not sure what to use. Any ideas.
4) Use smaller floats.
5) Call a pro. Might have to.
Any other ideas?
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On Sun, 22 Aug 2010 22:19:01 -0700 (PDT), noname87

What kind of float? If it is rigid plastic full of air, can you fill it with water and blow it out with air?
Otherwise, a bunch of smaller floats.
If you want to lift the dock, build a frame from 1x3s, line it with plastic sheet and sink it under the dock, turn it over and pump it full of air. (Think upside down boat) A shop vac will probably work. If you could come up with an old water bed mattress you are good to go without building anything. Maybe a big jon boat? When you are ready to drop the dock on your float, poke some holes in the plastic (or let the air out of the mattress/ pull the plug on the boat) and sink it again.
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noname87 wrote:

If it's hollow, fill the float with water and after it is secured in place pump air into it.
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noname87 wrote:

Get somw barrels. Fill them mostly with water. Position them under the dock with the filler bung downward, and fill them with air to lift the dock. Or, use plastic barrels for your floatation the same way.
OR, detach the dock. Pull the end up to shore and use a jack to lift it.
Or, inflate a raft or 4 under the dock.
Or, put a lot of weight on the other end to push it down so the desired end goes up.
Or, some combination of the above.
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On 8/23/2010 2:51 AM, Bob F wrote:

You used to be able to get truck inner tubes cheap, some of those are big!
Jeff

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One large float is going to make your dock uneven. Or wobbly if you put it in the middle. You need to add several smaller ones closer to the corners. And 24" seems too high? What is the size of your dock and what are the sizes of the floats under it now? I'm thinking you need several smaller floats. I have a 10'x10' dock on four 4'x4'x16" floats. With a 2x6 frame and 5/4 surface the top is about 18 to 20 inches above the water surface.
I'm guessing you are looking at one big float because one big one is cheaper than lots of smaller ones? Unfortunately that usually can't be made to work.
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Okay. some more info. This is a covered boat slip (U shape with metal roof). It is roughly 400 square feet. I currently have 10 floats that are 4'X6'X16". Eight of thes are submerged 60%. Two on the end are 90% submerged. My plan is to either replace the four corner floats with 24" floats which could raise the dock 8" height or rearrange the floats and add four 4x6x16" floats which could also raise it to 8". A third option is too replace all 10 floats with 24" to get a final height of 12". Both options would result in floats that are 50% submerged. Not ideal but it should fix my problem.
I am leaning towards the 16" floats which have a bouyance of 1850 lbs. A lot more work to rearrange the floats but less effort to submerge the floats. Still I need a 1000 lb+ of wieght.
The floats are polystyrene with a hard plastic shell.
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I can see trying the 24" on the corners. But I think you'll still end up uneven unless you put bigger floats out on the ends where it is 90% submerged. Floats are so expensive that I'd sure try to add more rather than replacing. But that only works if you have space for them. Was the roof added later? I know the 24's are often used if there is a metal roof on the dock. If you end up replacing the corners I'd try a 4x8 instead of a 4x6 and see if that brings the ends up a little.
Happens I need some 16" floats myself :-) Where abouts are you? If you end up having to replace floats you at least ought to be able to sell your old ones on craig's list.
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noname87 wrote:

Do they have a openable cap?
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Most of the modern floats do have plugs. They are filled with closed cell foam and it's not supposed to matter if they get a leak anywhere. I've never tested that myself. Where I am you are only allowed to use the plastic foam filled floats. On Kerr the army corp runs the lake and sets the rules. Dam things are pricey!
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The corners wiould include the spots where the floats are almost submerged.
I am a new owner of the house so I do not know thw history of when the roof was added. I suspect that the floats are 5-7 years old. Can these floats get waterlogged and lose buoyancy? I don't see how.
As you figured, these floats are not cheap. What is worse is what a dock builder charges to install. The quote I got was to replace all the floats for $8500. I figure 4000 for materials and 4500 for labor. I am sure it would float nicely. I figure a partial replacement would cost $1000 with my sweat labor. The end result woud be be about the same except my effort would result in a slightly lower dock.
I just need to figure out the best way to get them under the dock. So far, it looks like using a winch and smaller floats might be the way to go.
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From what I understand they are not supposed to get waterlogged. I have them on my dock and walkway to the dock and mine are 8 years old now. I have not seen any drop in my dock height since I built it. I know they are not cheap, I've been pricing them because I want to extend our walkway. All I have is a 12x12 square and a walkway. No roof.
If you are just adding them I wonder if you could lever one under using a long board? Another option would be to float the dock over to the edge of the water and jack it up. You'd have to move it around to do each corner.
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I really can't move it. The dock is attached (with piling guides) to pilings on two side. The third side has pilings about a foot away. The third side also has the end of a 20'X4' ramp sitting on it. The fourth side is open water. Once moved, it would be next to impossible to get it back in place. This dock is U shape, 22'X26' with a 10'X18' cutout for a boat slip. The metal roof covers the whole dock.
If the float are good, I estimate the weight to be about 14,000 lbs. Seems high to me.
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replying to Bob F, Klintonking wrote: Yes they do should I attach wood to the float first
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replying to noname87, Bud wrote:

You probably have completed your repairs by this time, but if you are dealing with tidal water and the depth below your dock isn't too deep. You can attach 2x4's 2x6' s to the corners of the dock at high tide. When the tide goes out, you slide the old floats out and the new ones in, probably no more than 8' of water depth.
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replying to Bud, Phil wrote:

Thanks. Still working on this. I did managed to add 2 2x4x16" floats as a temporary fix but still need to add more. The dock is on a lake,
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replying to Phil, richard wrote: **add air to air bladder or mattress under dock to lift area you need to work
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