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  #1  
Old 01-19-2011
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Anchoring a floating dock to the shore

So I'm contemplating building a floating dock on a friend's lakefront property for a 23' boat. It's on Lake Simcoe, north of Toronto, which is about 30km across and big enough to get a couple feet of wave action in storms.

After going through everything I could find online (a pile of eHows - see the related articles on the side, and a couple other places) the floating structure is straightforward and what you would expect: build a box of 2" x 8" x whatever, maybe put another stringer or two down the middle, brace it regularly with crossbeams, plank it, attach floats (don't forget to work out how much buoyancy you need), voila! Use appropriately sized marine-grade hardware. If you can build a deck, you can build a dock (just one letter apart ...).

But none of the suggestions online go into great length about keeping your dock in place on a lake with some wave action, especially with a heavy (maybe as much as 2 ton?) boat on it.

What makes sense to me would be to pour some big old concrete slabs shoreside, like you would for wooden deck posts. But instead of a 4x4 or whatever vertical, set a heavy-duty metal shackle into the concrete (hopefully on a base with a lot of surface area, not just a screw). Then run chain out to the base of the dock. Use a short hinged "gangway" section to connect the floating end of the dock to shore. Maybe also sink extra slabs a little ways out to the right and left and run diagonal chains attached to the dock 20%-25% of the way out (i.e. still in water too shallow to be the "usable" portion boat-wise) to counteract the otherwise serious lever arm that lateral forces on the end of the dock would have on the anchor points at the base.

Any thoughts? Anybody tried it?
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Old 01-19-2011
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at first glance i would be concerned that while the chains may prevent you from floating out, they wouldnt help you from running aground on shore? ie you are trusting your 'hinged gang plank' to hold the pressue of dock weight + boat weight against your two foot waves pushing you into shore. maybe if you set up a mooring for the dock, but id be leary about leaving your boat attached.
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Old 01-19-2011
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The only solution that I've seen that actually works (apart from massive concrete structures) is to drive a piling into the bottom, and use a metal hoop around the piling.

The lake our cabin is on doesn't maintain a constant level, and this is the only system that is both neat, and functional. In the past I've been known to tie a long rope diagonally to the shore, but it's in the way. Wave action will either move your anchors, or rip apart your dock.
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Quote:
Originally Posted by QuickMick View Post
at first glance i would be concerned that while the chains may prevent you from floating out, they wouldnt help you from running aground on shore? ie you are trusting your 'hinged gang plank' to hold the pressue of dock weight + boat weight against your two foot waves pushing you into shore. maybe if you set up a mooring for the dock, but id be leary about leaving your boat attached.
You're right, I didn't mention that end, and I should really do some diagrams of what I'm thinking when I get a chance to help me think this through better. A lot depends on how steep the shore is, and how quickly water depth develops.

I guess I would really want the butt end of the floating portion firmly up against solid ground, assuming there's enough of a vertical drop where the water starts to allow it. If the shoreline is shallow/gradual (like a beach), I guess I would really need a very heavily built hinged 'gang plank' to take the stresses in both directions - not that I necessarily see that as impossible to work out.

Before anyone asks, I'm only looking at floating designs right now because there are a lot of hoops to jump through (environmental impact studies, etc) to build a fixed dock, but we think a "temporary" (i.e. summer-only) floating dock skirts the requirements. Working on getting details on that.
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Quote:
Originally Posted by zedboy View Post
So I'm contemplating building a floating dock on a friend's lakefront property for a 23' boat. It's on Lake Simcoe, north of Toronto, which is about 30km across and big enough to get a couple feet of wave action in storms.

After going through everything I could find online (a pile of eHows - see the related articles on the side, and a couple other places) the floating structure is straightforward and what you would expect: build a box of 2" x 8" x whatever, maybe put another stringer or two down the middle, brace it regularly with crossbeams, plank it, attach floats (don't forget to work out how much buoyancy you need), voila! Use appropriately sized marine-grade hardware. If you can build a deck, you can build a dock (just one letter apart ...).

But none of the suggestions online go into great length about keeping your dock in place on a lake with some wave action, especially with a heavy (maybe as much as 2 ton?) boat on it.

What makes sense to me would be to pour some big old concrete slabs shoreside, like you would for wooden deck posts. But instead of a 4x4 or whatever vertical, set a heavy-duty metal shackle into the concrete (hopefully on a base with a lot of surface area, not just a screw). Then run chain out to the base of the dock. Use a short hinged "gangway" section to connect the floating end of the dock to shore. Maybe also sink extra slabs a little ways out to the right and left and run diagonal chains attached to the dock 20%-25% of the way out (i.e. still in water too shallow to be the "usable" portion boat-wise) to counteract the otherwise serious lever arm that lateral forces on the end of the dock would have on the anchor points at the base.

Any thoughts? Anybody tried it?
If you have ever been to Maine along the water. You should notice that there are very few slips / marinas. Most boats are on mooring because of the tides. To get to the mooring most landowners on the water have floats whuch basicly consist of a float or floating dock that you were considering to build. In general the floats are fixed in position by crossed chain to the bottom and with lines or chain ti the shore and a gang pank or walkway that runs from the float to land. Some of the walkways are attached at a pivot point on the float to accomidate the 10 foot tides. There is also a pivot point where the walkway attaches to land. Others have rollers (usually the larger floats) where the walkway rests on the float. Another way of adjusting to the tides. When not fixed to the walkway they use more chains to attach to the bottom and land.

If you PM me with your email I can send some pix. Don't have time to figure how to include in a post.
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btw, the cost of 'impact studies' and 'pouring big slabs' would probably significantly outweigh the cost of

1)well set mooring ball for boat

2)dink to get to her

3)floating swim platform for summer fun, with seperate mooring?

just a thought--if they will let you leave a boat tied to a mooring in 'public waters,' depending on your usufructary rights
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Quote:
Originally Posted by QuickMick View Post
btw, the cost of 'impact studies' and 'pouring big slabs' would probably significantly outweigh the cost of

1)well set mooring ball for boat

2)dink to get to her

3)floating swim platform for summer fun, with seperate mooring?

just a thought--if they will let you leave a boat tied to a mooring in 'public waters,' depending on your usufructary rights
Well the floating dock avoids the impact study.

And even if I get a guy to come in and pour concrete it's not going to run more than a couple hundred. I have a friend who's a contractor specializing in decks working with me on the project.
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Comparing an inland lake to Maine's seacoast is a bit ridiculous. There are no tides in an inland lake, and the seiche effect is relatively limited.

One option is to drive pilings down into the bottom and use the hoops to connect the pier to the pilings. Another option is to use helical or mushroom anchors and chain the pier in position.

Ideally, the shore-connected portion should be higher than the floating portion and a ramp should be attached to the shore-connected side and have wheels to allow it to roll back-and-forth along the floating side. However, if you're going to do that, you'll really need to use the pilings, since the dock really shouldn't be able to move laterally much at all.
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Plenty of close-to floats are positioned with 'stiff legs' - these will allow for a certain range of water level changes and keep the float from being pulled into the shore. Depending on the loads involved, you may not need anchors.

Something like this: This way there's no real stress on the ramp and you can tolerate most seasonal variations in lake level. The longer the stiff leg, the less lateral motion of the float w/ level.

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Originally Posted by Faster View Post
Plenty of close-to floats are positioned with 'stiff legs' - these will allow for a certain range of water level changes and keep the float from being pulled into the shore. Depending on the loads involved, you may not need anchors.

Something like this: This way there's no real stress on the ramp and you can tolerate most seasonal variations in lake level. The longer the stiff leg, the less lateral motion of the float w/ level.
Beautiful. I think this is the piece I was missing.

Now I'm finding lots of guys who supply hardware for these things - like this thing,

of course supplied by your friends and mine at The Floating Dock shop.

Will call them up and get their opinion on how much abuse a stiff-arm design can take, and report back.
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