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Old 28-04-2011, 18:21   #1
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How to Secure Floating Dock to Hold 10,000 lb Boat

Not sure if this is the best place to post this, but here goes!

Puchased a summer cottage, with an existing wharf and floating dock.
On a tidal river, about 1000 ft or so from the mouth and bay/ocean.
We are around a couple of bends in the river, so have excellent protection from waves, but the wind can still blow there.
The tide swing is about 5 - 6 ft, so there is a gangway that connects the fixed wharf to the floating dock. Only the fixed wharf is in the water right now, as the other docks were taken out for the winter.
The gangway (which is really just one of the docks) is about 4' wide and 15' long, and connects to the wharf with a couple of large steel brackets.
At the other end, similar brackets are used to connect the gangway to the floating dock, which is about the same size. There is an extra floating dock as well, but not sure if / how to position it.

I can weld, so beefing up the steel brackets would not be a problem. However, I think it was only ever used for smaller boats, and my 30' sailboat (at about 10,000lbs) is going to put a big strain on that dock, when the wind blows.

I am thinking about running some chain or large rope from the inner corners of the floating dock, to a couple of large bolders, perhaps drilling them and using expansion screws in them, at low tide, similar to fixed anchors used in rock climbing. Perhaps criss crossing them to take a pull from the opposite direction.. This may prevent the dock from straining, when the current or wind runs parallel to the river, but would not do anything to keep the strain off if the wind is directly pushing the boat into the dock, straining the gangway and brackets.

If anyone has proven ideas that may help, I would like to hear them.

Thanks in advance!
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Old 28-04-2011, 18:25   #2
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

I can't quite visualize it. Is something like this your situation?
http://www.google.com/imgres?imgurl=http://www.dockaccents.com/images/scan0001.jpg&imgrefurl=http://www.dockaccents.com/floating_docks.htm&usg=__78xilnnT-rDG4waWf33rT59iR4k=&h=285&w=386&sz=24&hl=en&start= 60&sig2=vevqM7dUKJBi5NF7KB1_Ng&zoom=1&tbnid=slksoT Vo9apfOM:&tbnh=133&tbnw=181&ei=iga6TcXvKcjZiAKf58W nDw&prev=/search%3Fq%3Dfloating%2Bdock%26um%3D1%26hl%3Den%26 safe%3Doff%26client%3Dfirefox-a%26sa%3DG%26rls%3Dorg.mozilla:en-USfficial%26channel%3Ds%26biw%3D1331%26bih%3D904 %26tbm%3Disch0%2C1520&um=1&itbs=1&iact=rc&dur=495& page=3&ndsp=30&ved=1t:429,r:15,s:60&tx=127&ty=37&b iw=1331&bih=904


See how this dock has booms extending out and wires used to hold it in position?
http://www.google.com/imgres?imgurl=...w=1331&bih=904

Is it feasible to drive pilings for the floating dock?

I have seen people run extension booms and run wire diagonally to stabilize the floating floating dock with the fixed dock or the shoreline.
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Old 29-04-2011, 04:55   #3
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

Hi David,

Thanks for the reply!

Yes, it is very similar to the 1st picture in your 1st link. The gangway is perhaps a bit shorter and wider than the one pictured, but same idea.

It may be possible to get permission / permits to install pilings, as I already have an existing wharf. If not, it is more difficult to get permits to build new wharfs, etc. I am not sure if i could afford to have someone do that right now, with other projects on the go.

There are alot of similar setups nearby but they normally just have small power boats, under 20 - 25' or so. I think with the increased windage on my boat, and increased weight, I will want some lines running as mentioned. (or pilings as you suggested).

The floating dock hasn't been used in a while, and I will need to put new floatation under it. Some people use fabricated floats, and many here use a bunch of food grade 50 gallon drums. I have read that it is much better to use more drums, and half fill them with water, so they float partially submerged. This gives them some ballast and the dock will not be blown as easily as if it were floating high on the surface.

I appreciate any thoughts on this!
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Old 29-04-2011, 05:24   #4
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

Around here a piling goes for about $500 installed. We did a 10 inch by 35 ft one last year. Adding a galvanized roller and bracket attached to the dock and sliding up and down the piling would add to the cost. This is common south of us where the tidal range is similar if not higher.

We installed a dingy dock at the club last year with fabricated floats and added water to the forward floats to make the water line closer to the leading edge of the dock. It's so kids can haul Lasers and Optimist prams in and out of the water. I don't see as adding water to the fabricated floats for a sailboat as required. It may reduce windage but it does add mass. To some degree the force on the piles is increased by either windage or mass. Fabricated floats are easier to attach to a solid deck such that all the fastenings are out of the water and don't need water added for a normal application. The height is optimized without the need for adding water. With 5 to 6 ft of tide I would want pilings. Two on the shore side is common. A 10 inch piling would hold the best and last the longest. Wood pilings last about 30 years depending on water temperature and salinity. Using drums saves the cost of the floats but that part of the solution is the cheapest part. It's all the rest that costs real money.

Most of these types of home made docks are fine for small runabouts and jet skis. It sounds like the dock you have isn't in good shape. In good weather it should be fine. You just have to consider it in poor weather. In the end the boat secured to a floating dock could rip out the cleats on the dock before the dock failed. You save the dock (less the cleats) at the expense of the boat. Owning your own dock does cost a lot of money but so do marina slip fees. If it makes you lose sleep at night then the dock isn't good enough.
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Old 29-04-2011, 06:08   #5
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

these docks have double gantries,and diagonal lines to the shore,with no attachment to the seabed,rated for 1.5 m waves and tidal flow up to 10 knots.
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Old 29-04-2011, 07:34   #6
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

Quote:
these docks have double gantries,and diagonal lines to the shore,with no attachment to the seabed,rated for 1.5 m waves and tidal flow up to 10 knots.
Really nice dock but a little much for a homeowner.
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Old 29-04-2011, 07:48   #7
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

Quote:
Originally Posted by Pblais View Post
Really nice dock but a little much for a homeowner.
yes about $450000 for that one,but the principal is the same.

a smaller version could be home built with 2 telegraph poles instead of gantries,polystyrene block covered with chicken wire and cement
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Old 29-04-2011, 08:05   #8
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

Helical anchors with elastic rodes may be an option. This company has some dock anchoring info on their website: Bottom Anchoring | Marina Dock Anchoring | Boatmoorings.com - -

I have no affiliation with this company.
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Old 29-04-2011, 08:21   #9
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

You say this is on a river. Are you in a tidal area? If so, knowing the tidal range would be an important part of figuring whether pilings were necessary.
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Old 29-04-2011, 08:57   #10
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

Quote:
Originally Posted by Bash View Post
You say this is on a river. Are you in a tidal area? If so, knowing the tidal range would be an important part of figuring whether pilings were necessary.
See Post #1
Quote:
Originally Posted by Northeaster View Post
... The tide swing is about 5 - 6 ft ...
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Old 29-04-2011, 09:10   #11
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

Engineering says if you attach the floating part to the fixed part with an ' I/I' type frame by hinges at each corner then it should behave. The frame would need to be wider than it is long and the hinges (and guy lines) all on one axis so lengths don't change as it goes up and down with the tide.
All the pontoons I've seen are hooked to vertical piling posts.
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Old 29-04-2011, 19:06   #12
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Re: Advice needed on ways to secure floating dock to hold 10,000 lb boat

Thanks for all of the advice this far. I am leaning toward rigging up something like the criss-crossed chain setup, picture in the Helix anchor link. I will check at low tide to see if any very large bolders are in decent locations, that could be drilled and bolted to secure the chain.
If not, I will look into helix, or other moorings. My neighbor has alot of experience setting traditions (old school) moorings, but I wanted to do a bit of research before talking to him.

re: pilings, how do they fair in areas where there is ice moving in the winter, as the floating dock would be taken out, and only the pilings would be sticking out?
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Old 30-04-2011, 18:18   #13
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Re: How to Secure Floating Dock to Hold 10,000 lb Boat

Most marina's protect their pilings with bubbler systems. The issue is not ice moving past the pile and forcing it sideways, but ice freezing hard around it, locking onto the pile. The tidal rise and fall of the ice then pulls the pile out of the ground. Dock owners, not using bubbler, tie their piles to each other and to the dock so if a pile does pull out, it doesn't float away. The piles then would be re-installed in spring.

The best answer to your question though is to look at the various dock installations in your area of the river and follow what they've done. If there are properties with pilings left in the water during the winter, go visit the owner see what is the reason for their success.
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