OK, the floating dock is starting to come together and I am trying to noodle out the anchor foundation at the shore and could use your input. I have attached three sketches. The rendering is of the dock itself is for size reference, The first sketch shows the gangway and the hinge mechanism while the second sketch shows the poured concrete anchor/foundation with just the hinge plates penciled in for clarity.

Will this set up be sufficient? I will drive 4 "T" posts as deep as I can get them into the dam an cut them off about foot from the dam surface so that the concrete has something to grab a hold of. My dam has a lot of rock in it and I fear that digging in it and driving post in it will be a lesson in patience, not to mention dealing with the water too. I might even try to post hole dig down an extra foot in a couple places to make a resemblance of sono-tube piers beneath the rectangular chunk of concrete.

Any opinions?

I think the floating portion will need something to stabilize side-to-side motion. Either poles driven in with "slip" joints that let the dock rise and fall, or cables connecting the end to shore (maybe crisscrossed under the gangway). The poles would probably work best for such a long dock.

I think you will need to anchor at pond edge, where gangway meets the dock, and end of dock furtherest in the water. In the water I used old tire filled with concrete, eye bolt in center, with chain crossed to oppsite side.

Concerte on ground may be Too big and start to sink that close to the water just due to weight. I think I would use post instead. Or just do the 8"x12" concrete beam with tpost.

Advantage to using a tire is you can roll on the dock to where you want it. I would not use a big truck tire. THe smaller 14" I used ended up about 180-200#

Thanks for the input guys! I am really trying to avoid poles in the water and I am not sure how well concrete anchors and cables or chains would work with my situation. My pond has about 3 foot of free board and it WILL use it eventually (I have too much watershed) and last winter was its first and it was dry, the pond went down about 1 foot. That's potentially 4 foot of travel that I need to account for in my anchoring system.

One thing to add, my little 1/4 acre pond is very well sheltered from wind so no constant wave action or side loading, just the occasional storm.

I am thinking about, similar to what Brian said, trying to dig two deep holes for sonotubes (or square forms) and attach the hinge plates to each concrete pillar. This should resist the side to side motion where a big chunk o' concrete might eventually shift back and forth and end up "walking" into the pond. The trick here is, how deep can I go before throwing in the towel? Only one way to find out, I plan to start digging this weekend if the weather allows.

At 31 feet long, that will be A LOT of torque, force, on those two hinges. Think about it as a 31' cheater bar, it won't take much force at the end of dock to start causing problems. I really think you will have to stabilze the other end some way.

I have seen 5 gal buckets of concrete with long eyebolts embedded and chains inside pvc up to the dock end used as anchors. Could also use coated wire rather than chain.

Maybe I'm just dense, but I can't seem to imagine how putting an anchor and chain/cable out in the water attached to the pond end of the dock allows for high and low tide (so to speak). If the chain is loose enough to allow for high water then it's not doing anything at normal level (it's too loose). If the chain is tight at normal level, the dock has to pick up the anchors or be submerged when the level rises to the emergency overflow and the anchors hold it down.

What am I missing here?

Now, I could attach to the corners of the first cross walk with chain or cable and anchor them to the bank at the same elevation as the hinge...this would allow for the dock to rise and fall but still resist the side to side forces. This option is a little unattractive to the eye, but would work.

I hope to convince myself that the hinge can be made stout enough to do this job by itself. It is made of 2-1/2" OD, 3/16" wall tubing and 1/4" plate and 1/4" angle iron. It's my ability to construct the concrete foundation that I'm fuzzy on.

I crossed chains under my gangway and added turnbuckles to tighten. My floating dock is shorter and wider than yours and still sways (need sea legs, but not so bad). I also added rails to the dock and gangway all around the chains to prevent anyone falling in over the chains. I don't think slides over pipes are attractive either, but I am not sure what other options you have. If your dock has plenty of flotation, maybe hanging submerged weight would slow the swaying, but I don't know. Maybe something like a keel perpendicular to the shore could work, but again, I have never seen it done.

If the objection is the aesthetics of the pipe/slide arrangement above the level of the dock, why not use telescoping poles with one end attached to the underside of the dock and the other embedded in the pond bottom, i.e. little pipe inside bigger pipe? There would still be a bit of sway as the difference in pipe sizes would need to be big enough to allow the dock to follow the pond level, but should be a whole bunch better than nothing.

Here's a pick of the shore hinge just for fun. It's going to be beefy enough I think. The gangway width is 4 feet for size reference. The holes in the hinge plate will easily except 3/4" anchor studs.

I have also thought about reconfiguring some of the dock pieces to allow me to get out past some submerged structure. The first cross piece would be right over some stump piles on the sides. The arrangement below would allow the dock to get inbetween them and get out into open water and yield a bigger platform.

I have red-marked in some cables that should give me the stability at the shore if it it needs it.

Please let us know how it works out. I think a number of us think that physics is working against your current plan, but everyone is wrong some of the time. You can always modify later if needed.

Unless I am looking at this incorrectly the cables should go out to the T portion of the dock. I can post a picture of what we did in a day or two.

Is the back portion fixed?

Here's a couple pics I found and saved for my own future reference. I think they show what others are trying to describe. To allow for changing water levels, the crossing anchors can be done with stretching/elastic ropes or inserts with cables. There are mooring springs that can be added to chains or cables too. Hope this helps

One thing to keep in mind is that arms, cables, and chains hooked to shore should be in the same plane as the gangway hinges so that water fluctuations do not tighten of loosen the stabilizers.

I think this would be your cleanest and easiest way, one pipe on each side behind your handrail post.

Very true RAH, I hear ya and thanks for participating!

I feel like I'm being pig-headed (which I'm known to be on occasion) so bare with me and know that I love each and every one of like a brother and a sister (Jimmy Buffet paraphrase).

I can see the good logic in the poles out in the water. I'm not sure how to do that now that the pond is full. My land is very rocky and it's too late to merely drive a pole in by hand. I'd hit a rock within a few inches and I'd be wasting my time. I thought about the garden hose water jet digging technique, but a rock is a rock.

Dam'd Waters, thanks for the pics. The submerged anchors work very well if the dock is allowed to float around some so that the chains have enough slack at normal level to allow for 3 foot of level increase. I need to keep my dock firm and stationary at normal levels, but still get the flexibility for higher water levels.



The stiff arms are going to be my fall back even if they are cables. This gives me the most hope, but adds two more holes to dig for concrete foundations.



I have run some calculations that use 75 mph winds blowing into the long edge of the dock. The resulting force on the dock is about 600 pounds at the mid way point. Transferring that force through the moment at the shore foundation yields a force on each sono-collumn of 2300 pounds. That sounds like alot, but I think two round or rectangular pillars (sono columns) that are sunk into the ground 3 to 4 feet have a good chance of resisting that kind of force. AND that's at 75 mph winds. At 50 mph winds the forces at the pillars drop to 1000 pounds. At 25 it's 500 pounds force. I think this will work so long as my hinge connections at the gangway and floater are good and solid.

Here's a visual for the shore foundation. The cylindrical portions would weigh 312 each and the rectangular step would weigh 840. It would all be rebar'd.

Not sure if standard auger pipes would work for you but they are designed for a full pond (search on "pole auger" and "dock post" at Menards website for examples). Even if nothing breaks, I expect the cables or chains will allow quite a bit of sway to the dock when folks are moving about near the end (based on my dock. I tend to try things my way first and gloat when it works or hang my head and fess up when it does not. My foray with a small blue catfish pond may end up the latter:) Good luck!

Pay close attention where and how you attach your bracket to the wood. To me, that is where problems will show first. If it fails it will be at the weakest point and metal bracket will be stronger than the 2x8. Might double up on the boards on the outside of gangway.

Good point Brian, it's not to late to beef that section up. I will be sandwiching the hinge angle iron on the outside with a backer plate on the inside. I will be working on it tonight. Maybe I'll get some pics of my progress over the weekend for the thread.

QA,

When I built my floating dock 3 or 4 years ago I had planned to anchor it to the bank with criss-crossed cables to add lateral stability. It is a 12x16 with a 4 x 16 gangway so it's not quite as long asy yours. After I got it in I was very impressed with the lateral stability without the cables, so I decided not to add them unless it was really necessary. I like pitching back under my dock since it's the only shade on the pond and the cables would be a hang-up liability. I watched it closely the first couple of years to ensure it wasn't a problem and it's as tight as the day I built it. We have had several near misses from hurricanes and on direct hit from a puny Cat-1. Just my experience but worth considering. Here is the URL to my photo server, you can back up one level to see the original build if you like.

https://public.fotki.com/jsing/hambrick-rd-1/dock-build-phase-2/?view=roll#1

I went with the exact stiff arm and cable system show in the photo. The only difference is my dock is a 30 foot covered pontoon boat. I used 20 ft sections of galvanized pipe and welded automotive tie rod ends on each end to give it some pivet room. I put turnbuckls on the 2 cables. Have had no problems with mine at all for several years now. If you wanted to beef up the galvanized pipe more, you could put rebar inside of it before welding the tierod ends on. Mine does not flex at all so I didn't use rebar. I screwed mobile home augers in the ground and attached the tie rods to them.

Just an update on my progress...

The hinge turned out pretty good especially after a few coats of paint.



The shore anchor went well. The sono-columns ended up being only 2 feet deep because I dug down until I hit rocks too big for my manual post hole digger and my patience to deal with. The rectangular head was oversized to compensate. It turned out to be 18" by 18" by 59". Overall it used 1900 pounds of concrete.



The dock was preassembled in the shop so that I could minimize the figuring and building at/on the water. It has since been disassembled back to the individual four framed sections without the decking so that my little tractor could pick them up and struggle them to the pond.



The weather has not been cooperating enough to actually get to the pond due to the wet and cold conditions. It's a bit dangerous getting the tractor on the dam due to the mud, not to mention the fear of installing the tractor in the pond instead of the dock. Waiting for drier weather now.

Thanks for everyone's participation in this thread! You'all have given me plenty to think about and some reassurance.

That looks super QA.

I like your dock hinge. Looks like something I would do.

Wow what a great project and result! Makes the 2 docks I am in the process of building (in the water) look like child's play. Weather needs to cooperate here in St. Louis as well. But it might snow here this weekend and that will just put me farther behind on spring pond projects. Nice job! BM61.

Really nice looking dock!

looks great! I should show that dock picture to the hoa this year so I can add one to my pond lol

Has any one tried putting an anchor on each end of the dock. Suspended from a pulley, one side of cable with 500 lbs of weight and on the other end say 300 lbs of weight, having the 300 lb weight just 3 feet below dock or half of the depth of the water. Float tanks may need to account for extra weight. That way you could have weight on the very end where it would do the most good. Or if you have a stable water level you could just have the smaller weight set on top of the larger one and it would only move when your water is going out of the spill way. Could be a swimming hazard but not much more than a large rock on the bottom. You may want two pulleys and run cable under the dock so the smaller weight could be on the other side of the dock so it would not be tangled with or around the anchor cable of the larger weight.
By the way your dock looks great!

That is going to be a really pretty dock on the water. Great build, and looking forward to seeing it floating.

Thanks for all the compliments, concerns, and suggestions!

It has finally dried up enough to get the first piece in. I have to tell you that the phrase..."If the Egyptians could build the pyramids, I could build a little dock." has also been very encouraging as I have noodled out the build and install.

I really just wanted to post the next step, mostly because I'm exited to add the next piece this afternoon, but some of you may be keeping up with the progress...

Please do add pictures as you progress. I'm always interested in seeing how different people go about projects.

Sometimes I steal ideas!

Here is last night's progress.



A little background on the design...The blue barrels float the gangway a little high. I have left access to the bungs so that I can add water if need be to sink that end a little. If you look close on the shore side of the blue barrels, I have a place for two more barrels just in case the first two needed some help. Well they don't so I will remove some of that extra work with added extra work. I did not want to need the extra barrels and have to construct the supports on the water, now I get to dismantle those supports on the water(no big deal). I may find that after I add the weight of the gangway decking that it levels out and I don't have to add any water, but we'll see.

It's a little wobbly at this point, but the connections between the 3 outer frames has not been tightened up yet and the decking will surely add some rigidity to it.

Why not just leave the extra barrel supports as is, and put deck boards over them?

That may actually happen Brian, but they should come off pretty easily and that would reduce places for stuff (bugs, snakes, debris, etc) to hangout. And, sometimes, I do things for no real good reason.

Under a floating dock, there is a lot of hangout spots. Between floats and deck, there is a lot of sq ft hangouts:).

I'm ready to see this thing all put together! Don't let a little rain, lightning, hail, or stray tornado slow the progress! Looking good so far.

Well, I did not have to work in horrible weather to get it done over the weekend, just chilly, windy & cloudy. It floats well. I may have mentioned that I cheated the float manufactures suggested weight per float on two sections. These sections are 12 feet by 4 feet rather than the suggested 10x4, 3 floats per and the added weight of the triangular seats added even more cheating, but the wood is 4 to 5 inches above the water. When I (at 185 pounds) stand on the outer most corners the wood just touches the water so I am calling it a success. I did add 13 gallons of water to each of the two barrels on the gangway, they really floated high. They were holding the second gangway up causing the very end to be dipping down. The addition of the water helped bring the very end up more so than level which helped with regard to the wood touching the water with my weight on it. Here are a few shots...

Looks like a great place to hang out under the umbrella on a warm summer day. Very nice!

That looks great! I built a much simpler square dock and it was a lot of work, so I know you have a lot of hours in that. You did a great job.

Thanks for the compliments Guys! I think I did pretty good for not being a carpenter.

I have no less than 120 hours in building it. That does not count the time to research, design, source materials, and get materials. I did most of it by myself. I can give two people credit for helping. One buddy for a couple hours to help mix the concrete and pour the foundation, and my FIL helped for a few hours when I was building the frames in the shop. Otherwise, it was me and my imaginary Egyptians (you know the ones that built the pyramids).

That is nice, I may have to copy this when my dock needs replacing. Maybe sooner.

If anyone needs any additional build info on the dock, feel free to PM me and I'll do what I can to help. I'm sure I learned a few things that did not get into the thread.