4-Post 20K Lift Wobble?
 

Lake Norman, NC (freshwater). Pilings are 30FT long, water depth is 12-15FT, and we have about 8FT of piling out of the water. I was told they drove pilings in ~5-7 FT. I am totally shocked because I can take my hand and easily make this lift sway back and forth 4-5 inches with an easy push? See You Tube video below. The lift installer built our dock, which is solid, and they are well known in area. They told me "with your water depth the pilings had to be so long that you are going to have some wobble, you can't avoid it." Still, is this normal and safe? We are planning to put a 35-39 Nortech with triple Merc's on the lift. Pics of lift and dock below along with video of the wobble.

You Tube

https://cimg9.ibsrv.net/gimg/www.off...914267619.jpeg

wow that is gorgeous. I'd love to build something like that someday. government wont even let you put a car port over boats in MD. Apparently the light doesn't get to the disgusting water below.

what are the pilings made of ? can you do some cross bracing below the water line,

Yikes!

:eekdrop:

Can you tie all four corners together at the top? ... and X-brace the frame at the top also. Maybe also tie the lift to the dock structure. That is way too much wobble.

I Am a little shocked that it looks like 4 x 4 pilings. Around here a lift that size would be on 12"-14" round pilings.

I wouldn't put a boat, not even a Sea Doo on that. On a windy day loaded imagine what is going to go on.

the pilings appear to be the same size as the dock structure ? 10 or so inches

I would expect to see some X-bracing side to side. And I would expect to see some longitudinal bracing down lower to create a boxed infrastructure.
Once that is done, you could tie it into the dock structure.

I'd take a ride around a look for other similar boat sizes to see how their lifts are fortified.

Looking closer I do think you are correct.

I have personally had 2 different 4 post lifts, and have been involved with install of quite a few more on various GC projects we have done over a 20 yr period, and all have had some piling movement. It is the nature of the beast, especially with your water depth, as installer told. If they were jetted, movement might dissipate a bit, as backfill around pilings sets/packs up over time. If they were straight up driven, then probably not so much.

Sure looks like more wobble than I'd be comfortable with. With your water depth there is quite a bit of unsupported piling above where the piling is driven in so 20 something feet of freestanding unsupported piling is going to move around. I'd think that front to back X bracing between the pilings on either side of the lift would help stabilize things in the bow to stern direction. Some batter pilings driven at an angle on the outside of the right side section and fastened towards the top would stabilize that portion in the side to side direction. Connecting the left side into the existing dock would stabilize that side. Batter pilings are used regularly in marine construction to reinforce free standing pilings so if your guys can drive pilings they should be able to do that I'd think?

It looks like the bridge dock, stairs and upper deck are fixed and the lower horseshoe shaped dock is a floater, so it can't be attached.

crossbracing will stiffen the pilings but with the weight of the boat it wouldn't be surprising if they settled deeper and the the thing goes all leaning tower.

aggravating for sure, even the best contractors make mistakes. There has to be a formula for piling depth depending on the river bed material/piling material & dimension requirements/water depth and load. Maybe 30 foot 10x10 or whatever size they are is at the max end of that formula for the material used. Either way, hope it gets resolved.

Utility poles are in the ground 10% of their height plus 2ft. So a 30ft pole would be installed 5ft. That is on dry, stable ground. In a swamp area, deeper.

I work with a guy that had a dock building business with his father for many years. I'll reach out to him on Monday and ask him.

My dock contractor in west Florida/Panhandle said 8' (subterranean) is the code for pilings...I had mine done 10'.

We have a 450 Nor-tech sitting on a 8-post 32k lb lift here in Cape Coral, it does exactly the same thing. It Does it with the boat on it or off of it. Remember its like a flag pole, that's a lot stick sticking out of the ground and water is not solid. In a previous chapter of my life I set a lot of telephone poles and they have movement at the top if you move them by hand(standing in a bucket truck). I had the exact same questions for the lift contractor down here in the Cape. Nice Dock!!!!

I just measured and the lift posts are 8X8 inch which is the same as our dock posts. Lot of mixed reactions on this thread, I think I'm going to have a different dock builder/lift installer come out next week and offer a second opinion and to see if there's a fix for this situation.

This new lift can't be mounted to the dock because our walkways are floating, but the main dock structure is on fixed poles.

Was the original piling & lift installer a licensed/bonded company with a good local reputation?
Can you visit another (more mature) site/lift the installer has done to compare?

This is a good suggestion that I was thinking about. Might have to hop on the PWC and see if I can find similar lifts in the area. Then hope I don’t freak out the homeowners by pushing on their lift pilings, lol.

I just went through a lot of this as I rebuilt my boat house in Florida after Hurricane Sally. So I understand the obsession.

1 1/2 years later pilings are still in the same spot, still wiggle, boat is still standing. I can video tomorrow to show you

Thanks. A video of yours would make me feel 100 times better. I’m PM you my cell if that might make it easier to text a video.