Dock box mounting options

[Twist]

I've got a 5' wide wooden deck on my home dock off the Chesapeake Bay and I'm looking to add a large (96")dock box. An option I'm considering is to replace a set of the 5'x2"x8" deck boards with 7-8' boards leaving a cantilevered deck onto which I'd mount the box. I've priced cantilever mounting brackets and they're stupidly expensive and almost as expensive as the 96" dock box itself if I put two pair of brackets on it. I haven't yet shopped someplace like Home Depot for a cheaper but robust option.

To complicate matters, about once every year or two my dock is underwater from storm surge so anything mounted at the deck height could be submerged. I'm thinking it would be really helpful to have some kind of secure way of attaching the box that can be unlatched from the decking to carry the box to high ground when this happens.

Any thoughts from the collective wisdom here?

 

[seasick]

Structurally the cantilever boards could work as long as the joists that they are bolted to are sound and the original deck is sized accordingly for the new load. Another concern may be the weight of the box when loaded with all your gear. That will put strain on the new deck boards and the entire deck structure. The second issue worries me though. If the water rises above the box and the box is sealed, it may exert a very large upward force on the entire dock. Having a way to remove it is one solution but what are the chances that there could be a high water event that occurs when you were not able to address in time.

I'm thinking that a land based box or small shed might be a better idea.

 

[glacierbaze]

"Home dock" says options. Is this a long dock across shallow water? How far is the boat from shore? Pics would help.
If you have room between the joists and the water, you could put a few 2 x 4's on edge, with joist hangers, and another 2 X whatever fits
between under the ends of the deck boards and the 2 X 4's.
In high water, the box will have the same lift whether it is sealed, or no lid at all. I would put a 4" pie plate, with screen, near the bottom, and be prepared to remove the contents, and let it flood.

 

[Twist]

Here's a photo of the dock:

During big storm surge events the dock deck can be underwater. Doesn't happen very often but every few/several years and it might happen when I'm not here to do anything about it. It's making me second guess putting the box cantilevered off the dock itself and maybe finding a place for it on that octagonal landing deck on the stairs down to the water.

 

[Ky Grady]

The octagonal landing would be my choice. Either replace bench on left and sit on dock box or place it to the right as you come down steps.

 

[glacierbaze]

Being that close, dry land for sure. Whether you want to add in 2 sets of stairs depends on your physical condition, what you store in the box, and how often it goes back and forth to the boat. Also depending on max storm surge, I might put it on an elevated stand behind the bushes, or re-arrange my kayak rack, and put it where the red one is.

 

[Twist]

I liked the solution suggested using wing nuts on carriage bolts that I went ahead with the dock installation. I replaced a total of four deck boards, two near the center for support, and one on each end for drilling and mounting. It's solid, cantilevered out of the way, and will be easy to remove it and bring it up the hill if there's a hurricane a'comin'.

 

[WaveMasterMario]

Mounting a large dock box on a cantilevered section sounds like a smart way to maximize space, but the cost of brackets can indeed be a dealbreaker. Instead of expensive brackets, consider using heavy-duty L-brackets or even custom-fabricated steel brackets from a local shop. For the storm surge issue, securing the box with removable anchor bolts could allow for easy detachment when needed. Checking out Home Depot for alternatives sounds like a good next step!

 

[Twist]

I got my installation surge tested when the remnants of Debbie came through the Chesapeake and created a bit over 4' of surge above high tide.

I decided the forecasted surge wasn't enough to warrant removing and relocating it and left it on the dock. It crested about 3" up on the dock box testing my grommet waterproofing solution which worked pretty well - just slightly damp inside. I was nervously watching it all morning yesterday as the surge peaked and receded and next time I'll just move it up the hill.

I also got to exercise my boat lift decision making but turned out it wasn't enough surge to reach the boat on the lift. I'm a belt and suspenders kind of guy so I did put a couple of lines on the outer piles to keep the boat off the dock if got lifted and I put a couple of spring lines on it to keep it more or less centered in the slip. I'm not sure why I put that line on the front except that it made me feel good that there was an extra line whose job was to make sure I didn't lose the boat I think during the next big surge event (and there will be one) I'm open to suggestions but will likely do the same thing unless it's more than several feet of surge.