Dock Rebuild Specs

[Gem99ultra]

We currently have a small fishing dock in one of our ponds that has become rickety and needs to be rebuilt. One of the many unknowns to me is how deep should the supporting beams be set below the ground surface. At normal water levels the beams at the deepest point will be approximately 8' above the ground surface in approximately 6' of water.

Any suggestions or general specs would be appreciated. Thanks.

 

[jaxs]

Simplistic questions deserve simple answers so here you go. Start with a 16' "beam" in deepest water. Push beam into ground with 7 psi force until force must be increased in order to drive "beam"deeper. If beam stops at less than 24" into ground,increase pressure until 24" is reached. Cut top off beam at desired level above water. Add inches cut from beam and difference in depth of water then deduct that figure from 16' to determine leingth of each subsequent beam. Each beam will support 1,000 pounds so if you are designing deck to support more load,those numbers must be revised but installation is the same.

 

[Streetcar]

In Jax’s example, he is using a 12x12 post and is valid for loading if the post stops driving. driving force needs to be higher than load for safety factor

 

[jaxs]

In Jax’s example, he is using a 12x12 post and is valid for loading if the post stops driving. driving force needs to be higher than load for safety factor

Op told us old dock is rickety, old dock is small,old dock is fished off of and he has more than one pond but didn't reveal what he is using for "beams",how much deck weighs nor how much live load beams need to support so I was forced to grab some #s from air overhead but what I specked is good for pier sizes commonly in use (12x12 not one of them unless op wants to take his Peterbilt on the dock to haul fish out.). As pier size increases, required depth decreases but all support same load.

 

[EddieWalker]

I'm no expert here, but in my opinion, it really depends on what the ground is like under the dock. If it's soft, or sandy, it needs to be deep enough to support the load. 2 feet should work, but it also depends on how heavy the dock is, and how many posts you have. Just two posts will want to sink faster then 4 posts, or more.

Depth of posts in the ground wont do much for "rickety"

I do know a fair bit about building decks, and diagonal bracing of the posts will do more to lock it together and make it solid then the depth of posts. If you had something solid to put under the posts, you wouldn't need to go into the ground at all to have a solid dock.

 

[Gem99ultra]

I'm no expert here, but in my opinion, it really depends on what the ground is like under the dock. If it's soft, or sandy, it needs to be deep enough to support the load. 2 feet should work, but it also depends on how heavy the dock is, and how many posts you have. Just two posts will want to sink faster then 4 posts, or more.

Depth of posts in the ground wont do much for "rickety"

I do know a fair bit about building decks, and diagonal bracing of the posts will do more to lock it together and make it solid then the depth of posts. If you had something solid to put under the posts, you wouldn't need to go into the ground at all to have a solid dock.

Thanks for the info. The dock is a single plane fishing dock approximately 15' long with 6 6"x6" posts now, and is cross braced. I have no idea as to how deep the support beams are now but the bottom is only dirt/mud. They've held up >25 years.

 

[EddieWalker]

I'm not clear by what you mean "rickety"?

Are the posts solid or rotten? Are you replacing them, or needing to install more posts?

If the posts are not rotten, but the dock is moving around, then it needs additional bracing, or the existing bracing has become loose.

I'm just guessing, but if it was solid for a long time, and it's not rotting on you, then it's very likely that the bracing has become loose. Did they use nails when building it?

Since the bracing needs to be as low as possible on one side, and as high as possible on the other side, the low side is probably under water. Using galvanized lag bolts and a wrench is about the only way to get this done while working under water. Ideally, you want to create an X between two posts. |X| needs to go in both directions. Width and length to make is solid.

 

[dmccarty]

Make sure the wood can handle being in the water if the dock is rickety because of rot.

Another option is a floating dock which would not require putting in columns.

Later,
Dan

 

[Gem99ultra]

I'm not clear by what you mean "rickety"?

Are the posts solid or rotten? Are you replacing them, or needing to install more posts?

If the posts are not rotten, but the dock is moving around, then it needs additional bracing, or the existing bracing has become loose.

I'm just guessing, but if it was solid for a long time, and it's not rotting on you, then it's very likely that the bracing has become loose. Did they use nails when building it?

Since the bracing needs to be as low as possible on one side, and as high as possible on the other side, the low side is probably under water. Using galvanized lag bolts and a wrench is about the only way to get this done while working under water. Ideally, you want to create an X between two posts. |X| needs to go in both directions. Width and length to make is solid.

Excellent tips! The support beam near the shore has rotted off. The other 5 are in fair shape but loose, i.e. they will wobble. The dock was built with nails only which probably accounts for them coming loose and becoming rickety.

We will follow your suggestion regarding using galvanized lag bolts for the underwater areas and use coated deck screws elsewhere. I'm assuming treated yellow pine should be adequate? Thankfully, lumber prices are starting to decline somewhat. The new dock probably won't last another 25 years, but neither will we.

 

[check]

Can you post pics? It is hard to give advice without seeing it.