Pontoon deck framing

[Pontoon24]

Hi.

I'm repairing a set of pontoons and my next step will be to construct the deck. The pontoons are the type that are flat on top with a 1" lip on each side to attach to the cross members. I believe from my research that most pontoon boats use aluminum extruded "hat" stringers covered with 3/4" pt plywood. I'm wondering about an alternative.

I would like to use 4" x 4" pt wood posts for the deck framing instead of the hat stringers.

I realize that I would need to isolate between aluminum pontoon and 4 x 4 instead of between aluminum stringer and 3/4 decking.

That 4x4 s will weigh more. A 24' boat will need 13 cross members at 24" on center. I'm guessing extra weight to be 100 to 200 pounds.

That I may need to add an underskin to keep the 4x4s from constant soaking and drying.

That I should make sure the 4x4 are dried and straight (not warping like often happens when pt lumber dries.

But, is there anything very wrong about framing the deck this way?

Thanks, Andy

 

[goldnrod24]

Re: Pontoon deck framing

You mean other than increased cost, weight, center of gravity, chance of warping and water soaking? I don't think so!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[Pontoon24]

Re: Pontoon deck framing

You mean other than increased cost, weight, center of gravity, chance of warping and water soaking? I don't think so!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If you know where I can buy the hat stringers for less than $10 a piece then I agree on cost. The ones I saw went for $50 a piece.

Center of gravity? You got me on that one. Not sure what you mean since they will be spaced evenly front to back. Enlighten me.

If I first dry them, and make sure they are straight then once they are bolted in place to the pontoons and secured along their length with deck screws, I doubt they will be able to warp.

Also, I left out 1 vital piece of info, This deck will only be 96" to 102" in width so were talking 4x4's 8' long.

Andy

 

[EGlideRider]

Re: Pontoon deck framing

Except for the increased weight, it should work although it is very unconventional. If you allow the 4X4's to dry, they will certainly warp. I think you would be better off to construct the deck very soon after purchasing straight 4X4's so they would not warp as they dry.

Make sure you post pictures of your progress.

 

[goldnrod24]

Re: Pontoon deck framing

You are adding weight higher above the waterline than stock. I'd think you'd be making your boat more top heavy or tippier (if that's a word).

 

[EGlideRider]

Re: Pontoon deck framing

You are adding weight higher above the waterline than stock. I'd think you'd be making your boat more top heavy or tippier (if that's a word).

Two or three hundred pounds only 12 to 18 inches above the waterline will not significantly raise the CG.

 

[Pontoon24]

Re: Pontoon deck framing

You had me worried there Randy, but I understand now what you mean.

Thanks EGlideRider,

I will post pics when I have something worth showing. I still would like to dry the PT before I use it and if I explain better you may agree. Mostly what I want to avoid is twist. I'm a contractor and know the ways of 4x4 PT pretty well. If the 4 x 4 bows when it dries but does not twist, I can lay the 4x4 with the bow (meaning the curve in the wood, not the front of the boat) fore and aft so that it will still make a flat floor. With 3 1/2 " to fasten the deck to a 1/2" or even bigger bow wont hurt. Any 4x4 that twists after drying I will not use. Letting them dry gives me a chance to further waterproof them. Also, those hat stringers look pretty beefy and maybe only a little lighter than a dry 4x4.

Thanks again, Andy

 

[Mr Crabbs]

Re: Pontoon deck framing

I guess if you are dead set on using PT, why not use 2 x 4 instead?

FWIW, it's going to take a lot of extra work to keep the PT from moving once it drys. Plus you are going to be exposing it to being resoaked.

 

[Pontoon24]

Re: Pontoon deck framing

I guess if you are dead set on using PT, why not use 2 x 4 instead?

Well, in imagining the stress on the floor when the boat hits a wave diagonally, I just thought 2x4 would not be enough. Also I'll be fastening the wood down with 4" ss bolts. Easy to do thru a 4x4 but would need brackets or something for 2x4. In construction I use a 4" wide sticky asphalt tape that I would put on the ends of the 4x4 where it lays directly on the top of the flat topped pontoon.

Thanks, Andy

 

[Jeep Man]

Re: Pontoon deck framing

If you are intent on using wood, I concur that 2x4 would be better (just as strong, and lighter). Brace down the center with 1x4 in between. If you underskin as well, you have no worries about splash. Drilling through for 3/8" or 1/2" bolts won't be a problem. If you assemble, brace and underskin before drying, there would be 0% chance of warping. Don't underskin above the pontoons. This will allow any trapped water to escape and the space to breathe.

 

[samo_ott]

Re: Pontoon deck framing

Seems odd but it should work. Are the 'hat' stringers that expensive? huh. post pictures as you go along.

 

[bitterboater]

Re: Pontoon deck framing

Some way or somehow, you will need to protect those toons form the PT wood.
Regular PT, as it sounds like you want to use does not do well against Aluminum. It tends to corrode it. Causing leaks and other dangerous conditions to occur.
Really, your best bet is to build an Aluminum frame and bolt or weld it to the toons somehow.
But do not use Regular PT wood, even dry.

 

[5150abf]

Re: Pontoon deck framing

I don't think it will work because of the mounting points, it can only attach to the tubes on the outside of the U tubes and I just don't know if the wood will put up with that kind of pinpoint load add in that yuou have to drill holes in it and you further weaken the wood.

You can do it but don't be suprised when you hear the distintive CRACK after you hit a big wake.

Having 2 hulls the boat naturally wants to scissor and it takes alot of structure to counter this and I don't think 2x4s will do it for very long.

 

[Pontoon24]

Re: Pontoon deck framing

I realize I need to isolate PT from Aluminum. Either I do it at the 4x4 joist or I would have to do it between aluminum joist and PT plywood deck and since I already read on here that many people use PT plywood with great success thats what I'll use. As I said above I have a nice sticky asphalt tape 4" wide to seal the 4x4 where it lays on top of the pontoon.

Also the pontoons are flat on top and have a 1" lip on each side with a row of bolt holes on 2' centers so each 4x4 will have 4 - 1/2 " SS bolts. The tops of the pontoons are 2' wide so there will only be 4' of wood between pontoons and the inside row of bolts.

Thanks, Andy

 

[Pontoon24]

Re: Pontoon deck framing

Oh yeah, 1 other small piece of info. This is meant to be a weekender style houseboat with a small 14 x 8 cabin, not something I expect to go cruising and water skiing behind.

By now I probably sound like I asked for advice and then just argue against it but I think all these arguments are surmountable and just want to make sure there isn't something I haven't thought of. Thank you all for your comments.

Andy

 

[ONERCBOATER]

Re: Pontoon deck framing

interesting, i hope your project works out and that you get long and useful life out of it.
Myself i used 2x4 up front and 2x4 and 4x4 in rear on mine...this was due to the fact that i extended my deck 2ft on ea end.
it is sealed and resealed and re re resealed with thompsons... and will be painted with oil based glossy enamel in the end. with the exception of the 2ft extended areas i left the aluminum hat channel in place. it doesnt look that strong but it is i believe both stronger and more resilient than wood in this application. mine has a 9ft cabin on it

Sean

 

[Mr Crabbs]

Re: Pontoon deck framing

If you are intent on using wood, I concur that 2x4 would be better (just as strong, and lighter). Brace down the center with 1x4 in between. If you underskin as well, you have no worries about splash. Drilling through for 3/8" or 1/2" bolts won't be a problem. If you assemble, brace and underskin before drying, there would be 0% chance of warping. Don't underskin above the pontoons. This will allow any trapped water to escape and the space to breathe.

Ahhh, now you have the makings of a torsion box if you capture the 2x between the deck and an underskinning. Very strong indeed, the cabinetmaker in me really likes that!

PT lumber, also known as CCA lumber is treated with Chromium (the binder) Copper (fungicide) and Arsenic (kills everything ). CCA leaching out (if it could) might cause some minimal staining on the aluminum if that matters. Sure wouldn't bother me if it did. Sounds like an interesting project, keep us informed.