Seat reinforcement?

[KC8QVO]

I have a set of seats with molded plastic bases. Ive done a bit of research and found the bases have been known to crack in a few places. They are "flimsy" - they lean back more than I think they should. Last summer I put a piece of sheet metal under the base of one. So far no issues. However, the sheet metal does not support the seat back mount, just the base. I want to replace that with a panel that will let me tie in to the seat back support bracket.

Any ideas on what thickness aluminum to use so it is rigid and not too thick/heavy? Id like the seats to hold up to some heavier and/or less careful passengers so Id rather go too thick. Im not real sure where to start, though. The steel sheet metal there now is around 1/16" and is too flimsy. Im thinking maybe 1/8" aluminum to start? Thicker? Or is that overkill?

Id like to do the plate reinforcement now while the seats are solid to keep them from breaking.

 

[KC8QVO]

On the same topic - the bolts holding the seat back on the base will need to be longer to make it through the reinforcement plate. In terms of all of the bolts - including the base bolts - is there a good method for keeping the bolts from rattling loose? I would use loctite but I dont want to make the threads stuck to where backing out the bolts breaks the threaded inserts free from the molded plastic seat base. Im thinking a lock washer or star washer between the bolt head and reinforcing plate? Or maybe a longer bolt and a jam nut with a split washer? Or is there a mild type of thread locker like loctite that will hold with less, but sufficient, strength?

 

[gm280]

Instead of redesigning your present seats, just buy a couple new ones and install and forget about reinforcing anything. JMHO!

 

[KC8QVO]

The seats, aside from the one I used last year, are brand new, never used. They were half price so that is why I got them and why I want to reinforce - cheap seats I can make better. They are really comfortable seats too. The one from last year has more padding and is a bit bigger, but both kinds are the same design and comfy.

 

[gm280]

The seats, aside from the one I used last year, are brand new, never used. They were half price so that is why I got them and why I want to reinforce - cheap seats I can make better. They are really comfortable seats too. The one from last year has more padding and is a bit bigger, but both kinds are the same design and comfy.

KC8QVO, I guess I'm not making a visual connection about what you are doing. Could you take a few pictures and post them for us to see what you are working with. Then we all can understand better and even make suggestions if we think we could help you out...

 

[KC8QVO]

I do have a few pictures. I will have to post them up later tonight though. Basically I bolted a plate to the seat base where the 4 mounting bolts are that covers the square part of the plastic base. The plastic is thick and reinforced, as opposed to a flat plate or pan, and that square of thick "reinforced" plastic is what sits on the metal plate I made. Where the seat back bolts to the base, though, is not at the same level as the mounting bolts for the base- there is about a 1/2-3/8" difference - not a big deal, fabrication-wise.

 

[KC8QVO]

Ive been trying to get pictures loaded up here for a half hour. I linked to them directly and that didnt work. So I tried to upload them and the file size is exceeded. Wow. What a pain. Give me a bit...

 

[KC8QVO]

No Title

Picture 1 - seat set up

Picture 2 - seat base reinforced now

 

[KC8QVO]

No Title

Picture 3 - bare seat base

Picture 4 - the color coding corresponds to my earlier post about the reinforced base and it being thicker - that is the yellow. The red areas are outlined where the seat back brackets bolt to the plastic seat base.

Picture 5 - I outlined the break areas here. The light colored areas on the seat base are openings where the seat foam is showing through. The areas between the 2 rear openings and the mount is a key area, as are the front corners of the seat base brackets on the sides.

 

[shrew]

Aluminum is lighter, however it might have more potential for flex, especially at lighter gauges. Steel has the potential for rust. I would use the thickest possible guage of either that you can feasibly work with. Aluminum will be easier to cut and bend. Thickness is going to be a compromise between what you can reasonably fabricate with the tools you have present vs. the items rigidity when installed.

Personally, I would look at removing and replacing the entire seat pan. The plastic seat pan is the common piece causing all of your problems. I'd replace with some PT plywood and seal the plywood to prevent water intrusion. It will solve both problems.

As for fasteners I would use nylon lock-nuts. That is what manufacturers in the marine industry commonly use in such applications.

 

[64osby]

I would use a piece of 1/2" exterior plywood (not PT in an aluminum hull).

Seal it up with spar varnish, oil base paint or epoxy. Especially the edges. Should last for many years.

 

[gm280]

Let me see if I have it now. You are wanting to add a larger plate material between the original plastic seat base that attaches to the seat swivel base? And the actual hinged aluminum is only attached to the plastic seat base and back and you think that area needs reinforced? Is that correct? If that is correct, I have a few points. First unless you are expanding the attachment bolts out to the larger plate you are installing, you basically accomplished nothing. The same bolt spacing hasn't changed and therefore neither has anything been reinforced. Secondly, the aluminum hinges are basically the same on near ever seat I have ever seen. Years ago seat were built with plywood for most everything. These days plastic has taken over. And that plastic must be work out pretty well because even the high-end seats are built that way with years of warrantee behind them. So I honestly don't know what you are trying to accomplish I guess... The only way to actually reinforce the seat itself is to install a non-rotting material between the seat and mounting base but with seat mounting bolts moved out to the edge of the seat. Then you changes the stress factor on the plastic based seat indeed. If I still have this all wrong, explain it to me again...

 

[KC8QVO]

If I still have this all wrong, explain it to me again...

You are partially correct. The object of what what I am trying to accomplish is transferring the extra stress, what causes the plastic base to flex, to a plate to direct it to the mount and not have the plastic fatigue. The seat back bracket bolts would have to be longer to make it through the plate, and at the same time the space between the plate and the brackets would have to be bridged with washers or strips of metal to fully sandwich and compress the parts together. With no material between there would be no way to get the force of the brackets trying to flex to the plate underneath. The space would allow the bolts to push through, the bolts, spacers, brackets, and seat base need to be locked together.

Reinforcing the seat base just with the base sitting on the plate and the mounting bolts holding it all in place will be sufficient - the only direction the base needs reinforcement is down (whereas the back brackets are torquing the base where they bolt up).