How can we do this? (Re-framing a casting deck)

[curls]

Last spring, my friend and I built a 3' x 5' rear casting platform for his boat. It worked well, was carpeted with expensive marine carpet, and although it was slightly flimsy, it served its purpose. That was until it met an untimely end by not being fastened down and not having the canvas boat cover on while on the highway. No need to say more about that...

To rebuild the platform, we were considering something like this:

=========== <-- 1/2" existing carpeted plywood
=========== <-- 1/4" new plywood "subfloor"
************** <-- Aluminum frame (1/4" thick walls, rectangular shape, from a dismantled townhome privacy fence. This stuff is perfect, and free!)

We don't want to waste the carpet that is currently glued to the 1/2" plywood -- it's very expensive. So the thought was to somehow secure the aluminum frame to the 1/4" new plywood, and then somehow secure that structure to the existing 1/2" carpeted plywood.

I was thinking maybe 6-10 countersunk bolts through the top of the carpet, fastened with large flat washers and nylock nuts on the underside of the 1/4" plywood sheet?? This would minimize the tripping/slipping hazards when standing on the carpet, still look OK, and be fully functional.

What we really need to figure out (and are asking for suggestions for!) is what type of fasteners to use to secure the two pieces of plywood together, and also, what type of fasteners to use to secure the aluminum frame to the subfloor (1/4" plywood sheet)?

Any ideas guys?

Thanks!

[MLR]

What type and size of boat is this for ?

And does all of this weight rest on top of the gunwalls? Or are you doing it right this time and putting a frame under the deck.

All marine fasteners should be stainless steel (and you thought marine carpet was high priceed)

Still can't figure out what adding the 1/4 inch sub floor is going to gain you. Your 3/4 inch plywood should be thick enough already, it just needs a good frame under it.

[curls]

We have 1/2" plywood right now, not 3/4".

We did it right the first time with 3 legs along one long edge, and the other long edge had the entire edge resting on the rear bench of the boat. (16' Smokercraft). It just wasn't fastened down properly when the incident occurred when he was towing the boat one day. Luckily it wasn't on a major roadway, and nobody was hurt (just a thousand bucks in rods and reels but that's it - lesson learned an expensive way!).

There is no weight on the gunwales -- the top of the platform is level with the top of the gunwales/storage. There is friction between the platform and the gunwales, but the weight is resting on the frame and its legs.

After re-thinking it, using the stronger aluminum framing (as opposed to the 2x2 cedar), we might not need 1/4" subfloor to prevent sag/bounciness. I think we can make a frame (2 widths of 4'6" frame, and 3 lengths of 2'6" frame joining those). That would require 10 sturdy fasteners to hodl the platform to the frame, which really isn't too bad if they are countersunk -- they won't be a hazard and won't look too bad either.

The legs will attach to the frame with bolts as well but they wouldn't need to be countersunk since it's below the platform surface and outta sight.

So stainless won't react with aluminum nor with ACQ treated wood? At least not in the next 20 years?

[MLR]

Sounds like you are on the right track now

Stainless shouldn't cause any problems with aluminum or ACQ but you will need to have a spacer between any ACQ and aluminum as there will be a reaction, they just don't get along and the alluminum will corode fairly quickly.

[CityIt]

use vapour barrier (6-mil poly...or similar) as your break between the aluminum and ACQ.....and will 2nd MLR on the point of not needing the extra 1/4" ply....1/2 is sufficient....PROVIDING there's a solid frame in place!!
If you're worried about bucks....why go with aluminum....and not PT Stock.....Build a virtually square frame for your platform...(the only angles in it will be against the bottom of the frame....and then cut the plywood so it is basically wedged in and cant blow out.....and put in supports in the middle(vertical)...basically build it so that there will be next to no 'sponge'....Also Stainless is expensive...but it lasts almost forever!! hope it makes some sense to you....Best of luck!!

Cityit

[curls]

use vapour barrier (6-mil poly...or similar) as your break between the aluminum and ACQ.....and will 2nd MLR on the point of not needing the extra 1/4" ply....1/2 is sufficient....PROVIDING there's a solid frame in place!!
If you're worried about bucks....why go with aluminum....and not PT Stock.....Build a virtually square frame for your platform...(the only angles in it will be against the bottom of the frame....and then cut the plywood so it is basically wedged in and cant blow out.....and put in supports in the middle(vertical)...basically build it so that there will be next to no 'sponge'....Also Stainless is expensive...but it lasts almost forever!! hope it makes some sense to you....Best of luck!!

Cityit

The aluminum is free since it's sitting under my deck. It was the posts and rails for a privacy fence that the housing contractor (Minto) put up, but we took down to build a full fence and deck in my backyard. Gotta love free!

The way I was thinking to re-frame this would be as follows:
It is a rectangle (3'x5'), where one of th elong edges will have full support along the rear bench of the boat as the frame will simply sit on the bench. That is good, no legs needed there. Then I would take the front 2/3rds of the platform and frame it by running a long beam along the front edge (almost 5' in length) and three short beams perpindicular to those, back towards the beam on the bench (basically the "sides", near the gunwales, and one down the middle). 2 legs along the front 5' beam (where it meets the left and right short beams) using fairly strong bolts to bolt aluminum-to-aluminum on two sides instead of one, for no play or looseness.

With that frame idea, the absolute largest area of 1/2" plywood without anything under it would be approximately 2'x2', which I would think is plenty strong for a one-man platform considering there will be zero sag from the aluminum beams underneath. Does that sound about right?

Stainless sounds like the way to go, and thanks for the 6mil plastic sheeting idea... should be easy to find laying around my house or his, and would be simple to work with as well.

Cheers!
Eric

[bass ackwards]

Aluminum Pop rivets work well through the plywood, you can get long ones from Ottawa Fasteners.

[curls]

Aluminum Pop rivets work well through the plywood, you can get long ones from Ottawa Fasteners.

Would they require a washer to not penetrate the plywood (especially plywood once wet -- soft) ??

I work next to OFS so I can get there anytime. Thanks for the idea. They'll be nearly invisible if no washers are required also.