What thickness plywood and type is best for a casting deck with carpet? 1/2" or 3/4"? Also what type

1/2 inch will flex quite a bit. I'd go with 3/4.

3/4, buy the best stuff they got at lowes or hd, I think my last boat was 42 dollars a sheet.   I always get the best 3/4 they got and make sure you seal it with fiberglass when you are done before you carpet it.  Will last long after the carpet is gone.

Depends on how you brace it. The type depends on the type of boat. Never use pressure treated on an aluminum boat. I don't like wasting money on marine grade. I just buy regular and seal myself.

15 minutes ago, riverbasser said:

Depends on how you brace it. The type depends on the type of boat. Never use pressure treated on an aluminum boat. I don't like wasting money on marine grade. I just buy regular and seal myself.

how do you see yours?

I've done one casting deck on a aluminum boat and replaced the floor in 2 fiberglass boats. The 2 floors just got glassed. The aluminum deck I sealed with a stain/seal from home depot. Did about 3 coats on all sides and then installed on boat and carpeted last. I owned it for 5 years and sold it to a friend. Its still as strong as new.

Plywood sturdi floor (5/8") sub-floor is up to 10% stiffer than oriented strand board (osb), which means there will be less deflection and bounce under your foot.

A good five ply 1/2" works but not anything HD or Lowes sells.

planning on using 96 in. x 1 in. Aluminum Flat Angle with x 1/8 in. Thick (https://www.homedepot.com/p/Everbilt-96-in-x-1-in-Aluminum-Flat-Angle-with-x-1-8-in-Thick-802517/204273955) planning on using 1/2in plywood

On the Tin Boats forum,  the dealer that the people suggest for any wood sealant (transom,  bunks, deck...) is 

OLD-TIMER S FORMULA 
One part Boiled Linseed Oil, 
One part Spar Varnish or Spar Urethane.
Two parts Mineral Spirts.

I've used this in the above applications and it worked very well

I wish I had read this stuff all those years ago hahaha. I always used the fiberglass resin and made one heck of a mess!!!

Fiberglass resin by itself, does not play nicely with plywood.  The best thing you can use is an epoxy resin based product such as Gluvit.

 

https://www.amazon.com/GLUVIT-EPOXY-WATERPROOF-8-lb/dp/B0149I886Q/ref=asc_df_B0149I886Q/?tag=bingshoppinga-20&linkCode=df0&hvadid=&hvpos=&hvnetw=o&hvrand=&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=&hvtargid=pla-4584070138401886&psc=1

 

I can hear the howls of disagreement but here goes.  Polyester resin is not waterproof.  It can absorb water.  When that happens the bond of polyester resin to plywood is compromised.  When that happens the outer layer of plywood will expand.and the resin cannot stretch enough so it cracks.  As time goes by the cracking accelerates.

 

To correct the result requires sanding the plywood to remove all the remaining resin.  Then coat it with resin and it should be good for the life of the boat.

 

If you want to save a couple of bucks use vinylester resin.  It is waterproof.

 

I'd use a quality exterior house or a marine grade paint to coat the surface before I'd coat it with polyester resin.

 

https://www.boatdesign.net/threads/protecting-plywood-with-polyester-resin.14325/