First up many thanks for your replies. Your time considering my issues is very well appreciated.
What am I aiming to achieve? Hand crafted wood mounts for placing photographic prints on to. I intend on offering several different mount options which will include clear polished and tinted polished edges (18mm +). Some unpolished with rounded (routed) edges/corners (9mm). I am well aware that MDF is the most stable medium for prints and plywoods have issues over warping however MDF is soulless. I intend on finding a way to make plywood work for me. Like all woods, in moist conditions they warp. From what I have read I suspect laminating sheets of ply will ultimately be the answer to stabilising ply as effective photo mounts.
What are you making that you need marine plywood for?
Actually I am experimenting with both Marine and Birch Plywood, both hardwoods of course. The reason for Marine is twofold. Firstly because I am interested in the variation of hardwood veneers found in marine ply which when sanded and polished are beautiful and every sheet seems to be different and they make an excellent background to prints. Also marine ply tends to be almost cavity free as does birch ply.
are the panels large enough that you could use a router table?
Yes they are. Size I am working on at the moment are (smallest 170 x 170 mm largest 500 x 500 mm although up to 1000mm would also be available) I have recently bought, off ebay, a router table and low wattage (700) router, which may well not be sufficient but i'll find out soon enough. My plan it to buy good quality cutters. This seems pretty consistent which much of the advice I have read on routerforums. You can get away with poorer quality router but not so table and cutters.
Are you suggesting I use the router table to prepare edges for polishing. If so how?
What size are these panels?
(smallest 170 x 170 mm largest 500 x 500 mm although up to 1000mm would also be available)
Are you sanding the tops/bottoms as well?
No just the edges
How are you planning on finishing only the edges without straying onto the tops/bottoms?
I am not too bothered about straying as I want the panels to be obviously hand made. Showing process helps to demonstrate that. On one side will be affixed a print in any case.
If I were to clamp together several panels to work on at a time then this would prevent polish from being placed on the sides for the interior panels in any case.
It sounds like a perfect application for a stationary belt (or disc) sander, assuming the panels aren't huge... one at a time
G1531 6" x 80" Edge Sander
This looks perfect although a bit outside my startup budget. One for later maybe. I have identified similar but on a smaller scale Clarke CS6-9C Belt & Disc Sander - from Machine Mart
Screw the pieces together and work all edges at leisure. When done plug the holes with a small dowel, but this could take as much time as moving the clamps!
Not an option for my purposes.
Thanks again for all your thoughts so far.