I have a 16ft alluminium center console, it was built in 1985. I guess 25 years is a resonable amount ot time for wood to last on the water, it has gotten quite soft ( the wood in the transom).

it looks pretty straight forward, take out all the scews- remove the old wood- make a template out of cardboard- cut the shape out of plywood-use waterproof glue to 2 pieces of 3/4 ply to achive the correct thickness- replace screws ( I am planning on sealing screws with waterproof silicone)

am I missing anything? any advice or opinions would be great!

Don't forget to give the plywood a few good coats of waterproofing poly (Especially the edges)

When we redid the transom on my boat we sealed the top with fiberglass and resin, it seems to be holding up quite well 8 years later.  Im sure if you put a couple coats of waterproofer on it would work also but you may have to reapply.  Everything else sounds right on, good luck and let us know how it turns out.

There have been posts on here before that say the chemicals in treated wood will corrode aluminum.  Most folks doing john boat decks use exterior grade plywood and either seal it with Thompsons water seal or resin only thinned with acetone.  I personally would use Clear Penetrating Epoxy Sealer from the Rot Doctor because I have had good success with it in the past.  The above suggestions may work just as well.  DO NOT totally enclose the wood in fiberglass.  It will get water in it somewhere, will not dry out, and it will rot.  Covering the top of the transom with fiberglass may be a good idea, as it should shed most of the water so it doesn't get between the two layers of wood.

I have an Alumacraft boat that needs new wood.  I contacted the Alumacraft co. for the specs on the wood.  1" solid oak for the inside and 1/2" marine ply for the outside is what they used on my boat.  I would say that any kind of marine clear varnish or any of the above mentioned products would work. Some would just require a replacement coat more than others.  

thanks for the advice guys! I just finished & it looks awesome! I glued & biscuit jointed 2 pieces of 3/4" marine plywood, then sealed it with 4 coats of spar varnish. I think it should last a long time....but in case it does'nt I made a second one at the same time! at least if this one only lasts a few years, it will only take me a couple of hours to pop the next one in.

Great idea about making two at one time!!!  Note to self