Has anyone ever replaced a transom on an aluminum boat? I have a 16 ft. polar Craft that has a bad transom. The metal on the outside looks good but the wood on the inside looks like it is rotted and cracked in a few spots. After a few internet searches, it looks like something that I may be able to do. I would have to remove the motor, some large screws and a few rivets. Take the old wood out and put in new. Drill out all the appropriate holes and reinstall all the bolts and rivets. Seems fairly easy.

I still have a few questions though. What kind of wood should I use? Or maybe they sell pre-cut transoms??? Do you need to treat the wood with any type of sealer?

I would really appreciate ANY advise.

Is the original wood plywood or solid board? If plywood, you would want to go with a good marine grade for the replacement because the glue would be less succeptible to moisture damage than other grades. A good exterior grade could pass since it wouldn't be directly in the water. I would still recommend treating it, probably with a polyeurathane treatment.

3/4 marine grade plywood is all you need.It is not that big of a job.

Is the original wood plywood or solid board?

It looks like plywood. Does anyone know of a good site that shows step by step instructions? Ive looked around and all I can find instructions on are the fiberglass boats.

Try to use the old wood for a pattern as best you can. Use marine plywood as stated above. I went one step further when I did my jon boat, I mixed up some fiberglass resin and "painted" the wood with it. It sealed it quite nicely from water ever penetrating the wood.
As duckhunter stated it's not a hard job to do.

This stuff is getting some pretty good reviews. The site has step by step instructions too.:
http://transomrepair.com/zk/