How do I replace this Transom?

Ive read on here that you can replace some of the rivets with bolts, but how waterproof are they? Some of the rivets I will have to replace on this boat are kind of low on the transom and will definitely be in the water.

It still feels somewhat solid, but on the outer edges its starting to look a little dry rotted, I would feel better If I could replace it all.

Once you chisel out the rivets and get the new wood cut out and routered, countersink the holes, put a gob of silicone in and a little around them, and cap each hole with a washer, and shove the bolts through. You get a perfect watertight seal around the washers, in the holes, and around the bolts. I would also recommend a bead of silicone along the edges of the wood before you torque the bolts down to keep any water from getting under the wood.

Drill out the rivets holding the wood in.Then cut a new piece out of exterior(not pressure treated) plywood.Next coat the new transom in water sealer or paint.Install the new transom with stainless steel bolts and lock nuts.Run a bead of 3M 5200 marine sealant around and in the holes from the outside.

Like the last guy said use 3m 5200 for you bolts and around the wood. This stuff is tuff and wont leak. You better have a rag handy because 5200 doesn't like to come off your fingers when it is dry. Good luck!

Thanks guys. I've started to paint my boat this weekend, and got all the stuff out of the inside. Looks like I'm going to have to rewire everything too. Whoever had it before was basically just wrapping loose wires around a battery terminal, and making wires longer by twisting two wires together and smothering it in black tape. which is not my style. So Im doing it all over from scratch before I start putting the deck in.

As far as the transom I will probably try and get some of those bolts and rivets out this evening to see what I'm going to be dealing with. The first picture which shows that little metal plate is covering a long board which looks to be pretty thick. It looks almost like about as wide as a 2x5. Then it has that little section of plywood on the other side which you see in the 2nd picture. This should be fun.