Re: 19.5' Crestliner Norseman DC project boat...
Is it necessary to use "marine grade" plywood when rebuilding a transom?
Yes. Use the best ply wood you can get your hands on. You will need to laminate two or three sheets together to get the correct thickness. You can use epoxy or Gorilla glue to do the laminating, but screw the sheets together to make sure you get them together nice and tight. Once they are glued together pull out the screws and coat everything in epoxy.
Make sure the aluminum is in good shape. I cleaned my and then painted it. Don't worry about filling the hole at this this point. I fitted my transom plate and found that aluminum was NOT flat, the wood was. So I very slowly pulled the wood and the boat together with long screws. This is important because the transom must be flat where the drive is going to install.
Next I filled the hold where the OMC drive went with 1/8"plywood and yes soaked it in epoxy. Then I made an adapter plate out of 1/8" aluminum that picked up all the old rubber boot screw holes and sealed that in place using 3M sealant. I believe it is 5700 but would have to check on that. Then, followed the instructions. Made a template and cut the new key hole. Installed the transom components, drive, motor, etc all per the mercruiser instructions referenced in an earlier post.
Pictures at
http://1974norseman.blogspot.com/ look in the July - October 2010 time period. I got the drive a little higher than I would like so take careful measurements. Basically, if your Crestliner Norseman DC is like mine you have an I-Beam running up the middle of the boat. The mercruiser setup should sit right down on that beam. I put mine about 1.5" above that beam, and that put the anti-cavitation plate about .75" above the bottom of the boat. You want it even with the bottom or actually below. My setup runs great, however, the 4 blade prop is a must. I never did get a 3 blade to keep from cavitating as the boat pushed over while planing. Also, have to make sure the drive is all the way down, or I get a little cavitation. I am certain my problem is from having the drive too high. However, using the 4 blade prop and running about 3000 - 3500 RPM all works great. I have put the hammer all the way down and she will run 32 kts at 4500 RPM with the 4 blade.
Now, once I am on plane, I can trim the bow up and down with no problems. 4-Blade does great.
. Its gunna be a group effort with me and a buddy and most likely converting it to an outboard boat with a bracket. This should be fun!!! A very slow build thead should be popping up soon but wont be any kind of fast cuz we are both college students. Should be fun right???