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[Lordwrench]

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[Bushwacker]

I'd recommend doing what Brown & Hauptner, the local SeaCraft dealer I bought my boat from, did to all the new boats they got from the factory. Before installing a motor, they pulled off the aluminum trim around the transom cutout, routed out the joint between the top of the transom skin and the inner liner, and then caulk it with 5200. Reason they did that is that Potter putty was laid on top of the transom core before they dropped the inner liner down on top of it. That polyester putty is very brittle and would crack over time, so then every time a wave came over the cutout into the splashwell (which is fairly common on a 20" transom, even with a light 300 lb motor on it!), water could eventually get thru those cracks and into the transom core. Although my boat was 3 years old when I bought it, I also caulked that joint before installing the motor, and I believe that's one reason that my original 43 year-old transom is still in good shape! When Don Herman opened it up in 2006 to fill in the cutout and install his bracket, he said it was the driest transom he'd ever seen on a boat that old!

Don't know what year your boat is, but the Moesly and early Potter O/B models (I believe '72 and older) often had a clever circulating live well under one of the rear seats like mine. It had a ~4" diameter screw-in plug & cup at the waterline installed through a hole in the transom core and attached to the transom skin with Potter putty. A single 3/8" tube cut off at a 45 degree angle and extending below the hull supplied water through a hole in that cup while a bunch of 1/8" holes provided the overflow. You can see the water tube installed on mine in the pre-bracket picture below. When the putty cracks, that feature will let water into the transom, so if you have that feature, it probably needs attention if it hasn't already rotted your transom!

Fortunately I recognized the potential problem shortly after I got the boat, so opened it up from the inside and found some some slightly damp wood! I dried it out with alcohol and heat lamps, letting it sit open for several weeks. I then soaked it with Git Rot, sealed everything up with Marine-tex, and epoxied in a PVC clean-out fitting which fixed the problem. When the bracket was installed, a mounting bolt needed to go right through that opening, so Don removed the plug and filled it in with some Coosa. I've used that bait well so much that I decided keep it functional and replumb it with a new water inlet line and overflow as shown in last pic. The water inlet also provides a handy raw water washdown - can't pull the scupper plugs anyway unless I'm running on plane, when that pickup provides plenty of water!

[Bushwacker]

Yes, you want to use 4200 or Life Caulk on something you want to remove later, like engine mount bolts. For sealing something like the inner liner/transom gap that wants to be a permanent seal, I would use 5200 except that it didn't exist in 1975, so I used the next best thing which was Life Caulk, which remains flexible and doesn't crack.

Looks like you already have a bracket on the SeaCraft. When you rerig it, if you run the rigging down thru the flotation tank like Don Herman recommends (see pic below), you'll have a neater installation that doesn't clutter up the swim platform as much. For a 30" bracket setback you need to allow for about 6' of length in the hoses and cables to run thru the rigging tubes. Don used to sell a rigging kit for about $40 in 2006 when I rigged mine. I also added a strip of rub rail to the edges of the bracket because it can get dinged when you're docking around pilings, etc.