New owner of SeaCraft 20 ma hull id number
 

New here to the site but looking at some amazing classics I’d like to know is there a way to determine the year of the hull by the hull Id number also are there any thing that I should be looking for on the transom as a issue with the integrity of it any know problems ect..

Generally the last two numbers of the hull ID are the year of manufacture.

As far as the transom, if the motor is mounted tilt it part way up and put your foot on it and bounce up and down. There should be little to no flex on the transom itself. If the transom bounces, its mushy inside.

Also look for cracking around the edges of the motor well opening in the transom itself, or separation of the aluminum trim Seacraft used to cover the seam between the transom and the liner. That part always cracks first.

If the motor is off poke around in the engine mount bolt holes, with an awl or a small pick.
That'll give you a good indication of core quality.
Look for the glass around the bolt holes on the inside of the transom puckering in and looking squished from the bolts squeezing a compromised core.
You can do a gentle sounding with a small peen hammer, tapping all over. Compromised core will sound dull, solid core will sound sharp.

Sounds great I’ll keep posting for future updates

So I’ve gotten the boat home and have discovered that the transom was raised at some point approximately 6-8” I’m sure it was done to accommodate a long shaft motor unfortunately it was done poorly any suggestions on how to replace just the raised piece

"raised piece" meaning fiberglass or core ? Or both ?

Sorry raised as in went from short shaft to a long shaft motor

And it needs core and glass — anyone use coosa board ?pros/ cons vs marine ply

Updated photos of 78 20’ ma
 

So the boats home and I’ve started the tear down process see pics below

More photos of the stern tear down
 

Lots of rot practically falling off the stern as I cut the fiberglass back ..lots of work ahead of me

I just started my restoration on my 20' MA, my transom was like a sponge. took the cap off and cut some deck up and started ripping her out, i did leave the outer skin to reglue to. ill post some pics once i figure out how to lol. And i do plan on using coosa for transom and a new deck.

Coosa
 

I noticed you asked about coosa board. Here's my take

Good: strong, water impervious to a point, lighter than ply wood.......

Bad: expensive, hard to cut ( will dull blades fast ).......

Probably much more to be said but that's it in a nut shell.

Ed

Penski Board is an option. I did my 20's transom from the outside with it (2006) and it has been fine so far. Don't know what materials cost now, but the Penski Board was not cheap.

I used Coosa for several reasons:
Light weight (26lbs/ft3)
strong with very high compression strength
won't rot
won't absorb ANY water
cuts and sands easily (almost too easily)

Like everything else, it has a few negatives:
is not great at holding screws without a bedding of some sort (through bolting is fine though)
low/no residual strength if it ever fails (ruptures rather than plastic/elastic failure)
dust from cutting is extremely itchy and dulls blades fast - just like FG
need to make sure that it is fully wrapped in layup since exposed edges can be failure source since it is so friable (the front and back surfaces have glass embedded about 1/16" deep)

oh yeah - I got it cheap due to a mis-quote :D

Yes. :(

Thanks guys for the input I’m looking at a full stern rebuild and only want to do it once ... any thoughts on a full stern with brAcket vs the traditional motor well design I like the security of the solid stern and understanding there is a cg issue but I’m most likely gonna repoower so I can make the needed adjustments when i rebuild ... just not sure the best way to go

Estimating CG Shift
 

In doing your homework you may want to see my post of 9-24-16 on Estimating CG Shifts. There is an example calculation which you can plug in your own numbers. You may also temporarily load some weights to simulate your final config before spending time and money. Lots of guys choose brackets for similar reasons. This gives you a chance to consider the effects. Best wishes!