1983 240 offshore-replacing rotton core transom and modifying/raising to accomadate twin f150 yamahas

[Logan pufahl]

So my cousin just bought/got a deal on a 1983 240 offshore, transom core is rotted (he knew this when buying) and plan on having it replaced with coosa board core, transom had twin 115hp Mercury 20 in shaft 2 strokes (low 300's lbs a piece), transom is factory notched.we want to raise new transom 5 inches (because of how low it sits to waterline) and keep it horizontally straight (no notches) and repower with twin f150 yamahas (487lbs a piece) is this possible? Or do we need to stick with f115's that weigh 375lbs a piece? current transom is rated for 280hp max. I'll attach some photos (it wouldn't let me attach the photo with engines off transom, I have them though)

 

[SkunkBoat]

No one can definitively say what the weight and HP rating of the new transom will be unless they are a marine architect...
That being said, if you use 2" coosa rated for transoms(Bluewater 26), properly sandwiched between glass and connected to good stringers, and the hull is in good shape, there is no reason to fear mounting a pair of 150's.
Going to 25" transom with coosa is not a problem, makes sense.
I hope you are leaving the outside skin intact and replacing the transom from the inside.

I hope you got the boat for free because its going to cost you several thousand dollars and lots of itchy time.

 

[UCPA111]

I recently did this project for my 1984 Seafarer. It was a chore, but turned out fantastic. I am not a fiberglass guy...my day job is plastics engineering. But, I just loved the boat style and wanted to restore it and started watching videos and reading about how people do this kind of project.

I purchased Coosa board 1" thick. I laminated those together. I used West System 105 epoxy system, 1708 biaxial fabric, chopped strand mat, and some other fabrics. Mostly 1708. I had a cutout transom and eliminated that and made a full height transom. We built a mold and made a gunnel piece that matches the existing gunnel.

You can follow some of my progress on my youtube page. https://www.youtube.com/channel/UCATvLuuBWqIPmRX0gH9FiMQ

If you look for Grady White Restoration you'll find the videos. I dug deep. Fuel tank removal, weight redistribution - moved new fuel tank forward, all new wiring, all new thru hulls and hoses, all new electronics, all new everything basically. I added a flotation transom bracket. Boat sits perfectly with all I did. I installed a 300HP Mercury Verado. It's over 600 #. I had the transom bracket customized and they did a fantastic job. I had the flotation chamber enlarged to provide a bit more flotation. I believe every cubic foot is around 62 # of flotation.

 

[trapper]

UCPA, WOW! Great work! Really impressed with you ability in doing this major rebuild. How did you get all the info together to give you the confidence to start the process? Look forward to seeing it completed. Cheers, trapper

 

[UCPA111]

UCPA, WOW! Great work! Really impressed with you ability in doing this major rebuild. How did you get all the info together to give you the confidence to start the process? Look forward to seeing it completed. Cheers, trapper

Well, I really liked the boat. I bought it for $2800. It had a blown motor, but the boat size and usability had my attention. When I got it home, I realized it needed more than some elbow grease. I started with fuel tank inspection (it was pitted) and then looked at transom...came on this site and others...and figured it was wet. I then watched some videos and did a couple weeks of online research. My Dad and I did the project together. He was game for trying something new, and so was I.

When I had the transom removed, I started investigating repower options. I came to the conclusion I wanted to enclose the transom and add a flotation bracket so I could add a heavier 4 stroke motor.

I am not afraid of big projects. When you have the glass cut and the epoxy mixed...your are committed!!! LOL!

I got all the mission critical elements in place for a maiden voyage this summer. Lake Erie (Erie, PA) had a phenomenal year for walleye. I didn't do any work on it this summer except fish. Put 100 hrs on the new motor.

So, there are a bunch of minor, cosmetic things I want to improve on the boat. I'll work on those this winter. Heated garage work!

Thanks for the feedback.

 

[suzukidave]

where is your fuel tank and how deep is your transom in the middle? before i got my 223 i looked at an early 80s 223 with twins. grady had installed the main tank shifted forward instead of aft against the bilge bulkhead like in most 22' hulls. they also had a installed a 25" transom measured at centre to accommodate the two offset 20" leg motors. if that is your set up and you are already unhappy with freeboard aft then i would consider installing a single big xl leg motor to reduce weight and also save some money since you will not need to raise the transom.

 

[UCPA111]

He has some pictures. It's pretty low. If it were mine, I'd fully enclose the transom (make gunnel straight across), get a custom flotation bracket, and either put on the 150s or consider a single Mercury 350 Verado or something comparable. I like twins, but fishing around them (especially if trolling) is more painful. I'd think a 350 Verado would improve performance over the 150s and definitely over the 115s.