Question on new transom core material

[Capecafe]

I'm restoring a 1978 MA and need to replace the transom. I am planning to replace and raise the transom from the outside and have a few questions for all the experienced boat rebuilders:

1. I have 1.5" of core material to replace. Since I am replacing from the outside I'll need to cut my replacement core into pieces in order to fit tightly back into the edges. Would a single core of 1.5" Penske board, cut into 4 pieces then sandwiched between two sheets of 18oz biaxial cloth with the original .25" outside skin epoxied on be sufficiently strong? A few of the outside transom replacement threads have used two layers of core with overlapping seams. I am repowering with a new 2016 Etech 150 that weighs 420lbs.

2. I have been told to be careful when raising the transom on the MA to 25" in order to avoid an issue with the motor mounting holes. It was mentioned to either go 26" or 24" to avoid a problem with the lower mounting bolts. Is this a real concern you all have worked around? It seems the new Etech has plenty of mounting bolt locations to work around this issue.

3. When determining my transom height, should I measure from the bottom of the keel up to the top along the transom, or top of the transom straight down to level of the keel?

I've attached a few pics of the boat when I found it and before I started the restoration. It was a freshwater boat it's whole life, but the through hulls in the splash well leaked and turned the inside of the transom to mulch. The foredeck and alongside the console were mushy and I've already re cored them as well as the fuel tank cover. I had a new 42 gal fuel tank built and have installed that with all new hoses. Plan on keeping the boat, so it's important I do it right the first time. I appreciate any thoughts you all have to help me make sure I get it done and done right. Thanks!

[Vezo, Part II]

Welcome! Did your MA come with a 42 gallon tank, and not the optional 68 (70) gallon? In other words, was there a small coffin box molded into the floor below the center consul? I have pics on this site somewhere of my 1979 larger tank removed showing the nicely gelcoated, and remaining foam, fuel cell cavity.

Vezo, Part II

[Capecafe]

Yes, it was the 42 gallon tank located in the "coffin" space below the console and aft of the leaning post. The original one had no leaks, since it had always been in fresh water, but the boat sat for about 10 years before I tore into it. I pumped out almost 40 gal of old fuel and there was so much gelatinous old fuel residue left I couldn't cut it enough to get the inside spotless. The baffles were catching a lot of the sludge when I attempted to swish it with acetone. Considering the money I spent on a new motor, I didn't want the fuel supply to be a potential problem. Capeway welding in Plymouth, MA made an exact replica, with the exception of the welds being a work of art and the tank was pressure tested and certified.

[thehermit]

A Vermont Master Angler. Epic score.

[Vezo, Part II]

Originally Posted by thehermit

A Vermont Master Angler. Epic score.

Agreed. Do you have a photo of the coffin box for a 40 gallon. Never seen one, and would have Ass-u-med it would have been forward and under consul. Thanks.

Part II

[Capecafe]

I'll get out to the boat and take a picture for you as soon as it quits raining here. Just finished the re-core of the deck cover and not installed the new tank yet.

[FishStretcher]

I think an engineered foam core sounds great in the transom. The fiberglas is what takes the load. So if you add glass on the inside, you will still need to grind back on the outside of the transom skin to join that stressed asking across the cut made to gain access. The rule of thumb is 1:12. So if you have an outer skin of 1/4 thick, you need to grind back 3" either side of the cut and glass that in with progressively wider strips of glass (tape?) to build back.

That joint will takes a significant part of the load to hold up the outboard when pounding around.

If the motor is under 400 lb and with a new, light transom, I think you will be happy with the result.

I have an old wet transom on my 20 MA and obscenely heavy hatch covers and splash well. With that and a 375lb outboard, you can get water coming up a scupper if you stand in a back corner. So Penske in the transom will help a lot. And a light fuel tank hatch cover will help a bit.


I am redoing my tank hatch cover today in nidacore and will start a new splash well next week.

Nice score for a 20MA!

Originally Posted by Capecafe

I'm restoring a 1978 MA and need to replace the transom. I am planning to replace and raise the transom from the outside and have a few questions for all the experienced boat rebuilders:

1. I have 1.5" of core material to replace. Since I am replacing from the outside I'll need to cut my replacement core into pieces in order to fit tightly back into the edges. Would a single core of 1.5" Penske board, cut into 4 pieces then sandwiched between two sheets of 18oz biaxial cloth with the original .25" outside skin epoxied on be sufficiently strong? A few of the outside transom replacement threads have used two layers of core with overlapping seams. I am repowering with a new 2016 Etech 150 that weighs 420lbs.

2. I have been told to be careful when raising the transom on the MA to 25" in order to avoid an issue with the motor mounting holes. It was mentioned to either go 26" or 24" to avoid a problem with the lower mounting bolts. Is this a real concern you all have worked around? It seems the new Etech has plenty of mounting bolt locations to work around this issue.

3. When determining my transom height, should I measure from the bottom of the keel up to the top along the transom, or top of the transom straight down to level of the keel?

I've attached a few pics of the boat when I found it and before I started the restoration. It was a freshwater boat it's whole life, but the through hulls in the splash well leaked and turned the inside of the transom to mulch. The foredeck and alongside the console were mushy and I've already re cored them as well as the fuel tank cover. I had a new 42 gal fuel tank built and have installed that with all new hoses. Plan on keeping the boat, so it's important I do it right the first time. I appreciate any thoughts you all have to help me make sure I get it done and done right. Thanks!

[Capecafe]

Thanks FishStretcher. My main question is whether or not to use a single 1.5" thick Penske board, cut into four pieces, with the outside and bottom pieces fit tightly into the sides and bottom of the hull?

I'd cut the Penske at 45 degree angles so the center piece was locked behind the edges and bottom pieces. I would lay in epoxy between the Penske pieces and with a layer of 18oz biaxial cloth sandwiched between the inside of the hull and the outside skin. I'd then scarf the outside hull skin to a 12:1 and filet in. That would provide for a new thick layer of epoxied cloth on the inside and outside of the new core material.

When all laid, will the four pieces of 1.5" Penske board be as strong a single piece when sandwiched between the resin soaked 18oz cloth and adhered to the original inside and outside skin?

This weekend I took off the aluminum motor well trim and original plastic thru-hulls to get a better idea of the extent of the rot and see how much work is going to be involved in cleaning out the rot in preparation for the new material. I've attached a couple pictures of the current condition. It amazes me the original engine still hung. Not only was it still hanging, the transom didn't even flex a bit when I bounced on the motor before pulling it. The port side of the transom is almost completely devoid of any type of solid core. The only semblance of a core left was under the motor mount and it is soaked through and easily peeled off the skin.

[DonV]

I do not think four separate pieces will work as described. If you want to go "wall to wall" and get the most penske you can get stuffed in the cavity why not two 3/4" pieces each cut in two pieces. The inside piece cut 1' from the left and the outside piece 1' from the right. You could then work each layer in as tight as possible still giving you a solid 1 1/2" with no seam in the middle of the transom. Each seam would still have a solid backing of 3/4" penske. Make sense? It will take a lot to trimming and dry fitting to get just right but it would still be as strong as you would ever need.

[Capecafe]

Originally Posted by DonV

I do not think four separate pieces will work as described. If you want to go "wall to wall" and get the most penske you can get stuffed in the cavity why not two 3/4" pieces each cut in two pieces. The inside piece cut 1' from the left and the outside piece 1' from the right. You could then work each layer in as tight as possible still giving you a solid 1 1/2" with no seam in the middle of the transom. Each seam would still have a solid backing of 3/4" penske. Make sense? It will take a lot to trimming and dry fitting to get just right but it would still be as strong as you would ever need.

Hi DonV- I had seen UrbanAngler post a transom project on a 20" SF using Coosa cut in four pieces to allow for snug fits along the outside edges and a solid core in the middle ( see pics of his lay up below). He used two layers cut so as to over lap all the core seems with a layer of 3/4" Coosa under a layer of 5/8" Coosa.

I have spoken to a couple materials people who've told me four pieces of 1.5" Penske butted tightly with epoxy and sandwiched between the 18 oz biaxial matt would be solid as a rock and behave as a single solid piece. I've been a little suspect since I can't seem to find a transom rebuild thread using a single sheet of core material cut, fit and epoxied in. A single piece of 1.5" with the epoxy soaked 18 oz mat on each side would be exact size of the inside dimensions of the transom and allow the skin to be adhered back on flush with the original cuts.