Repair 1950's, 1960's? Alumacraft transom?

[WI guy]

Looking for suggestions on width of outside transom board, material and bolts. I have ended up with two 14' Alumacraft fishing boats with early motors and am excited to get them in the water. The aluminum is good but both have transom problems. The 1950's FD has a punky outside transom I want to replace and the 1960's was always stored outside and is mostly gone. My plan is to remove the outside transom that is just punky and use it for a template to make two new ones. A helpful post from 2012 by Backwaters 2 used 1/2' for the outside and 3/4" oak plywood for the inside. I just need to replace the outside transoms on these two boats and note the manufacturer made these out of 1/4" stock. Thinking of using 1/4" marine plywood for these outside transoms with polyurethane. Any advice on material and width for this? Is 1/4" ok? Marine plywood? Also, wondering if something else needs to be done with the bolts to prevent leakage? Would appreciate any tips from someone who has done this before. Thanks!

 

[CV16]

I'd try to make it as thick as I could and still get the motors on. As for the bolts, coat them in a marine grade silicone and bolt it down. Have fun with them!

 

[Woodonglass]

You can use Ext. Grade Plywood and seal it. I like to use this...

The Best coating is Epoxy but it IS pricey. This recipe will hold up well for many years IF you really soak the edges well. As stated all holes MUST be sealed too as well as the bolts. I recommend using 3M 4200 sealant. I'd also recommend using 1/2" at the minimum. Are you sure the interior transom boards are in good shape?

 

[Watermann]

For the outside motor pad I would use aluminum most boats for the past 20 years haven't used the wood pads on the outside because they become weakened and rot from being wet all the time. If you do decide to use plywood, I've never seen 1/4" marine grade before, only 1/2, 5/8 and 3/4.

Don't use oak plywood in a boat, it's indoor furniture grade and not even close to being something you'd want in a boat. Do as WoG says above.

Silicone is a no go for aluminum as it contains an acid that reacts poorly causing pitting and is degrading the instant you put it on only use 3M 5200.

 

[Scott Danforth]

I agree with both Watermann and Woodonglass. Heck, even dear old dad did a 3/8" aluminum outer pad on the late 50's aluminum fishing boa.

 

[Ned L]

What the others say,... Especially 'oak plywood' would be interior,.... 1/4" marine plywood certainly does exist ( about $45 per sheet vs about $28 per sheet for ACX . This would be for Doug fir.). And don't use a 'silicon' bases sealant (for numerous good reasons).

 

[TruckDrivingFool]

On the FD's it seemed to me that the outside wood was more structural to the transom than just a scar board like on most tinnies, so I did some digging and found this thread with some good FD history/info

The outside transom plywood is 3/8" thick and the inside transom wood is 1" thick. Sorry but I haven't any experience replacing the wood. But I know the outside plywood is also bonded (glued) to transom adding it's strength to it and thus water sealed and giving no movement or flexing between the aluminum and wood. 3/8" plywood might sound thin but that's what all these AlumaCraft's have and they're all bonded to the transom. To remove it is a project.

Some reading in the Alumacraft section might also be helpful as the F series were/are a popular model.

Would definitely like to see some pics of it.

 

[TruckDrivingFool]

I forgot use stainless steel fasteners and 3M 5200 for sealer.