1970 Seanymph transom rebuild

[Bilbo349]

Hey everyone, new to the forum so thanks in advance. I am working on rebuilding the transom on my old 13.5 foot aluminum sea nymph. I'm guessing the age as it does not have a hull id that I can find.

Anyways, this is my first boat and attempt at this kind of work. So far I've removed the old wood, which was attached with standard bolts and clear silicone. The current transom is the aluminum hull sandwiched between a 2x10 on the inside and plywood on the outside with silicone and bolts holding it together. I am planning to use a 2x10 hardwood for the inside of the boat and a hardwood 1/2 plywood on the outside. I am going to coat the wood with a stain and then a waterproof poly. I planned to use the old pieces of wood as a template, unless the old ones were done incorrectly. I keep seeing transom built only with plywood but I thought it smart to use a 2x10 like what was on it.

I am going to seal everything with 3m 5200 and use stainless hardware . The wood on the the current transom sits about 2" above the aluminum, does it make sense to keep it that way or make it flush?

I'll be uploading images tonight when I can get to a computer, since I'm having no luck with it on my phone .

Thanks and I apologise if this has been covered but I'm having a hard time finding a similar transom to mine with the use of a 2x10.

 

[Bilbo349]

Here are some pictures showing the existing transom and the hull with the wood removed

 

[Hab]

Looks good, Keep going, Ive got a similar aluminum boat to rework. Im trying to get a bigger fiberglass hunk of garbage back to usable condition first.
Im guessing the wood height is meant to keep the motor clamps off the aluminum and keep the prop at such and such a depth, but i cant be sure of that.

 

[Bilbo349]

Looks good, Keep going, Ive got a similar aluminum boat to rework. Im trying to get a bigger fiberglass hunk of garbage back to usable condition first.
Im guessing the wood height is meant to keep the motor clamps off the aluminum and keep the prop at such and such a depth, but i cant be sure of that.

Thanks! I'm not envious of fiberglass work, that does not look fun.

 

[oldrem]

Kinda looks like someone cut the transom down for a shorter shaft motor then found out it should not have been cut. Shaft standards are 15" 20" (long shaft) and 25" (Extra Long). You measure vertically from the bottom of the keel to the top of the transom. You want to be close to one of those heights.

 

[Bilbo349]

Kinda looks like someone cut the transom down for a shorter shaft motor then found out it should not have been cut. Shaft standards are 15" 20" (long shaft) and 25" (Extra Long). You measure vertically from the bottom of the keel to the top of the transom. You want to be close to one of those heights.

Okay thanks for that information. I just measured the aluminum part of the transom to the bottom of keel and got 17". Then I measured the shaft length on my 1983 Evinrude 9.9 from where it sits on the transom to the cavitation plate and got 18" . Add an inch or so of wood to the transom and they are both 18"!

It doesn't look like it was cut by an amateur at least, the wavy parts you can see in the picture are identical on each side and it has a rounded edge.

My next question is does it make sense to use 3m 5200 to sandwich the wood and metal? I see that it says permanent and that makes me a little nervous.

 

[oldrem]

Okay thanks for that information. I just measured the aluminum part of the transom to the bottom of keel and got 17". Then I measured the shaft length on my 1983 Evinrude 9.9 from where it sits on the transom to the cavitation plate and got 18" . Add an inch or so of wood to the transom and they are both 18"!

It doesn't look like it was cut by an amateur at least, the wavy parts you can see in the picture are identical on each side and it has a rounded edge.

My next question is does it make sense to use 3m 5200 to sandwich the wood and metal? I see that it says permanent and that makes me a little nervous.

I did not on mine. I only used adhesive on the through bolts.

 

[Watermann]

Welcome aboard :wave:

The reason plywood is used is because it's much stronger than dimensional lumber as the layers are crossed so you don't have a single straight grain across the entire length of the transom. You could take an axe and beat on 1.5" of plywood nearly all day but a couple swings on dimensional lumber with the grain will split it in half.

 

[Bilbo349]

Ahh that makes complete sense. Well I'm 2 days of staining and waterproofing in so it'll have to do . It's a pretty light motor but I probably wouldn't trust a bigger motor hanging on the back. It hardly needs anything bigger though it planes just fine with me in it and that's fast enough for this rickety old thing!


I am also planning on adding some sheet aluminum where the motor contacts the transom on either side and angle aluminum along the top to protect the wood. Any advice for what to use for the metal? I see that my local Lowe's has a pretty good selection of sheet and angle metal.