Transom thickness 14' sea king semi-v

[jojocat]

Hi - I just became proud owner of a 1971 montomery wards sea king 14' semi-V (it's not flat anyway). It had the serial plate, and from that I was able to date it 1971 and the manufacturer code says it was made by smokercraft.

Anyway, got this baby in rough shape for $100! The hull is in pretty dang good shape - no major dings, and held water very well on a little maiden voyage using my lightwin 3hp. The transom is badly rotted, though, and the seats need to be replaced.

My most immediate need is the transom work so I can go fishing! My question is about transom thickness. This thing had obviously had transom work done by a previous owner. I've disassembled what was there, which was an approx 4' x 3/4" piece that goes across the to length of the inside stern, and then a trapezoid piece about 12" on the top, 4" on the bottom and 12" on the sides. Thickness of that outer piece measured 1", but I'm thinking it was originally 3/4". Outer piece is plywood, while the inside piece was solid. I'm attaching a couple of photos post-demoed - I'm not where the boat is, so that's all I've got for now.

I'm wondering if this previous owners work was an accurate replacement. Do those thicknesses seem reasonable? Otherwise, the dimensions seem to match what look to be original paint lines of the boat. I bought some 3/4 plywood, resin and some spar urethane after reading up here. Just wondering if I should beef up the thickness by laminating.

I have a 15hp evinrude 2 stroke I'd like to use on this eventually, so I want to make sure I'm rebuilding the transom up to original spec, since I think that 15hp would probably about be the limit.

Any insights are most appreciated. I was so happy to find a boat for $100. We just got a place on a little lake in WI that this should be just a perfect size for. And the price was spot on for being cash starved after getting the cabin!

 

[lckstckn2smknbrls]

I would add an extra layer of plywood above the knee brace going all the way across the transom.

 

[jojocat]

lckstckn2smknbrls » 02 Jun 2013, 15:23[/url]"]I would add an extra layer of plywood above the knee brace going all the way across the transom.

Thanks for the response. So Just extend the interior 3/4" board more, but no more thickness? I was trying to imagine how the torque works when the motor is providing thrust, and I was starting to think the thickness on the inside would be more important than the length. I think there would be kind of a twist going on from the inside, while the outside would be getting the brunt of the the "push" force.

If I extended the board down, I suppose I'd have to drill some more holes?

I see in your sig you are also a 71 monkeyward owner?? That's awesome. It doesn't seem like you see many flat bottom boats up here in the north - are they kind of made for shallow water? So do you have the serial plate on yours too? If so, is it leading with SMK (smokercraft) or was it another manufacturer for the jon boat they sold that year?

 

[bpswing]

I think most small aluminum boats have a 1.5" thickness. I just did mine using 2 3/4" marine plys glued and screwed together.

 

[jojocat]

bpswing » 03 Jun 2013, 13:12[/url]"]I think most small aluminum boats have a 1.5" thickness. I just did mine using 2 3/4" marine plys glued and screwed together.

Good to know. Did you use 1.5" on both inside _and_ outside? Seems like I've seen some things here claiming the outside piece isn't very important, which makes some sense to me since it's just basically the fulcrum of the lever arrangement. In the case of this boat, it's pushing there against the knee brace so maybe not so important for distributing the pressure?

 

[bpswing]

I used it only on inside. Grumman did not have it on the outside just aluminium.

 

[BoatingCop]

The transom thickness in mine was 1" but went most of the way down the transom. I'm going back with two half inch pieces of ply glassed together. My boat is a '59 14 foot v. Why kind of wood are you going with?

 

[jojocat]

I used it only on inside. Grumman did not have it on the outside just aluminium.

Good deal. I think the 3/4 on the outside should be fine then.

The transom thickness in mine was 1" but went most of the way down the transom. I'm going back with two half inch pieces of ply glassed together. My boat is a '59 14 foot v. Why kind of wood are you going with?

I think I'm going to ply 2 x 3/4" plywood for 1.5" total and extend it down the stern a bit. They have that "arauco" plywood at menards I've seen mentioned here for it's low-void merits so I think I'll go with that. Just having the 1.5" thinkness should make it plenty stiff, especially from the plywood. Wish I knew the motor capacity on mine. Hard to imagine it wouldn't be at least 15hp I guess.

 

[jojocat]

Well after I got back up to the boat this weekend, it seems from looking at the existing hardware lengths that the original thickness on the exterior piece was 1", and the interior was more likely 3/4". I did the opposite and had 3/4" on the outside and 1" on the inside, so I had to countersink the internal board a little for the hardware to be long enough.

After thinking about it a little more, it seems like the design is linking the inner and outer boards with through bolts to increase strength of the entire transom. It ends up being 1-3/4" wood thickness where the clamps connect, and by bolting the two pieces together, the relatively short inner board gets some extra strength against the backward twisting force from the motor from the outer piece which in turn presses against the knee brace for extra stiffness. Kind of clever really, downside being the outer board is exposed/immersed and pretty vulnerable to rot. Upside, saves some weight.

Oh well, live and learn. What I have on will work for the season...I just gave what I did a couple coats of spar urethane so I could use it. I'll end up redoing it at the end of the season and coat with epoxy for the forever transom.

It was good enough to mount my 15hp evinrude and try it out. Holy smokes, took a bit to plane out, but just me in the boat and little else, that puppy was flying.

Thanks for all the input!

 

[Colbyt]

I am fairly sure that the 73 I owned briefly had a 1" solid board inside and 1/2" ply on the outside. I deal with lumber quite a bit and I swear it was more the standard 3/4. It may not have been a full 1" but it was very close.

 

[jojocat]

I am fairly sure that the 73 I owned briefly had a 1" solid board inside and 1/2" ply on the outside. I deal with lumber quite a bit and I swear it was more the standard 3/4. It may not have been a full 1" but it was very close.

That's interesting. Who knows, I guess the hardware could have been swapped around at some point by previous owner. Makes sense the long inner board would be solid instead of ply since it's providing the strength across the length of the board. The rotted board I took off from the inside was actually solid, but it just looked like 1x4 pine so I can't believe that would be original. But yeah, I like the idea of at least 1" on the inside, so I'll probably just replace hardware and go with it.

 

[The Wirtzer]

I just finished redoing the transom on my 14 ft alumacraft. I used two 3/4 inch plywood pieces laminated together on the inside and one piece of 3/4 inch on the outside. I should have done 1/2 inch on the outside as my motor just BARELY slides over the transom now. I bolted through the inside and outside pieces, just like the original though I used 1/4 20 bolts instead of the smaller ones that the original rotted transom had. I also used plenty of 3M 5200 to seal it all up. It is REALLY strong now. I have a 15 hp evinrude that's going on it this weekend.

Tim

 

[jojocat]

The Wirtzer » 10 Jun 2013, 21:40[/url]"]I should have done 1/2 inch on the outside as my motor just BARELY slides over the transom now.

Ha, I hear that - my first stab at the inside board I did 2x3/4" plied together too, but when I thought about it and then measured the outboard clamp clearance, it looked like it wouldn't seat completely so I did it again with 2x1/2" plied. That 1-1/2" board is strong though...maybe it will be a little diving board off the dock. ha