Ski boat RESTO MOD! Questions on curved transom!

[djrowe007]

I am going to start a thread to introduce myself here sometime tonight. I will be uploading pictures of my restoration to everyone. I work as a marine technician professionally but this is my first go at restoring a boat. I am doing it to mainly learn and because I think it is a lot of fun. The rest I will save for my intro thread.....

​My question is, my transom has a pretty decent curve, I didn't realize how much it was curved until I through my cut piece of plywood in there for the transom. What is the proper way to fix this transom? I prefer not to use balsa, and for the record, the original transom was only 1/4" thick (being an inboard ski boat). The only thing going on the transom is a swim deck that I am going to make. Would it be possible to replace the entire transom with just fiberglass? I have a roll of CSM and a roll of 1708 biaxial.

​Pictures will come later if needed. Must go to work now

​Cya guys!

​Boat is a 1987 BAJA (YEAH BAJA) inboard ski boat. Good luck finding any pictures of them on google. If you know anything else about this rare find let me know.

 

[Baylinerchuck]

Looking forward to those pictures!! Instead of covering the entire transom in plywood, would it work to cover the anchor points of the swim deck with encapsulated plywood? The reinforcements would have to be large enough to spread the load, but I wouldn't think you need to cover the entire transom.

 

[89 resorter]

I'm restoring a Century Coronado which is also a straight inboard with a curved transom. I replaced my with the same transom design that was originally in the boat which is shown below with the exception that I used epoxy instead of poly to provide additional strength. I used foam insulation board to pattern the transom and transferred it to a sheet of MG plywood. I then cut it into staggered rectangles as shown and then epoxied them into place.

 

[kcassells]

You could simply cut kerfs into the ply. That will give the ply flex/bend to fit. Lots of PB to fill the kerfs. Definitely a 2 man job.
That technique is pretty common for curved transoms.
Welcome a board!

Another way to do it is to use 1/4" ply which will flex to the curve. Build up ea. ply to your finished thickness.

 

[Scott Danforth]

I would use poly core such as the nomex honeycomb in this application.

 

[sphelps]

I'm thinking along the lines of what kcassells suggested ...As long as there aren't multiple curves . Simple radius should be no problem ..

 

[djrowe007]

You could simply cut kerfs into the ply. That will give the ply flex/bend to fit. Lots of PB to fill the kerfs. Definitely a 2 man job.
That technique is pretty common for curved transoms.
Welcome a board!

Another way to do it is to use 1/4" ply which will flex to the curve. Build up ea. ply to your finished thickness.

​Well I tried this on a practice piece of plywood, the stuff I got seems to crack when I bend it. I tried 2 test pieces on the plywood I bought. One piece was about 3/4 the depth of the ply and the other cut was about half the depth of the ply and they both started cracking. It bends like a "U" both vertically and horizontally...

​I cut square patterns about an inch apart BTW which is what it originally looked like on balsa.

​89restorer
​I'd like to use that method but it seems like to big of a curve but it almost seems like I would have to use balsa to bend it that much and I don't want to.

​Scott Danforth
I have never used those materials however I have read a bit about them. Would they provide the needed stiffness that wood would proved when done properly?


I am going to upload some pics shortly tonight.

 

[djrowe007]

No Title

Photos orientation doesn't show correctly when uploaded I don't know why.

 

[Scott Danforth]

for an inboard ski boat, yes, they would provide the needed stiffness. however if you want to use wood, use multiple thin sheets and glue together in place

 

[djrowe007]

No Title

 

[djrowe007]

for an inboard ski boat, yes, they would provide the needed stiffness. however if you want to use wood, use multiple thin sheets and glue together in place

​Just looked up pricing on that stuff, wow it's expensive!! Any recommendations on where to get it from that is a trustworthy reasonable place?

 

[kcassells]

Wow that sure is not much of a transom. try 1/2" ply, 3/4" still would work. Cut kerfs deeper in center area. Kinda like tambour. When you flex it back to fit the pb makes up the loss of the wood and actually it'll be stronger when fill with pb.

 

[djrowe007]

No Title

Okay I got the piece of plywood cut every 1". Made the cut 3/4 the depth of the wood which I used 3/8" plywood. I am going to coat the transom with a layer or two of resin before sticking it on the peanut butter mix. What is the maximum thickness of peanut butter I should have in any one area? I know the stuff gets hot and can be brittle if it is too thick.

 

[kcassells]

Take a read on this. You may already but great info from the WOG. Woodonglass
Fabricating Decks, Stringers, and Transoms
Paint Your Boat with Tractor Paint...Say What!!!

 

[djrowe007]

No Title

So this is the way I decided to tackle bending the plywood...........

I cut kerfs in the plywood and by the way work much better on a bigger piece (the full transom cut) then my small test piece (2' x 2') that didn't seem to bend... obviously what was I thinking? Thanks for all the ideas, I posted my pictures of the clamps and how I drilled the bolts all in the same spot easily... Believe it or not having the right set of drill bits works so much better, even cutting oil on drill bits make a huge different in cooling the bit and allowing for an easier cut! Only broke one drill bit, didn't make that mistake again. For the clamps by the way I used a washer on the outside nut instead of epoxying the nut recessed into the 2x4, made more sense to me so I can later re-use hardware to maybe change the clamp size. Thanks to a bunch of you for helping me. Will update one last time on this thread when transom is completely glassed in.

​