'72 Hydrofoil Tridyne 22' transom and sole rebuild

[tripp2727]

so basically what you are saying is that i want to cut it, grind it, feather an edge, and relaminate it with thickened epoxy of course?? ok just making sure thats what you said.

[Steven]

By laminate, I mean lay new glass. Build the thicksness to what it was. Overlay from the ground bevel up covering the delaminated section.

[tripp2727]

Ok cool thanks i am hopefully going to be able to get my cradle built tomorrow and get the boat moved into my garage this weekend to begin the rebuilding process. I have to grind a few more places while its outside before i move it in but its coming along slowly but surely. Like my mom always says "how do you eat an elephant? one bite at a time."

[tripp2727]

Its been a few weeks since ive made any progress. Thanksgiving week I got my cradle built and the boat moved into my garage. It was a rather interesting process unloading the boat onto the cradle by my self. I used the push, pull, squat, deadlift, and bench press method to get the boat on that cradle. I wish I had it on video cuz it would be worth a good laugh.



Got my plywood and cut out my transom pieces. I am using 3 sheets of 3/4 marine fir from my local lumber yard for a total core thickness of 2.25". May be overkill but i would rather have it an not need it than need it an not have it.



I have a few questions about transom fitment...

1. There is a 2" gap between the outside skin and the transom core where the transom bows out a little. I know that when I mount the core I will carriage bolt the core to the skin but this seems like a big gap and i do not want to damage or crack the outside skin trying to force things especially since the liner was removed and the outside skin is rather thin now.

2. Would you recommend gluing in each piece of wood separately or laminating all three and dropping it in as one giant chunk? Im not worried about how heavy it will be but I want to make sure that the wood flexes and forms to the outside skin properly if possible.

3. Does the arch at the top of my transom core look too steep? I originally made the center of the arch 6" higher than the sides and that was way too much so i reduced it to 4". Im still not sure if it is too high.

Shine what arch measurements (rise/run) did you use on the aquasport? I like the look and curvature of that transom.

[gw204]

You're going to have to put those core pieces in one at a time. Now way 2.25" of ply are going to make that bend. You may even have to make some relief cuts to get the single sheets to conform.

The transom arch is a matter of personal preference. Do you what you think looks good. On my Mako 17, I think I did a hair less than 2" so it would match the aft section of cap.

[tech_support]

You will need to kerf the back side of the first layer of core before gluing it into the hull.

[tripp2727]

Ok that helps a lot. gw204 i like your transom arch so i think im going to bring mine down a little. I like some arch but not too much. I still want to be able to sit back there comfortably without feeling like im on a water slide.

Now more questions...

1. How deep should the kerf cuts be?
2. How far apart should kerf cuts be?
3. Do all sections need kerfs to mold to the curvature of the outside transom skin?
4. What is the lamination schedule for one sheet at a time? Do I have to wait for the previous layer to cure?

Also regarding epoxy is there a table or chart that lists how much raw epoxy in oz. is needed to cover "X" sq/ft of plywood. or how much glue it takes to sufficiently cover "X" sq/ft of plywood etc...?

Since I am new at this I dont want to waste epoxy by mixing too much but on the other hand I dont want to make too little and waste time having to make another batch while my first batch is kicking off.

[Cracker Larry]

Are you sure the transom is supposed to have a convex arc? I've replaced a few and when you cut out the core, the skin tends to sag and form an arc, when it was straight initially. I would put a 2X4 across it on the outside and attach each end to a come-along connected forward to the trailer or cradle. Then try to pull that transom skin flat. That's how I do it, anyway. Not many outboard boats are made with a curved transom.

I would almost bet that the manufacturer did not kerf the core when the boat was made.

Also regarding epoxy is there a table or chart that lists how much raw epoxy in oz. is needed to cover "X" sq/ft of plywood. or how much glue it takes to sufficiently cover "X" sq/ft of plywood etc...?

I've never seen any charts, but for a lamination that size I would guess about 16 ounces. The way I would do it is to mix a batch of glue with 12 ounces of epoxy. It won't be enough, but it will tell you how much more you need to cover it. After you mix the glue dump it all out on the transom and spread it with a notched spreader. Once it's spread out, you have plenty of working time in these temperatures to mix the additional amount needed and spread it.

[tripp2727]

Are you sure the transom is supposed to have a convex arc?

No im not sure and after looking at some pics i think you may be correct.

What do you think from looking at these pics?


not a great angle but it looks pretty straight to me. It also had a metal cap that was straight across not curved.


Ill try the 2x4 and come along trick and see what i can do. thanks for the advice.

[Cracker Larry]

Yes, that transom was straight. The curve is induced by removing the internal support. It's a sag, not a hull curve. You should be able to easily pull it straight again. Don't laminate it up with that curve in it.