1981 Grady White 240 Offshore - Transom Replacement

[scubapk01]

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Transom Thickness Question

I need a bit of advise this morning as I am about to order the plywood.
As per the last few posts, the center section of the transom is thick fiberglass. I cut into it in several placed to confirm. So I either side I need a good 1/4in (maybe 1/2in) thick piece of plywood to make it flat across the back.

Should I then go with -
3 x 3/4in Plywood + 1/4in (as listed above) for a total of 2 1/2in thick
or
2 x 3/4in + 1/2in plywood + 1/4in (as listed above) for a total of 2 1/4in thick

Secondly if I have to cut each piece in 2 in order to get it to fit inside the boat where should those cuts be?

[jacquesmm]

Let's make it clear, the green layer is solid fiberglass 1/2" thick.
In that case, either combination is good. In each case, you have 4 layers to bond and the final core thickness is within 1/4".
The core thickness of 2-1/4" is more than sufficient. You will add fiberglass and epoxy glue layers and it will get close to 2-3/4".
I would go for the 2-1/4" combination.

[scubapk01]

Let's make it clear, the green layer is solid fiberglass 1/2" thick.
In that case, either combination is good. In each case, you have 4 layers to bond and the final core thickness is within 1/4".
The core thickness of 2-1/4" is more than sufficient. You will add fiberglass and epoxy glue layers and it will get close to 2-3/4".
I would go for the 2-1/4" combination.

Yes the green is the existing solid fiberglass. - See below

So I will first of all add a layer or fiber glass to the port side where the existing fiberglass is very thin. (to match starboard side)
1st layer will be 1/2in plywood either side of the center fiberglass section (Image below).
2nd layer 3/4in
3rd layer 3/4in
4th layer 1/2in
then fiberglass

The 1st leveling layer (with the existing center solid fiberglass section) has 2 joins and not as strong as the other layers.



It I cannot get layers 2,3 and 4 in place in one piece where should I cut them?
So using the grid overlay as listed below where should I cut?
Example
Layer 2 - A3 to G3
Layer 3 - A14 to G14 (oppoiste to Layer 2)
Layer 4 - A7 to G11 (sort of in the middle)

Just guessing here
Will wait for your advice

[jacquesmm]

But why would it not fit in one piece? The transom is less than 8' wide. One sheet of plywood will cover it all.
Is It higher than 48"? In that case, add a small piece at the bottom, offset the seam for the next layer by 12" upwards and third layer like the 1st one.
The part to which we bolt the motor or the bracket is the one under the most stress = upper part.
Now, epoxy glued plywood never breaks at the epoxy seam, it breaks in the plywood.
What we are looking for here is max. stiffness at the clamp level.

[gw204]

I think he means he can't get the core pieces in in one piece because the remaining sections of the cap and liner prevent it.

If you were to cut the last few inches of the cap off you could slide your core in from the top. That being said, if you run the core all the way up without sectioning in you'll have those little sections where it juts out to contend with. But based on the size of the red core diagram you have already taken that into consideration and planned a break there.

IMO, you should grind that center section down so it's flush with the rest and build up the one side so you have uniform thickness. Then put another layer or two down across the entire thing followed by your core pieces and inner skin. Don't forget to increase the height to 30" and build in some splash guards.

[jacquesmm]

Thank you gw204.
If the cap is the problem and you must make it in 2 pieces, I prefer to have the seam well below the clamping area.

And I agree about grinding the whole thing flush. It will be much easier to work that way, use less epoxy and you will eliminate the risk of voids.

[scubapk01]

Thank you gw204.
If the cap is the problem and you must make it in 2 pieces, I prefer to have the seam well below the clamping area.

And I agree about grinding the whole thing flush. It will be much easier to work that way, use less epoxy and you will eliminate the risk of voids.

Thank both for thoughts.
Not what I wanted to hear about grinding the center section flat, but I do agree as the best way to avoid voids.
Some more fun with grinder this weekend.

Not sure if I can install in 1 piece or not yet. I will make a template and try. Do not like the idea of cutting and removing the top cap (yet)
Thank you both again for great advice

[jacquesmm]

I forgot that you kept the cap on. We have a good number of Grady Whites transom replacements on this site!
because of the flare of the sides, the transom is wider at the top and it is almost impossible to push a new core in straight.
Try what you propose with cardboard template, you may be able to wiggle it in.

[scubapk01]

I forgot that you kept the cap on. We have a good number of Grady Whites transom replacements on this site!
because of the flare of the sides, the transom is wider at the top and it is almost impossible to push a new core in straight.
Try what you propose with cardboard template, you may be able to wiggle it in.

The good news if there is any is that the plywood for the transom does not go all the way to the top in this model.
1/2 way up the angle changes. See below



You can see the difference in angle on the upper parts of transom either side in the below pic.

[jacquesmm]

I looked at your pictures again and maybe we can handle that differently.
You will have 3 layers.
Look at your picture with the transom surface in red.
The first layer will be in 3 pieces, cut horizontally at the level of the motor clamp, at the line marked C.
The second layer is cut vertically in the middle, two pieces.
The third layer is the same than the first.
This would allow you to install everything with the cap on.
Two remarks:
No splices around that piece in the middle, grind it down please. One vertical splice is enough.
If you go for 3 layers, two 3/4" and one 1/2", put the thinnest one in the middle.

The grinding of the middle will take some time but the work that follows will be cleaner and stronger. And you don't have to remove the cap.