Transom rebuild question - Avon searider SR5.4

Repairing deficits in the skin ought to be done before ply. Any space issues these cause can be hogged out of the ply and epoxy putty with cabosil will take up the small margins you make in the ply.

okay?

 

Hi @fallguy thank you VERY much, and thank you for taking the time to make a drawing, MUCH appreciated! LEGEND!! A lot of information, I have one more question:

Do I understand correctly that you recommend to first tab the skin to the deck/hull before inserting new ply? I was thinking the previous days something similar, as I don't like the glass layers in the connection, to install the first layer of ply, then tab as you describe (transom/sole) and then add a 2nd layer of ply and tab again. The idea is that I plan to use few layers of glass between the 2 layers of plywood - as the original construction had, and the first layer of ply was connected to the deck/hull originally. Thank you for the recommendation, I'll follow it.

Yes, I will cut off further the skin of the transom that will expose completely the crack and as you say first address the crack. I also contacted westsystems that they where kind enough to provide a bit of guidance on the repair in the same line of thought as you described on how to address the crack.

I've just cut off the pattern for the whole transom, and I want to see how I can best fit it. It seems that this is not possible without cutting further the transom skin, in particular the green area here which will expose almost all of the crack. It pretty much looks like it ends where the green border ends (bottom right):



This is because the ply goes deep into the sides of the boat, as in here which is the widest point (alternatively I'll need to cut further close to the green arrow to slide in the plywood):



I am thinking it is preferable (?) to cut the green area above (both sides) and rebuild this part with the ply as a form of a mold, than trying to glue the new ply underneath that part (as there will be gaps/errors that I will need to fill with thickened epoxy). I don't know if this is optimal, but so far is the best solution I can think of (my ignorance is a bliss). I've seen one repair like that on the same boat, which gives me a bit of confidence, but then again, first timer...

Thank you again for the comment on addressing the skin issues before putting the ply in!! My plan is to cut the ply this weekend so I can figure out how to best insert it and see if i need indeed to cut more. Then start experimenting with laying fibreglass of different types in demo constructions (corners similar to the transom/deck connections etc) and understand how many layers of which type i need to get the appropriate thickness etc. Weekend approaching, and I'll work on it again .

Thank you!!

 

You did not answer my query.

Does the crack extend further than the edge and toward midships?

 

The way to address the repair changes depending upon the extent of the crack. I can’t quite tell what is going on next to the hole or along the blue line I drew. If you apply torque to the transom top how much opens?

 

Thank you again! The crack is constrained to where the green polygon is, and is apparent only from the exterior side where the tubes attach. There is no crack in the connection of the transom skin to the deck/sole of the boat. Only what I grinded down. The ply was coming very low to the deck before I grind down, this is what it looked at a previous stage of the rebuild. I had to clean the rotten ply where the green arrows are. The ply was stopping approximately around the red circle and there was only fibreglass (or fibreglass and thickened epoxy, as it has weird shape in some parts) around the drain hole. The ply was more rotten to the port side (where the crack is) and I assume this is because the crack was allowing water to get in from that side. The crack is basically on the exterior of the hull where the tube is attached, i haven't seen it anywhere in the interior.




There is a small flex when I push back but it doesn't open further than the last, it cannot be seen from the interior on the solid fibreglass part (hull). It for sure doesn't transfer further to the transom everywhere I digged in. I am fairly confident it is not major structural problem.






Some more pictures where the non wet glass can be seen.





Again MANY thanks!!

 

Grind a taper into the crack. The crack thickness to zero. I’d go about an inch or whatever you can. For 3mm, 3 pieces of 1708. Place them into epoxy putty made with cabosil, then each piece is bigger.

Then, if you have access to the other side; add some more glass.

Then, once you add the plywood, tab it to the sole, biggest pieces first.

Plywood needs to be precoated with epoxy to prevent it from sucking resin from fillers.

I prefer to use 1/16” to 2mm vee trowel on both sides of the bond for flat surfaces. You need a way to get the plywood tight. Usually, the best way is to make some bolt holes and repair them.

 

Thank you, just to verify: it is my understanding that since the crack does not extend to the connection of transom skin with deck, you do not suggest to tab there BEFORE inserting the plywood, correct? Many thanks

 

Correct. But fix the crack first. Just no reason to tab the skin. I was confused about the extent of the crack.

 

Some progress (weekend jobs), after a loooooooooooooooot of grinding down (and some fibreglass experiments), i finally did my first repair. Starting from attending the cracks on the external transom skin as @fallguy suggested (thank you!).







Once all repairs are in, then it's turn for glueing the plywood (two layers), the first piece is cut:



So far I've used 600 g/m^2 quadraxial fabric and it's been relatively easy to wet out with westsystem epoxy (or at least easier than I thought it would be), so I'll probably stick with that for the rest of the repairs. I still have one more experiment to finalize behaviour on corners (with filleting) in comparison with 400g/m^2 double bias (+/- 45 degrees) before the transom glueing. Despite mistakes I've done (and learned heaps from), I believe I have positive net result, so quite happy.

By the way, the crack I was worried about, was not an issue, as I had to clean that area to fit in the ply either way:



Cheers and again thank you for your help. I'll post updates as this goes on and ask more questions.

 

Those patches look excellent.

 

PIt should be noted those cracks were caused by stress and some structural deficiency.

When you repair the transom; if possible, best practice would be to radius the top edges and overlap the fiberglass from the inside over the outside and in. This is, of course, tricky at the inside corners. What is normally done is avoiding sharp corners or adding them back at the end. So those sharp inside bend are rounded with putty as well as is the back top of transom. So you first add putty to the top inside corner, then you radius it to allow glass to roll over. If at the end, you want a square transom; it is done with fairing fillers. If my remarks are not clear; let me know.

 

Not sure if these pics show a round transom top edge or not, but this has a 3/8” radius on each side of a 1.5” transom.. and this has 8 layers of db1700..

If you don’t glass the top of a ply transom; it WILL split open. This one is a hd foam core..

 

Thank you for the pointers and additional insight! By the way your work is professional level (!!!).

Yes, I agree with you that the cracks where a result of structural deficiency (some previous owner), the ply was completely rotten and I assume that was the reason, and - from digging into it - I don't think it was ever replaced in the past. So probably that was the cause, and then they added the metal plate cover (which was acting as "the transom", nothing else was even remotely solid).

Yes, it is my plan to add round corners and wrap as you describe, but I plan to do so after I will install the 2nd layer of ply. My plan is to add 1-2 layers of fibreglass internally to the skin, then ply, then 5 layers of fibreglass (equivalent to 4mm thickness in total), then 2nd ply, then another 5 layers with the wrap you mention (here I round the corners of both ply layers). Externally to the skin I will add one layer of structural integrity and, after fairing, one last layer of thin (4oz) woven cloth. The woven is to give, after fairing (if I've done my homework correct, I'll revisit this part as it is not my immediate concern), to give a better look, before painting (I'll use paint instead of gelcoat).

Again, than you very much for your pointers, you are of great help.

 

If you don’t glass the top of a ply transom; it WILL split open.

Yes!! I haven't thought this might be the case, but I was planning to wrap around, thank you for that!!!! Just noticed it!!

 

Dear All,

reporting some more progress. I've added the first layer of plywood (18mm) + 5 layers of 600gr/m^2 quadraxial (4mm thickness), and I am now ready to put the 2nd layer of plywood one and complete the transom with internal fibreglass + tabbing, and external fibreglass. The whole transom thickness will be (most probably be) ~50mm+***. There will be wrap around the top of the transom with fibreglass once I add the internal and external fibreglass layers.



the top left white thing is sunlight hitting the transom. Note there is no real "tabbing" at the moment, as this is just the first layer of ply. I am trying to follow the structure of the boat that existed from the factory, where it seems there where two layers of glass (one between two ply sheets, that was ending joining with the hull and a second skin (internal) that was tabbed to the hull.

this is the 2nd plywood layer that will be glassed in with proper tabbing, hopefully, very soon.



I don't think I'll change the transom thickness to more than ~50mm ( ~8mm skin(external in total, what it had plus 4 more layers of quadraxial) + 18mm ply + quadraxial (4mm) + 18mm ply + 5mm quadraxial (internal) skin ~= 53mm). The original one was 40mm thickness and could support up to 340LBS of weight for max hp90 (2T). I am adding a small reinforcement as if I need to replace outboard in the future, it will be 4 stroke and they are a tad heavier for the same horse power. I am currently reviewing the book elements of boat strength to understand more about the scantling number (and thus, transom thickness) although from what I am reading by searching online 50mm thick is about OK for up to 200HP (which I won't go either way, max to add 115hp in the future which is what Avon did in some of these boats).


Thank you very much all for your help, and as always, if you have any comments / suggestions, please share your thoughts.
Regards