Questions on Epoxy Resin & Transom Replacement

[Dave666]

I know some here wont agree, but I have decided to do my transom replacment using Expoy rather than polyester. However, I would appreciate any advice on the following questions;

1) How much resin should I buy? Its a bit cheaper for the larger amounts. My Stringers & floor are solid fiberglass, so its just the transom, reglass the rear floor and rear gunnell(doing from the inside), plus the usual filling, small modifications & repairs.

2) Which Expoy? - West System, Epiglass HT9000, and Bote Cote are the ones I am considering. Has anyone used Bote Cote? Sound good as it claims no amine blush & no sanding between coats, 2:1 mix ratio, no additives or extenders.

3) Which fiberglass cloth & layup method? As I will be pulling / skiing people behind the boat I want the transom to hull bond to be super strong.

Thanks in advance

[stevemid]

Epoxy is epoxy. All those are good brands. It is more important to follow the instructions for your choice.

I bonded my transom in with 6 layers of 450gsm DB tape. On the outside 100, 200, 300mm wide. On the inside 3 layers of the same but 300mm first, then 200 then 100. I would do it all in one go, that way you don't have to worry about sanding between coats, etc.

Do you know the technique? You're going to need to create rounded corners for the fibreglass to follow. On the outside corners, sand a nice smooth, 10 to 15mm radius. On the inside join, you have to create a cove with bog. Use something like a tounge depressor. I lay my glass right on the wet cove rather than letting it go off and sanding later.

Technique:
Measure the length of your transom join.
Cut all your strips at once.
I would recommend that you wet out one strip at a time on a sheet of heavy black plastic
Hint: one square meter of 450 gsm glass will need about 450grams of epoxy to wet out.
The glass needs to go transparent to be considered wetted out. I use a 100mm paint roller for this and just keep working the epoxy into the glass. Only mix enough epoxy for the glass you're wetting out. Mixed epoxy sitting in a container will go off in 15 minutes in winter. Once spread out, it'll take forever to go off.
If you are bonding to ply, you'll want to give the ply a good wet of epoxy first as the ply will suck the resin out of the glass.
Position your 1st strip evenly on the hull and the transom
Use an incorporating roller to " incorporate" the glass into the surface and make sure there are no air bubbles, no lifted glass, no 'white' spots.
Now wet out your next piece of glass and continue as above.
Once you've completed either the inside or the outside, you should apply a layer of peel ply to cover the join. Again roll this out till you get rid of all air bubbles.

Based on the above and the length of your join, you can calculate how much glass you'll need.
Buy at least as much epoxy (by weight) as glass, probably a bit more for wetting out the ply.

You Tube is the University of everything. Just google, your question and someone will have a video showing you how.

Have you done any test laminating? Probably a good idea.

PS you will need acetone for cleanup and rubber latex gloves. The Coles ones are good

Good luck
Steve

[Dave666]

Thanks Steve – I am ok with the basic details like coving on corners and wetting & rolling fibreglass, but its the detail relating to this particular job I am unsure about. You mention “outside” and “inside” join, but all my work is on the inside, as the outer fibreglass skin is still in place. I was going to take the following process;

Step 1 – Preparing & laminating the plywood.
Cut two sheets of marine ply to the exact side of the old ply, so about an inch gap around top & sides. Sand all over with 80grit to abrade the surface. Cover / soak both sheets in a product called Norseal Wood Treatment to soak in and seal the ply. Laminate the two ply sheets together with epoxy and one layer of Double Bias (DB) 420gsm. (correct??)

Step 2 – Glueing the ply into the boat transom
I read somewhere that Chopped Strand Mat (binderless so you can use it with epoxy) creates the strongest bond to existing surfaces and should be the first fiberglass layer when bonding new to old??

Based on this I was going to cover the inside of the existing fibreglass transom skin with epoxy , wet out one layer of CSM 600 onto the transom skin, cover one side of the laminated ply with epoxy, then place on a bed of bog (do coving) and clamp into place. (correct??)

Step 3 – Glassing the transom in
This is the part I am most unsure about – the layup technique for strength & appearance.
My thoughts - Bog the side gaps, coving the corners. Based on this theory that the first layer should be SCM (?) lay CSM 600 over the total inside transom and run the CSM 600 about 300mm up the hull (walls, floor, stringers). When laying the fiberglass joins should overlap by about 50mm? Repeat the process two more times with DB 450? Final layer peel ply.

Any advice / thoughts would be appreciated. Thanks
Dave

[Rip it up]

Hey Dave,

Just a few questions first.

What size is your boat?
What weight outboard are you putting on? Is it bigger than your builders plate?
Why is the transom being repaired?
Was the old fibreglass waterlogged?
Are you adding knee braces back down to you existing stringers.

Ok epoxy is a great choice. I use FGI in 20L kits. 5:1 pumps kits. Clean easy and always correct.
450 double bias is my cloth of choice.

West system have a glue powder on the market. 403? Can't remember the number. Or another good powder is cabosil. Both powders can be used to glue your ply laminated to existing glass. Don't be shy with the glue and squeeze the laminate using a series on well placed holes in you existing transom skin.

I would be trimming your ply to a neater. The closer you get it the better the transition of forces to the side skins. A solid lump of bog will crack.

Fire you questions away.

[Rip it up]

94949
One I did earlier. Using poly honeycomb core and epoxy. 94950

[Dave666]

Rip It Up - The boat is a late 70's Pride Montego - 19ft & very solid half cabin (same as the Caribbean Baron). Engine is Yamaha Salwater 2stroke 115hp. The boat is rated to 150hp. Yep, the wood inside the trasom is wet / soft & stuffed, from top to bottom. I hadnt considered adding knee braces, just trying to make sure my lay up technique & overall process is ok.

Are you suggesting I would need 20lt of resin for the transom & floor repair? Sounds like a lot.

My main questions are in my post above where I have broken the process into 3 steps. I would appreciate it if you could have a read and let me know if any parts dont sound right

Thanks
Dave

[Rip it up]

Ok. Dave.

Step one. Good idea with the soaking of the ply. Joining of the two ply sheets can be done with a single layer of double bias and epoxy. Heavy weights on a concrete floor will sandwich. Remember that timber soak up epoxy a little, so leave the fabric super wet. Suit up and use baby powder on you arms and hands, this will block the pores. Attack it and grind everything you need to in one sitting. Giving yourself plenty of overlap. Vacuum / wash down interior and leave to dry.

Step two. I would skip the CSM. Glueing to the old transom wall can be done with glue fibre mixed into epoxy bog. Squeeze out the excess. I use 90 x 45mm pine stud to clamp the transom / ply. Through the motor bolt pattern. Two timber studs with 2" square washers and 12mm threaded rod. Sometimes existing ski hooks can help get the corners into position as well. Use vasoline on the threaded rod to stop epoxy sticking to it. Cove to the walls, the larger your cove the less cracking issues. Sacrifice a 2" stainless paint scrapper and turn the end into a semi circle. Awesome coving tool. 4" double bias tape over the wet cove. Peel ply the tape join.

Step three. Lay up method. Two full layers overlapping the tape 50mm each time. One layer in between just bigger than the bolt pattern for extra thickness. This will help stop the washers and nuts from the motor cracking the laminate and sending water into the ply. Peel ply to finish. All three layers can be laid wet if you have a helper to mix resin.


Tips.
You should have resin left if you use a 5L kit.
Depends on how good you are with wastage.
Work in the cool of the night in a shed if possible.
Have all you materials on hand.
Double glove and use blue nitriles, they last longer than latex.
Use a small squeegee (like a credit card size) to push air bubbles outof double bias.
4" microfibres mini rollers also spread resin well.
Work as clean as you can.
Scrape up any excess bog mix when wet.
Peel ply everything you can. It means less grinding.
Peel ply can be bought from spotlight/lincraft as an ugly colour "rayon" poly jacket lining material. Sometimes I get it for $1/m.
A wire buff wheel on a 4" grinder will clean your scrapers of hard resin/bog.
Flowcoat can be laid successfully over fgi epoxy when using peel ply, as the amine blush stays on the peel.
94966
Another polycore transom with flowcoat finish.
94967
Recently sprayed the hull.

Enjoy it. Very rewarding when complete.

[Dave666]

Thanks Rip It Up – great post with lots of great tips, I really appreciate it. Can I clarify some of your points (these will sound like stupid questions)

Step 1 – All clear. After I seal & laminate together, do you think I should be covering the total ply in epox (& lay fiberglass??) before I glue into place? Just not sure if a sealer is enough (on the inside) before I glue onto the transom skin?

Step 2 – When you say - “glue fiber” mixed into a bog - are you talking about a high strength filler powder (the one with glass fibers in it)? Also, not sure what you mean by “4” Db over the wet cove” – does this lay vertically just over the cove, joining strips by 50mm, or lay the strips horizontal, in which case how far onto the transom and hull do you go?

Step – 3 – So no CSM just layers of DB450? Two full layers and an extra layer just bigger than the motor bolt pattern - correct? You say overlap the “tape” by 50mm – Dont you use large pieces of cloth rather than strips of tape? Should both layers of DB450 run up the hull/stringers/floor by 300mm?
Thanks again
PS – your project looks great, what paint are you spraying?

[odes20]

Just saw your thread. I have rebuilt 2 transforms on 20ft Yalta s that now have 175 Suzy 4 strokes hangin on them for 4 years now . Not a crack anywhere, and we did them from the outside!. And before I get shouted down for that , I can tell you that even this method is strong as if done properly. We also raised the transom height from the old 20 inch transom to 25 inch to cater for the taller motor. Used Epiglass ht 9000. Seeing you are doin it from the inside you are doin it the easiest way. Apart from all the fine print offered on method , I can say Epoxy is super strong, and the fundamental issue is to completely enclose your new laminated ply timbers. A lot of boats were never fully sealed on the top of the transom . No wonder water gets in . So trust the strength of epoxy , fully overlay all timbers , and only epoxy to ground back to fiberglass internal boat surfaces. ( Remove sand off old gel coat/ flow coat at least 100 mm back from your new work
By the way, you don't need to make or use a lot of bog. Maybe a bit just bed the transom bottom edge when setting it in. You don't need it on internal corners . That's a waste of time and materials. The epoxy will hold all internal corner matting no probs. no need of knees either ! Waste of time . Just do it as it was originally ,no dramas. It will be stronger than the original seeing its epoxy
Cheers!

[Dave666]

Thanks Odes20 - While I am asking questions about Epoxy & layup technique, I am currently at the the stage of digging the old timber transom out.

It was interesting taking the floor out. I have a copy of the original 1970's brochure for this boat and it claims (exact wording) "fully intergated fiberglass floor liner which incorporates a fiberglass stringer system and completely eliminating timber in the underfloor area". Even in my recent phone calls to Carribean they say the same thing.

Well as you can see in the photos below, the floor has a thin piece of timber plywood and two timber dowels that have been encased in fiberglass for strength. Hmmm - thankfully the wood in mine is all dry. The stringers while fiberglass, seem very light to me, perhaps its the triangle shape that give it strength (engineering??).

I have kept the cut out floor mold for its shape - but not sure how I will put it back in. Worry about that later, transom first.

[stevemid]

Dave666
I see what you're doing now. Odes20 and Ripitup experience is more relevant to your job than mine is so I'll leave it to them as they're giving you good advice.

WRT the dowels, they were probably not there to give strength but to give the "U" shape to the fibreglass which is what really gives the anti-flexing reinforcement. I'm not so sure about the ply in the floor though because that looks like a composite construction technique (the ply being the "core") and I assume that if the ply gets wet, the strength of the structure will be hurt. That means you have to be careful driving screws into it as the water will follow the screw down and eventually saturate the core. With composite construction you drill out an over-size hole, fill it with cabosi bog let it go off then seat the screw in the centre of the bog so the water has no where to go.

Good luck with the project, it's lookin' good.
Steve