Avanti Transom Repair and More

[crasea]

First I'd like to say this is a great site. The FAQs and how-tos and some of the projects here have been really helpful.
I started on the replacement of the transom in my 1983 17' Avanti fish-n-ski boat shown below.



Here's before I started cutting.
http://gallery.bateau2.com/albums/userp ... rmal_3.jpg

After I got into it, you could hear alot of "oh great" and "aw ****" as I found more problems. I'm sure this is no surprize to most of you.
I now have the old transom cut out from the inside.

I'll go into the stringers and sole later, but I first want to ask some questions about the transom.
I'm planning to use 3/4" marine plywood (double) for the construction. Each piece will be double coated with thin epoxy.

So the first questions: The epoxy resin will be thinned with acetone and the hardener will then be added to match the pre thinned resin volume?

After coating, the 2 pieces will be bonded together. I have read a couple different ways on this. I believe I should use a peanut butter consistency resin wood flour mix applied with a notched trowel (what size?) and then clamped or screwed together lightly. My old transom had glass between the sheets. Is this necessary? Recommended? If so, that raises more questions for a beginner. There's cloth, mat, woven, roven etc and I'm not sure what to use where. I have read about the biaxials and believe the theory about them being better. So, If recommended, what would I use between the plywood? And another silly question: When I see something like 15oz cloth, is that the weight of a square foot of it?

So after the core is ready I will apply a bed or layer of epoxy putty for the transom to sit on top of. Also a trowled layer of epoxy putty? will be applied to the aft side of the core with no glass and pressed against the outside skin. This will be held against the skin with screws from the outside and/or 2X6s on the inside. If using screws through existing holes what do you think the maximum distance could be between them?
I'm going to read a little more before moving on to the inside skin, I think I've asked too many questions anyway.
Any answers to my questions or corrections to the above will be appreciated.

Craig

[tech_support]

Welcome to the forum. You did a very good grinding job

So the first questions: The epoxy resin will be thinned with acetone and the hardener will then be added to match the pre-thinned resin volume?

DO NOT THIN THE EPOXY when you are gluing structural pieces - it will weaken the bond. All our epoxies are plenty thin to begin with.

You DO want to pre-coat the wood parts before putting on the epoxy glue (thickened epoxy). the wood will soak a little epoxy up, but not very much.

Just the little notched spreader is all we use (I use the wide gaps)

Use epoxy and biax (no matt) for the inside skin. Matt is not needed with epoxy and it only soaks up (wastes) resin. For the outside skin mat does serve a purpose (no build up cheap bulk for puncture resistance)

For bedding the core to the outside skin. Check out what we did on the aquasport transom...

http://forums.bateau2.com/viewtopic.php?t=11294

you will do the same thing with your plywood core.

You can space out your bolts a little more because your plywood core will not bend like our foam core did. I would say a bolt every 12" would allow for even pressure. NOTE: do not tighten then bolt too much, you want that epoxy to stay in there and fill the gaps. Its good idea to use too much glue and tighten the bolts until it begins to squeeze out evenly all around

Joel

[crasea]

Thanks Joel,
I'd hate to screw this up after the invested work.

One thing I missed is whether any glass goes between the 2 plywood sheets, or just glue?

Then it's on to materials. Looks like the MarinEpoxy is a little more economical. Everything original on my boat had an amber or orange hue, looking kind of like the system 3 epoxy. I know not to use polyester on epoxy, but are there ever bonding problems between epoxies, provided the area is properly prepped?
Normally, would a gallon of resin with 1/2 gal of hardner be enough to glue, bed and cover the transom?
For the fiberglass, and just considering doing the transom, this will all be done with biaxial cloth?
So I will need the square area of the transom times 1? 2 layers?
For putty for the fillets and the glue, these are both made by adding wood flour to the resin?
I'm guessing more is added for the putty than the glue. Is hardener added after the desired consistency is reached?
Again, sorry for so many questions, and my thanks for the help.

Craig

[tech_support]

One thing I missed is whether any glass goes between the 2 plywood sheets, or just glue?

No need for glass between, just epoxy glue

Everything original on my boat had an amber or orange hue, looking kind of like the system 3 epoxy.

That is the polyester

I know not to use polyester on epoxy, but are there ever bonding problems between epoxies, provided the area is properly prepped?

An epoxy over polyester bond is much stronger than a polyester over polyester. its called a secondary bond (mechanical bond) any time you put new resin over cured resin.

Normally, would a gallon of resin with 1/2 gal of hardner be enough to glue, bed and cover the transom?

1.5 gallon of epoxy will make a lot of glue, should be more than enought o bed the transom in

For the fiberglass, and just considering doing the transom, this will all be done with biaxial cloth?

tape and cloth, i will confer with Jacques and email to you a lamination schedule for the trransom

So I will need the square area of the transom times 1? 2 layers?

see above

For putty for the fillets and the glue, these are both made by adding wood flour to the resin?

yes, you should get at least 5 pounds

I'm guessing more is added for the putty than the glue. Is hardener added after the desired consistency is reached?

With epoxy, you do not mess with the mix ratio:D More hardener will actually keep the epoxy from curing correctly

Again, sorry for so many questions, and my thanks for the help.

Craig[/quote]

[crasea]

Thanks alot Joel,
You're a great help. I do need to clarify one question though. When making putty I didn't mean extra hardener, just when to add the hardener. I'm thinking of time here. If I add the hardener and then start mixing in the flour and then adding a little more to get it right and so on, I'm afraid I'll be standing there holding a rock. So I was picturing adding the flour to the unactivated resin first, and then adding the hardener. Never made this stuff before.

[UncleRalph]

You mix the resin and hardener completely and then add fillers.

Ralph

[crasea]

Thanks Ralph,
I'll have to keep a little extra material on hand in case I'm too slow.

[jacquesmm]

You'll get a lamination schedule by tomorrow. I did send a few choices to Joel and he will check what makes economical sense: standardize fabric type etc.

[crasea]

Great! Thanks!

[Digger873]

Mixing a lot of glue with wood flour by hand can really be a pain.
I started mixing by hand and when I did the transom I needed a second person to mix for me. It isnt always practical to have a second person for me so I went to wally world and bought this..

2.49 and makes mixing very fast and more consistant between mixes, and you can mix fast enough not to need a second person
I am no expert but it worked very well for me, working by myself.