1978 Tri-hull transom rebuild - have question about mixing fillers to lay in the core

[ELoller]

Hello,

I have been pouring over this forum and others to get the info I need to finish my transom rebuild. I am having trouble finding answers to the questions I have.

I am trying to lay in my transom core. As you can see in the pics I decided to go in from the back of the boat. Seeing as how I need to repair some thin spots on the rear edge of the hull, I figured I could repair and strengthen the outer edges when I glass my outer skin back in. Cutting the cap would alot more work to do in my opinion.

Here is the problem I am having. I am using milled glass and cabosil as fillers for my butter. A family friend that has much more experience with fiberglass than I told me to use 1% hardener to resin mixture. So 500 ml of resin would be 5ml of hardener for a 30 minute working time. I seem to be having different results with how quickly the butter kicks off and hardens.

Here is how I planned to lay in my core.

- make enough butter to slather in around the remaining bottom lip of the hull. So i would essentially have enough that would fill in any possible hollow areas and really hold in the wooden core in place. My core is pretty tight and needs to be tapped in lightly with a rubber mallet to fit in the groove. I want to build up enough butter to seal it all in
- also intended to trowel butter on both surfaces of the transom parts to be stuck together. Using a v notch 1/4 x 3/16 trowel to trowel on the butter.

I tried tonight to execute the above plan. I mixed 500 ml of resin with 5ml of hardener. I only got about 15 min of working time and I barely got any butter in the lip and troweled on before it hardened on me. I want to build up about a 1/4 inch of butter all around the outer lip. I had a friend troweling and I was filling the lip.

Does thicker butter cure faster?
What ratio of hardener to resin do you recommend for my application?
What ratio of cabosil/milled glass to resin should I use for a good non sagging mixture that will give me maximum working time and still cure hard?
Am I overdoing the butter in the lip or not enough?

Im afraid to not put in enough hardener in the butter and my transom not cure. I have not put in enough hardener before on smaller repairs and had to start over. I figure I only have one shot to lay in this transom and if it cures too fast Im gonna have a big problem and if it doesnt cure at all then I have a problem.

Any thoughts at all would be a big help.

Thanks!

 

[ELoller]

Pics

 

[glenn property of pam]

what is your day time and night time temp where you are working.

 

[jigngrub]

Maybe try fooling your material into thinking it's cooler outside. Put your material in the house or a cool spot over night and start work in the early morning hours.

I'd sand most if not all of that cured resin off your transom wood, you only want to resin the wood when you're going to start installing it or laying glass on it for a much better bond than trying to work on top of cured resin.

 

[Woodonglass]

As GPP says, Temps and humidity play a big part in "Kick" time. Sitting your resin in a tray of ice can help fool it into thinking it's not so hot outside. Your mix and technique sounds right to me. You may need to incorporate the aide of a helper to enable you to speed up the process. My mix ration is 500 ml of resin 750 ml of cabosil and 40 ml 1/4" milled fibers 5 ml MEKP. I'd mix up 3 batches WITHOUT the MEKP and have them sitting ON ICE ready to go. I'd have three 5 ml batches of MEKP ready to go too. I'd have my clamps and everything else all layed out and a couple of Dry Runs under my belt to ensure I KNEW who everything was going to go. Then I'd dump the MEKP in the first batch and start troweling and when I was almost done tell my helper to start mixing the next batch so it would be ready when I was done troweling the first. No hesitations or delays. If you do that, you should be able to get the transom buttered and installed in 15 minutes. You could drop it to .75 MEKP but I would NOT go any lower. Stick with it. You'll get it done.

 

[jbcurt00]

If you mix a quart volume in a gallon container, it won't kick as fast as a quart mixed in a quart container. It's all about catalytic heat, once it starts to kick in a large volume it will start to kick FAST. To much heat can make the resin brittle as well.

Getting it out of the bucket (a large volume) and onto the work surface (in smaller volumes) is a priority, getting it troweled smooth is 2nd.

AND practice installing the transom. Several time, esp with the clamping system your using to keep the plywood transom firmly where you want it while the resin cures.

 

[ELoller]

In the daytime it is about 95 - 99 deg Farenheit. Nightime is about 75 - 80. Im in the Dallas TX area.

I like the ice bath technique to trick the resin into thinking it is colder... I was also told to put the uncatalysed resin into the fridge to cool it off before using it.

Jigngrub - I thought I was told to "seal" my transom core with coats of resin before inserting and laying it up. Was I misinformed?

Thanks for all of the suggestions. I am going to give it another shot tonight.

 

[jbcurt00]

You only got part of the resin layup right. You only need to wet the wood out w/ resin, and let it tack over, NOT completely cure. This is solely to prevent the dry plywood from wicking resin away from the layup surface & starving the connection between the CSM/1708 you are applying the resin to and the underlying plywood.

As a waterproofing measure, we suggest applying a layer of CSM to the transom plywood before you install it, as well.

So you've got the fiberglass transom skin prepped, the plywood transom cut & prepped.

• Wet out 1 side & all the edges of the plywood transom. When it tacks over (normally 10-15min) apply fresh resin, apply the CSM and make sure it is fully wetted out.
• Once cured, re-prep the edges & flip the plywood over. Apply resin to wet out the ply, on the UNCOATED side only, then in 10-15min, re-apply resin to the flat side & all the edges , lay on the CSM and make sure it's fully wetted out.

Your transom is now sealed, and the edges were wrapped twice.

Once cured you're ready to install the plywood transom onto the prepped transom skin.

Revisit this link:

Fabricating Decks, Stringers, and Transoms

 

[ELoller]

Sounds like I have a lot of sanding to do because I don't think my core will fit after adding the csm. So this is a must do, to seal my transom core? No other options using poly resin, without csm? man I really misunderstood some comments in other threads.

 

[ELoller]

Do I need to use csm on the inner skin when installing the transom as well. Now I feel all confused about whether I should use csm or 1708 between the inner and outer skins? I was under the impression I could sorta (glue) in the core with good flat surface prep and troweling resin on mating surfaces. Almost like laying in and grouting in a huge piece of tile. Then doing the same (after the core has cured) to the outer skin. I'll leave my outer hull finishing questions for later... Lol

 

[jbcurt00]

I suspect you did miss a good bit since you cut the back outta the boat. It's much better to work from the inside............

You want the plywood well sealed against water intrusion. This is a BIG job, you don't want to do it again. And its the interface between the OB & the boat, so you want it to be substantial & strong.

It will be much more difficult to give you good advice as you have done it drastically different then most. You won't be getting PB squeeze out around all the edges & using that squeeze out to make fillets.

 

[jigngrub]

Sounds like I have a lot of sanding to do because I don't think my core will fit after adding the csm. So this is a must do, to seal my transom core? No other options using poly resin, without csm? man I really misunderstood some comments in other threads.

You don't have to wrap your transom in CSM if your going to completely encapsulate it after it's installed, and if you're going to have to sand it down a lot to get it to fit I wouldn't bother.

That's the one of the problems with going in though the outside of the transom, you don't have any room to play with, had you gone in from the inside your thickness wouldn't have mattered quite as much. You would still need to be pretty close, but would have a little more room to play with.

I would sand off all the cured resin on the wood, apply new resin just before installation to the PB face, sides, and bottom. Let tack, apply the PB and install. Clamp the wood securely and let cure.

When you layup the outside, apply resin to the bare wood again and let tack... then do your outside layups. How do you plan to layup the outside?

 

[ELoller]

I don't think my application would've been easier to go from the inside because of getting into the stringers and they're not rotted. I plan to glue the outer skin on by troweling resin on bare wood and the skin and then clamping. I then plan to step grind the cut I made to a 1:12 ratio and use 1708 to build back up. I appreciate all your advice, polite and harsh. Got some salty dogs on here!

 

[ELoller]

Sorry it won't make paragraphs on my phone and I'm out here sanding!

 

[Woodonglass]

Eloller, Here's what my experience and research tells me. Since you're going at this Bass Ackwards, you need to have a bit of extra room to allow for a bit more PB between the transom core and the inner skin of the boat. This transition must absolutely be totally structurally sound and secure.with a thick coating of PB and ample squeeze out around ALL edges. This means the transom should actually be about 3/8" shy around all edges and a bit thin prolly more like 1 1/4" to allow for thick lay up of PB and the new Outer skin. Don't need any CSM on the wood Just coat it with Resin and when it tacks up it's ready to install. Your inner skin seals it on the inside and you'll be doing plenty of layups on the outside to seal it. This is what it should look like when looking down from the top side. the Blue is the Glass Skin of the boat, Yellow is the PB, and the Brown is the New Transom core. Once its installed, you'll grind and feather the edges and then do multiple layups of CSM and 1708 to rebuild the outer skin and tie it back into the hull. Again, this is how I'd do it. It's your boat and you can do as you see fit. Others have their ideas and you can do what makes sense to you.

 

[ELoller]

I follow you Wood. Thanks for the advice. While I think the gaps you are telling me to allow for PB to fill in seem a little excessive I will be trying to get it close to that.

Have I mentioned this is a 15ft boat with a 1983 70hp Evinrude? My #2 piston blew a ring a few weeks back and I decided to pull the powerhead and send it in to get rebuilt. It has never been rebuilt according to the original owner (my uncle). I am not ready to let it die because I grew up fishing on this boat with my dad, brother and uncle. It holds a special place in my heart and now I have a 2 yr old and 10 month old that I want to enjoy this boat as much as I did. I learned to ski, fish, sleep on overnight fishing trips, run jug lines and drive a boat on it. SHE WILL LIVE AGAIN!

While the motor is getting rebuilt I decided to look for leaks in the floors and hull. Of course you all know that I found a rotten transom. Really the transom core was pretty much missing about halfway up the back about where the lower engine mount bolts were seated. Honestly I never noticed the transom flexing or the motor bouncing all over, probably because of the steel plating that was added by the original owner (my uncle). He never mentioned the transom was rotten but he gave the boat to me for free so Im not mad. :happy:

So I think that as long as I get the wooden core sealed against water penetration (tacky resin layer put on just before installing) then lay in a thick layer of PB around all the edges with some good squeeze out on the edges with minimal voids, it should be stronger than OEM. I also plan to put the steel plating back on for extra security.

This is my first transom rebuild guys, I know its not the traditional way but I have seen plenty of people do it this way successfully online. I have a lot of experience with fiberglass from building show cars and hi end audio systems. Never had much use for making PB. We just used body filler to fill in cosmetic gaps. Hence the original issue I was having with mixing it. 1708 is also new to me so I am sure I will have some questions about laying up my outer skin unless you think I am going about it the right way based on my description above?

Anyone else wanna chime in and give the cadet his licks?!

Thanks again everyone for the advice, I know some of you are annoyed with my tactics but I this is where I am and any help you can give me is much appreciated.

I mean if knuckleheads like me didn'€™t come on here and lay his rebuild out there for all to see and pick apart, then what would all of you master builders have to make fun of right?!?

 

[ELoller]

double post

 

[jigngrub]

Thanks again everyone for the advice, I know some of you are annoyed with my tactics but I this is where I am and any help you can give me is much appreciated.

Na, just an unusual build.

I think either way would've been just as difficult, but going through the inside would've given you a little more room to play with and you wouldn't have to worry about all of the cosmetic work you're going to have to do to blend this fix in. All of the builds I've ever seen done like this look like a Billy goats butt sewed up with a grapevine when the OP calls himself finished... and I'm curious to see what yours is going to look like when you're done since you have finish fiberglass experience.

I don't comment on bad finish work because it really doesn't matter, so if I tell you it looks good... it looks good.

I will however comment on bad structural work and I do have concerns on how you plan to tie everything back together. I'd dump that old outer skin in the trash and go with all new layups... but that's probably just me.

 

[Woodonglass]

A lot of the Marinas in Florida and Texas do transom repair this way. There are some boats that make it necessary to do the transoms this way. It would have been nice to have left a bit more glass around the edges but it is what it is. Your transoms strength actually comes from the inner tabbings to the hull. Since you wont' have those and only have the PB adhering to the inner skin and then depending on the existing tabbings to the hull you will now have to depend on the new tabbings of the outer skin and tieing the two sides back together. I have seen some of the Florida and Texas shops do some exceptional work to the point where you would never know it had been done "Bass-Ackwards" and so it can be done. I think it's easier doing it from the inside and I also think you get a stronger transom. But I also know either method can yield a working transom as long as you follow good glassing protocols. Stick with it and we'll be here to help when ever you want/need it. But in the long run, it's your boat so you need to do it the way that makes the most sense to you and the way that you'll be happy with. I for one am not annoyed and if I came across that way I apologize.:blue:

 

[ELoller]

Yah I think I cut it a little close to the edge but the very bottom of the hull needs some repair anyways. The outer hull on the lower edge looks to be damaged from years of abuse. So i figure ill grind it down a bit and build it back up to make that stronger too.

I dont know if you can tell from the pics but I have cut the cap back enough to drop in the core from above. Sliding it down till it marries up with the bottom lip. This cut opened up the inside of the boat for me and I plan to lay a new layer of CSM to strengthen the inner skin and overlap that new layer over the top edge of the entire transom, except where the motorwell is in the way. Then overlapping the new layer around the wall of the inner hull a few inches forward.

Would it be smart to run some stainless screws through the inner skin BEFORE I layer on my new CSM from the inside, to help tie it in better?