Carbon/Kevlar Transom

Hello All,
I'm at a turning point in my project. I was going to use this advanced material for cosmetic but I'm having second thoughts. I have 8yds. of 2X2 carbon HS twill and 8 yds. of Carbon/ Kevlar runs warp, carbon runs weft twill. Both 5.7 oz. 3k bundles.

I was curious what would be the most effective schedule for the transom layup? I still have the inner skin and looking to stiffen it up.

My sole was rotted and the transom is bonded seperate into the hull.
There is some flex if you climb on the outboard trimmed up and I'd like to stiffen it up. Can't find any signs of rot in the transom at all. I think the rotted sole contributed to this flex.

Unfortunately with the fuel tank in place there isn't room for knee braces. The tank sits against the transom. so my thinking is strengthening all directions with the stiff materials to accomplish my goal. I will use Resin Research epoxies,Peel Ply where it's needed, and if it's for show 2 part polyurethane for UV protection.

As far as the sole, I've coated 3/8ths marine grade as much as it would soak up and 6 oz 8 harness S-2 glass on both sides. The stringers use no wood or foam and I really like the idea of neither. I've gathered in a rough environment the epoxy/foam bond line won't fail but just inside that the foam doesn't hold up. I'm sure it would depend on the application.

Any input would be much appreciated. I think God put me on this planet for his own amusement I must do things wrong first and learn the correct way afterwards.

 

These pics show the 22oz triaxial layed along the sides after grinding all of the PER and old glass out.

Again Any suggestion are appreciated. If I've already shot myself in the foot with what I've done so far please for someone elses sake point it out. I'll correct it.

I made the mistake of letting the resin cure without Peel Ply. I'll sandblast the surface to get a bondable texture

 

Well, it's hard to tell exactly how good a job you've done with the glasswork so far, but it looks like you're being quite meticulous about it. Then again I'm far from being an expert in this type of repair.
I'm not such a fan of these carbon/aramid mixed-fibre cloths. I think they're more cosmetic than structural. The substantially different properties of the two fibres almost guarantee that loads will not be shared equally between them, making it very difficult to engineer them efficiently.
Even if there's no room for full knee braces, just about any bracing you can add to the transom will help. A fast boat like that with a big outboard hanging off the back is subject to a lot of very strange load cases, especially in the area near the motor mount.

 

I consider the two are like cheese and chalk. One stretches a mile, the other is very stiff. They both have good tension quality, the kevlar has poor compression quality. It all would be on the inside in tension is the only advantage.

I originally was going to just cover the 22oz on each side with this material, then UV protect it. Maybe two layers of cabon under the floor and across the transom? Extend the stringers to the back?

I will come up with something for bracing, Peel condition isn't that great. What's the best way to bond 90* to the transom and it hold up well?

 

Marshmat
Thanks for the comment and the reply. These pics might help show the 22oz layup. I learned alot on that section, If you want it flat you need to make it flat first. I should have used the peel ply to keep the material from floating were it was resin rich.
I still need to sandblast some areas and fair it. I started to belt sand and realized I was grinding off what I just layed up. Big time rookie mistake I admit. I hate 20/20 hindsight and didn't want to experience too much on this project. I have time and over time I have acquired the better materials.
I took some PVC 4 in wide fence post and layed some wet S-2 glass to make stringers that I can cut to fit. Glass them in to strengten under the sole. The epoxy did try to etch into it although it's not suppose to.
You might find this real crazy but I thought about installing knee braces and using them as the sides of a fuel tank under the sole. Is it possible to seal the tank under the sole this way? Is this too risky?
How far from the transom do I need to bond in order to have enough surface area for it to stay.
More pics
Thanks

 

I hate to say it but that material is not for what you are doing. It is ment to be cosmetic in a molded aplication with a clear coat. A good 2415 or 1808 would be more aplicable.

 

Hello Boatguy
That was my original idea with the aramid, but even the carbon? I thought two layers of the low grade carbon would be better than the best e-glass combination?
Aramids I realize are hydroscopic in nature. I have worked with this aramid and it will tear up some razor blades. It's not dyed glass.

 

These high tech fabrics, are best used in a cored construction, where you can isolate the tension and compression loads, by material placement within the schedule. An example would be using Kevlar on the inside, where it's high tensile qualities can be of advantage and carbon on the outside, to incorporate it's fine compressive attributes. Kevlar has quite modest compression strength, where carbon has very limited tensile. It's very important to engineer (literally) these types of laminates, or poor performance (laminate failure) can be expected.

It does appear (though not really clear, in the photos) you have room for at least two knees, on your transom and they would be a welcome relief, to the stresses involved. Tabbed in plywood, of suitable grade will suffice. Tab the crap out of it and save the fancy (and costly) stuff for applications where you'll really need it. In fact, you don't need any of these fabrics in your laminate, though further examination of the failure would be a wise course, before attempting to "engineer on the fly" in an effort to fix it.

What you really need is additional bulk and further stripping of the equipment. Remove the engine if you've not done so, strip the bolster and anything else in your way, it makes things a lot easier. Bulk up what you have there with E 'glass and skip the high modulus laminates. Brunswick 1603 (0-90 biax w/ two 8 oz. of uni.) will provide you a light, strong reinforcement or Knytex 1208 (45-45 biax w/ two layers of uni, stitched to a 3/4" oz. mat) if you want to get fancy, but frankly, you're over thinking this repair. Ortho or iso (preferred) resins will be more then sufficient for this job.

 

your right par good old iso will do the job, why is everyone sold on epoxy

 

Thanks for the replies, When I first found the soft sole I took my boat by a couple of boat repair shops. I firmly believe I would be doing this job again in about the same time the original failed.

The sole didn't have one drop of resin on the underside and was I'm sure absorbing moisture after the 1st time it was launched. The gel looks great but i guess they figured what you can't see won't hurt you. One quote was US $500.00 less than what I paid for the whole boat. Turnkey repair= $7500.00 I paid 8K.

I thought this would be a simple sole repair is why I didn't derig the boat, another lesson learned. It is a fair job but I think this is the most fascinating time to be interested in composites. Formulators and material companies are really creating a lot of fantastic possibilties for all of us.

The reason I went with epoxy is everywhere you turn anymore you can find reputable people stating this: http://www.raka.com/UserManual.html

Larry at RAKA
In the past, before the marvelous properties of epoxy were
realized, people fiberglassed wood with polyester resin.
Polyester resin has much less waterproofing and adhesive
qualities than epoxy. Water will eventually find its way
between the fiberglass and wood and start to creep. De-
bonding of the fiberglass can occur above the waterline
and most certainly below the waterline. This is not just
theory. Most of your older production built yachts that
have fibreglassed plywood decks have de-bonding
problems. The following is a very basic and brief
explanation of fiberglassing. If you are inexperienced and
planning a big job, definitely research more detailed
information on the many methods and types of materials in
use today.

This is from GLEN-L's site
http://www.glen-l.com/supplies/pxman-intro.html
The difference between epoxy and other marine glues is one of strength. Other types of marine glues shrink as they cure and are usually brittle. Epoxy is a non-shrink, non-brittle glue that is strong within itself.

Joe Parker (tech support=West Sytems)
Told me the first concern is to realize this is a secondary bond. Epoxy shrinks around 2% fully cured but the nice part is 1% shrinkage takes place while still in gel state. The effect on the end product is minimal. PER 4-6% through it's life and VER 6-8% but this shrinkage takes place after gelation.

As far as the bond line I'm told the epoxy is the only true adhesive with a bond holding 2000 PSI. VER is at 500 PSI and inferior PER at 300 PSI. Anytime I see Chopped Strand Mat suggested in a schedule it"s required to help a low adhesion resin or to build bulk or both. Ultamite fracture strength of a panel equals the thickness Squared. Vacum infusion makes for a weaker panel using the same schedule. Around 30%+ of the thickness is lost.

E-Glass stands for electrical with qualities desirble for making electrical circuit boards. I understand they can be used to build bulk and with that strength while saving money.
S-2 Glass was designed by Owens Corning for the stablising wings on the back end of a air dropped bomb and stands for structural glass. Seems they had a problem with those little guys way back when.

As you can see I'm not doing the low budget repair that many others are doing that you guys cordially help. I sure don't mean any disrespect in any form. I"m not a know it all but very curious. The more I learn, the more I realize how little I know.

PAR
I have a fuel tank that butts up against the transom the full width. I was going to tie the sole (with a stringer underneath) to the transom to the cap.
You stated
An example would be using Kevlar on the inside, where it's high tensile qualities can be of advantage
This is my thinking exactly

Ya'll are correct, I'm probably overdoing this boat. I'll use the carbon/kevlar for cosmetic and go with e-glass. Can I mix some S-glass in there?

I appreciate any input and my hat is off to ya'll for your help. Many of you experienced hands wonder why the inexperienced would go to extremes with materials like myself. I never want to do this job again....LOL

BTW Here's a few pics of what I took apart. The core gassed off and blew a hole in the top layer of material. There was about 1/4 inch of resin on top of the sole against the transom and dry material underneath. White material everywhere. When I crossed a wake at a 45* angle the whole boat would twist torsionally, you could feel it.

 

Remove the engine, remove the tank, remove the controls (or get them well clear of the area). This gives you room to work and takes a healthy strain off the hull.

Add reinforcement to the inner face of the transom and insure this is tabbed in well to the hull shell. Reinstall the equipment.

Kevlar on the inside skin of a "cored" structure is logical, but is completely unnecessary in your application.

Epoxy is a fine product, especially for the amateur. It surpasses both of the typical production resins, hands down in every way. If you're more comfortable with epoxy then this is the way to go and I certainly advocate the backyard repair person use it.

 

Thanks PAR
I will do all you say, and yes without a shop this is quite a challenge.

Add reinforcement to the inner face of the transom and insure this is tabbed in well to the hull shell.
Is 8-10 inches satisfactory for tabs or 15 inches?

I'm not familar with the fiber mentioned, do you recommend something different for epoxy layup. I do have some mmore 22 oz stitched triaxial?

Is it still necessary to use CSM with the epoxy? If so for adhesion or bulk?

 

Part of the trick with tabs is that the layers shouldn't all be exactly the same. They'll need quite a few layers of glass to support the motor loads; I'd vary the tabbing width from 3 inches out to about 12-14 inches and with the glass fibres at different angles in each layer, if you can. That way you have the most strength right at the high-stress point (the inside corner) of the tab between the knee and the bottom or transom, and there's decent strength in all directions.
Some of the composites-shop guys like to specify fabrics by their code numbers. Much easier to understand, and ask for, what it actually is rather than what its number is. 8-10 oz plain-weave cloth is a good choice for tabbing, it can take sharp corners very well unlike the heavier cloths and directionals which tend to bridge over corners, leaving an air bubble. Make sure to check that if the fibre is coated, that the coating is compatible with the resin of choice.
I'm seeing a lot of chopped-mat and air voids in the last round of photos there. The factory may have cheaped-out; you don't have to and so can do it right
S- and E-glass are similar enough that I wouldn't be too concerned about mixing them. Using high modulus fibres here would just be a waste of money though. If you can afford epoxies they're definitely worth it.
I'd avoid putting any structural loads of any sort on the fuel tank. It should be well secured, of course, but it will probably fatigue and crack in short order if asked to behave as a structural member.

 

Matt, I was waiting for someone to shoot the tank under the sole down. Thanks I wasn't married to the idea. I will be using the epoxy for everything and the reason I like s glass is the fiber fraction as well as the modulus.

I hope to never see a gel coat crack around the splashwell. As you mentioned about the CSM and voids in the pics, really nice work. I'll sandblast the surface before I start laying any material and with a little help it will be far superior to original.

I will lay the first layer 90 0, the second layer +45 -45, third layer 0 90 and so on. Each reaching farther away from the transom by 2 inches. I'll get with Larry at RAKA tomorrow for more material.

I'll try to get some better pics of what I have done so you might better see where I need help.

Again Matt and eveyone Thanks a lot for your patience and your help


BTW My son and I almost completed our A-frame today.I've been working a lot of OT and generally have one day a week to work on this project.

 

Fuel tank under sole is fine, provided it meets all the appropriate regs and standards. But you can't transmit any external loads- from the sole, hull or transom- via the tank, it should take only the loads caused by the fuel it contains.