What material do I need to fill a gap or hole in my hull?

[MAtkins]

I've got a 17.5' bass boat that I had to replace the transom on.

I've got the new wood epoxied in and the back/bottom epoxied back on as well but I need to fill about a 1/4" gap between the existing boat and the piece on the back/bottom that I cut off and have now epoxied back on.
For the bulk of the job I'm using a 1:1 epoxy resin.

I found some epoxy putty at Home Depot but don't know if I dare use that on a boat.
The exterior surface will be covered with 1.5 oz. chopped strand mat and epoxy resin.

What can/should I use (cheap!!) that will fill that gap and a few unrelated small holes (1/2" x 1").

 

[Coho Ghost]

Re: What material do I need to fill a gap or hole in my hull?

MA,

Pictures of what you are trying do would be a big help toward giving you the right advice.

Coho Ghost

 

[ondarvr]

Re: What material do I need to fill a gap or hole in my hull?

Don't use mat with the epoxy.

 

[MAtkins]

Re: What material do I need to fill a gap or hole in my hull?

Why not mat with epoxy?

 

[GT1000000]

Re: What material do I need to fill a gap or hole in my hull?

Why not mat with epoxy?

My understanding is that CSM uses a a binder that epoxy can't break down...

Definitely some pics of what you are working on would help us see what you see and maybe give some better advice...

Best of luck!
GT1M

 

[Georgesalmon]

Re: What material do I need to fill a gap or hole in my hull?

CSM is held together with a sprayed styrene soluble binder, one common binder is chrome silene (sp). The styrene in polyester, vinyl ester, etc. resins dissolves the binder and lets the resin bloom and encapsulate the glass strands. Epoxy won't to that, you'll be left with the epoxy resin doing most of the structural work and the glass won't add much to the strength. All glass material looks white, that's the binder, glass is clear. When the styrene in the resin dissolves the binder it gets clear. We used to do a "wet out" time test to check different brands of glass. Put some CSM over a piece of graph paper. Then apply resin. The time it takes to be able to see the graph paper through the glass is the "wet out" time. Important because the binder must dissolve before the resin cures or you lose a lot of strength. Actually we found (not often) some foreign brands of glass (Chinese, mostly) had a lot of or poor binder and failed. Try it with epoxy,,,,,,,

 

[ondarvr]

Re: What material do I need to fill a gap or hole in my hull?

The other part of the issue.

Mat offers little strength when compared to other fabrics, so you will be using the most expensive and highest strength resin with the lowest cost and weakest type of glass. Plus while polyester does benefit from the use of mat, there is no benefit when using epoxy.

 

[MAtkins]

Re: What material do I need to fill a gap or hole in my hull?

WOW! That's an excellent explanation George.
Thanks.

I need to end up with an exterior finish.
So I have to use laminating resin?

The 'corner' in the pic is the port back corner.
I'm showing a shot from the side and another from underneath the boat.

 

[ondarvr]

Re: What material do I need to fill a gap or hole in my hull?

You need some strength on the outside of the transom, so 1700 or something similar should be used. What did you use on the inside?

You don't want to sand on the glass itself, this will weaken it, plus it's very difficult to sand, make a putty mix of epoxy and micro spheres with a little silica and skim it over the surface as a fairing compound.

 

[MAtkins]

Re: What material do I need to fill a gap or hole in my hull?

Thanks.
I like that better than laminating resin.

I'm guessing I've gotta find & buy 'fiberglass micro spheres' and silica?

 

[ondarvr]

Re: What material do I need to fill a gap or hole in my hull?

There will be many places to find these materials in FL, plus they are very light, so if needed shipping is cheap.

 

[Woodonglass]

Re: What material do I need to fill a gap or hole in my hull?

As ondarvr asked, what kind of "tabbing" repairs have been done on the inside of the boat? These will be critical to the strength and structural inegrity of the overall repair. The exterior repairs will mostly be cosmetic but will add some addiional strength. www.uscomposites.com will be a good source for your materials. Fillers The Pheol Microballons will make a good filler for you. Fiberglass Cloth The18 oz E Glass woud be good to wrap the outside corners and the bottom of the hull.

 

[MAtkins]

Re: What material do I need to fill a gap or hole in my hull?

I epoxied 3/4" marine plywood to the existing 1/4" fiberglass & stringers with some chopped strand mat between them.
I used a pretty good bit of epoxy & got it pressed in there pretty good. I couldn't tear it back off.
I did the same thing between the 1st 3/4" plywood & the second (making up a 1.5" thick transom).
So, yea there's chopped strand mat in there but lots of epoxy and I made sure it was pressed up pretty tight.

As best I can tell, the boat would tear apart before that transom would come off.
I epoxied the back of the boat to the plywood and used lots of epoxy.

I epoxied 3/4" marine plywood (triangle + tongue) pieces into the stringers (the wood was rotted out) and got them up into the length of the stringers as far as I could go.
This is the glass back of the existing boat before I epoxied the wood to it.

 

[ondarvr]

Re: What material do I need to fill a gap or hole in my hull?

The inside laminate is normally rather thin when it comes from the factory, and by cutting through the outside laminate so close to the hull bottom and sides you limited the amount of bonding area you have to gain back the strength you need.

Normally you would cut the transom in about 3 to 4" from the radius, this allows sufficient surface area for a strong bond, it also eliminates the need to wrap around the radius onto the hull bottom and sides. Wrapping the laminate around the bottom and sides creates a great deal of work to get it strong and correct.

Right now you have a very small bonding area on the outside, so you need to make sure the inside is strong enough to take a larger share of the load. So glassing more material on the inside will be required.

The mat doesn't hurt you, but it doesn't help much either, you need woven or stitched fabrics to increase the strength to the level you need.

 

[73Chrysler105]

Re: What material do I need to fill a gap or hole in my hull?

I would wrap the entire transom and over each edge about 12" to tie the rear skin back into the rest of the boat. The way you replaced the transom is the worst way to do it because the integrity of the hull is compromised. You will need to feather edge the cuts, fill the gaps with PB layer in strips of glass to cover the PB and gaps in increasing width layers. I would start with a 2-4" overlap of the gap sections then 4-6", then 8-10" and a final full wrap of the entire transom with a 12" overlap. This would provide the transom strength back such that if the wood does ever rot back out the back of the boat should not fall off. In you current configuration if the wood does rot out that outerskin wouldn't have anything to hold onto and would be gone in a splash.

 

[MAtkins]

Re: What material do I need to fill a gap or hole in my hull?

Yea, this is definitely the first time I've done this and mistakes were guaranteed.
It is an '84 bass boat that isn't likely to see toooooo many more years of life.
I just rebuilt a Mercury 150HP V6 and didn't want it to fall into the lake when I break it in.

I don't see how I can do anything to the inside.
It's solid from the inside factory laminate (1/4") as seen in the pic, to the outside of the boat (as shown in the very first pic above).
Also, the plywood is epoxied to the stringers very solidly.
It's all glass, epoxy & wood. I'm convinced it's there to stay.

If I understand correctly now I'm looking for:
Arosil/Cabosil -> fumed silica
microspheres
1708 biaxial fiberglass cloth

I did notice that i cut the hull too close to the edge.
I was thinking I might need to glass up around the edge.

But again, the back isn't coming off that wood, even if I stop right now.
My main concern is that I get the seam completely sealed and ready for gelcoat.

 

[MAtkins]

Re: What material do I need to fill a gap or hole in my hull?

73Chrysler105 hmm, I see.
I wondered about the integrity of the hull and decided against fighting with the cap.
I couldn't really have gotten at the stringers like I needed to that way anyhow.

You're right, if the wood rots again, the back of the boat probably fall off.
I think my list is the same, I just need to make sure I've got enough epoxy & cloth to do the job.

Back to that dang grinder . . .

 

[Woodonglass]

Re: What material do I need to fill a gap or hole in my hull?

I'm sorry but...You're not understanding how critical it is to have inside structure attached to the transom. The weight and torque that the 150 hp motor will put on your transom is such that the way you've done the repair will not be adequate to sustain the forces placed on it by the motor. Epoxy is strong but NOT that strong. IMHO the repair as it stands right now, is destined to fail. With some additional cutting of the rear section you could gain access to the sides of the hull to place the glass tabbings needed to beef up the repair. You don't want 1708, it has MAT attached to it. You only want 17 or 18 oz cloth. No Mat attached. But as always, it's your boat and you're free to do with it as you see fit.

 

[MAtkins]

Re: What material do I need to fill a gap or hole in my hull?

What I did was really close to what I saw that the factory had done.
The motor was running on the boat with the transom *completely* rotted.
I didn't notice it until I took the motor off the boat.

The wood I put in replaced the existing wood that I dug out of it, the same size.
I epoxied wood into the existing fiberglass stringers and epoxied the plywood to them.

I *really* don't want to rebuild this boat. It will never be even near worth the cost.
NO MAT! thanks. I'll make sure I get 17 oz. cloth and do it in layers as suggested.

 

[Woodonglass]

Re: What material do I need to fill a gap or hole in my hull?

Uhmmm, no that's not how it was done at the factory. This link has some drawings on how a transom should be installed correctly."Fabricating Decks, Stringers, and Transoms"