Fiberglass stringer foam repair

[Antax]

Hello everybody, after getting my 95 Glasstream Yamaha build straightened out I have another project. I just acquired a 1998 Glastron SE175 with a 3.0 Volvo-Penta.

The Glastron has fiberglass, foam filled stringers (VEC?). I have searched a bit and found quite a few posts about who does it, benefits of it and when it was done but I couldn't find anything on what can be done if the foam has moisture in it? The previous owner had removed the floor and left it exposed to the elements. Since Glastron didn't seal the holes where they added the foam the foam has moisture. Right now the stringers look ok and don't appear to be delaminating but what can be done about the moisture in the stringers? I drilled a couple holes in the base of the stringer in the engine bay. There's no water gushing out but the foam is definitely wet.

My thinking was maybe I could cut the top off of part the stringers, remove the foam, glass the tops back on and refill them with foam but I dont know how this would effect the integrity of the boat. Its only a 3.0 4 cylinder so it's not going to get any real stress from the engine like my 19 ft with the 5.7 Yamaha.

What are your thoughts? I realize the boat may not really be worth it but its a hobby.

 

[JASinIL2006]

My Larson has those same stringers. (I think they are pre-VEC, actually, but I'm not a 100% sure. From my research, the engineered stringers were developed and used a year or two prior to VEC being used in Larson and Glastron boats.)

When I restored my boat, I didn't need to mess much with the stringers, except near the transom, where I cut them out so I could replace the wood and re-glass it. Personally, I'd cut the stingers near the hull (on both sides of the stringers), scoop out the foam, glass the stringers back in, and refill with foam.

The advantage of cutting near the hull, rather than near the top of the stringer, is this: you will need to slap on a number of layers of 1708 to restore the cut stringer. By doing it near the hull, you don't need to worry about the thickness of the new glass interfering with the deck laying flat. You also can run the layers of 1708 down to the hull, essentially re-tabbing the stringers.

Trying to cut and re-glass the engineered stringers near the top would be a lot more challenging, I think. Down low, you can apply as much glass as you want, and it won't interfere with anything.

 

[Antax]

That's a good point about cutting near the hull. I was thinking about trying to make sure the hull doesn't warp while the stringer was cut out but I would think the benefit of tabbing the stringer back in at the hull would be better. How much of a section should I cut out at a time, 1ft, 2ft, 3ft or cut out the whole thing? I believe I could cut out a small section and dig the foam out. Maybe even cut out a couple small sections. One at the transom and one closer to the bow/helm.

My transom is rotted out too so I'll also have that to deal with. I'm guessing thats the wood your referring to?

 

[JASinIL2006]

First of all, I would not cut into the stringer at all unless the hull is properly supported to guard against deformation.

Then, I’d cut the stringer in as long of a section as I could; I’d take it out in one piece, if possible. Keep as much structural integrity as possible.

You need the stringers out of the way to fix the wooden transom core, so doing that while you’re working on the stringers is smart.

 

[Antax]

Thanks JAS, I read your thread on your 97 Larson Bowrider tansom rebuild. Looks like it turned out great. After you reglassed the stringers at the transom did refill them with foam? Does the foam add any structural integrity or is it just for flotation and/or possibly to fill the area? Maybe you mentioned it somewhere and I missed it.

 

[Scott Danforth]

foam ads initial structure on engineered stringers

you could simply use a wire cup brush on a flex shaft and grind out the old foam thru access holes every 2 feet, then fill with new foam

 

[Antax]

I guess the main question may be do I even need to remove the foam? What worries me about the moist foam is when it freezes it could bust the stringers but would the foam hold enough moisture to cause damage?

 

[Antax]

Thank you Scott, that was actually my first thought. Cut the top off of the stringers in a couple places and find something to "chop up" the foam and vacuum it all out.

 

[Hab]

FWIW, I struggled with the stringers on my project also. I was nervous as heck to cut them completely out, but I did. Mine had wood cores. If the cores ever were attached to the fiberglass the water had broken the bond long ago and the wood just fell off the hull and out of the cut stringer. After all the effort and expense of full stringer replacement, Im convinced that the core is more or less a mold and all the strength/stiffness is gained by the fiberglass and the geometry of the fiberglass. If i do another project I will cut the tops, dig out any water logged material and then recap. I dont know that I would even bother replacing the core. I would probably add another layer or 2 of fiberglass to outer sides of the stringer just to make me feel better about it. Mine were very simply to work with. If yours have an irregular cross section or other shape like JASinIl2006's his method may be better.

 

[Woodonglass]

The wood in wood cored stringers IS structural NOT just a mold. In order for the core of a stinger to be a mold the stringer walls need to be about 4 layers of 1708 fabric and glass. Mfg use wood cuz it's quick and easy but also strong. Most boats are built with a life span of 10 years or less.

 

[Scott Danforth]

if there is wood, or aluminum in a stringer, it is a structural element of the stringer system

if there is nothing, or only foam in the stringer, its an engineered stringer with a lot more fiberglass thickness (about 5-6mm thick at a minimum. some are 10mm)

as WOG stated, manufacturers use wood because its cheap, does the job and gets the boat out the door quickly for the manufacturer to make a profit. most runabouts have a design life of 15 years. that is planned obsolescence to stay in business and keep making boats.

your 1998 boat is 22 years old. it has actually outlived its design life by 7 years prior to a major overhaul.

 

[JASinIL2006]

The walls on the fiberglass stringers in my boat were easily 10 mm thick, may be more. The fiberglass in the stringers was actually considerably thicker than the fiberglass that forms the hull. if your boat was built with the same pre-VEC technology that was used in mine, and it sounds like there's a good chance it was, I believe they formed the stringers/bulkheads the same way they do the whole: layer of gelcoat was sprayed into a mold, followed by many layers of fiberglass. When the structural elements were removed from the mold, they were tabbed to the hull. In my boat, the foam inside the stringers clearly was not adding anything structural to them. In fact, it was pretty clear that the foam was poured or piped in after the stringers were installed.

It probably would be possible to cut open sections of the stringers while they are installed in the boat and try to find some device that would scour out the foam and then vacuum it out. To me, that sounds like quite a bit more work, and I think it would be hard to get the all foam out of the corners and nooks and crannies. if that happened, you would be leaving behind wet foam that would possibly interfere with the new foam adhering to the inside of the stringer.

I was fortunate in that the foam inside my stringers was not wet, and if it had been wet, I don't know if I would've bothered removing the stringers to get that foam out. I probably would have removed the stringers, because that's how I am, but I'm not really sure it would have caused a lot of problems if it had remained in there. I just don't like the idea of leaving any wet foam below the deck.

The bottom line, I think, is that you can probably get at that foam and remove it in a number of different ways. The key is to just make sure that, when you glass in the sections you removed, that you make the glass patch is at least as thick as the material you cut through to get at the foam. Hope that helps…