1975 Glasstron stringers/foam help

[wrksuks]

I have a 75 Glastron with an 85hp Johnson. I tore off the decking with the intent of replacing the old foam with the newer/better expandable foam. when I got the floor off I could see that the stringers were pretty much completely rotted out, some of them were gone altogether, leaving just the glass that was around them. My question is this--can i get away with just filling the hull with pourable/expanding foam? I understand that stuff is tough as nails and adds a ton of structural integrity, that's why I was going with it in the first place. Will it be strong enough to replace the stringers or do they do something more that I am not thinking of? I think when I add the foam it will make everything rock solid down there, but that is just a guess. Any pointers would be great. Thanks in advance

 

[frank246]

Re: 1975 Glasstron stringers/foam help

Unfortunately there is no other right way than to replace the stringer(s) and floor, mostly when the stringers are gone the wood inside the transom is also rotten. The stringers in combination with the floor glassed in make the hull rigid and are the structural parts for the boat.
The foam is just there to prevent the boat to sink directly to the bottom of the lake in case the boat is completely filled with water and most leave the foam out after a rebuild as this only holds water and moisture.
The old foam is water clogged and caused the rot in the first place.
Better check your transom by rocking the motor, there should be absolutely no flex, tab with a hammer (inside the boat) and the transom should sound rock hard and not dull, poke it with a screw driver especialy in the lower section of the transom.
Common issue on older glastrons though.
In case of a rebuild use douglas fir for the stringer(s) and exterior/marine multiplex for the floor and no pressure treated wood!
good luck,
Frank

 

[wrksuks]

Re: 1975 Glasstron stringers/foam help

thanks for the input. the transom appears to be in good shape. checked it all over and didnt notice any problems. the foam i am looking at is 8# density and the product description says it is as strong as soft wood. it seems like if i fill the entire hull with this tougher foam it should solidify the whole boat. replacing stringers seems like it may be out of my range of abilities, but the foam can be done for a couple hundred bucks. I have been driving the boat for a few months and havent broken anything yet, so no matter what, the foam will make things stronger right? the logic seems sound, but i dont want to sink my first boat to find out i was wrong.
thanks again for your help

 

[cvtech1]

Re: 1975 Glasstron stringers/foam help

I have a 1977 Glastron and the floor had been replaced but I'm not sure of the stringers.If you feel comfortable with the foam I say go for it, the foam will not sink your boat. Worst case after a couple of years you may have to replace the stringers and remove the foam. I know you posted this several weeks ago and I would like to know what you did.

 

[wrksuks]

Re: 1975 Glasstron stringers/foam help

Well I went for it. Didnt see any good way to replace the stringers, not sure I could pull it off on my budget. I drilled holes in the stringers and got as much of the old wood out as I could, then I filled them with the foam. I went with 4# foam and put some makeshift stringers next to the old ones. I bolted the new wood, which I coated with resin, to the filled stringers with toggle bolts. The end result, I have to say, is as sturdy as anything I have seen under a boat floor. The new sub-frame is hard as a rock and has no give anywhere. I am terribly impressed with rigidity of the foam encased like that. I am pouring the rest of the foam for under the floor tonight and should have it all put back together sometime tomorrow. If all goes well I will launch it next weekend, January or not, and see what things feel like. I don't know how it will hold to the water this summer when the big boats are out there, but as of now everything feels rock solid. I will post results later after some field testing, with some pictures if I can remember.

 

[cvtech1]

Re: 1975 Glasstron stringers/foam help

Good for you, hope all works well. If only the stringers where bad and with you reinforcing them sounds like you did no harm. I will be heading down that road soon with my Glastron pretty soon even though the previous owner said the floor has been replaced, I am not sure of the stringers. Post picture as soon as you can,would love to see work.

 

[wrksuks]

Re: 1975 Glasstron stringers/foam help

I know it has been a long time since I wrote on this post, but I have spent all my free time playing on the boat. I have found some of the pictures we took during the rebuild. Keep in mind we are in Missouri, in the middle of winter, and actually in the middle of a snow storm when we did a lot of the work. We had to build a cocoon around the boat to hold out the water and hold in the heat. We brought in a heater to get the cabin up to around 68 degrees so the foam would expand properly and the glass would cure right.

Dont know if I did these pics right, i thought i could put them directly into the post with a description.
1. This is what the stringers looked like when we took the floor off.
2. This is another of the stringers, or rather where the stringers were. See the hollow in the fiberglass.
3. We filled the old stringers with foam and embedded a piece if wood to sturdy up where the old cut-out was.
4. This is another embedded piece of wood replacing a cross piece. we built a channel down the middle to move water and still leave as much room for foam as possible.
5. Here we are done with all the woodwork in the back. We glassed in all the joints, used toggle bolts through the stringers, foam and new wood, and used stainless deck screws to tie all the new wood together.

 

[wrksuks]

Re: 1975 Glasstron stringers/foam help

I wish I would have taken more pictures. I can't find any of the foam work, but basically we put new decking on the new floor that we built, drilled 1" holes in the decking and filled every nook and cranny under the floor with the expanding foam. When everything was dried and cured I glassed over the holes we drilled, sanded it all down, and put the carpet on.
1. Just installed the new carpet.
2. Carpet done. That little heater was our lifesaver for this project.
3. Everything done. Seats mounted. We are ready to rock and roll.
4. Project complete and it is still winter. Time to work out the bugs before the real season hits.
5. Break time. That's my partner Brian, the cocoon was actually his idea. Who could have known it would work so well.

We ride this boat daily in the main channel of the lake of the ozarks. Last weekend we took it about 15 mi to party cove and spent the whole day wakeboarding in the state park. We rode through some of the biggest water i have seen, and were actually leaving the same time that a houseboat got sunk, but our little boat held up beautifully. I won't gauge our success until after at least one whole season, but so far our makeshift stringers have handled more abuse than most boats this size ever see.

 

[A-Train]

Re: 1975 Glasstron stringers/foam help

Having been there for part of the restore, I can attest that there were some wild ideas flying (typically after sitting in the cocoon with fumes for too long) and there were times that I doubted (up until we launched it) but they figured out what needed to be done and then figured out a way to do it. Now if we could just figure out why the motor is temperamental...