Am I crazy, a different idea to replace stringers, will this work?

I bought a 40 year old, one owner Correct Craft ski boat last fall, on a complete whim!
I thought I would buff it up and have fun with it this year. So I started stripping the hardware, interior, etc., then decided some of the floor could use replacing , then decided some parts of the stringers did not look so good... anyway, the boat is now stripped down to a bare hull. The stringers need replaced, I would like to replace them with something that cannot rot.

I will remove the top surface of the glass off the stringer and dig, pry, drill, out the wood. Leaving an empty fiberglass channel. I looked at the sea cast product,pour a transom or stringer product, but I think it will be a very heavy, and stiff solution. I could insert douglass fir back into the channels wet out with resin and glass the stringers back. But that too will eventually rot.

The other issue I would like to solve is flotation. The boat has none. If I foam every cubic inch under the floor (which I can't do because of the engine, trans, wiring loom, steering have to remain somewhat accessable). The boat will still not be bouyant, so I will be using spray foam behind the side panels, around the fuel tank, and adding foam in the bow.

I like the idea of pouring a composite material into the stringer channels to take the place of the wood, the quantity of material will not be small, about 13-17 gallons, it should also be filled to add strength and toughness (chopped glass?) This too will prove to be heavy and could be very stiff.

I was thinking about what kind of fiberous material to add to the mix to increase volume, decrease density, add strength, toughness, and even a little flexibility. What about braided polyester rope? Would it wet out with resin, would it just melt, what about epoxy resin, or vinylester? Could I get a matrix that has the properties of the wood it replaced.

Is this a crazy idea, or might it just work?

Fire away, I'm curious as to your thoughts on this. Should I just stick to tried and true and put the fir back in?

 

OK dont take my word for it. but from what I can gather .,,what about the new composits that they are building back decks with ...the kind on your house? dont know the tencil strength, but sure someone here does. some guys are using it for decking.

 

Composite decking has almost no strength, it is made of mixed recycled plastic and wood fibers, has lots of polyethylene in it, therefor it has an oily texture and no adhesives will stick to it. Think of partical board Starboard.

 

ok ; cant think of anything else now that will work, maybe wood ?

 

You could fill the stringers with pourable closed cell foam and then glass over them again. The only danger is stability (buckling) problems. The original stringer had wood to stabilise all parts and poured foam is not doing the same job. A structural expert who knows what he is doing would have to look at it.

The safe option would be to remove the old stringer completely and start new again. You could then use structural foam in sheet form to shape the stringers. That stuff is not going to rot and weights only about 80kg per cubic metre. Only problem is that it's costly. Someone with some composite experience should also tell you how much glass you have to laminate over the foam. If you do it wrong you might end up breaking the stringers and you wuld have to do the job again. I would be very carefull with structural components like that.

 

go with fir and epoxy, this is still your best bet. if you seal the entire stringer there should be no rot for many many years. if you have awooden hull polyester will stick for about 3-6 years then it will start to delaminate.

 

I replaced a rotten transom where, in the corners, where the plywood didn't quite meet the sides, the builders had filled up the space with 1" thick nylon rope and saturated it all with polyester resin. It was some of the hardest stuff to dig out that I ever had to dig out. It was real stiff but not rock solid. One side was fine, the other side was the reason for the rotten transom as the bottom end hadn't been completely covered in fiberglass cloth and worked really well at wicking bilge water up the side right up to the top of the corner. Sam

 

Stick with the fir. Wood has one of the stongest strength to weight ratios you will find. The key to your success is to insure that you encapsulate the entire stringer with epoxy. Keep the moisture out and you'll keep the rot out.

You could replace the stringers with closed cell foam and layer glass over the foam to regain the needed strength, but in all likely hood, you will end up with a heavier boat.

 

Thanks for all the replies, I'll just put the wood back in. I think that I will try to leave the fiberglass channels in place and rough up the insides with a large diameter grinder, as I read about in another post. This will let me keep a reference to the shape and overall height of the stringer, and also let me mark the motor mount locations.

After I have shaped the new stringer should I treat the stringer with a penetrating epoxy prior to putting it back? Are there any alternatives to the CPES, It seems very expensive / weight or volume. Could I just thin out layup resin with 15% to 20% acetone so it will wick into the wood. I will coat the strtinger with layup resin, slide it into the channels then clamp the channels back to the wood. Maybe add some chopped glass to the mixture to act as a void filler.

I also read somewhere that only one stringer at a time should be replaced, why is this? To help the hull hold its shape? If this is the case, I will replace the secondary stringers first then the main stringers one at a time.

Thanks again.

I'm sure I'll have more questions, once the ugly work is done, I'll be wanting to know about linear urethane topside paint for all the surfaces above the gunwhales.

 

pressure treated wood works well, just make sure its bone dry.

 

did you cut gussets in them? to allow water to flow.

 

If I understand the situation, you cut the glass off the top of the stringer and dug out the wood leaving two vertical flanges. Now you want to put in wood and put the old glass back?

Once again I'll get on my soapbox and remind you to support the hull shape very well while the structure is removed.

Just throwing out ideas: we used to make a transom pour by mixing polyester resin with Cavisil and milled fibers. Cavisil is a type of micro balloon. They are tiny glass balloons, like a powder. They are used to make the resin thick without adding much weight. Milled fibers will impart some strength and you end up with a mixture which can be poured or troweled like a putty if you add more Cavisil. How about pouring this mixture into the hole and then put a new glass cap. One potential problem is that the more of this material you use, the more heat will be generated.

It may be too much work to cut and fit the wood back into the hole. If it was my boat and I went the wood route, I would fit the wood in place using the old glass stringer as a guide. Stick the wood into the hull with some putty or something, cut off the old stringer, grind the hull around the stringer out about 8” to accept a new layer of glass. Fillet the inboard side where the stringer meets the vee of the hull to eliminate an acute angle which would otherwise be there. Cover the stringer and hull with two layers of glass with the edges staggered.

Like Mr. wdnboatbuilder said, put in limber holes to make sure you don't trap water. Resin coat the holes if wood is exposed.

For the foam use the level flotation guidelines on the USCG web site. Foam can do more harm than good if it's in the wrong location on the vessel.


Good luck.

 

I have a 1970 Chris Craft 25' Lancer and it has fiberglass top-hat stringers with a hollow core. In addition I recently saw a show where they were building a new 20' production boat with the same type stringer. The stringers were layed up separately and then glassed into the hull afterwards. The core was then filled with expanding foam for noise reduction and flotation. If you opt for this method, you would maintain the existing flanges and bond the new glass to them, just make sure you feather out each succesive layer of glass onto the hull to increase the bonding area of new to old. As for supporting the top layer that would lay across the flanges, you could fill the void between them with the foam, shave it off at the top of the flanges and glass right over the top of it. Just so it's clear. The top hat shape would be created out of multiple layers of glass, each being one piece from one side of the stringer to the other. So you would start by laying your mat on the bottom of the hull, running up one flange, over the top, down the other flange and down onto the hull again. No rot, light weight, 36 years old on my boat and still strong, and if they're using it in modern production, then how can you lose.