Repairing a stringer and need advice on which cloth to use

Andyf32

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I am repairing a 6 foot section of a stringer. I have removed the wood and left the 2 fiberglass sides in place. The stringer is 2 1/2" wide and 12" high. I plan on using fir laminated together to get up to the 12", fit it in place and key it into the rest of the stringer.

The question I have is what cloth should I use to cap the stringer once the new wood is in place? Being that it is only 2 1/2" wide I assume i need a fairly flexible reinforcement. I plan on going down 2 to 3 inches onto the existing fiberglass.

Thanks in advance for any help.
And please be safe out there!
 

Brooksie

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The "cap" is really unimportant structurally, just to keep water out. The larger question is how are you going to "key" the new wood to the old stringer? This is where the strength is really needed. A lap joint may work almost as well as a scarf if it is long enough and you can find a way to cut it. This is definitely a job for epoxy with it's high bonding strength and additional flexibility
 

ArchHibb

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What is the thickness of the existing fiberglass wrap?
Thin fiberglass means wood core is structural and must be structurally tied into adjacent pieces, like Brooksie said. Cap it with some CSM to make waterproof.
Thick fiberglass, say 1/2" or greater, then the wood could be acting more as form for the fiberglass which, due to its 2x12 shape, acts as beam. Start with CSM then layer on some 1708 and build to match the thickness.
 

traditions

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Is the glass stuck to the stringer on either side of where you removed it? If it is , you would be farther ahead to go and cut it all out and glass in a new piece. There isn't really a good way to slide in a piece of wood and adhere it to the existing glass. Get some 1708 and a couple gallons of resin and glass in a new piece and be done with it.Use hull and deck to stick it to the hull and radius the edges where it meets the hull.
 

Andyf32

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Let me see if I can answer all of the questions:
Brooksie - One end of the stringer ends at a bulkhead, the other end I plan on cutting 3 steps into the existing stringer to mate the new piece to. Using one of those vibrating cutters to cut the steps.
ArchHibb - The glass is very thin, the joint is right at a bulkhead. I know the bulkhead does not do the same thing as a stringer but hopefully it will help.
Traditions - No the fiberglass was not stuck to the wood much at all. And there was no bedding compound down to the hull. I was going to hot coat the wood and existing skin and use screws to draw it down to the new material.

Thanks all for taking the time to answer my question. Now if I can get some supplies before everything shuts down.

And just a note to Bill, This is by far the best site hands down when you need to get some "REAL" boat repair advice.
 

Tunatown

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I would cut the bad section out glass and wood plus grind 6-12 inches of glass off the good section then re glass the entire new stringer
 
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Genius

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I'm surprised no one has mentioned a scarf (or even a butt) joint with epoxy/colliodal silica 406. Then glass over as suggested. I think that would be fine IMO.
 

speedwagon

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I'm surprised no one has mentioned a scarf (or even a butt) joint with epoxy/colliodal silica 406. Then glass over as suggested. I think that would be fine IMO.
brooksie mentioned scarf joint above.
I would cut the bad section out glass and wood plus grind 6-12 inches of glass off the good section then re glass the entire new stringer
this sounds easy and add a long scarf joint.
 

Brooksie

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Thinking out loud but : What about cutting the top off the whole stringer, prying out the old wood, and laying in a new piece with thickened epoxy, screwing from the sides, then recapping just keep water out.
 

Bill

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I would hot coat the stringer once you get it all cut and then bed it in hull and deck . For the cap just use 1708 a couple 2-3 layers put a little hull and deck on top of the stringer and along the seam on each side where old glass meets stringer... just as you are about to glass it it will help it wrap around and not cause air pocket..do while the hull and deck is still wet.. grind down that seam to a knife edge before hand. wet out the back side (chop strand) on a piece of cardboard it makes life a lot easier
 

Andyf32

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Tunatown - I was thinking about removing one side of the fiberglass. What is there is sound and unfortunately I am not as good at fiberglassing as most of you are and would not trust my skills to do a good job.

Genuis - that is what I am going to end up with at this point is a stepped or possibly even a butt joint at this point. It would be pretty hard for me to cut a scarf joint between the fiberglass skins.

Brooksie - what you describe is actually exactly what I am going to try to do. I may try to use clamps rather than screws.

jbkroh - I have looked at those transom compounds a lot. If I can't figure out how to get a piece of fir back in there I may end up there.

Bill - Good advice, I have built some stitch and glue kayaks and learned to put my fillets down and glass them in while still wet. I would not have remembered that had you not mentioned it.
 

Tunatown

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That’s a tuff spot but you can do this glass work is pretty simple for the most part and you have gravity working in your favor you could cut the rest of the top and engine facing side out remove all the rot and shit out of old stringer leaving the outboard side grind the glass on the inside and where the new mat would go over a little and down on the hull on the inside the section of would the goes back in you want to roll a batch of resin on it and let it kick before you install if not the wood will absorb some of the resin away from your mat if you didn’t and doing this you will get a much better bond the install 2 layers of 1708 good to go you could even screw a few screws from the back to hold in place when you glass the prep work and clean up are way harder then the glass work there
 

Genius

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Dang. I thought this might be a gut/refit. I can't even imagine doing this with an engine and all the auxiliary equipment still in place.
 

Andyf32

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Tunatown - Do you thin the resin you coat the wood with? I will be using polyester resin and polyester bonding compound.

Genius - The engine is out but the generator is still in place. But you would be surprised what little things keep getting in the way. The bonding wires are like a spider web.

Jjammer - Not totally sure where the main source was. There is a weep hole thru the stringer which could have taken in water at the bottom of the stringer. It has crusader engine mounts and the cup shape would certainly hold water until it could seep in by the lag bolt. Riser joint is just above the mount so maybe a leaky riser at some point. I wouldn't think it would take that much in thru the engine mount but most of the rot was at the top of the stringer.
 

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