stringer replacement ?'s

scarabfreak

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Mar 18, 2004
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Hello all, <br />I am new to the forum but, I have been reading for a while. I have a couple of questions that I hope you guys with your infinite knowledge could help with. I am replacing the stringers in a 29' Scarab sport. I have the deck off and the old stringers out. I have refabed the new stringer out of 3/4 marine grade plywood and I laminated 2 boards together to make the new ones 1 1/2" thick. I am ready to put them back in. My questions start here. <br /><br />1. I have read about encapsulating them in glass and epoxy. Is this something I do prior to installation? Should I cover in epoxy let dry and then glass the new one in place? What is the best epoxy to use for this? <br /><br />2. I plan to use some sort of glue/epoxy to put between the hull and stringer to help keep them from moving before I start to glass in place. What is recommended for this? Can I use 3m 5200? Or do I even need to "glue" in place? <br /><br />3. I plan to use a couple of layers of biaxle to glass the new stringers in place. Is there something better to use or is this cloth sufficent? <br /><br />I have worked on a few boats and I know how to lay fiberglass pretty well. I have used glass to make a bunch of interior stuff for lowriders and speaker enclosures. This is by far my biggest project and I just want to make sure I do not miss anything that should be done. Any advice would be greatly appreiciated! <br />Thanks in advance!!
 

Bondo

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Re: stringer replacement ?'s

Sounds like you're headed in the Right direction...........<br /><br />1,& 3) Ya, you want to cover the stringers, But do it In-Place...... Much Simpler to do,+ saves a Ton of Sanding.......<br />Biaxial is Great, it Lays better... <br />Roving is also handy for semi-flat areas....<br />Mat has No place in a stringer job......<br /><br />2) "What is the best epoxy to use for this? " <br />The Cheapest you can Find......<br />Use Thickened Epoxy Resin, Not 5200..... Keep your chemicals all the same when possible.....(another KISS thing)
 

scarabfreak

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Mar 18, 2004
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Re: stringer replacement ?'s

Thanks for the info. I figure better safe then sorry. When you say thickened resin how do I get this? Is it something I add to my fiberglass resin like a microbead balls or something to that nature or is it something different all together?
 

Hooty

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Re: stringer replacement ?'s

Use talc to fill the epoxy.<br /><br />c/6<br />Hooty
 

Bondo

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Re: stringer replacement ?'s

Cabosil is the Industry Standard, Thickening agent......<br />You'll want a Peanut Butter consistency........<br />Micro-balloons are good for a fairing mix, or to add to the Cabosil thickened mix,<br />But not alone... the Epoxy can leach out of the Micro-balls, before it Kicks......<br /><br />Check out this site, Lots of very good Info here,<br /> http://www.epoxyproducts.com/marine.html
 

Hooty

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Re: stringer replacement ?'s

If you'll check your "Industrial Standard", you'll find that Cab-o-sil is a thixotropic agent and not a filler. It does nothing for the physical properties of the resin. Nothing beats talc and it's not expensive.<br /><br />c/6<br />Hooty
 

CTD

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Nov 13, 2002
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Re: stringer replacement ?'s

Some thoughts<br />Seems like I remember reading somewhere that on boats longer than about 20ft many manufactures used a insulator (foam) strip between the stringer and the hull. The idea is to have the hull be able to flex a little to reduce stress at the stiff stringers. Sounds like you have a major project going, one you want to take your time doing and do it right. When working with large quanities you can get epoxy for about the same price as polyester so I would recomend using epoxy and bi axial cloth. If you use roving use a thin mat between each layer. When working with epoxy if you do your layers before it cures no sanding is required, once cured it needs sanding before the new layer is applied. You could tie all the stringers together with strips of wood on top to hold them in place. US composits has the best price I have found on epoxy. For a 29 footer you'll need a lot just for the stringers. Their volume prices get down to $25 a gallon or so. Also if your building up thick areas with epoxy I would add milled fibers to the mix for strength.
 

Hooty

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Re: stringer replacement ?'s

Good point CTD, but the primery reason for the foam (or any material that'll compress, i.e. cardboard) is to absorb the shrinkage of the stringer tie-in material and prevent the shrinkage from puckering the exterior of the hull. Have you ever looked at the exterior of a hull or deck and seen the pattern of the wood stringers/stiffeners on the back side? Thats due to the tie-in shrinkage. That shrinkage can be prevented by using two or three steps tying the stringers in instead of one. Remember, "the greater the mass, the faster the gel, the higher the exotherm and the more sever the shrinkage." <br /><br />c/6<br />Hooty
 

scarabfreak

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Mar 18, 2004
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Re: stringer replacement ?'s

Thanks for all the help everyone! So your saying I should put some sort of buffer between the stringer and the hull. What is best and how much should I use. I am about to start the glassing process tomorrow. I got both the stringers shaped and I have one blocked up in place ready to glass. I bought an epoxy glue to attach the stringer to the hull but, I guess I should not use that now? Will cardboard work as this buffer material?
 

scarabfreak

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Mar 18, 2004
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Re: stringer replacement ?'s

Hello all,<br />Ok I have the stringers ready to glass in place and I was wondering! I plan to use biaxial and I was wanting to know if I can cover the stringer from the floor on one side of the stringer over the top to the floor on the other side as one lay-up. I plan to do this in about 2 foot sections. Will this delaminate at the top. The new stringers are 2" thick. Or should I do it a different way. Maybe not going completely over the top and down the other side. Maybe so the sides and then glass the top in separate. Thanks!
 

CTD

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Nov 13, 2002
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Re: stringer replacement ?'s

I think you will have a problem getting the cloth to lay flat going over the top but I'm not familiar with bi ax. What I did on mine was to glass to the top edge with one layer. Then I added narrower strips of mat and roving for strenght at the edge mating with the hull. For the top edge I soaked it with resin to seal and when I put the floor down I put a layer of mat on the top edge to further seal and bond the floor to the stringers. It wouldn't hurt to try a spot, if it works fine if not just grind it off. I tried stapeling the mat to the sides of the stringers to hold it flat but when I wet it out it stretched and still wouldn't lay flat, bi ax might be stronger and work. It dosn't hurt to try things like that. As far as insulating the stringers from the floor Hooty knows more about this stuff than I do and what he said made sense about the shrinkage because a manufacture would want to put a lot of material on and be done with it while you wont be able to put that much on at once.
 

scarabfreak

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Mar 18, 2004
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Re: stringer replacement ?'s

hello all it's me again. I have pic's! Sorry for taking so long. I do not get a lot of time to work on this project due to my schedule. So here is what I have. I have made up some thickened epoxy with microballons. I took a one inch putty knife and ran this mixture along the sides and under the stringer to make a nice transition from the hull to the stringer and sanded it smooth. 40 grit so not to smooth but, I took off all of the major spots. I cut some 6 inch strips of bi axial and ran this to tab in the stringer and then I came back with full size pieces all the way to about 1 inch from the top. I do have the top of the stringer rounded so when I get there it will lay easier. So tell me what you think! <br /><br />Ok how do you add the pic's?
 

CTD

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Nov 13, 2002
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234
Re: stringer replacement ?'s

I don't know how to post pictures, I think you have to have them online somewhere and then connect them somehow or post a link to them. Anyway this gets it back to the top.
 
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