85 sunport stringer repair question

[Jesse]

I have been reading and reading on stringer repair/ reconstruction. I still have a few questions that I am not finding answers to. First, I was wondering what new boat stringers were made out of, or even what supra started using for their stringers once they turned away from wood. Personally I would imagine there are a lot of other materials that could be used, but I have also read that some hulls are stiffer and some have more flex. I am guessing this is important information. I am under the impression that the 85 supra sunsport skier is a stiff hull. If this is correct, would I be able to do solid fiberglass stringers? I have loads and loads of scrap fiberglass, and I can get polyester resin at a very good price. If the existing fiberglass structure of my stringer is still intact, couldn't I just cut or grind the top off the stringers remove the rotted junk, fill with fiber glass scraps and pour the resin in. I think I would probably use 3/4" plywood or doug fir wood to fill in some void but the fiberglass and resin would be the main structure of the stringer.

If I had the time and money I would enjoy tearing the boat apart and rebuilding everything, but for now I have access to the materials listed about and can peck away slowly at the process mentioned hour or so a night. I do have the ability to remove the cap and motor. Is it as big of a pain to remove all the rivets as I am imaging ha.

My sunsport is un useable now as the transom is shot, so the stringers need repaired before I can get the boat on the water. Since I bought the boat knowing I would eventually be restoring it I don't want to waste money on a band aid, but id like to get on the water sometime this summer. any thoughts are appreciated

[chris young]

I've been thinking a similar type repair for my boat if I ever get to it (digging out the rot and filling with resin) From what I've seen, the stuff to use is called Nida Bond. I've posted this video before, but I think it's worth re posting. http://www.youtube.com/watch?v=_CMsjayPACs

Personally I think super strong stringers are overkill. It's my opinion that the main purpose of the stringers (with the exception of the ones under the motor) is to tie the floor to the hull, and it's the overall structure that provides the stiffness, not the stringers themselves. To answer your question, I'm pretty sure it's some type of high density PU foam that is used for the stringer core in the new boats.

[bens250ex]

If I ever did another one I would use that liquid system they use for outboard transoms, or at least use it for where the motor mounts. It could easily be done but will prob be expensive.

[Jesse]

I did some more research. Nida bond is a polyester based resin. I still need to figure out what parts it from a typical casting resin. I also discovered that Epoxy resin bonds excellent to polyester resin, but polyester resin doesn't bond as well to epoxy.

So hopefully I will start tearing the my sunport open tomorrow. Still need to remove the gas tank. I am planning on cutting the ski locker base out. Later I will run a support around the bottom of the ski locker and then put the cut out back in. Their is a good chance I will be taking the cap off, but for now it will be easier to get the tank out and this way I will have access to area below the ski locker in the future.

[Jesse]

I have found more information. The reason for removing the stringers completly and starting from scratch, is to create a solid bond from stringer to hull.

From my searches there are rotted stringers that have debonded from its fiberglass casing. I have also seen stringers thst have delamed. There is defitnatly a difference. I still need to rip my boat apart but if the fiberglass construction is solid I am going to continue with my cap removal poured stringer. As of now, I do not see a problem usong polyester resin in the stringer cavity.

I also read that arjay 6011 is similar to nida bond but less expensive. I also read you should put down wood flour with epoxy under the stringer to prevent hull cracking

[bens250ex]

Would just poured resin be brittle?

[Jesse]

I think so, but you mix cabosil, milled fibers, microballons to give it more structure. I have poured some epoxy molds using microballoons which turned out like a really hard plastic. the milled fibers didn't turn out but I am going to try it again. I would aslo add fiberglass which would be where the strength would be.

[Jesse]

http://www.correctcraftfan.com/forum/new_reply_form.asp?TID=5211&PN=2&TR=47

heres a link to a forum where a couple guys did their stringers in a similar fashion. One guy used Seacast resin and the other guy used Arjay 6011. I am trying to register to see what the outcome was but its taking for ever to get the activation email.

[lively]

Please for the sake of doing shit right , do not poor resin and chop strand into a made up stringer and think it will work , do some research and look how Fiberglass gets it's strength . Then you will see that plain resin will heat up , heat up so hot when puddled and will prob make you gel coat bubble on the bottom . Do the fill stuff mentioned above if you want to just pour it in and go . But it's not cheap , 500.00 for 5 gal and you will need like 4 I would guess to be safe


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[Jesse]

Thanks for the input lively, this is why I am asking. I work with epoxy resin on basically a weekly basis. I know whatever is left in the cup will get hot and kick sooner than what has been poured out. Never really thought much of it. Like I said i have poured molds with epoxy and they have turned out. All I know about polyester is it is stiffer and has less of a bond. I wouldnt use chop strand i have 4oz and 6oz scraps of fiberglass, but it probally wouldn't make much of a difference if it would overheat.

[chris young]

So this weekend, I was discussing this with my best friend, who is a structural engineer, and he set me straight on a couple of points, and confirmed my thoughts on the others.

The overall structure is what is important here, don't think of the stringers as the structure that stiffens the hull. It's the fact that the floor is bonded to the sides of the hull, and the stringers. The job of the stringers is to tie the floor to the hull. That part I had right, where he set me straight was in how strong the stringers needed to be. I thought that this being the case, they could be very flimsy and still do their job, but apparently they still need to be fairly substantial. So, what we need are stringers that are as strong as the original construction of new wood covered with the lay up that Supra used. IMHO the most cost effective repair would be to re-enforce the existing stringers with enough material to compensate for the rotted wood. But if leaving rotten wood in your boat gives you the creeps, then the next best would be to hollow them out, fill them with foam, and build up a good heavy lay up. The absolute best, again, my opinion, would be to use the Nida Bond every where. Regardless of how the rest of the stringers get done, I think if you can pour the nida in the motor stringers, that would be a very good fix.

[lively]

http://img.tapatalk.com/d/14/05/26/upemenu5.jpg 2 by Douglas fir , filets with pl and poly / csm torn up into fibers . Just understand that when we use poly/ epoxy . Any FRP for that matter the resin is not the strength , the glass is and the right mixture of both I learned that less resin is better . I used roughly 30 gal for my rebuild including fixing the top cap and the transom


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