GRP and stringers (moved from practical forum)

Sixpence

Sixpence

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This topic has probably already been coverred so if anyone can link, please do so
I have now reached a point where all woodwork on board has been ripped out due to water damage from leaking windows. The problem is that some of the stringers have rotted and also had to be ripped out. Will it be alright to fit new pieces of wood to replace the rotten bits, then fibre glass them in. And as all the galley and other woodwork butting up to the hull has now gone, how important is it to fit replacements, as in , do they add to structural strength
 
Well I think it is, this one seems like it's for wooden boats. Stringers are usually put in a fiberglass boat to control oil canning that is to stop the hull from flexing and should not be omitted. Its not really the wood that gives the strength but the fiberglass over the wood. Although wood is probably the least expensive material to use as a form.
 
Sugest that you go down to the local library and get a book out on GRP construction.
If you encapsulate wood it will rot if it gets damp, Grp is not waterproof. allyou need is to make some tophat section and that will replace the stringer. the wood is only a former ,the strength is in the GRP. In fact we used to use paper rope as the former.
 
Not a phrase I've heard before so maybe I am in the right place . Would it help if I filled the remaining hollows with expanding foam , then a cover of ply with a coat or two of epoxy or something like that
 
First stringers are usually above the waterline in fact I've never seen any below. Second I presume you will be painting hopefully with a gelcoat. If I were doing this I would use airex or like foam but you have to buy a minimum amount how much do you want to spend. From your inquiry it sounds like you are redoing an old boat how long did the original wood last?
 
I think the boat dates back to the 70's , but it was left on hard standing before I bought her. By that time the rain had filled the insides a few times and obviously soaked through to the wood , which absorbed it making it swell , thereby splitting the grp and gradually getting worse over the years . The idea is to fit stringers , glass into place , build up layers , then cover with a waterproof coating , possibly epoxy . I think that filling the remaining voids with expanding foam , and sealing that in with glassed over ply , would give extra strenght and insulation
 
Any alternative suggestions, I'm trying to make sure any water goes straight to the bilges where it can be pumped straight out, but also increase the strength of the hull and its insulation, I just thought foam would do the job
 
Fiberglass absorbes water as do foam. balsa core etc wood rots in fresh water (rain) gets wormy in salt water, steel rusts aluminium work hardens and cracks. It amost makes me want to sell my boat.
But then nothing is perfect. it seems to me that the above mentioned boat survived (mostly) after being repeatedly filled with water and dried out for thirty years. If I remember correctly British boat builder in the seventies seemed to be inamoured with chopper guns so the quality wasn't there anyway.
Your advice in going to the library for boat repair books is a good one, may I suggest Fiberglass Boats by Hugo Du Plessis.
Also forget the expanding foam and although epoxy does have its place this isn't it
 
What I have seen used in the past to replace the rotted wooden stringers in early 70's build Boats is 25mm or so Glass resin pipe glassed over with 6/8 layers of Glass/fibre above the water line as suggested and use the pipe as a cable run.
 
If this is a vessel of any size and meaningfulweight I would suggest a survey which will put youon the right track and be invaluble if at any time you wish to sell,imho.
 
Yes Got to agree with this we have just had "Mercia III" (1905 wooden Gaff Cutter) surveyed all we have done so far can be seen from both sides and the chap said my report & fee will put far more on the value of our boat.
 
I'm confused , I am not interested in increasing the value , only in making her safe , if a survey will tell me what I need to do then I will get one done , but if it will only give me a , "you need a battery isolator sign " routine , I'll get that done later , I'm after practical advice on what to do . Does the positioning of the former cupboard against the hull make a difference etc . I'm already kicking myself for paying someone to fibreglass wooden stringers in . Anyone know of an alternaive to the idea of expanding foam , or am I heading in totally the wrong direction ?
 
G'day Jogi,

I like your breakdown of the materials in common use and the failures, as you say "nothing is perfect"

And fully agree with "Also forget the expanding foam"

But I'm at a loss as to why you would say "and although epoxy does have its place this isn't it" can you expand on this please?

Avagoodweekend......
 
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