Repairing floor stringers

[Butch .H]

Have you seen the componants that are used for a 747 wing

[BHOFM]

How can the wing of a 747 hold up hundreds of tons?

Because the wing is full of structure! Ribs and spars!

[naturewaterboy]

Jim,
A soda can is pretty damn thin... especially these days! I remember, back in the day, when Coors were the only thin cans - all other cans were way heavier. Nowadays I had to change my exercise routine - 12 oz. curls - have do do more reps now...

I did put plywood back in my stringers, not for bending loads, but for just what you mentioned - if you want to bolt something to the stringer, like an engine maybe, it needs to be filled - and not with some whimpy foam.

[the1much]

i got some old STEEL beer cans,,,,talk bout a work out hehe
and its all common sense,, if the wood or foam was just for something to "lay up" on,, then they could just make a mold of a stringer, lay that up,, take from mold and stick it in the boat,,,,,but NOBODY does that,,,wonder why?

[seagull369]

Thank you everyone for keeping this thread alive. Every post gets me 1 step closer to getting this project headed in the right direction (beer cans included ).

Just to clarify, the cellular pvc trimboard I've been talking about for the floor is somewhat of a different animal than the pvc like in plastic pipes and fences that some of you might have in mind. AZEK a popular brand of the stuff. It doesnt crack (at least under normal temps) but rather sags, much like TREX can when not supported underneath in sufficient intervals. I don't dismiss, however, what you've all said about glass not adhering to it well and frankly, considering the $115 cost of a sheet of 4'X8', I doubt I'll be taking the risk to find out.

I noticed PAR saying honeycomb (such as nidacore, I'm assuming?) or other "core" material would be sufficent to use in the stringer channels there. If I dont end up using honeycomb, do you think the pvc plumbing pipe idea I mentioned earlier would make a decent core material? The other posts that suggested I could use foam (covered in bi-ax) and/or it's the -glass on top of the core that really does the work, make me think the pipe would be all right. In case you're wondering, I compared an equivalent size piece (both that would fit in my boat's stringer channel) of PVC to one made of wood- which was originally in my boat- and did find PVC (schedule 40) to be limp-ier/ not as rigid as the other, esp. in longer sections. ABS pipe has also crossed my mind.

Sorry I keep picking your brains on this stuff, but your answers really are helping me tremendously.

[the1much]

whatever you use as your stringer "core" the glass NEEDS to bond to it,, or you'll have air pockets, even using wood you should scratch up the wood, and radius all your corners,, inside corners, and outside ones,, just so you dont get those air pockets. plastic has alot of uses on a bot, like,,,ummmm,,,,,, cup holders, and,,,,ummmm,,,,,ya SOME uses,,,none of them structural. IMO

[PAR]

The whole point is a that a core needs to withstand compression loads, some flexural loading and to be a successful core material it has to remain attached to the laminate.

I was speaking about the cellular PVC, now being marketed as "wood replacement" material for a number of tasks, mostly decking and siding on houses. It's very intolerant of heat or cold, becoming brittle or deforming, plus all the other stuff I mentioned.

ABS, the more rigid PVC's, HDPE, UHDPE and most of the "new" plastics can satisfy some of the core material requirements, but not all. If it can do all of the job it's asked, it will fail.

It's your call . . .

[mongo75]

I would use nothing but wood (for the costs alone) but fom "does" work seeing as how alot of the big boys use the stuff. As far as using half a piece of pvc tube for a FORM, I've seen it done alot of small pieces like hatches, to support the underneath. I would suppose the same could hold true for adding strength to a hull, however I would never use it as a replacement for a true stringer.

I'm getting a chair and popcorn for the rest of this forum LOL

[seagull369]

Ahh, ok, it's the bonding part that's important... I understand. As far as wood, will the glass adhere well enough to a pressure treated type in the stringer or would it be best to use non-PT?

[mongo75]

I'd use non-pt. IIRC, isn't PT wood infused withsome kinda chemical as well? I'd just use good old plywood (or solid timber if you're just making engine beds) and coat it with epoxy so it soaks in good, then glass it over and be done.

[the1much]

theres no sense in using marine grade,, just plain ole ply., it will (SHOULD) be totally encapsulated in glass so there should be NO need for anything "better"

[PAR]

Marine grades of lumber are constructed better, have more veneer layers, fewer if any voids, far fewer defects and are reliably stronger. Construction grades are cheaper, but you don't know what you've got inside (if anything), they're weaker, don't bend well, can fail suddenly if stressed, etc.

In a perfect world, you could coat anything with epoxy and it should keep out the wet stuff. In reality, the epoxy will get chipped, banged, gashed or other wise breached, which will let in the moisture. Knowing this it's usually cheaper in the picture, to install the good stuff, so in the event of a coating failure or breach, the wood can tolerate extended periods getting wet, without issue, before proper repairs can be made.

In the 17' daysailor I'm just finishing up, I used nothing but 1088 Okoume. It cost about 60% more then cheaper 6566 meranti, but the hull is 20% lighter and measurably stronger as a result. This means when I met another boat of similar configuration, they kick it's butt.