Need help in stringer design (All fiberglass and NO wood)

[thurps]

Re: Need help in stringer design (All fiberglass and NO wood)

I agree with Mark42 about glass over foam. Using pvc you might be asking for trouble due to the high modules of expansion compared to fiberglass. Foam is easy to work with an you can get it in almost size. Just make sure it’s a urethane foam or a similar one that won’t melt when it comes in contact with resin.

 

[ManOfwar690]

Re: Need help in stringer design (All fiberglass and NO wood)

the second design is best but use aluminu stips insead of wood and use self taping ss screws to screw the deck down done deal

 

[kalla man]

Re: Need help in stringer design (All fiberglass and NO wood)

why dont you glass the stringers in air-tight, the trapped air space will give you more floatation than any foam can give you.

i like the idea of the aluminum strip used instead of wood
on your second design..thats your ticket~~~~~~~~~~~~~~~~~
THE PROJECT.......
s99.photobucket.com/albums/l309/kallaman/

 

[Saskatoon2005]

Re: Need help in stringer design (All fiberglass and NO wood)

If I glass the stringers in airtight....do you think I can do without foam floatation? Will the airtight stringers float a water-filled hull?

 

[iwombat]

Re: Need help in stringer design (All fiberglass and NO wood)

The reason for the pvc is simply to hold screws. Foam doesn't hold screws that well.

Once the deck screws go in - there goes your airtight stringer.

 

[ondarvr]

Re: Need help in stringer design (All fiberglass and NO wood)

PVC pipe will not hold screws well, and don't worry about the pvc being compatible with fiberglass in bonding, expansion, flex or anything else. The only reason to use it is for it's shape and ease of fabritating, it will have no positive or negative influence after that, so if you use it, use the thinnest wall pipe you can find. There are resins that will bond very well to PVC, but you would need to buy a drum of it at a time.

It can be very difficult to build a water tight compartment, most of the time water gets in, but never gets out.

If you want to screw the floor down, then the aluminum strips are your best bet.

Many floors are just set on the stringers, or set on the stringers into still wet glass, some are glued down with 2 part glues of various types. The glue or wet glass methods will smash down a little and allow for some uneven areas on the tops of the stringers.

Method #2 will be stronger since you would have 2 vertical, or almost vertical walls per stringer.


I use pour foam in my boats, aluminum and glass, but they're all kept indoors when not in use. They feel more solid and are quieter, especially the aluminum, with foam.
I won't say it's the best way to do it though, all methods have their short commings.

 

[Saskatoon2005]

Re: Need help in stringer design (All fiberglass and NO wood)

Hmmmm,

"The reason for the pvc is simply to hold screws." said iwombat...

"PVC pipe will not hold screws well," said ondarvr...

All these replies that aren't adding up are starting to worry me....LOL!

So where does one buy these aluminum strips and how to I attach them to the underside of the fabricated stringer? Can you buy them at the local Home Depot? Will the resin hold them onto the stringer? Do I lay mat up over them to get them to hold? Thanks for the replies...

...at least we all agree that the second idea of mine is much more stronger and the pvc will be used to shape the stringers. Now just to figure out a proper way to attach the stringer to the floor....LOL!

 

[Bondo]

Re: Need help in stringer design (All fiberglass and NO wood)

It can be very difficult to build a water tight compartment, most of the time water gets in, but never gets out.

Ayuh,....... That's Also why I prefer a Foamless Hull.....
Water WILL get In,+ will Never Leave.....Period....
My boats are put together with Limber Holes to Drain, Any,+ All the water introduced to the boat, into the Bilge to be pumped overboard......
That's also Why I've been advocating the Soda Bottle Floation,.... They will give some Floation,+ they'll Drain......
As far as the possible Structural component of adding Foam,....
I prefer to Build my Hull Strong enough, that I don't Need the Foam......

There's No Doubt that an All Fiberglass stringer system can be built,...
And the Reason your 2nd picture is Better is because it Forms a Structure, Triangler at that....
1 thing to remember about forming,+ building the Stringers is,....
Sharp Corners are a Stress Point in Fiberglass,.... Use Radius'ed Corners......

I'd just Glue the Floor down with Epoxy Paste,+ Not bother with Screws at All...........

 

[ondarvr]

Re: Need help in stringer design (All fiberglass and NO wood)

I see the construction methods used in building boats every day on the job, good and bad, wood and or aluminum (better) are used for backing to hold screws, if pvc worked it would be used. PVC pipe can be glassed around and used as a stiffener and then to run wires through, but don't put screws in it. You can get aluminum at any good sized hardware store, but glueing it down is better for a water tight fit.

If you do want to pre-make all F/G stringers, just take a couple 2x12s set a the angle you need and then shape the top how ever you want, you can use PVC cut in half if you want it round, or a 2x4 and make what ever radius you like. Make the mold to the longest length you will need, I don't know how many you need, or how long they are, but you don't need to lay it up the full length if you need some that are shorter.

Use a generous amount of mold release wax on the wood, don't worry about whiping it off and they should come off the mold easily.
You can make the stringers the thickness you need in the end, but they will be heavy and harder to cut to the correct shape, or you can make them thin so they will be lighter to handle and easy to cut, then you can glass over them once they are in place. They need to be glassed in place anyhow.

 

[thurps]

Re: Need help in stringer design (All fiberglass and NO wood)

In the old days they used to just lay down cardboard carpet rolls and glass over them.

 

[iwombat]

Re: Need help in stringer design (All fiberglass and NO wood)

PVC pipe won't hold screws well?

I make stuff out of PVC all the time (non marine) and it holds screws just fine, that's why I use it. I've got two racks holding audio and computer equipment made out of PVC that I'm staring at right now.


We're all just tossing ideas at you. You should fab up at least a couple of solutions in small versions and test them out before you make the real ones anyway.

 

[Saskatoon2005]

Re: Need help in stringer design (All fiberglass and NO wood)

Thanks for the imput guys, you have been a huge help in determining what route I will take, I will keep you up to date as to what I decide to do, with that in mind, I haven't heard any solutions to foam in the hull, and would like to hear whatever ideas you have. Maybe pop bottles will work, because I don't want to use foam, because like you said," Water WILL get in the hull!"

I live in Canada so another problem I have is any water that does get in may freeze in winter, rupturing the closed cell layer. then it melts. Water in the hull every winter means that the foam layers will get broken down over time and work as a sponge rather than closed cell. If the winters here were not so harsh, I would definately go foam. But I need some ideas thrown at me to consider.....you guys have been sucha great help so far, lets keep the good times rolling....LOL!

 

[ondarvr]

Re: Need help in stringer design (All fiberglass and NO wood)

PVC can do many things well, until it doesn't. Like compressor air lines, they can hold up for years and then suddenly explode when they get jarred or hit lightly with something. I've fabricated many things out of PVC pipe and sheets when I was making water filtration systems for places like Sea World and the big casinos and resorts in Las Vegas, it's great stuff but not for this application.

The screws would be subjected to all kinds of loads being worked back and forth at high and low temps, thats not what PVC pipe is designed to do.

 

[Saskatoon2005]

Re: Need help in stringer design (All fiberglass and NO wood)

Okay, so NO PVC, got it! Now what about foam replacement on the inside? What can I use instead of foam?

 

[ManOfwar690]

Re: Need help in stringer design (All fiberglass and NO wood)

well for your aluminum strips make your form then turn it upside down and lat the strips in place ad a few pieces of glass and resing as hold downs just like 3 strips of glass every foot apart one strip every foot one on each end too as far as foam how big did u say your boat is over 21 ft you donot need it under you must have it just dont put any in the bilge of the boat from bow to stearn the the center of the hull clean and your foam on the sides will stay prety dry and the boat will drain nicely

 

[Saskatoon2005]

Re: Need help in stringer design (All fiberglass and NO wood)

MAnOfwar690,

I don't know exactly what you are saying. Is it possible for you to draw it out on a piece of paper and then take a picture of it and upload it here? I think a drawing would much help in your design idea...Thanks,

 

[Bondo]

Re: Need help in stringer design (All fiberglass and NO wood)

I've gotta question WHY you'd want to Prefab the Stringers in a Mold,..??..??......

Why not just Cast them In-Place,..??.....

 

[Saskatoon2005]

Re: Need help in stringer design (All fiberglass and NO wood)

Yeah casting in place is a great idea, except difficult to do without leaving the pvc in boat which I don't want to, or getting the aluminum in there after glass has been laid up.

 

[Bondo]

Re: Need help in stringer design (All fiberglass and NO wood)

Leaving the PVC will hurt Nothing,.....
And,...
You can just Place your Strips whereever you'd like, when you get to that Point......

 

[ondarvr]

Re: Need help in stringer design (All fiberglass and NO wood)

As I said in one of the other current threads on this rot proof subject. Leaving the PVC in will have no positive or negative effects, just don't rely on it to do anything other than be a shape.