"Composite" Stringers has it been done???

[daydreamer1252]

Here we go, time for some thoughts, advice, and probably some controversy.
Stringers...

There are literally thousands of homebuilt aircraft, one that traveled around the world non-stop and another that made it to outer space that are of COMPOSITE construction. Basically foam core with glass cloth/resin over it. This construction is tremendously strong and very lightweight.

Will this technique work for srtingers? If not why not?

It would seem that it would be an ideal method for replacement work. Additionally the foam will not rot or waterlog.

Let the comments commence. Thanks all.

 

[jcsercsa]

Re: "Composite" Stringers has it been done???

hay daydreamer1252, been done !! there are some boats that dont have any wood on them at all strait from the factory !!I am doing my two outer stringers in pvc deck boards !!! John

 

[ondarvr]

Re: "Composite" Stringers has it been done???

The only thing that keeps people from doing it more often is the cost, good stringer core products are typically very pricy, it can more than double or triple the cost of a repair when compared to wood.

 

[Robj]

Re: "Composite" Stringers has it been done???

I am in the process of working on a boat, a Boston Whaler copy that does not have stringers, all fibreglass and foam. The problem is, that due to poor design, the foam is saturated and have since cut the deck out to replace the foam, which is also part of the structure in this boat. So regardless of whether you have composite or wood stringers, if the foam gets saturated, you will probably end up replacing it. If you can prevent water ingress, then the foam remains dry and more than likely so would the wood stringers.

Have a great day,

Rob.

 

[BillP]

Re: "Composite" Stringers has it been done???

This has been going on with production boats for a long time...15yrs? Google Compsys in Melbourne, Florida. They make foam/glass stringers for many of the well known boat mfgs...the list of names is long. The stringers are pre-formed (to boat mfgs specs) to fit the hull exactly and "drop in" with minimal labor. There is no cutting or trimming (literally remove from the shipping box, set into the hull and apply resin). Glass cloth is bonded to the foam stringer during manufacturing so no cloth cutting is required. Cost of a stringer is high but the payback is in less labor and material waste.

 

[mtnrat]

Re: "Composite" Stringers has it been done???

I used Coosa composite for stringers, transom and floor. Worked great, but very expensive.

 

[wca_tim]

Re: "Composite" Stringers has it been done???

dry wood, saturated with thinned resin and layered with glass.... IS actually a composite... just the poor mans / layman's version I guess...

 

[jcsercsa]

Re: "Composite" Stringers has it been done???

The only thing that keeps people from doing it more often is the cost, good stringer core products are typically very pricy, it can more than double or triple the cost of a repair when compared to wood.

YEP I did pay just over double for mine !!

 

[Coors]

Re: "Composite" Stringers has it been done???

My 4winns had a 1x in the stringers to shoot foam on, then glassed 3/8" thick. The glass is the strength. The rotten wood only mattered at the engine mounts.

 

[iwombat]

Re: "Composite" Stringers has it been done???

The biggest drawback to using only fiberglass for stringers is attaching the floor. Screws hold very nicely in wood. Fiberglass - notsomuch. That's one of the main reasons wood is still used for stringers.

 

[fishrdan]

Re: "Composite" Stringers has it been done???

Compsys in Melbourne, Florida. They make foam/glass stringers for many of the well known boat mfgs

I saw a stringer job somewhere (100+ pics of the build) using these foam stringers, looked to be a pretty quick and easy install over wood stringers. If foam stringers are used in new boats and foam/pre-glassed stringers are used to rebuild boats, why couldn't a DIY guy make foam stingers? Cut/fit 2" thick insulation foam for stringers, glass the foam stringers into the hull and then PL (or peanut butter) and screw the deck to the stringers. PL (or PB) would bond the deck to the stringers and seal all of the deck-stringer screw holes.

It seems that everyone says fiberglass creates the structural strength in stringers, so why use wood at all? I'm sure foam/fiberglass stringers have a thicker layer of glass to compensate for the lost rigidity of wood, but foam/glass seems to be a better construction method since the foam won't rot out like wood.

My 73 SeaSwirl has a 3/4" plywood keel stringer, but I noticed the 4" wide stringers were constructed with a 1/2" plywood top and foam core, There was no vertical wood in the 4" wide stringers for structural strength. I assume the only reason they used the 1/2" ply in the top was to allow the deck to be screwed/stapled down.

I'm thinking foam stringers need to be installed properly to make a strong hull (no voids between foam and hull) where wood stringers can be fudged a bit and still provide a strong hull. IE; foam stringers are a precision fit where wood stringers are slowly built up in the hull (cut/fit wood stringer, bed, fillet then glassed in.

 

[oops!]

Re: "Composite" Stringers has it been done???

ok guys ....here we go....

first....a foam stringer encapsulated in wood has been done for years....bayliners have them... they just use the foam to get the shape to glass over.......remember...glass can be as strong as steel !........the problem is glass is not totally waterproof, so the foam in the stringers gets waterlogged.........to do a b-liner, you cut the top off the strings and re foam them....then re glass the top.......easy as pie !


as ondarvr said ....there is compisite products out there....but they cost big money....

there is a product on the market called "pensky board".
they are using it in the newer glasstrons and campions.....(if my information is correct)....it never rots....it is stronger than plywood....(even in a stringer situation)...it is also lighter than traditional plywood......

this means you have a super strong "wood like" product...that will last for a long...long time .....but it is 10 bucks a squair foot !

the deal is.........is that standard plywood....when done properly....will last 20-25 years.......(thats allmost half as long as john is old ! )
and at 25 years....standard wood will out last the average boat owners desire to own the boat......so why build at $10 sq foot when 2 bucks will do the same thing?......

the products are there.....if you want to spend the money...!

cheers
oops

 

[fishrdan]

Re: "Composite" Stringers has it been done???

Thanks for the insight oops!

You brought up a good point that fiberglass is not completely waterproof and will wick moisture through the glass, forgot about that. It's certainly a drawback for both wood and foam stringers. Looks like the best way to stop stringer water intrusion is to go with a composite core material which is impervious to water,,, the expensive stuff which is not cost effective for an older boat.

I guess it's best for a DIYer to copy the manufacturer's stringer construction, but do a better job of glassing and sealing them from water intrusion.

 

[daydreamer1252]

Re: "Composite" Stringers has it been done???

Thanks all for the insights!!

oops, thanks for this.

first....a foam stringer encapsulated in wood has been done for years....bayliners have them... they just use the foam to get the shape to glass over.......remember...glass can be as strong as steel !........the problem is glass is not totally waterproof, so the foam in the stringers gets waterlogged.........

Now, let's use styrofoam blocks (blue or pink) and glass over them I think this will mostly solve the waterlogged foam problem!! Wouldn't it?? Cut and paste!!

obviously continue the discussion, I am enjoying it!

 

[Coors]

Re: "Composite" Stringers has it been done???

Why use the water-sucking foam?
I had foam stringers, with a 1x, to spray the foam on.
Threw the last owner leaving the plug in, and leaky cover-water went in through the engine mount lags.
the stringers were rotted inside, but the shell was the strenght. The rotten wood in the mounts was the problem; stringers good.
I still cut the tops off, dug the crap out.
But, I replaced the innerds with plastic outdoor decking board (more volume) p-nutted down.
Then poured epoxy and roven/biax in it. Had to use wood on the mounts, used an old piece of douglas fir glu-lam I had.
I was lucky, as 4winns transom is glassed separate from stringers.
The point is; no foam, therefore no rot again, but the foam wasn't a issue to begin with- it was the mounts rotted.
Once I got 5 feet from the transom; no wet crap.
It was a pain, but getting MAS epoxy from the local discount boat store was only 3 gallons= $450.
And so easy to work with, if you buy the pumps.
Easy, and no worries.

 

[fishrdan]

Re: "Composite" Stringers has it been done???

Thanks all for the insights!!

Guess I should have said that :redface:

daydreamer, I think we are on the same page as far as what we would like to do. I was thinking of taking the 2" blue insulation foam and;

- cutting it down into stringer sized strips, lap jointing for longer stringers and sandwiching for thicker stringers
- forming it to the hull contour
- routing off the corners with a 1/2" 1/4 round bit for better FG laydown on the corners
- sealing the foam with a rubberized coating to avoid water penetration
- bedding to the hull with peanut butter or PL
- glass in the stringer as normal
- pre-drill decking and stringer screw holes
- Apply PL to the tops of each stringer with a healthy dab around each screw hole
- screw decking down to stringers
- drill 2-3" holes through decking and fill with pour foam
- plug holes and glass over the screws heads and plugs

Sounds like it would work, but I don't know if it's better, easier or stronger than doing using wood stringers

Why use the water-sucking foam? I replaced the innerds with plastic outdoor decking board

I think floatation foam is a necessary evil as you need something to keep the boat afloat if it gets swamped, adds rigidity to the hull too. If water gets below deck with floatation foam in there you're kinda skrewed either way it goes, stringers soaked or rotted and the foam water logged. I want floatation below the deck and haven't seen anything that compares to foam, even though foam has it's problems.

As for foam in the stringers, it seems this is the way boat manufacturer's are heading and why not rebuild a boat the way the new ones are being made? The only thing I wonder about is the density of the foam they are using for the stringers?

The plastic decking material sounds like an option for stringers, but isn't it heavier than *ell, hard to cut/shape and really wobbly-flexible?

 

[wca_tim]

Re: "Composite" Stringers has it been done???

Thanks all for the insights!!

oops, thanks for this.

first....a foam stringer encapsulated in wood has been done for years....bayliners have them... they just use the foam to get the shape to glass over.......remember...glass can be as strong as steel !........the problem is glass is not totally waterproof, so the foam in the stringers gets waterlogged.........

Now, let's use styrofoam blocks (blue or pink) and glass over them I think this will mostly solve the waterlogged foam problem!! Wouldn't it?? Cut and paste!!

obviously continue the discussion, I am enjoying it!

the only possible issue I see with using polystyrene foam... is that styrene is the liquid in pol resin... and is quite a good solvent for polystyrene... in other words, the glass resin will dissolve the foam... would just have to be sure that the foam you used was solvent resistant... such as poly urethane foam or some others...

 

[Coors]

Re: "Composite" Stringers has it been done???

Guess I should have said that :redface:

daydreamer, I think we are on the same page as far as what we would like to do. I was thinking of taking the 2" blue insulation foam and;

- cutting it down into stringer sized strips, lap jointing for longer stringers and sandwiching for thicker stringers
- forming it to the hull contour
- routing off the corners with a 1/2" 1/4 round bit for better FG laydown on the corners
- sealing the foam with a rubberized coating to avoid water penetration
- bedding to the hull with peanut butter or PL
- glass in the stringer as normal
- pre-drill decking and stringer screw holes
- Apply PL to the tops of each stringer with a healthy dab around each screw hole
- screw decking down to stringers
- drill 2-3" holes through decking and fill with pour foam
- plug holes and glass over the screws heads and plugs

Sounds like it would work, but I don't know if it's better, easier or stronger than doing using wood stringers



I think floatation foam is a necessary evil as you need something to keep the boat afloat if it gets swamped, adds rigidity to the hull too. If water gets below deck with floatation foam in there you're kinda skrewed either way it goes, stringers soaked or rotted and the foam water logged. I want floatation below the deck and haven't seen anything that compares to foam, even though foam has it's problems.

As for foam in the stringers, it seems this is the way boat manufacturer's are heading and why not rebuild a boat the way the new ones are being made? The only thing I wonder about is the density of the foam they are using for the stringers?

The plastic decking material sounds like an option for stringers, but isn't it heavier than *ell, hard to cut/shape and really wobbly-flexible?

They use foam because it is cheap, and out of warranty, when you realize what it will now cost you for repairs.

 

[ondarvr]

Re: "Composite" Stringers has it been done???

Products can always be made better, the problem is the cost gets so high that most people can't afford them, so they look for a price point where people can buy the product. If that means it won't last as long if not cared for, then it turns into a problem at a later date, but for the first many years it works well and if it is cared for then it will last much longer. When you combine low cost products with poorly trained workers and buyers that don't properly care care for them, then it becomes a much bigger issue.

 

[Coors]

Re: "Composite" Stringers has it been done???

buyers that don't properly care care for them, then it becomes a much bigger issue.
Reply With Quote And that is a huge problem.