Composite stringer grids
 

Many manufacturers are touting "no wood/no rot" construction, and some are
using a composite grid system (fiberglass over some type of foam) to replace
traditional hull stringers and forms. Several bay boats I am interested in use
this type of construction. Of course, from a marketing perspective, it sounds
great. But I'd be interested in some real world opinions. Is such a boat less
prone to flex? Does it result in a more solid boat? Are there other problems
to be aware of? Any pre-purchase inspections that can be accomplished,
assuming it's even possible to see the below-deck structure?

Comments appreciated.


-- Rich Stern
www.nitroowners.com - The Nitro and Tracker Owners Web Site
www.mypontoon.com - The Pontoon Boat Web Site
www.fishingreportdatabase.com - The Fishing Report Database
www.mysporttrac.com - The Sport Trac Web Site

Composite stringer grids
 

Rich Stern wrote:

Many manufacturers are touting "no wood/no rot" construction, and some are
using a composite grid system (fiberglass over some type of foam) to replace
traditional hull stringers and forms. Several bay boats I am interested in use
this type of construction. Of course, from a marketing perspective, it sounds
great. But I'd be interested in some real world opinions.

OK

Is such a boat less prone to flex?

Than what? It is certainly less prone ot flex than the same hull with the same
layup and no grid of any type. Is it less prone to flex than the same hull & grid
with wood as the grid core? No, because wood is stiffer than foam.

In order for the grid to be stiffer due to the foam, then either the hull or the
grid (or both) have to be of stiffer construction such as triaxial weave, vacuum
bagged, etc etc.


Does it result in a more solid boat?

Not necessarily. If the grid is not laminated properly then it may not even last
longer. Foam doesn't rot but some types can become saturated and all types can
delaminate.

Some people hate foam core construction, probably because there are so many bad
examples that have long term problems. But it can be a great type of construction
*if* the details are properly done.

Are there other problems
to be aware of? Any pre-purchase inspections that can be accomplished,
assuming it's even possible to see the below-deck structure?

There are a number of things to inspect that indicate good quality work. Without a
lot of details plus pictures, it's difficult to compress 'how to do a structural
survey' into one usenet post. I'm not the greatest expert anyway.

http://boatdesign.net/articles/foam-core-properties/

Some resources on the web, another good place to look would be in your nearest
library in books on surveying boats.

Some people will say 'foam core = crap' and they probably have some bad experiences
with poorly done foam core. Like anything else, there is good and bad. When it's
good, foam core construction can be very very good.

Fair Skies-
Doug King

Composite stringer grids
 

Rich,

I have a 1978 Winner 24 I/O which has fiberglass over foam in the
stringers. Since we hadn't used it in a few years, I had it surveyed
last winter before putting any money into a trailer, etc. The
surveyor found absolutely no issues with the hull, stringers or
transom which he said is very unusual for a 25 year old runabout.
Your mileage may vary of course but it is a fact of life that water
almost always finds its way into wood, or wood core stringers if you
keep the boat long enough. Good engineering and construction, using
the best materials for the job, is still the secret to longevity
however regardless of any one factor over another. My Bertram 33 for
example has a lot of structural wood but it is top quality marine ply
and heavily encapsulated with resin and fiberglass.

================================================== =

On 18 Nov 2003 21:18:00 GMT, (Rich Stern) wrote:
Many manufacturers are touting "no wood/no rot" construction, and some are
using a composite grid system (fiberglass over some type of foam) to replace
traditional hull stringers and forms. Several bay boats I am interested in use
this type of construction. Of course, from a marketing perspective, it sounds
great. But I'd be interested in some real world opinions. Is such a boat less
prone to flex? Does it result in a more solid boat? Are there other problems
to be aware of? Any pre-purchase inspections that can be accomplished,
assuming it's even possible to see the below-deck structure?

Comments appreciated.


-- Rich Stern
www.nitroowners.com - The Nitro and Tracker Owners Web Site
www.mypontoon.com - The Pontoon Boat Web Site
www.fishingreportdatabase.com - The Fishing Report Database
www.mysporttrac.com - The Sport Trac Web Site

Composite stringer grids
 

Karl Denninger wrote:

2. Cores in decks and hullsides (above the waterline) are acceptable,
PROVIDED they are properly encapsulated. This means that there are
NO PENETRATIONS without the edges of the core being sealed with
epoxy. No way for water to get in, no problems. Note that this
means that hardware must be THROUGH BOLTED; screwing it down into a
cored structure is NOT ACCEPTABLE.

Agreed, but then thru-bolting hardware through a core is also not acceptable. The
compression will deform the core, and then of course water gets in, plus some
helpful person usually tightens the bolts after a while and that makes it worse.

Core should be tapered to a solid laminate where there is hardware thru-bolted.

Fair Skies-
Doug King

Composite stringer grids
 

On Tue, 18 Nov 2003 18:43:02 -0500, DSK wrote:

Core should be tapered to a solid laminate where there is hardware thru-bolted.

+++++++++++++++++++++++++++++++++++++++++++++++++

That works of course, but there are other ways. Drilling an over size
hole, coating exposed core with epoxy resin, refilling with solid
glass, and then redrilling is a perfectly acceptable method of
ensuring core integrity and absorbing compression loads.

Composite stringer grids
 

If your stringer is relying on the wood core for strength, it's poorly built.

The wood core, foam core, Cheez Whiz core or whatever has served its purpose
when it has functioned as a form for the layers of glass and resin that follow.
A well engineered stringer can be completely hollow, just like a box beam, and
have more than sufficient strength.

Composite stringer grids
 

On 19 Nov 2003 01:33:42 GMT, (Gould 0738) wrote:
If your stringer is relying on the wood core for strength, it's poorly built.

The wood core, foam core, Cheez Whiz core or whatever has served its purpose
when it has functioned as a form for the layers of glass and resin that follow.
A well engineered stringer can be completely hollow, just like a box beam, and
have more than sufficient strength.

================================================== ======

No argument from me on any of that but I'd suggest that if you are
just using wood in the stringer to form the fiberglass, then you are
adding unnecessary weight and wasting perfectly good wood. I suppose
you could argue that using wood might be desirable as a rigid building
form, with no reason to remove it later.

Wood is actually an excellent structural material of course, as long
as it is the right type of wood, and properly encapsulated. The
theory of building cored structures is that the skins carry the load
similar to the parallel surfaces of an I-beam, and the core material
acts as the "web" of the beam to add stiffness. This creates a much
stiffer (less flexible) structure, at a much lower weight. The catch
is that the core material must retain its integrity over time and not
separate from the skins.

Composite stringer grids
 

Wally,
Okay, but were the Silverton's stringers wood core or foam?
Paul

"WaIIy" wrote in message
...
On 18 Nov 2003 21:18:00 GMT, (Rich Stern) wrote:

Many manufacturers are touting "no wood/no rot" construction, and some
are
using a composite grid system (fiberglass over some type of foam) to
replace
traditional hull stringers and forms. Several bay boats I am interested
in use
this type of construction. Of course, from a marketing perspective, it
sounds
great. But I'd be interested in some real world opinions. Is such a
boat less
prone to flex? Does it result in a more solid boat? Are there other
problems
to be aware of? Any pre-purchase inspections that can be accomplished,
assuming it's even possible to see the below-deck structure?

Comments appreciated.

My 30ft 1989 Tollycraft has foamed stringers and it's solid as a rock.

My friend has a 1989 30ft Silverton and he replaced half the stringers
he could get to.

Your mileage will vary.

Composite stringer grids
 

Chuck,
Okay then why the concern over rotted wood in the stringer? I would
imagine that the water got in through a poor job of sealing the wooden
stringer, so why not seal it up and not worry about it? But does an older
boat like an 89 Sea Ray depend on the wood for its strength or the
fiberglass coating? I know a fellow that had his boat (88 Sea Ray 300
Weekender) out of the water for three seasons while he dried out his
stringers and checked for moisture with a meter. I think he then bored some
holes in the stringer and filled with epoxy. Was he wasting his time? His
complaint was that Sea Ray drilled limber holes through the stringers and
didn't seal the limber holes causing the water absorption. I'm just trying
to determine how wide and important of a problem is this.
Paul

"Gould 0738" wrote in message
...
If your stringer is relying on the wood core for strength, it's poorly
built.

The wood core, foam core, Cheez Whiz core or whatever has served its
purpose
when it has functioned as a form for the layers of glass and resin that
follow.
A well engineered stringer can be completely hollow, just like a box beam,
and
have more than sufficient strength.

Composite stringer grids
 

DSK wrote:
Core should be tapered to a solid laminate where there is hardware thru-bolted.

+++++++++++++++++++++++++++++++++++++++++++++++++
"Wayne.B" wrote:
That works of course, but there are other ways. Drilling an over size
hole, coating exposed core with epoxy resin, refilling with solid
glass, and then redrilling is a perfectly acceptable method of
ensuring core integrity and absorbing compression loads.

Sure, but you have to do that yourself. I thought we were talking about fromt the
factory.



Karl Denninger wrote:


Uh, and use a backing plate. Even better, build the backing plate into the
hull in place of the core in that spot.

But if it's in the center, it's not a backing plate ;)
It has to be underneath both the tension & compression skins of the deck structure.

I read a description of an uncored but very light & strong boat hull, which had a
"subimposed" structural grid. Anybody have any good ideas what that means?

Fresh Breezes- Doug King