What to use under stringers

outlaw, are you rebuilding or manufacturing from scratch?

there's a couple trains of thought here that come to mind when it comes to stringers. laying the stringers directly to the hull will present a problem that must be addressed with a proper installation. with stringer 'core' set directly on the hull you will be creating a bending moment where the edge of the core meets the hull glass. the core must be filleted to the hull before being glassed in. this will help distribute the load along the bending moment and transfer some of the force into the stringer itself eliminating the potential for cracking along the 'joint'. david pascoe addresses this issue here: http://www.yachtsurvey.com/HullFailPart1.htm. again you can address the problem by bedding the stringer core in a flexible adhesive that will cushion the force and then fillet the core or you can raise the stringer 1/16" - 1/8" from the hull by shimming and tacking with a fast set adhesive, then fillet. the article mentioned in ratrace's post also addresses this.

 

Stringers and frames

1Much,
I have actually walked across the decks of the Nina, Pinta and the Santa Maria (replicas), I was 12; I have walked the decks of the USS Intrepid. I have looked at countless diagrams of wooden ships; All in fine detail. But no where, and I mean no where, do I find a detailed diagram, "Pic" of a FRP/GRP stringer and stantion design. Geeee, there are only about a million FRP/GRP boats floating around NJ alone. For example, just the posts on BoatDesign.net covers hunderds of pages on stringers; stringer repair, stringer design, stringer size, stringer bonding, on and on and on. Why is this topic such a secret?

_____________THIS IS JUST A TEST: DO NOT REPEAT THIS IDEA_______
I am going out on a limb and develop a Hypothesis from total ignorance:
Stringers in a FRP/GRP boat are just there to hang the motors on and a place to bolt the bottom of the bulkheads; in fact, stringers--while they do stiffen an FRP/GRP boat, they should not reduce the amount of flex inherent in such a boats design. In addition, stringers that are too rigid and stiff may cause an FRP/GRP hull to fail. Therefore, all stringer must have an inherent property that which is similar to the boats hull material; too, the stringer are best placed, bonded, and slightly elevated from to hull so as not to inhibit the hull flex.
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OK, now start tearing that apart. point out every little error.....

 

Much,
Chew on this:


The principles of good stringer design are simple. They must run uninterrupted from one end of the hull to the other. They must be of adequate height to width ratio, i.e., structural modulus, to resist impact loading on the hull skin, be of sufficient strength to carry the engine load, be stabilized against lateral movement if high profile, and be securely attached to the hull so that they don't break loose. The profile, or top of the stringer, should run in a straight line. If there are any changes in the profile, then special design reinforcements must be added.

This part I don't get: "resist impact loading on the Hull skin"....

 

I think that means that the loads from a "slam" should not go through the stringer to the hull and break out the bottom of the boat

 

Wow, this is great.....................................

Hull Design Defects
Part II
by David H. Pascoe, Marine Surveyor

http://www.yachtsurvey.com/HullFailP2.htm

 

I was right...................




Example of hard spot caused by improper stringer design and installation. Bottom hinges around hard edge of stringer wood core. At right, wood core is elevated by a soft material so that it does not touch the hull skin and the load is bourn by the more flexible tabbing.

When

 

What the hell is panting....?


This is rarely a problem to the hull side itself. The cracking usually occurs as a result of severe panting because the sides are thin and unsupported. The sides themselves don't fail because the panels are so large and the flexing occurs over such a large area that the radius of bend is too large to cause damage to the laminate strictly as a result of panting. However, because the stress is transmitted vertically up the hull side, the forces of interlaminar shear are very high. Therefore,

Definition of Panting:
The pulsation in and out of the bow and stern plating as the ship alternately rises and plunges deep into the water
Publisher: http://www.free-marine.com/glossarynt.htm

 

Ya know, I was just thinking:
If, for example, you look at a large 53' tractor-trailer trailer it has a very thin deck and very thin walls. If, you look at a flat-bed tractor-trailer trailer, it has a massive beam under a very, the same, thin deck....

What did we learn ?

 

do ya think someone like bayliner would put stringers in their boats for no reason?,,just cause they wanna give ya something extra for ya money?,,,them little outboards dont use the stringers,,,,so why would someone like bay put there?,,,,,and ive been on them replicas too,,,use ta play in mass. all the time
,,,,think of it like this,,,a piece of sheet metal is WAY stronger if you run a bead ( stringer) through it,,then it is as a flat piece of metal,,,,,the stringers are just a way of putting a "bead" in ya glass.,,,there,,that should get something started hehe

 

that trailer also bends,,,when empty, look at it,,,,the middle of the trailer is higher then the ends,,,,till ya load it and it flattens out,,(spent 3 years in back of the damned things running the largest " Family Dollar warehouse ".
and the "beams" in the trailer,,,are made from the same thing the rest of the trailer is,,,,it all flexes basically at about the same rate,,,,and the reason we put wood or foam in stringers is cost,,in fact,,whats "inside" ya stringer,,has to "flex" easier, then the glass round it,,,,the "filler" is just that,,,filler,,,but if it "flexed" "harder" then ya glass,,,it would rip apart.,,is all i can come up with today,,hehe,,,still recoverin hehe

 

Stringers are a reasonably simple engineering concept. A boat hull is a girder. Though 'glass boats seem to be a homogonous structure they typically aren't. 'Glass alone isn't stiff enough to produce these types of structures, so you have to picture the hull, much like a wooden or metal structure, unless incorporating sandwich construction methods.

The bottom of the boat would be the lower portion of a girder, the lower flange if you will. The stringers and other internal elements form bridging (think of these as the webs of a metal or wooden truss for example) to the upper portion of the girder, which in this case is the sole in some areas and the deck cap in others. The triangulation of the bridging to the upper and lower flanges creates a girder and a rigid, self supporting structure.

An I beam without it's web (the piece between the upper and lower flange) would be little more then two floppy pieces of steel. With the web, it's a stout beam, and the same concept.

 

Nascar: Crome-molly Stringers/Roll Cage

Par,
yea, nice analogy.
I was thinking about using an aluminuim Type (don't know what grade) but 1Much won't let me. Much, what happened with Ellis Bros., when they used an aluminium stringer? You didn't finish the story.

Par, I was looking a set of pic's done by a surveyor who openend the bottom of a Viking(from the insdide). It looked like a HoneyComb Matrix with the Stringers as wide, almost as the Panels between them..massive. I wonder what was in them, or how they were formed up. They didn't look like the typical 2x8.
Par, got any pics of stringers and stuff in boats you have rebuilt..

 

they did it in 3 boats,( well 3 that i remember,,i think,,hehe,,,,,we re-did in less then year after,,,,they seamed to have had a cool "ripping" effect,,, and i think (not real sure its my memory or someone elses,,hehe) but i think 1 broke,,,,but that could of been for different reasons,,,,they didnt keep that designer/ engineer round long hehe

 

ratrace 2,

It is almost irrelevant what you "put" inside the "stringers" if they are glasses into the boat with engineeres longitudinals. Foam can be used to great effect, simply but it in blocks and shape the foan to suit the shape required, use hardwood under the engine(s), or else have the beds beefed up to suit the load, or both. Transveres frames are made exactly the same way, as are the "stringers" in the topsides.

Think carefully about locations in the topsides when designing as they either intrude into cabin space, or if thought about, can be used as form work to support cabin soles or shelves as required.

 

Stingers "a cool ripping effect"

Hey, 1Much:
was that cool ripping effect like when you tear down that old paneled wall in the basement of the house you just bought. If, the "ripping" was longitudialy, from bow to stern, I think I can explain that in a couple of months. Basically, one of two things, in theory:

One, the hull was too thin, given the modulo of the aluminium girders: the torsion of the hull twisted the two aluminium stringers until they ripped the hull like the panelling in the basement.

Two, the framing (transverse) allowed the stringers to load the individually, placing more tension one than compression on the other, one stringer and not the neighboring stingers/girders....Thus a slamming load will push down an individual stringer when the load should span all of the stringers, hardspot longitudinaly.
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Hey, LL ( hey mate): you say, " [Stringers]. . . if they are glasses into the boat with engineeres longitudinals". I'm going to read between the lines and interpret that to mean, you can use any material you want to design the shape of the Stringes as long as they are engineered longitudinals; thus, they have to have an engineered strength to weight ratio that matches the design of the hull. Fine, but here is the question: I don't just glass the foam into the boat. I build a stinger with the foam and then glass the Stringer into the boat.
For example, Viking has some massive stringer design in their larger 60' boats, I mean huge, the stringer is as wide as the panel they span.
Maybe you could give me a little more on how the parts go together. Mabe define "engineers longitudinals" for me.....thanks buddy.
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Par, man:
"the boat hull is a girder", you say.
One point of contention: 1st, why, then, use putty between the hull and the Stringer?
I still like the girder, wooden boat analogy, though.
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OK, my theory of how best to think about Stringer.
Stringer are, theoretically, nothing more than the bones in your foot.

Unlike girders, bones in your foot move about under your skin, that is why we need the putty the 1Much recommends but much like "LL" recommends, the bone structure needs to be of sufficient strength to withstand the stress, and as Par would say, it needs to be tied together with bridging, all the other stuff..
For example, your bones are very round, i.e. no sharp edges so they don't punch through you skin ( like a compund fracture: see Ellis boats) ; they flex, (so hire an NA as LL recommends) and stuff is attached to them, smaller stuff.


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