What is the purpose of stringers?

[Bubba1235]

Looked at several boats with wood stringers and I confess I'm confused when people say they are structual. I agree they are structual but the question is, to what? The boats I've looked at all had the stringers mounted around a half inch off the Fiberglass hull and then filled with "glue" and I've been told that is required so the hull can flex without cracking. So if that is true is the stringer providing any structual strength to the hull or are they really required in order to install a deck and engine?

 

[Slide]

Re: What is the purpose of stringers?

Stringers provide longitudinal resistance to compressive stress. A fiberglass boat is simply an open shell that will tend to flex inward on itself during operation; you'd have to make the glass prohibitively thick in order to achieve the same strength in compression. A boat's hull operates similarly to an airplane wing, in that tensile stress is distributed across the entire hull whereas compressive stress is concentrated into the main structural members (stringers). As long as the design has a mechanism of transferring that load to the stringer (glued/tabbed in, etc), the stringer will perform as it's supposed to.

-Your friendly neighborhood structural engineer

 

[tpenfield]

Re: What is the purpose of stringers?

The purpose of stringers ??? . . . . Oh Bubba, you've been around here long enough to know . . .

 

[mjfrederick]

Re: What is the purpose of stringers?

The purpose of stringers ??? . . . . Oh Bubba, you've been around here long enough to know . . .

I'm new here... but from what I gather, stringers are installed by the boat manufacturer so that they can be replaced once they've rotted due to poor initial installation or poor boat maintenance by the PO.

 

[Scott Danforth]

Re: What is the purpose of stringers?

years ago I was designing a base for a large welding robot. the purchasing manager asked if we needed all the gussets that were on the print - because it would be cheaper without them. I said no, we had them left over on the screen, and thought we would use them....

Stringers in a boat are like joists in a house. they provide strength.

 

[mjfrederick]

Re: What is the purpose of stringers?

You sir have an evil streak in ya!!! (I like it.)

Yeah, I recently came into the possession of an old boat that I was hoping I could have on the water in no time. Did a little research, found this forum, and now it's a full restore. As much of a pain that it will be, it'll be worth it in the end to have a better-than-new 34 year-old boat! I'm a rosey-eyed pessimist... :facepalm:

 

[Slide]

Re: What is the purpose of stringers?

I'm new here... but from what I gather, stringers are installed by the boat manufacturer so that they can be replaced once they've rotted due to poor initial installation or poor boat maintenance by the PO.

Perfect explanation!!

If you want to visualize what stringers do, take a sheet of paper, grab the edges, and pull on it. It doesn't deform due to this tensile stress. Push the ends together as in compression and it immediately buckles. Now tape a ruler to the paper and push on it again: paper does not deform. In this way your paper models a thin-walled structure - just like a boat hull. The stringers prevent the hull from buckling or cracking.

 

[Coho Ghost]

Re: What is the purpose of stringers?

In a way, doesn't a properly tabbed and glassed deck, aside from the stringers, actually provide the compression strength? And don't the stringers then stiffen the deck, which the deck transfers to the hull? I'm no engineer, just had these thoughts and am curious.
What say you experts.

FWIW
Coho Ghost

 

[tpenfield]

Re: What is the purpose of stringers?

In a way, doesn't a properly tabbed and glassed deck, aside from the stringers, actually provide the compression strength? And don't the stringers then stiffen the deck, which the deck transfers to the hull? I'm no engineer, just had these thoughts and am curious.
What say you experts.

FWIW
Coho Ghost

It is kind of like an "I" beam . . . if the deck is attached firmly to the stringer, then, yes, the deck becomes part of the equation and helps out quite a bit. The actual height of the stringers also determines the strength, etc.

 

[Slide]

Re: What is the purpose of stringers?

In a way, doesn't a properly tabbed and glassed deck, aside from the stringers, actually provide the compression strength? And don't the stringers then stiffen the deck, which the deck transfers to the hull? I'm no engineer, just had these thoughts and am curious.
What say you experts.

FWIW
Coho Ghost

"Stringer" and "stiffener" are interchangeable terms, structurally speaking ("stiffener" is generally used for smaller structures, or supplementary stringers).

As for the deck, yes, you get a modicum of compressive strength from it. But as tpenfield noted, the height of the member in compression along the stress axis determines its strength. Decks are thin; stringers are not. A fully bounded stringer/deck structure is essentially an I-beam, which is a very robust platform.

 

[Yacht Dr.]

Re: What is the purpose of stringers?

Looked at several boats with wood stringers and I confess I'm confused when people say they are structual.

It really depends on the build of the boat. .. You have IB .. OB .. or IBOB .. its all Energy transfer to the build of the boat ( Power plant ).

but the question is, to what? The boats I've looked at all had the stringers mounted around a half inch off the Fiberglass hull and then filled with "glue" and I've been told that is required so the hull can flex without cracking. So if that is true is the stringer providing any structual strength to the hull or are they really required in order to install a deck and engine?

Every bond point is Structural .. the stringers on some boats are needed and beefed up for IB or IBOB .. not really so much for OB only boats .. the energy is transfered Via different points ..

YD.

 

[coolbri70]

Re: What is the purpose of stringers?

in my boat they hold the foam and support the floor but mine are fiberglass, saw an old advertisment larson said the strength was in the laplines, each one like an i beam, the po was using it without a floor