what stringers really do?

[likefish]

How do stringers really work?

My question is asked because I am trying to figure out where the strength comes from in the hull of a boat. If white wood is/was used in the production of boat stringers is it not safe to assume that hunderds and thousands of boats are in use today with rotted out wood stringers? If so why not more problems?

I am assuming it is because the glass is the strength and the wood is simply the form over which the fiberglass is shaped. Fiberglass beams, fiberglassed to the hull, foamed in between seems to be very structurally significant from bow to stern (which is where I am assuming the stringers provide structure).

Am I way off in my logic?

also a question is if stringers fail what is the result? I am really looking at this from a physics angle. Looking at the forces it seems that hollow stringers with a floor glassed in over them is extreamly structuraly sound.

Thank you for the insight!

 

[a70eliminator]

Re: what stringers really do?

While I'm no expert on boat design, I would think the stringers are most important when it comes to I/O boats as they carry the loads of that V8 sitting back there. Kinda like a unibody car?

 

[Bondo]

Re: what stringers really do?

I am assuming it is because the glass is the strength and the wood is simply the form over which the fiberglass is shaped. Fiberglass beams, fiberglassed to the hull, foamed in between seems to be very structurally significant from bow to stern (which is where I am assuming the stringers provide structure).

Am I way off in my logic?

also a question is if stringers fail what is the result? I am really looking at this from a physics angle. Looking at the forces it seems that hollow stringers with a floor glassed in over them is extreamly structuraly sound.

Ayuh,.... You've got the Theory,....

The Actuality of it is,...
Yes,... There's many boats out there with Problems....
That's why the iboats forums are as Huge as they are...

Production boats are usually built with Just enough materials to get the product out the door,...
And, is built to Last til the end of the warranty, or the end of the payment book....

 

[ondarvr]

Re: what stringers really do?

Your thinking is right on track, for the most part stringers stiffen the hull.

The core (in this case wood) can be used as just a shape, or it can add some stiffness along with the glass, it just depends on the design and amount of glass used. The longest lasting method would be hollow stringers with limber holes to allow water to drain to a low spot. Wood is used because it's low in cost, light and easy to work with, plus if used correctly can last for a long time, using it correctly is the problem. Other materials can be used also, foam, cardboard, pre made fiberglass shapes, etc, but most cost and weigh more and don't see an advantage until 10 to 15 years down the road when the wood gets wet and turns to pulp.

The strength they add can be for different purposes, a hull may not need the stringers for strength, they may just be needed to eliminate unwanted flex, or the stringer may be engineered into the entire structure and without them the hull would be too weak to hold up. Sometimes they?re just added to support the floor and aren?t needed for anything else.

 

[Frank Acampora]

Re: what stringers really do?

From experience I can tell you: If a stringer fails near the transom, the hull will develop a "hook" at the break in the stringer while underway. The hook will increase in severity with increasing speed. This will significantly reduce the top speed the hull is capable of acheiving. I suspect it would also eventually stress the glass to failure. I never let mine go that fast before I repaired it.

 

[likefish]

Re: what stringers really do?

specific to my questions:

I have a 1983 Wellcraft V20 center console. It is powered with a 2004 Evinrude 200HP OB. I have removed the entire floor from in front of the rear storage boxes to the bottom of the raised raised deck. While looking I noticed that my stringers are HOLLOW! but at 250lbs i can walk on them without them giving a bit. All of the foam is DRY! From all of the reading i have done I am not in too bad of shape.

I was considering attempting a stringer rebuild but am very hesitant due to the boat behaving so well over the summer. The transom is Dry and solid accordign to my thump test and some inspection holes.

Assuming the above. I have considered the following:

1) Epoxy a new floor onto the stringers. Glass the floor and call it good.

2) Drill 1' spaced holes in the top of the stringers and pour in a stiffiner. (closed cell foam? poly resin? something else?).............

3) Cut out the tops of the stringers, remove what wood I can and slide new stringers down into the cavity, pour in poly to fill voids and reglass the tops.

I dont think i have the skills or the budget to do do a full stringer replacement from the ground up

Thanks again for any insight!

Love this forum!

 

[oops!]

Re: what stringers really do?

hmmmmm...

a few things.....you say your stringers are hollow...?

does that mean they are built hollow....(i dont think so) or that the wood in the stringer has rotted totally out and now there is just a fiberglass shell there?

if the latter....i would replace the wood. there are other things you can use but the wood id cheapest.....doing it right this time it will last another 30 years.

just leaving it alone and glassing over the existing stringer....(you allready have the shape) it will be very difficult just to drop a new deck on it as there is nothing to attach the deck to.

the job is not hard....it just takes time.

cheers
oops

 

[92excel]

Re: what stringers really do?

well its your boat and you can do whatever you see fit.

People have scabbed stringers onto the current stringers..
some have just added more glass to make them stiffer.

it all depends on how long you want your fix to last.

the best idea is to rip out whats bad and replace it!

the reason is it makes it a safer rig and there is no reason to half fix it and have to do it again in a few years. If done properly, a stringer and new deck will last you 20 years give or take a few.

i originally didnt want to do my stringers as i was nervous like you, but once i drilled into them and black almost potting soil "wood" came out.. i perfer the piece of mind that it was done correctly.

 

[ondarvr]

Re: what stringers really do?

Now its changed from stringer theory to how do I fix this boat.


If the stringers are supposed to be hollow, then do nothing and put in a new floor, if there had at one time been wood in them, then you should fix them. How you fix them is up to you.

Take a closer look at the transom and then check it again, don't fix everything else and then in a few months find out you missed some rot.

 

[Tail_Gunner]

Re: what stringers really do?

......Being the knuckle dragger that i am...i thought the wood in a stringer system was the real support in a hull design. So i bedded the wood on to the hull with a polyurethane compound. Then i layered the stringers with 6 layers of biaxle tape....They seam to be like beams of steel running down the lenght of the boat. Followed them up with 8lb structal foam......if the hull fails with that kind of structure....then i will know there is really not a redneck style to rebuilding a boat..

Ok Ondarvr do you think that will fail???

 

[DJ]

Re: what stringers really do?

Some boats DO have hollow stringers made entirely out of fiberglass. That, of course, requires: molds, lots of fiberglass and a lot of skill. But, a great, long lasting design.

Some other high end boats make stringers (solid) 100% out of fiberglass, read-heavy. Others use "Dyvinicel" which is a composit honey comb material. Again, expensive and requires skill to work with.

Wood, as mentioned, is by far the cheapest and easiest to work with. If the right wood is used and treated correctly, it will outlast most of us.

What kills a lot of stringers is what is attached (screws, etc.) to them without proper sealing.

I remember, a long time ago, investigating a fuel smell in a really "spiffy" new conversion van. The smell was from the dinette table pedestal attaching screws being driven DIRECTLY into the top of the fuel tank.

You get the idea. You can spend all the time and money, in the world, making perfect stringers. But, if you drive sheetrock screws into them, they won't last.

 

[ondarvr]

Re: what stringers really do?

Ok Ondarvr do you think that will fail???[/QUOTE]


Only if the straps come loose on the highway.