Stringer debate

[schrater]

A common check during surveys of older boats is whether there are dead or “wet” spots in the fiberglass stringers. Tapping on them can indicate if rot has entered. This can be a major repair job and can often knock down the asking price of the boat quite a bit.

But is this really a big concern? Are there many real-world examples of stringers giving way? I have heard credible sources say that the strength of a fiberglass stringer comes from its box design and that it would be just as strong if it was hollow. The wood interior was only there to help form its initial shape and structure.

Is the wet stringer test more than just superstition?

 

[HopCar]

I know of boats with foam filled stringers that get their strength from the thick glass on it. My guess is that if the builder put wood in it, he’s counting on the wood for most of the strength. The glass is just there to keep it dry.

 

[kapnd]

The original calculations that the boat was built on most certainly factored in the wood as a substantial portion of the stringer’s strength.
For the stringer to remain “just as strong” after the wood rots, it would need to be very heavily glassed indeed, as the long flat sides without the benefit of being bonded to the core will be pretty flimsy, the taller they are, the weaker.
A stronger “stand alone” shape would more resemble an I, C (channel), hat, or inverted U shape.

 

[psneeld]

You just fon't know unless you talk to the manufacturer/designer.

I have seen where the eood mattered, and where it didnt.

If I had to guess, on larger boats, say over 30 the eood was structural and under 30 it wadnt structural or ultimately it didnt matter.

But thats a gross generalization and I wouldnt bet the ranch on it.

My dock neighbor on a 32 older Pacemaker found 2 large cracks in his stringers this year, he chose to fix snd not even drop thd boat in the water.

 

[O C Diver]

My Cherubini has both foam core and wood core stringers. The engine bed stringers are wood cored, fiberglassed in, and then a heavy steel plate is bolted through the plate and fiberglass into the wood. I have no doubt that even though the fiberglass is thick, the wood is structural strength in those 2 stringers. The foam cored stringers obviously achieve all their strength from the fiberglass.

Ted

 

[Westiculo]

Agreed with everyone - depends on the make of the boat. I only have experience with two. In my grand banks, the stringers are foam filled so all strength is from the glass. In a Marine Trader I looked at, much of the strength was from the wood, and it was all but rotted out. The hull was totally compromised.

 

[Datenight]

I never trusted the stringers on the old boat a Sunkyung Marine 37' sedan. After about 12 years of ownership I cut out the old stringers and fabricated new. The old were glass over plywood forms. The glass was good but tapping on them indicated the wood was gone.

Removed the generator and fuel tanks. One of the tanks needed repair which I covered here a while ago. With the way clear I laid the sawsall on it's side and cut out the stringers and tank supports. Then ground everything clean. As I lifted out the old supports the rotted wood fell out.

I made new out of plywood saturating each layer before it was screwed and glued together. The stringers were bonded in place then glassed. The solid wood is way overkill but I made then the same thickness as the original hollow units. I am sure I could have made them half the thickness and still have been plenty strong.

Rob

 

[Datenight]

Maybe I should have posted on the Rot Porn thread!

Rob

 

[denverd0n]

Of course, everyone is giving you theory, while what you asked for were real-world examples. So, yes, I've seen a boat where the stringers gave way. It was first noticed as a vibration that kept getting worse and worse. Inspection revealed that the engine was crooked. Both stringers had rot. One bad enough that it was no longer supporting the engine mount adequately.


So, again, yes, they can give way if the rot gets bad enough.

 

[foggysail]

I never trusted the stringers on the old boat a Sunkyung Marine 37' sedan. After about 12 years of ownership I cut out the old stringers and fabricated new. The old were glass over plywood forms. The glass was good but tapping on them indicated the wood was gone.

Removed the generator and fuel tanks. One of the tanks needed repair which I covered here a while ago. With the way clear I laid the sawsall on it's side and cut out the stringers and tank supports. Then ground everything clean. As I lifted out the old supports the rotted wood fell out.

I made new out of plywood saturating each layer before it was screwed and glued together. The stringers were bonded in place then glassed. The solid wood is way overkill but I made then the same thickness as the original hollow units. I am sure I could have made them half the thickness and still have been plenty strong.

Rob

STRONG!!!! WOW, about 3” thick? Your pictures indicate you did a fine job repairing your boat!!!

 

[Datenight]

STRONG!!!! WOW, about 3” thick? Your pictures indicate you did a fine job repairing your boat!!!

Yes, four layers of 3/4" plywood.

Rob