Rotten stringer

[Claudiopinto]

I have a sailboat that has an encapsulated stringer that is rotten, at the junction of the deck and hull, as shown in the image I tried to draw. The deck is fiberglass to the hull from the inside.
Does anyone have any ideas on how to fix it? and what material should I use wood, plywood or c70 foam boards.
I was thinking about cutting a piece of the deck until the stringer is visible and I could remove it, replace it and glass over the deck and hull on the outside. But I like to hear your opinions. Thanks

[Fore and Aft]

Claudiopinto I would be removing the stringer from the inside and replacing the rotten stringer with timber well bedded in epoxy glue. When you remove the inside fiberglass casing you should leave the bottom piece as a shelf for the new timber to rest on. Then just glass it back in place with probably a couple of layers of 450gm double bias and a layer of peel ply to save the grinding. To hold the timber stringer in place I was wondering if you could use a timber prop across the cabin and a wedge so you can get the stringer tight against the hull. For me the idea is not too damage the exterior hull or deck.
Cheers

[MicHughV]

Well, this is what I would do.
I'd try....to the best of my ability.... dig back left and right with sharp a implement and remove as much of the original rotten wood I could see or find.
I believe that the wood is there to give shape to the fiberglass around it and not as a structural component.
Then I'd tootle on down to my local hardware store and buy a can or two of the expandable foam and squirt it in there as far back as I could and also the opening.
Once the foam has hardened, it can be sawn/sandpapered flush with the fiberglass hole.
Once that is complete, I'd give the fiberglass " casing" a good clean and rough up the surface with some heavy grit sandpaper at least 12-18" each side of the hole and get some fiberglass cloth and resin and patch up the hole. so you will end up with a patch that is more or less 36" long.

[boatpoker]

That is not a "stringer" it is a "shelf".

I have no opinion as to it's structural importance or potential repair process without knowing model and year of the vessel.

[Claudiopinto]

Originally Posted by boatpoker

That is not a "stringer" it is a "shelf".

I have no opinion as to it's structural importance or potential repair process without knowing model and year of the vessel.

The boat is a Elizabethan 29 from 1989

[Claudiopinto]

Originally Posted by boatpoker

That is not a "stringer" it is a "shelf".

I have no opinion as to it's structural importance or potential repair process without knowing model and year of the vessel.

I drill some small holes and have the wood wet in more places, not just this section.
This part is the worst, but is rotten in a few places

[capt jgw]

Just as importantly, the hull/deck joint is probably leaking and that's where the water that rotted the shelf came from. That will need to be addressed or the new wood will just rot out again.

[MicHughV]

I thought you might find some more wet wood if you drilled elsewhere.
As before, dig out as much of the old wood rot as you can at each hole location. May have to make the " holes" a bit bigger at each location.
That expandable foam I mentioned earlier has a plastic straw you can insert into each hole to fill it with foam, then patch each hole with fiberglass and resin.

[boatpoker]

Originally Posted by Claudiopinto

The boat is a Elizabethan 29 from 1989

There were several builders of that model and many changes made over the years including changes to the moulding of the hull deck joint. Many of these boats were sold as hull & decks to be completed by home builders so quality and method are variable.

Some were built with the hull deck joint under the the wooden toe rail fully sealed with glass fiber and some were not.

The shelf supports the entire deck structure in most of these boats and would be considered structural as the deck and bulkheads hold the sides of the hull where they are supposed to be. What are the cross sectional dimensions of the shelf from the inside of the vessel and is the wooden shelf covered with chopped strand or woven fiberglass roving (they came both ways and it makes a difference) ?

[Claudiopinto]

Originally Posted by boatpoker

There were several builders of that model and many changes made over the years including changes to the moulding of the hull deck joint. Many of these boats were sold as hull & decks to be completed by home builders so quality and method are variable.

Some were built with the hull deck joint under the the wooden toe rail fully sealed with glass fiber and some were not.

The shelf supports the entire deck structure in most of these boats and would be considered structural as the deck and bulkheads hold the sides of the hull where they are supposed to be. What are the cross sectional dimensions of the shelf from the inside of the vessel and is the wooden shelf covered with chopped strand or woven fiberglass roving (they came both ways and it makes a difference) ?

I don't know who the builder is, it doesn't say anything on the papers.
the dimensions are 40x70mm and it is woven fiberglass roving.

[GordMay]

Originally Posted by boatpoker

That is not a "stringer" it is a "shelf"...

Stringers are longitudinal forms, that are laid in line with the keel, to add extra strength, and structural support, to the boat. Along with the boat’s ribs and bulkheads, the stringers form a grid, that holds up the boat’s decks (floors) and stiffens its hull.
Stringers are somewhat like floor joists, and traditionally are attached to the boat’s ribs and bulkheads.

[MicHughV]

back in the day....timber was used to create the "form" for the stringers, which were then glassed over.
these days, pre-formed foam is used in lieu of wood, as it is lighter and not susceptible to rot.

[SailingHarmonie]

Originally Posted by MicHughV

back in the day....timber was used to create the "form" for the stringers, which were then glassed over.
these days, pre-formed foam is used in lieu of wood, as it is lighter and not susceptible to rot.

In a traditional stringer on a fiberglass hull the interior material is only used as a mold, all of the structural stiffness is from the fiberglass overlay. In some cases the stringer was actually molded over cardboard half cylinders which obviously provided no structural strength of their own at all.

The design of this is terrible. A hull/deck joint is one of the toughest to seal and keep sealed. The wood would be expected to rot away. Just based on the shape of the fiberglass "box" that results it is not a significant structural member, but rather a crude attempt to glass hull to deck.

If it was my boat, I'd work from the inside, cut the fiberglass box away completely, get rid of the wood, and glass the hull directly to the deck. Strong, and leak free. Or just keep it as it is.

[MicHughV]

Well, I totally agree. The wood stringer originally used was there to provide a " mold" for the fiber glass, hence my suggestion to fill the void with expandable foam is it will provide a surface for the fiberglass overlay....a simple easy fix.
Cutting away the entire fiberglass box will be quite the project, not something I'd consider doing myself.

[RaymondR]

Originally Posted by boatpoker

That is not a "stringer" it is a "shelf".

I have no opinion as to it's structural importance or potential repair process without knowing model and year of the vessel.

I'd replace it with timber and not encapsulate it but use an epoxy sealer to let it breath.