Ply Formwork , structural or not? SO 51.1

[PaulvR]

Hi All,

I have a 1995 Jeanneau Sun Odessy 51.1 in pretty much Bristol condition.

The hull structural members show no sign of any stress whatsoever, not even hairline cracks, no-where. There is no sign of any problem, inside or outside the hull. The boat is regularly sailed, and sailed hard.

However, the ply formwork in some of the The longitudinal stringers and thwart ship floors has rotted out through water ingress via limber holes over the years.

Is it safe to assume that the boat is a GRP hand laid vessel and the ply is just formwork and not structural? I'm fine with this thinking, and the "if it ain't broke don;t fix it" philosophy so far....but I do have a niggle about the longer sections and the floors and long. stringers bucking, even though I know this won't happen...

I am grateful for any advice!

thanks,
Paul.

[tkeithlu]

Plywood between the layers of fiberglass do just what you fear - keep the layers of fiberglass from buckling. It's just as structural as the webbing in an "I" beam. That said, it's not clear that you have a problem, if the hull is not flexing under hard sailing conditions. If it is starting to flex, I should think that the stringers could be reinforced with aluminum beams or boxes glassed on.

[Adelie]

Plywood is probably structural.

[PaulvR]

Thanks guys,

I am thinking of cutting 'windows' in the stringers, cleaning them out, then stuffing with ply and epoxy, and glassing up again.

It is just that cutting up a perfectly good structure to fix 'what ain't broke' really hurts!

Little perpendicular knees glassed in on the sides would totally prevent buckling too!?

thanks again.

[MicHughV]

you could try this.....

drill some holes into the fiberglass stringer, wherever you think a problem is, fill a syringe with WEST epoxy and squirt this into the hole. You can buy plastic syringes at most medical outlets or even hardware stores.

the trick is to squirt the epoxy into one hole until you can see it come out of an adjacent hole...

[boatpoker]

Call Jeanneau and get the right answer without guesswork

[boatpoker]

Originally Posted by MicHughV

you could try this.....

drill some holes into the fiberglass stringer, wherever you think a problem is, fill a syringe with WEST epoxy and squirt this into the hole. You can buy plastic syringes at most medical outlets or even hardware stores.

the trick is to squirt the epoxy into one hole until you can see it come out of an adjacent hole...

If the wood is wet or even worse, decayed, the epoxy wil be a free floating hard lump that adds nothing to the strength. It wont stick to wet wood.

[MicHughV]

the purpose of the epoxy is not to strengthen the wood...but rather to fill any voids or holes...the shape of the fiberglass is much like a box beam, similar to a square metal tube...the wood is there to make the " shape" for the fiberglass..

in double skinned hulls, you'll see " foam" sandwiched between two layers of glass, which is much the same thing....

[boatpoker]

Originally Posted by MicHughV

the purpose of the epoxy is not to strengthen the wood...but rather to fill any voids or holes...the shape of the fiberglass is much like a box beam, similar to a square metal tube...the wood is there to make the " shape" for the fiberglass..

in double skinned hulls, you'll see " foam" sandwiched between two layers of glass, which is much the same thing....

Yes some mfg's used cardboard, foam or plywood as forms for the stringers/floors where they were simply forms for structural glass. In those cases the wood can completely rot away and make no difference to structural integrity. Injecting epoxy in these cases accomplishes nothing.

In many others, the wood is part of the structural integrity and decay can have devastating consequences and again injecting epoxy accomplishes nothing.

That is why I suggested the OP Jeanneau rather than relying on internet guesses.

[MicHughV]

true, some boat manufacturers use foam instead of wood inside stringers.......I have a fishing boat that uses some type of lightweight pvc pipe to form the " molds" used for the glassed stringers...

Jeanneau obviously would know exactly...not sure how wood would get wet inside a glassed stringer...but then again....it is a boat....

[PaulvR]

So the water gets in though via the limber holes drilled by Jeanneau, and various installers after the fact......the Limber holes are not especially treated in any way, which is how water eventually over the years is wicked up by the exposed ply/pvc pipe in the 'tunnel' between bilge sections.

It is the fact that these limber holes are not drilled inserts, that makes me think the ply was just form-work, perhaps even simply box section?

There are literally thousands of Sun Odessy 51.1's our there sailing all over the world....the fact that this is not a common issue, and the fact that my modestly used 1995 shows no sign of any stress at all, makes me think it is just formwork...or we'd hear of multiple catastrophes out there....??

I am trying to reach Jeanneau directly to ask....I have to direct my question via the nearest dealer, which is Martinique! Wish me luck!

thanks all for the advice!