Can someone identify where this mysterious water is coming from? (Photo)

[Manateeman]

A thru hull with a nut ...good boatbuilding? Not in my opinion. Good boatbuilding is an Apollo seacock or Groco seacock or adaptor plate and valve.
Thruhull are straight threads and are not compatible with tapered thread valves.
Seacocks should be affixed to the hull independent of the thruhull.
At this point it’s Not clear how well the Entire liner ...is attached to the hull.
It helps the poster if comments are based on experience gained as a professional boatbuilder. Right now there is just not enough information from the OP .
Happy trails to you
Captain Mark and his no ketchup no hot dog manatee friends

[boatpoker]

Originally Posted by Manateeman

A thru hull with a nut ...good boatbuilding? Not in my opinion. Good boatbuilding is an Apollo seacock or Groco seacock or adaptor plate and valve.
Thruhull are straight threads and are not compatible with tapered thread valves.
Seacocks should be affixed to the hull independent of the thruhull.
At this point it’s Not clear how well the Entire liner ...is attached to the hull.
It helps the poster if comments are based on experience gained as a professional boatbuilder. Right now there is just not enough information from the OP .
Happy trails to you
Captain Mark and his no ketchup no hot dog manatee friends

Beneteau are reknowned for mixing NPS throughulls with NPT residential plumbing ball valves. ....... http://www.pcmarinesurveys.com/Paul%...20Seacocks.pdf

[boatpoker]

Originally Posted by Manateeman

At this point it’s Not clear how well the Entire liner ...is attached to the hull.

Check out this one that wasn't attached !
Liner Bonding Failure

[aclmck]

Core penetrations are done either by removing the core and filling or by tapering the core and glassing down to the outer skin from the inside


Both have advantages in the first removing the core and filling has its advantages in that it can be achieved in nearly any spot on a boat and easily done at any point in a boats life, it is commonly also used when fitting aftermarket fittings to anywhere on a boats surface, it has an advantage in that it can be done when no rear access is available.

The second removal of the core and glassing to the exterior while strong has disadvantages over the other in that it uses a lot of area to achieve the same result (on a 20 mm core you need to cut back at least 40 mm plus grind back for glass adhesion this could easily be a hole in excess of 150 mm)can’t easily be achieved at anytime through a boats life, and can’t be achieved from the side exterior of a structure

What I mean by easily achieved is that it needs to have the internal surfaces RE painted etc or liners removed and refitted as the fitting doesn’t cover the works and also finding an area large enough is a issue in many boats

[dad_n_Seattle]

Thanks to everyone for participating in this thread. I think I've come to a satisfactory conclusion.

So the 1992 Beneteau First 265 is a solid GRP hull with an extensive inner lining that also provides structural support to the hull. In several parts of the hull, there is either a plywood reinforcement where transducers are expected to be installed (bow), and where factory thru-hulls are located, solid GRP reinforcement across both layers (liner and hull). I verified this with some factory documentation I found in the boat.

This is why when I removed the salt water inlet strainer, some folks thought my hull was thicker than expected. That thru-hull was factory set, so it was reinforced with solid GRP. The strange cavity-like appearance visible from the outside seems to be a wierd by-product of the resin reinforcement. It turns out it is solid, just not well painted and semi-translucent. I stuck a long wire into the old hole where the screw was, and I could not get it to show up in that 'cavity', but it went in deep, so the conclusion is that a 3/4" screw is enough to go through the hull into the space between the hull and liner, which definitely has standing water in my case.

Conclusion is that other than a lot of salt water between my hull and liner just out of reach of the bilge intake, my hull seems to be still sound. I got rid of the old brass grill-dome type saltwater inlet and replaced it with a normal bronze groco, with plans to add a saltwater strainer inside (west marine universal strainer).

On to the next problem (Volvo Pental 2001) !

[Cadence]

Regarding drilling exploratory holes and filling with epoxy. Keep in mind you need access to the inside to build up several layers of glass and epoxy as a backing plate. It's not just puddying the hole with epoxy and some glass component.

[Clivevon]

Glad that was sorted. A few sleepless nights though, I bet. Boats....

[Bbolino]

Likely water from a through hull that wasnt bedded correctly.
I would never put anything through a wooden cored hull except in the designated penetration areas that the better boat builders provide or without creating one. The odds of getting water into the core are too high even with the best bedding techniques
I assume its a balsa wood core - unfortunatelly balsa turns to mush when it gets wet.
The first thing i would do is not re-launch the vessel.
You can use a moisture meter but an experienced ear and sounding hammer is probably better. An infrared scan of the hull is even better.
Assuming the core is intact and hasnt broken down or delaminated you need to get it dried out as fast as possible. Any good boat yard will have methods to do so. One way is to tent the boat and heat the enclosure with a good vacuum attached to a penetration in the hull. Keep it there until its dry
Then deal with any core damage and seal the hull
You may be lucky enough to have caught it early
If the core is damaged it can be repaired it just tedious

[Mockingbird]

The evidence I see indicates your hull is cored and holding water. Fiberglass cores are scored to allow them to conform to the hulls cores. These scores can hold water. In addition, balsa can absorb a lot of water. If your core is balsa this is a big problem because balsa rots. If the core is cross linked or linear pvc foam it is generally considered not so much a problem. Based on the lack of color in your leak I think it likely you have such a foam core. Balsa usually breaks down in time and discolors the water. There was an excellent Professional Boatbuilder Magazine article on this several years ago.

We once had a customer with a similar problem on a Krogen. That vessel had Airex core in the hull. We drilled a series of 3/16" holes at about 10" centers along the lower edge of the core inside the hull. These slowly drained for weeks, but eventually stopped. As far as I know there was never a subsequent problem.

[mitiempo]

Originally Posted by Mockingbird

The evidence I see indicates your hull is cored and holding water. Fiberglass cores are scored to allow them to conform to the hulls cores. These scores can hold water. In addition, balsa can absorb a lot of water. If your core is balsa this is a big problem because balsa rots. If the core is cross linked or linear pvc foam it is generally considered not so much a problem. Based on the lack of color in your leak I think it likely you have such a foam core. Balsa usually breaks down in time and discolors the water. There was an excellent Professional Boatbuilder Magazine article on this several years ago.

We once had a customer with a similar problem on a Krogen. That vessel had Airex core in the hull. We drilled a series of 3/16" holes at about 10" centers along the lower edge of the core inside the hull. These slowly drained for weeks, but eventually stopped. As far as I know there was never a subsequent problem.

The hull is not cored.

[coxfirm]

Originally Posted by dad_n_Seattle

I stuck a long wire into the old hole where the screw was, and I could not get it to show up in that 'cavity', but it went in deep, so the conclusion is that a 3/4" screw is enough to go through the hull into the space between the hull and liner, which definitely has standing water in my case.

Maybe I don't quite understand what you are describing, but if I do understand your situation correctly, if it were my boat, I'd fill that screw hole with epoxy and some chopped glass and maybe layup a patch of fiberglass cloth over it if the inside is accessible. Then I'd drill back a smaller length screw that did not penetrate all the way through the hull. I haven't had one of these clam shells hull strainers on my saltwater intake for 20 years and it has never cause a problem. I try to eliminate as many hole in my hull below the waterline as possible. I certainly would not like to have a screw that I don't have access to going into my boat's hull.

[skipmac]

Originally Posted by mitiempo

All Dashew's Sundeer 56,60,and 64 were balsa cored by TPI.

Did not know TPI built the Sundeers. They did a good job on the balsa core of my Pearson hull.

[Mockingbird]

I understand that now. Was not aware it was a Beneteau,.

[sailorladd]

That sounds like osmosis... sea water is being soaked up through and around the water strainer...have you tasted the water to see if it is salty?

if so, it has to be osmosis, from the pressure ...You need to remove the strainer, drill into that hole where you saw the initial leak, and even a few places around where the strainer was seated... allow to drain out and dry and then using an epoxy paste, fill in these drain holes, even hammer in some hard wooden plugs, and when you reseat the strainer use a quality underwater sealant like 5200 or similar...

[ChessieSailor]

Did you find the source? With that amount, perhaps its water trapped between an inner and outer hull layer. Its not good, hope you found it.