Fiberglass interior section strength...

[Supercat568]

I've got a new to me 1985 Pearson 27. It's got typical core rot here and there, no big deal. However, the previous owner left the diesel tank filler off since the repower 3 or 4 years ago and the boat has a strong diesel smell inside. I installed the fuel filler hose and then kept removing things from the interior hoping that the smell would go away. It didn't.
Then it rained the other day and since I don't have all the leaks fixed yet some water got in. Suddenly the diesel smell was overpowering again. So finally I pulled the floor up and found significant core rot which had become saturated with diesel over the past few years.
The fiberglass interior section adds strength to the hull. But is that strength needed or is it above what the designer intended? I understand that besides the designer there's only a few people who know for sure, so I'm hoping that someone here has done similar work and has an educated guess based on work on their boat.
Thank you

https://youtu.be/XoCK-YIp35g?si=A0jtUIs9PX7d1rzG

https://youtu.be/heWn_BWb5k8?si=X5CH2bAbuwwv8qjM

[Supercat568]

Does anyone think that a sailboat would be designed such that it needed the additional strength of the molded fiberglass interior section? I'm thinking no.
Also, on this boat, the bulkhead is securely attached at the bottom and hull but the top there's a thru hull fitting that hangs down adjacent to the bulkhead and is attached with two screws. I would imagine that the top is also very secure but it's an unusual setup. One picture is the thru hull fitting at the top and then as it attaches to the bulkhead. If I remove the two bathroom walls, bulkheads, I need to install something that's as robust, right? This is in the plane off the mast and shrouds so it's got to be very strong. How much could I remove of those walls, bulkheads? I'd like to open up the interior, a 27 foot sailboat doesn't need two sinks and a shower! I was thinking of building a table over the head that would be hinged at the bottom and rotate towards the opposite side when the toilet is needed, the other picture shows what I'm thinking of covering the toilet with..
Any thoughts?

[Supercat568]

I should've included this comment in the 2nd post: since there were no replies to the first post I must've asked the question wrong, so here's a little different way of looking at it. Thank you

[catsketcher]

Gday

I don't know anything about Pearsons but they look like a standard polyester 1970s production keelboat. I don't even own a keelboat, I design, build and sail catamarans, but there are some giveaways that tell me you can drop the floor.

If the cabin sole and the hull were a structural single piece then the hull skin or frames would be tied to the floor somehow. But they are not. This means the cabin sole (the floor we stand on) is not needed for strength.

If it was me I would but putting a little web of epoxy saturated ply in between the ribs. Then I would place a curved cabin sole straight onto the ribs and the little 6mm ply webs between them. I would use probably 9mm ply, well epoxied underneath. I would use epoxy to fit all the new pieces because epoxy has such good secondary bonding characteristics - it just sticks.

There is no worry with a little step - you will get used to it really quickly.

Of course you will need to make hatches to access the bilge but a curved cabin sole on top of the frames will actually make the hull stiffer. It will act as the top flange of a beam. But I would not neglect to add small the ribs running fore and aft between the current glass ribs (at the same height) every 400mm or so. Fillet them on with epoxy fillets (I would not glass them) and add a piece of douglas fir at the top flange. Then when you lay the 9mm ply cabin sole on top you will have a good bonding area for the epoxy glue to attach to the ply cabin sole.

You could get clever with the ribs. Maybe there is a foam sandwich boat being cut up near you. If so, grab a piece of deck and cut it up for the frames. Remember to cut small holes in the bottom of the ribs to allow water to move. If using ply, ensure you add 3 coats of clear epoxy before adding the cabin sole.

cheers

Phil

[wyb2]

I’m not familiar with the Pearson 27. I have owned two production boats from the mid 80’s, a 36 and now a 25.

My semi (and self) educated guess is that the wide, flat, horizontal areas of the liner that make up the cabin sole you walk on are there to be walked on, not to support the hull. However, anywhere the liner is roughly perpendicular to the hull, and tabbed to the hull, is potentially structural, and possibly critical. In both boats I’ve owned, the liner has been clearly structural in several places where tabbed to the hull, especially around the center where the keel, mast, and chainplate loads are.

In your second video, where much of the sole is gone, it doesn’t immediately strike me that you’ve compromised the structure in any meaningful way yet. The part where you point the camera down under the remaining lip, where it’s tabbed to the hull, that I would not mess with unless you were going to rebuild with equal strength.

[boatpoker]

The cored liner and glassed frames are what hold the comparatively thin hull skin in shape. Any weakening of that support structure will lead to the hull flexing somewhere it was not designed to flex. The potential for unpredictable consequences without Finite Element Analysis are high and we know you are not doing FEA.