380: Flex in Lagoon 380 hull below waterline

[rabbi]

Originally Posted by Bean Counter

Lagoon 42 Spec sheet:


"Balsa core hull, solid laminate under the waterline."


https://api.cata-lagoon.com//images/...il-2018-gb.pdf

For some reason I stumbled over this old thread. Lagoon changed the spec sheet, now it says "balsa cored hull" which is in line with what I had seen at the last Düsseldorf boat show before Covid.

I don't think they changed construction methods but only corrected a cut & paste error.

[Piscis]

XCS Boats, which seem very close to Lagoon, production wise, still states:

"- Balsa core hull, solid laminate under water line"

in their Brochure...

[SVPilot]

I've seen what may be a similar problem on another Lagoon 380. On the inside of both hulls the fiberglass below the waterline had separated from a couple bulkheads. These ones were just under the steps into the hulls. I think the pounding of the ocean had separated them. They are only glued with some sort of thickened Polyester or Vinylester (not sure) but no fiberglass tabing. That 380 had recently crossed the Pacific.

If it is a similar problem it isn't very difficult to fix.

Originally Posted by MTF

Hi
Thanks for the great information on this forum so far.

I had a 2007 Lagoon 380 hauled for a pre-purchase survey and the surveyor found issues. Specifically, flexing in hull skin below waterline which he thought may be delamination. A composites worker at the yard also thought delamination was also present in the hull. I could depress the glass easily with my hand and it flexed about 5-7mm with a slight crunching noise till it hit what we thought was another layer behind it. I cancelled the deal due to high estimated costs of repair.

See attached vid of flexing.

The owners and broker were shocked and rehauled the boat a day later, ground an affected area and found no issue. They stated it’s thin glass between the bulkheads.

I know Lagoons are built to a price point but I’ve not seen solid glass below the waterline flex so much and so easily. Is this normal in an L380 or does it look like it’s suffered damage, had a poor repair or manufacturing defect?

[cammd]

I wouldn't buy any boat with a skin that thin below the waterline, wouldn't take much of an impact to create a hole.

[rabbi]

Originally Posted by SVPilot

I've seen what may be a similar problem on another Lagoon 380. On the inside of both hulls the fiberglass below the waterline had separated from a couple bulkheads. These ones were just under the steps into the hulls. I think the pounding of the ocean had separated them. They are only glued with some sort of thickened Polyester or Vinylester (not sure) but no fiberglass tabing. That 380 had recently crossed the Pacific.

If it is a similar problem it isn't very difficult to fix.

The bulkheads under the steps are not bulkheads but only furniture for holding the floor, they don't extend above floor level.
The one 50cm aft of that one is the structural bulkhead in that section (which in my boat is glassed in place but I have seen it glued as well).

The furniture is typically glued in place, and can separate over time.

[redneckrob]

Originally Posted by cammd

I wouldn't buy any boat with a skin that thin below the waterline, wouldn't take much of an impact to create a hole.

I don't see anywhere in the thread where the thickness of the fiberglass was measured? The determination of the strength of a fiberglass layup has a lot of factors independent of thickness and in most cases at least somewhat independent of how much it flexes. We had enormously strong sections of fiberglass in the helicopter I flew that flexed quite readily if you pushed on them in the right direction.

I think the Lagoon 380 might be the most produced catamaran ever, and to my knowledge none have sunk because the fiberglass schedule in the hull was too thin. Just like "common sense" would say the earth is flat, sometimes "common sense" in something like fiberglass layup schedules should be ceded to the knowledge imbued in the collective hundreds of years of research and experience of fiberglass experts.

[rabbi]

Originally Posted by cammd

I wouldn't buy any boat with a skin that thin below the waterline, wouldn't take much of an impact to create a hole.

Then just don't buy it. Buy a real ship. An ice breaking tug or something.


I remember some German fella built a super strong 17m aluminium cat. Sunk in the middle of the atlantic after some impact.

[Manateeman]

It would be helpful to all readers to TRY to stick to the facts.
Cases with some documentation.
For example, a core laminate construction in a ski or surfboard which flexes could be compared to a similar application in boatbuilding if the poster includes actual engineering calculations.
Another example. If two of my manatee crew fall over drunk onto my aluminum dinghy and it sinks, clearly it’s displacement and capsize calculations should be investigated further.
Production boats and take home pizza are basically sold by the pound.
You get what you pay for.
Gumby suits not included.
Captain Mark

[rabbi]

my mistake - I read the story years ago and I got some details wrong. Not 17m but 18.5m, sinking on trans-atlantic 550nm from Azores


The building blog 2004-2009
blu:venture - Bautagebuch des Hochseekat -blu:kat-

The sinking reported in May 2012:
https://blog.blu-venture.de/2012/05/...ng-von-blukat/

[team karst]

Originally Posted by rabbi

For some reason I stumbled over this old thread. Lagoon changed the spec sheet, now it says "balsa cored hull" which is in line with what I had seen at the last Düsseldorf boat show before Covid.

I don't think they changed construction methods but only corrected a cut & paste error.

On mine, the transition of balsa is easy to see, in the heads is one easy point of inspection. Balsa stops at waterline. Another easy view is in the crash lockers. I've cored in both areas for thru hulls.

[rabbi]

Originally Posted by team karst

On mine, the transition of balsa is easy to see, in the heads is one easy point of inspection. Balsa stops at waterline. Another easy view is in the crash lockers. I've cored in both areas for thru hulls.

The question was about the 40 & 42 which have a different building method than the 380.

The 40 and 42 are blasa below the waterline - at least the boats shown in Düsseldorf boat show had a cored underwater section (I lifted the floorboards and could easily identify the uncored recessed areas around the through-hull fittings).