380: Flex in Lagoon 380 hull below waterline

[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?

[MTF]

https://youtu.be/HEv07qssvzo

Video of the hull flexing

[atoll]

sounds like a core failure ie balsa turned to mush due to water damage

[admiralslater]

Be very wary pf this boat. We built our pdq36 with a light laminate on the core because we where saving weight but there is no way even after 15 years that I can depress the skin by hand

[boatpoker]

I found areas of the hull (uncored) in a Lagoon 450 that were only 3mm thick.
Water was leaching right throught the hull. The white areas of the thermal image below show some of the thin spots. This shot is around the drive leg with the cover plate removed.

The other two shots show my awl bent and hooked inside the hull (where I poked it through) and placed a piece of black tape on the outside. The third shot shows the thickness as indicated between the black tape and the hook.

[MTF]

Hi Atoll, I thought these boats were solid glass below the waterline and balsa core above?

Thanks Admiralslater, yes it does seem very thin doesn’t it? Would it help to thicken and reclassify the thin areas and wood this fix the issue?

Boatpoker that’s good to know and the moisture meter reading on the hull suggested water was getting inside as you noticed on the thin sections you investigated on the 450

[a64pilot]

First boat we were going to buy you could flex the hull exactly like that.
In that case it was due to two things, the shape of the hull was flat there and not rounded like an egg, and the laminate was thin.
An egg of course gets most of its strength from its shape, not the thickness of the shell.
It took both to be able to flex the hull, if the hull had a rounded shape you couldn’t flex it, and if the hull had been thicker you couldn’t have flexed it.

In this case it was a known issue I found out through the users group, the fix was to cut the floor out of the head and glass in a stringer, which of course reinforced the thin hull.
This was a Mono, so it’s not a Cat thing.

I think it’s entirely possible that what you found is “normal” and other than a flatter spot in a thin hull you wouldn’t have found it.

A lot of modern boats don’t have “excess” glass, but don’t seem to be breaking up, so there must be enough.

[tdotson]

When i bought my ‘05 380 the surveyor tapped all over the bottom with a hammer and got nothing but a nice “ring”. The boats in general are solid, sounds like this on has problems.

[rabbi]

That area is uncored solid glass in a 380.

The 380 hulls are thin and it is possible to depress the skin by hand in some areas between bulkheads. Same for the uncored areas of other cats I have owned.

Now who knows how much thickness is required? Most folks in the forum have ideas & anecdotes to share (like myself) but very few have the qualifications to give a definite answer.
My take: I doubt there is any cat model that has done more circumnavigations than the 380 and we haven't heard they break up frequently. So maybe its strong enough.

[Jim Woodall]

This may be a serious issue, but in my search for a catamaran I was advised by a couple of brokers and one well-regarded surveyor that it should be far from a deal breaker, if the boat is solid in all other respects.

We often think brokers tell us what we want to hear to make a sale; however, I thought both were being forthright about the issue. It first came up in looking at a 2009 Leopard 40. The second time was a 2010 FP Lipari 41. Both boats had flex similar to that shown in MTF's video. I also saw it on a Lagoon 420. Each broker gave similar explanations and insisted it's not "that uncommon". I got the same general explanation and opinion that it was normally a minor issue from a well-regarded, Florida-based surveyor who had no connection with either broker. I also got a couple of opinions that differed.

What I did learn is that many boats do have areas of flex in their hulls, it was demonstrated to me several times on cats and monos alike. The owner (for 30 years) of the boatyard I used for over 15 years, thought it to be more than a minor issue and something that definitely needed attention, but again seldom a deal breaker. He said he had seen it often over the years in both high-end and production boats. He said a proper repair was generally straight forward. Of course, he does own a boatyard, what else would he say?

The hull flex issue, be it minor or not, was one of several things that eliminated both boats early on in my search. My wife and I ended up buying a 2019 Lagoon 42 and our boat doesn't appear to have areas of flex in the hull.

[boatpoker]

Originally Posted by rabbi

That area is uncored solid glass in a 380.

The 380 hulls are thin and it is possible to depress the skin by hand in some areas between bulkheads. Same for the uncored areas of other cats I have owned.

Now who knows how much thickness is required? Most folks in the forum have ideas & anecdotes to share (like myself) but very few have the qualifications to give a definite answer.
My take: I doubt there is any cat model that has done more circumnavigations than the 380 and we haven't heard they break up frequently. So maybe its strong enough.

I think it's a matter of degree. Having a large enough flexible area adjacent to a tabbed (rigid) bulkhead could result in hinge fractures over time. I've seen a few of those. I surveyed a Hanse 35 that was so flexible in the aft quarter below the waterline that I could depress it one half inch by hand with only moderate pressure. I did not buy the brokers .... "It's fiberglass, it's supposed to be flexible" .
I would not have bought that boat.

[rabbi]

Originally Posted by Jim Woodall

My wife and I ended up buying a 2019 Lagoon 42 and our boat doesn't appear to have areas of flex in the hull.

If I'm not mistaken the Lagoon 42 has balsa cored hull below the waterline. Flex in a cored hull is a different story than flex in uncored solid skin.

[Bean Counter]

Originally Posted by rabbi

If I'm not mistaken the Lagoon 42 has balsa cored hull below the waterline. Flex in a cored hull is a different story than flex in uncored solid skin.

Lagoon 42 Spec sheet:


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


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

[Bean Counter]

to the OP, did you go around the other hull and see if that one pressed in as well at the same spot?

[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

Thank you , I stand corrected!

I thought all recent designs like 40 and 42 were balsa below waterline.