Multihull Structure Thoughts

tropostudio said:

I highly recommend folks check out the Rusin VanDyke videos on YouTube of him sailing and camp cruising around Lake Erie. Looks like a great little vessel.

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tane said:

I wonder, if the strip portion is really worth the extra effort over a simple chine. Sure it has less wetted surface & there is (maybe) less turbulence when sailing at a slight angle, but we do not have a high tech all-carbon no-effort-spared speed record machine here after all...

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oldmulti said:

The following is a summary of several web sites on issues with Lagoon catamaran bulkheads. Main bulkheads and secondary bulkheads on certain models have had issues. As one owner said “From my research on L400, not big issue if not worried about upwind performance. If bulkhead cracks. then you gotta fix it.” Other owners seem to want to go to windward and are little more concerned

Lagoon 450 bulkhead issues 2021: 450 450 Bulkhead issues - Report them please. - Cruisers & Sailing Forums https://www.cruisersforum.com/forums/f139/450-bulkhead-issues-report-them-please-249741.html

“It appears that the main mast bulkhead on the L450 was underbuilt. It is a defect that is hidden under the trim and will not cause damage in the marina. However with 100s of boats out sailing oceans it is starting to show up too often to ignore.

It is repairable and the repaired boat will be better than new, but the repair involves removing a lot of cabinetry and $$. It would be easier and cheaper to solve on the production line, but that means the manufacturer would have to admit to the problem and retrofit all unsold inventory.

The OP is trying to start an organized program to address the issue, but is meeting resistance from the manufacturer and the current owners who have taken the head in the sand approach. I don't see the manufacturer as the solution--like defective airbags in cars--the manufacturer doesn't have the resources to fix the problem on their own.”

Facebook group regarding the bulkheads is: Facebook Groups https://www.facebook.com/groups/902269000568556

Lagoon 38 bulkhead issues 2019: Re-tabbing Bulkheads on a Production Catamaran https://www.boatdesign.net/threads/re-tabbing-bulkheads-on-a-production-catamaran.62499/

“Problem statement: After numerous years of full-time cruising in the Caribbean, we have noticed that many of the smaller bulkheads and furniture paneling has separated from the hull. This specific manufacturer has a history of poor varnish application and service life. Finally, after one too many rough passages, we began to notice that some of the glue joints (it is believed to be Plexus, but if anyone knows what was being used in France back in 2003 please let me know) have failed at the wood interface. It is only the wood interface that the adhesive has failed. During some destructive testing, I did observe that the bulkheads were varnished prior to tabbing and that the varnish under the fillet has lifted from the wood, thus creating a tabbing failure (through no fault of the actual adhesive).”

Lagoon 440 bulkhead issues 2020: How to upgrade the bulkhead on a Lagoon 440 https://catamaranimpi.com/2020/07/28/how-to-upgrade-the-bulkhead-on-a-lagoon-440/

“According to the Lagoon factory there are main structural bulkheads and non structural bulkheads.

The structural bulkheads are the mast bulkhead and the engine compartment bulkhead. They provide some rigidity to the hull. These are tabbed in.

Then there are several smaller non structural wood bulkheads which form the floor frames. These are stiffened by a composite process, a kind of resin putty is applied to fix them to the hulls.”

“A common occurrence on a Lagoon 440 is that the non structural bulkheads get cracked.

Later models such as Impi which is a late 2009 model have the entire main bulkheads from mid hull starboard to mid hull port glassed all the way around. However, some earlier models were not glassed on the top section where the deck meets the bulkhead under front windows / above the water tanks. The issue then is that the ‘mast forces’ through the mast support post can work this section loose. Therefore, it is important to remove the water tanks and glass that section in if not already done.”

“To recap – the main bulkheads are glassed in from midship of one hull to midship of the opposite hull, the outer sections are fitted with a resin or resin putty type bonding material which although very strong is not strong enough to hold in severe flexing situations.”

“For this reason when we purchased Impi we decided to tackle the serious parts of this – let me use the worst section as an example – itʼs no secret that on a 440 and some 450ʼs the weak point is the port side bulkhead under the forward cabin section where one climbs over to get into bed.”

This is information and please read the web sites and facebook page for further detail. Comments are welcome but please keep to known facts. Jpegs of the Lagoon 440 bulkheads attached. The PDF is a photo of the Lagoon 38 bulkhead.

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brian eiland said:

I just ran across this video that appears to suggest there is a sizable number of vessels with this design problem with the Lagoon 45's ??

I'd like to see more details on the construction of these bulkheads. Is it the strength of the bulkhead itself, or a tabbing problem with installation??

If it is as widespread as video suggest, are there other subject threads on this forum that discusses the problem?

This can be a learning subject

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Support | Lagoon

www.catamarans-lagoon.com

HelmutSheina said:

Brian here is a link to a response on Lagoon's website.

Support | Lagoon

www.catamarans-lagoon.com

Perhaps this topic deserves its own thread where we can support owners and repairers, and turn it into inspection and repair instructions in case Lagoon closes?

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Lets put this way, there are quite a few builders that believe they can simply put a BIG SLAB of stainless steel ‘chainplate’ at the side of the hull shell, and thru bolt it, and that is adequate for attaching the shrouds, etc. In many cases this is true, and it has worked out okay. It’s not exactly an ‘engineered solution’, and in the case of unballasted boats seeking to be very lt-weight, it’s certainly not a finessed solution. I don’t think Alinghi nor some of the ocean racing multihulls would be satisfied with these ‘brute solutions’, but I have seen more than a few cruising multis with these same big slabs of SS.

I don’t really care to get into a name calling exercise here, but I might make the suggestion that you have a discussion with some of your local boat surveyors. I imagine they have quite a number of stories they can relay on any number of cases.

And then just consider the many thousands of vessels that ‘tabbed’ their bulkheads and other reinforcements (substructures?) in with polyester resin wetted-out fabric. Polyester resin is great for sticking to shoes and skin, but it certainly doesn’t like to stick to itself. Ask your surveyors about some of these problems….how many has he seen come unbonded.

How many production manufacturers might suggest that it’s okay to hoist their vessels up by the chainplates….this should be doable, right?

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It's interesting to me that designers are willing to tackle the enormous problem of accommodating these loads, and spend so little time developing means to eliminate them altogether. Kite rigs never develop--in any part of their structure--loads in excess of their actual net thrust.

A typical racing mainsail, say 500 sq ft, might develop a total force of some 500-750 lbs, in winds of 18-22 kts. In order to do so, it will directly develop mainsheet loads of more than a ton, forestay loads to match and shroud loads in the same range--and mast compression loads equal to the sum of all 4. If a multihull, this compression load will be taken by dolphin striker intoto water stays taking 6-8 tons of load (which is devolved back into compression of the forebeam)--all to get a lousy 500 lbs of sideforce out of the mainsail.

Is it too obvious to think that this is kinda, well, dumb, when you can use a kite which has no weight, and develops a *total* force of 500 lbs? The kite has no interior forces higher than this (if it did--say by design--such forces could be dissipated into multiple bridle lines at the source) and the only force on the hull is simple tension--applied at a single point, very close to the boat's daggerboard. The hull structure thus needs no ballast, no beam (beyond that needed at the dock to keep the boat upright), no "56 ton" water stays, no heavy crossbeams, no mast, no boom, no bowsprit, no central pod, no shrouds, on and on.

Sure, kites aren't yet developed sufficiently to replace mainsails. This I grant. Once upon a time *mainsails* were not sufficiently engineered to take the loads they routinely accept today; the science has progressed. My question is why is nobody working on the kite angle, despite the astonishing reduction in weight, inertia, windage, and cost they can offer? Alinghi cost an absolute bomb; for a small fraction of that sum, really high performance kites could have been developed, and these sort of problems would disappear for all time. I just don't get it...

Dave

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brian eiland said:

Kite Rigs

ran into this posting over on that subject thread,...couldn't resist posting it

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10 "Disposable" Catamarans Built To Fail (Avoid These)​