Lagoon 400 Bulkhead an issue?

[tuskie]

Originally Posted by robert sailor

If you own a Lagoon you will be bias so what's the difference, almost everyone has bias opinions. It is the rare person who can keep their mind open and learn from the critics as well as those in your tribe that drank the same cool aid.

It's only an opinion, but I don't consider myself biased.(!) Unlike other forum contributers, I have posted just as much about Lagoon (or catamaran) problems as I have posted about their positives. Boats are designed and constructed with compromises, so anyone who makes out that their boat is perfect is either biased, ignorant or trying to sell.

In this thread, not only has the isue been confused with misinformation and sidetracks, but we've also seen a picture of a sawn piece of plywood purporting to be a stress cracked Lagoon bulkhead and a supposed "surveyor" classifying all Lagoons as junk. When this sort of rubbish is peddled, no wonder where is a perception of bias. Of course , no verification of these "facts" has followed.

So, if you bother to re-read the thread, you'll find biased and unfounded anti Lagoon statements presented in response to the OPs request for specific information. Same same.

[robert sailor]

Originally Posted by rallyman1122

I will agree to a point. But if you own a Lagoon, you have experience, not bias. If you are a mono hull owner, commenting critically in a multi hull thread, that is bias

Yes you do have experience which is worthy but it's human nature to support decisions made. We even go so far as not reading information that is contrary to our buying decisions. How many smokers do you know that read reports confirming how bad smoking is for you, it's the same thing with all the decisions we make. If we have long keels on our boats we find reasons to prefer them over fin keels etc. Read all the different opinions and behind most of them is bias, not all of them but most. It's just how humans operate.

[arsenelupiga]

here are some pics form my visit to lagoon factory. After another look, i am more convinced main bulkhead is not structural and removing it all together will not substantially alter boat stiffness.

Pic 1. hull&bridgedeck is one piece only therefore structure very strong & stiff. Older generation cats that have bonded hulls to bridgedeck using metal pieces etc need structural bulkheads. And because of ignorance or not knowing any better 'experts' think this is the case with lagoon as well, i suspect.

pic 2
main bulkhead in L 38.

pic 3
cat transport at lagoon factory. When boat raised, it flexes so that both hull drop around 10 cm. If main bulkhead was structural, bulkhead or fiberglass would quickly break.

Not saying water is not an issue, even big, as I do not know, however, main bulkhead is not supporting stiffness of the boat. Anyone wants to challenge this, i mean excluding blah blah, provide some evidence first.

[neilpride]

Ok Mr, where is exactly the point where the mast rest?? i bet you a cold beer is the main bulkhead.... I have few cut out samples of FG in the shop, and quite honest they are not impresive in thicknes, so those Lagoons without the main bulkhead break apart in short order in any sea state,,,, saying that the main bulkhead is just cosmestic is plain wrong, partitions and cabinets furniture glued in place can be cosmetic , any bulkhead tabbed with FG is not.....

[arsenelupiga]

Originally Posted by neilpride

Ok Mr, where is exactly the point where the mast rest?? i bet you a cold beer is the main bulkhead.... I have few cut out samples of FG in the shop, and quite honest they are not impresive in thicknes, so those Lagoons without the main bulkhead break apart in short order in any sea state,,,, saying that the main bulkhead is just cosmestic is plain wrong, partitions and cabinets furniture glued in place can be cosmetic , any bulkhead tabbed with FG is not.....

good question. will get back to you.

[neilpride]

2 picture to the right corner, main bulkhead with tabbed partitions, there is where the mast step put all the compression load..

[BigBeakie]

Facinating if true! If there are no structural bulkheads in the boat, what gives it torsional rigidity, to deal with the wracking movement? If they are relying on a monocoque shell to resist these forces, that would explain the need for very heavy layup.

Does anyone with some boatbuilding knowledge/experience know how these newerLagoons are built wrt bulkheads? I have seen older models ( pre L400) with glassed in bulkheads, but perhaps at some point they switched to adhesives like Plexus?

[arsenelupiga]

Originally Posted by neilpride

2 picture to the right corner, main bulkhead with tabbed partitions, there is where the mast step put all the compression load..

excellent observation, however this is not L400.

[arsenelupiga]

Originally Posted by BigBeakie

Facinating if true! If there are no structural bulkheads in the boat, what gives it torsional rigidity, to deal with the wracking movement? If they are relying on a monocoque shell to resist these forces, that would explain the need for very heavy layup.

Does anyone with some boatbuilding knowledge/experience know how these newerLagoons are built wrt bulkheads? I have seen older models ( pre L400) with glassed in bulkheads, but perhaps at some point they switched to adhesives like Plexus?

you may want to contribute some substance instead of bashing without any evidence.

[neilpride]

Originally Posted by arsenelupiga

excellent observation, however this is not L400.

Doesn't matter mate, they are built with the same principle, main bulkhead and mast step resting in the bulkhead.

[BigBeakie]

Originally Posted by arsenelupiga

you may want to contribute some substance instead of bashing without any evidence.

Just to be clear, please don't be defensive, I am not bashing, I am asking. You are the one who has been to the Lagoon factory and seen this first hand. So you can enlighten us on this bulkhead question.

So I am asking (because I am puzzled), if what you are saying is true that they don't rely on transverse structural bulkheads to provide torsional stiffness to prevent wracking, how do they do it???

You do realise what you are implying (effectively, no structural bulkheads) goes against most engineering principles re boatbuilding that I'm aware of? It goes against the way good, oceangoing cats have been built for many decades?

Put simply, to my limited knowledge, (and I have only built 2 cruising cats, one of which has circumnavigated) stiffness in a cat is a very good thing to aim for. The forces when working to weather to twist the boat (wracking moment) as one bow rises to a wave, are very significant and put enormous loadings on certain points. If you don't believe me, go ask any NA that knows multihull design.

Full width, transverse, bottom to top, structural (i.e. REALLY strong) bulkheads are used at (at LEAST) 3 positions along the boat, to provide stiffness & torsional rigidity. They hold the boat together. And good construction uses as many internal components to supplement and re-enforce this stiffness, such as glassed in sub floor partitions, longitudinal members, furniture components etc etc. AFAIK, this is how a good strong bluewater cruiser is built.

Now, you are saying Lagoon do something completely different with their bulkheads. So, enlighten us please.

[arsenelupiga]

checked and you guessed it mast does not rest on bulkheads. No cold beer for neilpride.

It rest on bottom of nacelle. Now i understand why there around 2cm thick fiberglass.

This is better engineering in my opinion. In large beam on breaking wave situation boat can twist a lot without critical structural issues. Yes, main bulkhead, that is of normal thickness, and not double, will break, furniture as well, if real bad, but this will not structurally destroy boat.

In similar case if that bulkhead structural, first wave will weaken/break bulkhead or worse fiberglass, second one will take boat out.

I am very comfortable with that setup and gives me lot of confidence when facing bad weather.

It appears lagoon started this approach with introduction of nacelle, around 2005. And more than 1000 boats floating. Last one L 42 appears to have same design, minus nacelle water collection, i guess. Have not heard single issue with that.

Also my boat very stiff. In 25 kn true beam reaching no loose shrouds. Actually I have not seen it loose yet in 1600 NM.

I am all for clearing things up. It is safer.


sorry forgot to add: main bulkhead purpose is to hold watertanks and electrical installation, one would guess 800 kg when tanks full. Pretty serious task, however not structurally critical.

Please provide some evidence if you do not agree.

[tuskie]

Thanks Arsenelupiga,

Very informative and well explained. There has been more BS, biased crap and misinformation about Lagoon bulkheads on this forum than any other topic. Except anchors!
All from "experts" who know more about catamaran design and construction than Van Peteghem Lauriot-Prévost (VPLP), the Lagoon designers. It's a wonder these geniuses haven't been snapped up by leading naval architecture companies to design cutting edge multihulls while they still know everything.

Maybe they are just ignorant w__kers?

[sailnow2011]

Originally Posted by tuskie

Thanks Arsenelupiga,

Very informative and well explained. There has been more BS, biased crap and misinformation about Lagoon bulkheads on this forum than any other topic. Except anchors!
All from "experts" who know more about catamaran design and construction than Van Peteghem Lauriot-Prévost (VPLP), the Lagoon designers. It's a wonder these geniuses haven't been snapped up by leading naval architecture companies to design cutting edge multihulls while they still know everything.

Maybe they are just ignorant w__kers?

Guess what, if there are a bunch of people who hate lagoons, and find them to be a bad design, then be wary. No other brand of cat or mono outside this one company (jeaneeau) has more people thinking they are junk, worthless, or unsafe. Sure, many are floating. What that means is they are floating, not 10,000 are crossing oceans daily. A boat at a dock can be made of plywood, just look at flying Hawaiian. When they go to sea, in anything but nice conditions is when they start to see issues. As have been proven by the monos designed and built by the company, their boats DO sink.... or at least float upside down after a bad design in the keel lets go.

If people are hating a lagoon as much as they hate a CQR, there must be a reason.

[robert sailor]

Originally Posted by sailnow2011

Guess what, if there are a bunch of people who hate lagoons, and find them to be a bad design, then be wary. No other brand of cat or mono outside this one company (jeaneeau) has more people thinking they are junk, worthless, or unsafe. Sure, many are floating. What that means is they are floating, not 10,000 are crossing oceans daily. A boat at a dock can be made of plywood, just look at flying Hawaiian. When they go to sea, in anything but nice conditions is when they start to see issues. As have been proven by the monos designed and built by the company, their boats DO sink.... or at least float upside down after a bad design in the keel lets go.

If people are hating a lagoon as much as they hate a CQR, there must be a reason.

I would not be so hard on Lagoons. The company is offering a product that buyers want and they have been very successful doing just that. A large percentage of their yachts are built for the charter market and fill that need very well. Look they are not racing machines, quite the opposite but they provide huge space for their length and are extremely comfortable at anchor or the dock. They were not designed as offshore passage makers but many cruisers have crossed oceans in them in the low latitudes with few problems. Keep in mind, these are not top of the line cats, they are built to a budget but they seem to get the job done.