Lagoon bulkheads

[Pelagic]

Originally Posted by wingssail

Oh really? I didn't know that.



I do understand that wooden boats of old often had movement in their structure, which the advent of fiberglass cured. It that what you are referring to?

Yes if we are talking about production fiberglass monos at an attractive price point, they went thru a similar learning curve on bulkhead structure.
Cheoy Lee's come to mind when I first visited the Lantau yard in the 80's.

Even venerable builders like Feadship when struggling with weight issues and sound dampening floating interiors have to rectify mistakes.... sometimes at enormous costs

[fourlyons]

Originally Posted by smj

Are heavier cats always stronger than lightweight cats? Or do heavier cats have more loads on them making them weaker?

I'm sure you know this, but of course there is no correlation between weight and strength in any built structure.

I'm no expert on multihulls, but I'm not so sure that heavier cats will always experience higher loads than lighter cats. Won't a lighter cat (all other things being equal) be faster, and with greater speed, comes greater loads in some areas?

My comment about the Lagoons not being particularly light was in response to the comment that since it's a cat it must be lightly built and therefore more susceptible to damage. But of course, a boat can be very light, and very strong.

[Pelagic]

Originally Posted by fourlyons

I'm sure you know this, but of course there is no correlation between weight and strength in any built structure.

If we are taking about sheer stresses and spreading the load over larger areas and with greater thickness for rigidity.... then that does take more of the common materials and therefore makes the boat heavier

Of course you can use the more expensive carbon fibers and Kevlar to reduce weight. ... but that falls outside economic production boats

[smj]

Originally Posted by fourlyons

I'm sure you know this, but of course there is no correlation between weight and strength in any built structure.

I'm no expert on multihulls, but I'm not so sure that heavier cats will always experience higher loads than lighter cats. Won't a lighter cat (all other things being equal) be faster, and with greater speed, comes greater loads in some areas?

My comment about the Lagoons not being particularly light was in response to the comment that since it's a cat it must be lightly built and therefore more susceptible to damage. But of course, a boat can be very light, and very strong.

The lighter cat tends to sail on top of the water where a heavier cat sails through the water, more like a monohull. This brings added stress and more bridgedeck slamming.
Also a lighter cat can have a much smaller rig and smaller sails which reduces stress on both boat and crew.

[donradcliffe]

I think Fourlyons is at least partially right. The stresses on boat structures are proportional to their accelerations, and anyone who has sailed to weather knows there are harder and more frequent bone jarring accelerations at 12 knots than there are at 6 knots.

[wingssail]

Originally Posted by smj

The lighter cat tends to sail on top of the water where a heavier cat sails through the water, more like a monohull. This brings added stress and more bridgedeck slamming.
Also a lighter cat can have a much smaller rig and smaller sails which reduces stress on both boat and crew.

Originally Posted by fourlyons

...I'm no expert on multihulls, but I'm not so sure that heavier cats will always experience higher loads than lighter cats. Won't a lighter cat (all other things being equal) be faster, and with greater speed, comes greater loads in some areas?...

Originally Posted by donradcliffe

I think Fourlyons is at least partially right. The stresses on boat structures are proportional to their accelerations, and anyone who has sailed to weather knows there are harder and more frequent bone jarring accelerations at 12 knots than there are at 6 knots.

Originally Posted by Pelagic

If we are taking about sheer stresses and spreading the load over larger areas and with greater thickness for rigidity.... then that does take more of the common materials and therefore makes the boat heavier

Of course you can use the more expensive carbon fibers and Kevlar to reduce weight. ... but that falls outside economic production boats

Originally Posted by Pelagic

Yes if we are talking about production fiberglass monos at an attractive price point, they went thru a similar learning curve on bulkhead structure.
Cheoy Lee's come to mind when I first visited the Lantau yard in the 80's.

You guys have branched off into hypothetical and anecdote land. This is all hearsay and opinion.

Can anybody cite any science or measurements or statistics here?

And Pelagic, what evidence do you have that Cheoy Lee had a bulkhead issue in the 80's. My experience with those boats was that they were over built, nothin like light weight.

[smj]

Originally Posted by wingssail

You guys have branched off into hypothetical and anecdote land. This is all hearsay and opinion.

Can anybody cite any science or measurements or statistics here?

And Pelagic, what evidence do you have that Cheoy Lee had a bulkhead issue in the 80's. My experience with those boats was that they were over built, nothin like light weight.

Having owned both type catamarans mine is hearsay from experience. But seriously, a little common sense mixed in?
If you have 2 40’ catamarans sailing in the same waters both making 7 kts of boat speed, one flying 1200 sq ft of sail and the other 350 sq ft of sail which one has more stress on the structure?

[Chotu]

actually, it’s not hearsay at all.

it’s proven fact. Just talk to any actual Catamaran designer. They will tell you the same thing.

The force on the boat is a product of momentum. P(momentum) = mv

Notice there is a mass factor in the equation for momentum. There is a velocity factor, but the boat is going the same speed. At 8 knots, A boat with half the mass has half the momentum and therefore half the stresses on the structure. This allows one to create bulkhead attachment points that have half the strength ane still be just as good as the heavy boat. It also allows one to use half the sail area and half the engine horsepower. That gives you a weight savings and also half of the load on the rig and half of the load on the hull from the engines.

And you think it sounds extreme? A boat weighing half as much?

A lagoon 52 weighs 57,000 pounds. I’m actually shocked. I didn’t think the number was going to be that big.

my 50 foot catamaran weighs 18,000lbs. The similar size lagoon is almost 3 times as heavy as mine. No wonder there are bulkheads are popping off. My boat therefore has one third of the momentum and one third of the stresses and strains on the structure. And mine is probably 10 times better built.

My bulkheads are filleted and fiberglassed all around in a complete circle to the hull. All the way around the bulkhead at every point it touches the hull, it is set with an epoxy cove and then fiberglassed to the hull just like this picture. but of course my bulkheads (made of foam corecell and glass) go around in a complete circle. This is just a partial. But this is the way it is constructed properly.





Adding more and more weight to a catamaran is something called a design spiral. You add a few pounds here and there, and then you have to beef up the structure to support those pounds which makes the boat heavier, which in turn makes it so that you need to have more support structure which in turn makes the boat heavier. then because it’s so heavy you need to increase sail area and engines or it won’t move, so you have to beef up the structure some more, and that makes it heavier. Etc. etc. it’s nearly an endless loop.

And if you want to picture the lighter boat going faster, put my boat at 24 knots and the lagoon at 8 knots and we have almost as much of a load on my structure at 24 knots as the lagoon has at 8 knots.

Note: I am simplifying and keeping things linear. So it doesn’t get too weird in the conversation.

[Chotu]

and finally, this is a huge factor in collisions as well.

If you hit something with a lightweight Boat, you have a much better chance of not destroying the boat. The momentum goes into the hull wherever the thing hits. The less momentum (speed times mass), the less force put on the hull at the point of impact.

The surveyor that checked out my boat after the moorings failed and all of the boats got crushed in the corner against the seawall including mine, mentioned that’s why my boat survived and several sunk. I had cosmetic damage from it. A lot of cosmetic damage. But the boat held together perfectly because it was more strongly built than the (small) momentum the impacts imparted to it.

it was because my boat was lightweight that it wasn’t damaged like the others, several of which sank.

obviously, Production Catamaran companies don’t include any of this information. They don’t want you to know it. They would rather make the shiny beautiful interiors with multiple bars, huge Viking refrigerator freezers, stuff like that to attract you to buy it. The characteristics that make it a good boat comes second to the amenities.

[fourlyons]

Originally Posted by smj

Having owned both type catamarans mine is hearsay from experience. But seriously, a little common sense mixed in?
If you have 2 40’ catamarans sailing in the same waters both making 7 kts of boat speed, one flying 1200 sq ft of sail and the other 350 sq ft of sail which one has more stress on the structure?

Sure, but that's not the scenario I described. I said all other things equal, as in sail area. That is what makes the light boat in my example faster. Your example has boats of equal speed. As Chotu pointed out, acceleration (not quite the same thing as speed, but maybe close enough here) is half the equation for force. F=M*A Double the weight in the heavy boat, but triple the speed of the light boat, what do you get?

Plus, who is going to go to the expense to build a super light cat only to tool around at 7 knots?

[danstanford]

Originally Posted by malbert73

The current Groupe Beneteau structural practices in both monos (Beneteau) and multis (Lagoon) reflect IMO too far on cost cutting side.

The extra cost of properly tabbing in the structural grid before placing furniture in the Beneteaus, and the extra cost of properly built and tabbed bulkheads in Lagoons while still in build phase - would have to be negligible compared to overall cost- I am estimating 5K tops per boat in materials and labor. But the market eats the boats up at boat shows so until consumers start caring it won’t change.

So I do take exception with the practice of “cheaping out” on structural members. I have owned and operated several old boats (1966 Luders 33, 1984 C&C 30, current 1987 Tartan 40) and none had ANY bulkhead or structural issues. Age/cosmetic sure, but I wasn’t tearing boat apart to fix bulkheads.

It’s just not that tough to make the bones of the boat “permanent quality” while it’s being built. And it doesn’t add that much weight compared to everything that gets put in later.

No doubt the cost of doing it right is a small fraction of repairing it later, but as consumers we reward the cut corners with our orders as long as the price is better. Home builders have been fighting this battle for many many years. If your product is superior and it costs more you will struggle to get orders in much volume.

[smj]

Originally Posted by fourlyons

Sure, but that's not the scenario I described. I said all other things equal, as in sail area. That is what makes the light boat in my example faster. Your example has boats of equal speed. As Chotu pointed out, acceleration (not quite the same thing as speed, but maybe close enough here) is half the equation for force. F=M*A Double the weight in the heavy boat, but triple the speed of the light boat, what do you get?

Plus, who is going to go to the expense to build a super light cat only to tool around at 7 knots?

My point was the lighter cat could maintain the same speed as the heavier cat while being well reefed down thus much less stress on the boat and the crew. Sure, if the lightweight cat was flying full 1200 sq ft of sail it would probably double the speed of the heavier boat, have equal stress from sail area but probably equal or less stress on the structure as it would be sailing on top of the water.

[Simi 60]

Originally Posted by malbert73

.

It’s just not that tough to make the bones of the boat “permanent quality” while it’s being built. And it doesn’t add that much weight compared to everything that gets put in later.

And as I've said before, there are hundreds of places to save weight on a heavy boat like the lagoon, properly built bulkheads is not one of them.

Get rid of Corian benchtops as an example
Replace with laminex
Price difference covers cost of proper bulkheads
Weight difference covers the extra weight of proper bulkheads

[Pelagic]

Originally Posted by wingssail

And Pelagic, what evidence do you have that Cheoy Lee had a bulkhead issue in the 80's. My experience with those boats was that they were over built, nothin like light weight.

I lived in HK in the 80s and during warranty period,... took over the management of a new CL 66 built supposedly to ABS CLASS!

Then took boat to Seattle via Japan>Alaska.... many loose bulkheads and other issues so advised this same superyacht owner to sell it.

Also in late 80s another VERY disgruntled 66 owner had actually displayed his boat at the Ft Lauderdale Show ...FOR SALE ...after gutting and exposing many failed issues and latent defects....including bulkheads...
It was very interesting to say the least and did not make the Lee Brothers happy!

One point in all of this that should be remembered is that a good design is useless if not executed properly....

The Cheoy Lee yard back then...was a horrible place to work in for the employees so can understand that some of the workers had poor attitudes and standards.

[wingssail]

Originally Posted by Pelagic

I lived in HK in the 80s and during warranty period,... took over the management of a new CL 66 built supposedly to ABS CLASS!

Then took boat to Seattle via Japan>Alaska.... many loose bulkheads and other issues so advised this same superyacht owner to sell it.

Also in late 80s another VERY disgruntled 66 owner had actually displayed his boat at the Ft Lauderdale Show ...FOR SALE ...after gutting and exposing many failed issues and latent defects....including bulkheads...
It was very interesting to say the least and did not make the Lee Brothers happy!

One point in all of this that should be remembered is that a good design is useless if not executed properly....

The Cheoy Lee yard back then...was a horrible place to work in for the employees so can understand that some of the workers had poor attitudes and standards.

CL66? You mean like this one? Oh yeah, I see the relevance.

I lived in Honkers in the 2000's and the only thing left in Penny Bay was Disney Land. But around the world Cheoy Lee boats built by those disgruntled workers live on.

Googling I see that there were no "Lee" brothers. Cheoy Lee has been, since the founding, and still is, run by, the "Lo" family. They were early adopters of fiberglass boat building, now work mostly in metal.

I can not find any reference to poor treatment of workers in the 70's, or at any time, but knowing China, it would not surprise me. There was however a lot of ground contamination from the shipyard; had to have a big clean-up. But doing a poor job because you don't like the working conditions? I doubt that.

But go ahead, Mr Pelagic, and tell us more about monohull sailboats with bad bulkhead problems.