Shocked by hull material catamaran

[a64pilot]

Originally Posted by 44'cruisingcat

Plenty of people are happy to sail slowly and motor most of the time. Not me.

That is exactly it, to a large extent. Weight is evil, it sacrifices performance, it increases wetted area and destroys acceleration.
Light makes right.

Some though are willing to sacrifice speed and light wind performance for what we consider to be a tougher and longer lasting construction.

[noelex 77]

The best definition of a cruising boat's speed is based on the time taken to complete a passage plus the time to effect repairs.

Too light can sometimes be very slow .

[arsenelupiga]

Originally Posted by a64pilot

That is exactly it, to a large extent. Weight is evil, it sacrifices performance, it increases wetted area and destroys acceleration.
Light makes right.

Some though are willing to sacrifice speed and light wind performance for what we consider to be a tougher and longer lasting construction.

funny you say that. I had recently sailed parralel singlehanded in 5-7 kn of wind, broad reach against 70 ft racing mono with many crew. Both boats white sails only.

It was clearly embarassment as noone was looking at me when I was gaining against them. Eventually they got slightly ahead...

I did manage to improve my sail trim skills, no doubt.

[Stumble]

Originally Posted by a64pilot

Are there really cored boats with 25 mm outer skins? If the outer skin is 1", then what is the core for? Insulation? I'm not trying to be sarcastic, just 1" well laid glass ought to be Hell for strong without any core.
I have drilled though my IP in a couple of places installing the generator seacock and other thru hulls, and I have not seen anything even remotely approaching that kind of thickness and I'm of course a single skin. IP's reputation is not that of a thinly built weak hull?
I would be surprised to find anywhere that the glass is 1" thick

There could be, but it would be a weird design. Panel stiffness is dictated by the loads andby the distance between frames and bulkheads. So the wider the spacing of the internal framing the thicker the panel needs to be. It is not impossible to imagine designing a boat with no internal support structure that needed 1" thick panels to get sufficient stiffness. It would be counter to all modern design, but it's possible.


What i think gets lost here is that skin thickness is all about strength. It does nothing else for a boat in normal conditions. And frankly boats don't need much strength. They just aren't loaded much that way and fiberglass is really incredibly strong. What boats generally need, is stiffness, and stiff and strong are very differently things.

Dyneema rope has bubkis for stiffness, but a huge amount of strength. They are not the same thing at all.


Fiberglass is actually pretty amazing stuff. An epoxy and S glass laminate is actually stronger (tensile strength) than epoxy and carbon fiber by about 50%. But nothing, or almost nothing in a hull is ever placed in tension. It is almost always stiffness that matters for a boat. So why lug around thousands of pounds of fiberglass laminate that adds nothing to the failure mode of the boat?

Even in this damage, the strength of fiberglass was never at issue, it was the abrasion resistance of it. And frankly that's a whole different kettle of fish.


The reality is that for most boats the required stiffness is a couple of orders of magnitude more important than its strength. And thebest way to get the required stiffness is to add thickness. Within reason it doesn't even matter what adds that thickness, more roving fiberglass, a core, CSM, carbon fiber, concrete, etc. none of it matters, the important question is how thick is it.

So why is carbon fiber so desirable when it is weaker than fiberglass? Because it weighs about 1/3 less and has three times the stiffness than S-glass. But if you just needed strength you would use glass every time.

Note -all comparisons are general in nature I took some liberty in the rounding.

[a64pilot]

Originally Posted by noelex 77

Too light can sometimes be very slow .

The light makes right is supposedly a quote on what was above the door of the President of Grumman Aircraft back in WWII.
It is half of the quote, the whole quote was
"Light makes right, right up to the point of structural failure"
Grumman Aircraft had a reputation for exceeding strong, but heavy aircraft. Their nickname was "Grumman Iron Works"

[a64pilot]

I would say that in this failure, puncture resistance had a lot to do with survivability. It's likely why a steel hull if your on a reef is hard to beat, Steel will bend and distort and all kinds of things before it's punctured and allowing water in the boat.

[Dockhead]

Originally Posted by Polux

I don't agree with you. I believe the Oyters are well built boats, not different from other top brands in what regards building quality and no, they are not built for speed (they are not performance boats) but to sail well that is a thing most modern boats are designed to do.

The problem on that particular boat (and on the sisterships) was an engineering error, that was assumed by Oyster. Lots of Oysters around, including many new ones, they are sailed extensively without problems.

Polux disagrees with me? How shocking! Why -- that's never happened before! ROTFLMAO.


I do agree that Oysters are generally well built, fantastically well built. But I think that the one that lost its keel is carp. The layup is extremely thin, and keels falling off is just -- well, we've discussed this a few times before -- totally unacceptable. I would not trust any other aspect of that particular design, once the designers made that kind of mistake.

"Built for speed" is the charitable interpretation. But I just don't believe it was built for cheapness. So that thin layup can only be for the sake of weight and speed. And they took it too far.

[Dockhead]

Originally Posted by Stumble

There could be, but it would be a weird design. Panel stiffness is dictated by the loads andby the distance between frames and bulkheads. So the wider the spacing of the internal framing the thicker the panel needs to be. It is not impossible to imagine designing a boat with no internal support structure that needed 1" thick panels to get sufficient stiffness. It would be counter to all modern design, but it's possible.


What i think gets lost here is that skin thickness is all about strength. It does nothing else for a boat in normal conditions. And frankly boats don't need much strength. They just aren't loaded much that way and fiberglass is really incredibly strong. What boats generally need, is stiffness, and stiff and strong are very differently things.

Dyneema rope has bubkis for stiffness, but a huge amount of strength. They are not the same thing at all.


Fiberglass is actually pretty amazing stuff. An epoxy and S glass laminate is actually stronger (tensile strength) than epoxy and carbon fiber by about 50%. But nothing, or almost nothing in a hull is ever placed in tension. It is almost always stiffness that matters for a boat. So why lug around thousands of pounds of fiberglass laminate that adds nothing to the failure mode of the boat?

Even in this damage, the strength of fiberglass was never at issue, it was the abrasion resistance of it. And frankly that's a whole different kettle of fish.


The reality is that for most boats the required stiffness is a couple of orders of magnitude more important than its strength. And thebest way to get the required stiffness is to add thickness. Within reason it doesn't even matter what adds that thickness, more roving fiberglass, a core, CSM, carbon fiber, concrete, etc. none of it matters, the important question is how thick is it.

So why is carbon fiber so desirable when it is weaker than fiberglass? Because it weighs about 1/3 less and has three times the stiffness than S-glass. But if you just needed strength you would use glass every time.

Note -all comparisons are general in nature I took some liberty in the rounding.

Typical of English boats is massively strong hulls. Why do you think the old Oyster 55 displaces 27 tons light ship? Because it's got 80mm of solid GRP in the bottom.

Is that overkill? I don't think so, not for a long distance cruising boat which might encounter ice, rocks, whatever. Now they could have done it better with cored construction, but that's a different conversation. I don't agree that strength of the hull is not important. The hull carries all the loads of the rig. How many boats have you been on where you can hardly open or close the doors below when the rig is powered up? Which groaned, creaked and twisted in a seaway? It's not only bad for the hull, wearing it out, it's bad for the rig, and bad for sailing efficiency.

Another reason for massive hull construction is impact/penetration resistance.

Yet another is carrying high loads where the keel is attached -- look at the Oyster whose keel feel off, in the other thread. Tell me the thin hull layup (totally out of character for Oyster) had nothing to do with the failure.


What kind of boat has 22mm layup in the outer skin of a cored hull?

Answer: the kind of boat which has chainplates like these:





It's when the design brief calls for massive overkill in the structure.

[minaret]

You guys are all hung up on sailboats. I work on large power boats on a regular basis which have scantlings which far exceed the numbers we are discussing here. 1" core skins are not so rare at all in that world. I have after all posted pics here of a 64' Nordhavn bottom with solid glass over 4" thick. Took me 126 plies of laminate to rebuild.

[minaret]

Originally Posted by Stumble

There could be, but it would be a weird design. Panel stiffness is dictated by the loads andby the distance between frames and bulkheads. So the wider the spacing of the internal framing the thicker the panel needs to be. It is not impossible to imagine designing a boat with no internal support structure that needed 1" thick panels to get sufficient stiffness. It would be counter to all modern design, but it's possible.


What i think gets lost here is that skin thickness is all about strength. It does nothing else for a boat in normal conditions. And frankly boats don't need much strength. They just aren't loaded much that way and fiberglass is really incredibly strong. What boats generally need, is stiffness, and stiff and strong are very differently things.

Dyneema rope has bubkis for stiffness, but a huge amount of strength. They are not the same thing at all.


Fiberglass is actually pretty amazing stuff. An epoxy and S glass laminate is actually stronger (tensile strength) than epoxy and carbon fiber by about 50%. But nothing, or almost nothing in a hull is ever placed in tension. It is almost always stiffness that matters for a boat. So why lug around thousands of pounds of fiberglass laminate that adds nothing to the failure mode of the boat?

Even in this damage, the strength of fiberglass was never at issue, it was the abrasion resistance of it. And frankly that's a whole different kettle of fish.


The reality is that for most boats the required stiffness is a couple of orders of magnitude more important than its strength. And thebest way to get the required stiffness is to add thickness. Within reason it doesn't even matter what adds that thickness, more roving fiberglass, a core, CSM, carbon fiber, concrete, etc. none of it matters, the important question is how thick is it.

So why is carbon fiber so desirable when it is weaker than fiberglass? Because it weighs about 1/3 less and has three times the stiffness than S-glass. But if you just needed strength you would use glass every time.

Note -all comparisons are general in nature I took some liberty in the rounding.

This is the reason that cored construction is actually much less common in larger vessels. Once your cored construction reaches a point where the panel stiffness of the two skins required for needed design strength is more than sufficient, core is redundant. I work on vessels over 100' fairly often, sometimes far over. Very few of the glass examples have cored hull structures, because the needed thickness of the skins in a cored panel to provide sufficient strength is already plenty stiff enough. In other words, if you need a 1" external skin with a 3/4" internal skin to meet design strength requirements, but 1 3/4" solid panel has sufficient stiffness, what does the core do for you but complicate construction and introduce more failure modes? Generally speaking, I think cored construction is small boat stuff. Once you hit about 60', solid construction provides plenty of panel stiffness as it needs to be about 1 1/2" or up anyway, which believe me is plenty stiff. It's only the light weight thin construction that fiberglass makes possible at smaller sizes that creates highly flexible panels. It's why they don't have this issue with wood construction, it naturally needs to have a sufficient htickness to provide design strength that it also provides sufficient panel stiffness, even in fairly light scantlings.

[44'cruisingcat]

But is 80 mm enough? Why not 800mm? Who gets to decide how much is enough? Is there any science, or is it just emotion? (BTW I'd say a 55 foot boat that weighs 27 tonnes isn't going to be a model of sailing efficiency even if it doesn't flex much...)


The OP obviously felt that the Lagoon was SHOCKINGLY underbuilt. But if the glass was 4 inches thick and still had holes ripped in it would that be any better? Should it have been 8 inches thick? 8 miles maybe?


It could be argued that every boat or ship that ever sunk was underbuilt. Could it withstand a collision with runaway torpedo? An Exocet missile? A nuke?


You can build an aircraft to withstand a crash. But it won't fly.

[minaret]

Originally Posted by noelex 77

The best definition of a cruising boat's speed is based on the time taken to complete a passage plus the time to effect repairs.

Too light can sometimes be very slow .

Now that one I'm going to use. One long yard refit and your passage time was just severely reduced!

[DotDun]

Originally Posted by 44'cruisingcat

But is 80 mm enough? Why not 800mm? Who gets to decide how much is enough? Is there any science, or is it just emotion? (BTW I'd say a 55 foot boat that weighs 27 tonnes isn't going to be a model of sailing efficiency even if it doesn't flex much...)


The OP obviously felt that the Lagoon was SHOCKINGLY underbuilt. But if the glass was 4 inches thick and still had holes ripped in it would that be any better? Should it have been 8 inches thick? 8 miles maybe?


It could be argued that every boat or ship that ever sunk was underbuilt. Could it withstand a collision with runaway torpedo? An Exocet missile? A nuke?


You can build an aircraft to withstand a crash. But it won't fly.

That's been my thinking reading this whole thread. All those bemoaning too little of construction, NO! It was purpose built, and doing the intended task. It wasn't built to grind away on sitting on rocks/coral. If you believe you need tough enough to withstand a similar incident, you are welcome to build such a boat. Just remember to bring big fuel budget and don't cry and make excuses when I sail circles around you!

[SV DestinyAscen]

Originally Posted by 44'cruisingcat

But is 80 mm enough? Why not 800mm? Who gets to decide how much is enough? Is there any science, or is it just emotion? (BTW I'd say a 55 foot boat that weighs 27 tonnes isn't going to be a model of sailing efficiency even if it doesn't flex much...)


The OP obviously felt that the Lagoon was SHOCKINGLY underbuilt. But if the glass was 4 inches thick and still had holes ripped in it would that be any better? Should it have been 8 inches thick? 8 miles maybe?


It could be argued that every boat or ship that ever sunk was underbuilt. Could it withstand a collision with runaway torpedo? An Exocet missile? A nuke?


You can build an aircraft to withstand a crash. But it won't fly.

Yah - not really sure what people are on about. The boat didn't fail because of bad design or improper construction. The hull went against a solid object repeatedly. It isn't an ice breaker.

There are examples of hulls not properly designed - like Australia One.

Then there are examples of hulls properly designed but improperly implemented at construction process design. Like the Oyster. The glass laminates weren't sufficiently wetted in the failed examples and didn't have the strength the design required. IOW the nautical architects underestimated how difficult it is getting the production manager and workers in line.


Neither applicable to the catamaran in question.

[minaret]

Originally Posted by SV DestinyAscen

Yah - not really sure what people are on about. The boat didn't fail because of bad design or improper construction. The hull went against a solid object repeatedly. It isn't an ice breaker.

There are examples of hulls not properly designed - like Australia One.

Then there are examples of hulls properly designed but improperly implemented at construction process design. Like the Oyster. The glass laminates weren't sufficiently wetted in the failed examples and didn't have the strength the design required. IOW the nautical architects underestimated how difficult it is getting the production manager and workers in line.


Neither applicable to the catamaran in question.

Again, not concerned about the damage in the pictures, only the construction scantlings thereby exposed. Apparently it doesn't matter how many times it's repeated...