Shocked by hull material catamaran

[Just Another Sa]

Originally Posted by minaret

When we built Schumacher's last design, "Cascadia", a 77' ultralight, it too had solid carbon skins exceeding 1" thickness in many places. And that's an "ultralight" which hits hull speeds in excess of 24 knots, designed by a legendary race designer.

So you think 1 inch solid skin proves 1 inch skins for cored construction is required or is somehow comparable?
A guess many places refers to ballast keel connection area or around rudder shaft etc. Anyway 1" of solid carbon is stronger than 10 mm of solid steel used in many >700 ft long ship hulls, and thus an overkill for boats in hull areas not subject to any point loading, like ballast keel attachment.

[Just Another Sa]

Originally Posted by neilpride

Its those 2 or 3 MM outer skin enough for Osmosis protection in the long run, i mean how thick is the gelcoat layer ??

So you think outer skin laminate provides osmosis protection for what exactly?
Normally people consider something else is providing osmosis protection for the outer skin laminate if it is polyester. In the case of Lagoon, the laminate is made of vinylester and e-glass.

https://en.wikipedia.org/wiki/Vinyl_ester :
"Vinylester, is a resin produced by the esterification of an epoxy resin with an unsaturated monocarboxylic acid."

[neilpride]

Originally Posted by Just Another Sa

So you think outer skin laminate provides osmosis protection for what exactly?
Normally people consider something else is providing osmosis protection for the outer skin laminate if it is polyester. In the case of Lagoon, the laminate is made of vinylester and e-glass.

https://en.wikipedia.org/wiki/Vinyl_ester :
"Vinylester, is a resin produced by the esterification of an epoxy resin with an unsaturated monocarboxylic acid."

Its infused with vinilester or he have a layer of vinilester for Osmosis protection?
And yes beefy outer layer help .. but the point could be stop or minimize core wáter ingression... The only protection for the core are those 3 or 4 mm of glass...Thats why i ask ....

[44'cruisingcat]

Originally Posted by minaret

Yes, and we are comparing it to the pics here of a 56' boat. Should there be THAT much difference in the scantlings?

A 56' boat that doesn't derive it's righting moment from a keel or ballast.

In multihulls the bulkheads and beams carry the major structural loads, in monohulls much of the righting moment loads of the keel are carried by the hull skins.

So you'll typically find much thicker laminates around the keel area of a mono than you'd need anywhere on a multi.

[Just Another Sa]

Another one:
Foam Core Materials in the Marine Industry
This is the same link you took your wrong pic from and I quote from that.
The formulas before the pic you posted informs us:

t = skin thickness
c = core thickness
b = beam width
d = distance between centroids of skins = c + t
E = modulus of elasticity for the skin laminate
the formula for flexural rigidity is: D = E * I = E * b * (t^3 / 6 + t*d^2 / 2)

case A for 3 mm thick solid laminate:
both skins are 1.5 mm thick meaning t = 1.5
core is zero, c = 0
d = 1.5 mm
Weight is 1.5 mm * 1800 kg/m^3 * 2 = 5.4 kg / m^2
D = E * b * (t^3 / 6 + t*d^2 / 2) = E * b * (1.5^3 / 6 + 1.5*1.5^2 / 2) = E * b * 2.25

Case B for 6 mm thick cored panel: (2*t + c = 6 or t + d = 6)
t = 1.430233
c = 3.139534
d = 4.569767
Weight is 1.430233 mm * 1800 kg/m^3 * 2 + 3.139534 mm * 80 kg/m^3
= 5.400 kg / m^2
D = E * b * (t^3 / 6 + t*d^2 / 2) = E * b * (1.430233^3 / 6 +1.430233 * 4.569767^2 / 2) = E * b * 15.42122

D of case B / D of case A = 15.42122 / 2.25 = 6.853875 (NOT 12 times)
for the same 5.4 kg / m^3 areal weight and twice thickness.
Exactly as I already calculated before.

Case C for 12 mm thick cored panel: (2*t + c = 12 or t + d = 12)
t = 1.290698
c = 9.418604
d = 10.709302
Weight is 1.290698 mm * 1800 kg/m^3 * 2 + 9.418604 mm * 80 kg/m^3
= 5.400 kg / m^2 Again the same as required.
D = E * b * (t^3 / 6 + t*d^2 / 2) = E * b * (1.290698^3 / 6 +1.290698 * 10.709302^2 / 2) = E * b * 74.37289
D of case C / D of case A = 74.37289 / 2.25 = 33.05462 (NOT 48)
for the same 5.4 kg / m^3 areal weight and 4-times thickness.
Exactly as I already calculated before.

In conclusion, your own source agrees with me and contradicts with you!
The pic is wrong.

[Just Another Sa]

Originally Posted by neilpride

Its infused with vinilester or he have a layer of vinilester for Osmosis protection?
And yes beefy outer layer help .. but the point could be stop or minimize core wáter ingression... The only protection for the core are those 3 or 4 mm of glass...Thats why i ask ....

It is infused with vinylester resin.
I don't know what surface paint is on it or not, but nothing prevents the buyer to add any protective paint he/she feels should be there before antifouling.

[44'cruisingcat]

Originally Posted by Polux

Contrary to balsa core it is not a big problem if the core is wet and the degradation of the core is incomparably smaller and the reparation much cheaper.

I had seen it done several times: They make a lot of holes on the affected area, wait sometime for the water to come out and then with a big pressure machine they blow for some days hot air on the holes. Finally when it is bone dry they inject under pressure epoxy resin till all spaces are filled. Simple and efficace without the need of any destructive work on the hull.

Here you have a good article on cores (balsa and foam).
Getting To The Core Of Composite Laminates : CompositesWorld

Actually if there is water in a foam core then it's a VERY BIG problem. Only closed cell foams are used in boat construction. If water has entered the core it can only be in two ways: either the structure of the foam has broken down, allowing water in, or the laminate has separated from the core.

[Just Another Sa]

Originally Posted by 44'cruisingcat

Actually if there is water in a foam core then it's a VERY BIG problem. Only closed cell foams are used in boat construction. If water has entered the core it can only be in two ways: either the structure of the foam has broken down, allowing water in, or the laminate has separated from the core.

Or the core has cuts in order to bend it without heating it, and cuts are unfilled at the construction stage and air between blocks is now replaced with water.
Not likely to happen using infusion, but in some other methods ...

[jimbunyard]

Originally Posted by Just Another Sa

Anyway 1" of solid carbon is stronger than 10 mm of solid steel used in many >700 ft long ship hulls, and thus an overkill for boats in hull areas not subject to any point loading, like ballast keel attachment.

Care to add a reference to this 10mm hull thickness claim?

Best I could find was many pdf documents showing convoluted formulas for figuring different parts of the hull, with the single defining characteristic being that they were all based on load; i.e. it's likely that there are different thicknesses in different parts of different hulls based on different loads.

The one practical, trustworthy example I could find was a report of a failure (broke in half at a hull lengthening joint, no less) by the Ship Structure Committee, where the original deck plating is 30 mm (1.18 inches). Hard to imagine the hull plating, especially at the waterline and below, is any less...

And of course there are plenty of not-so-trustworthy accounts of the 'about one inch is the industry standard for cruise and cargo ship' category...

From the SSC;

"The deck plate in the existing ship was 30mm, while the deck plate in the new midbody was 33mm."

Just for grins, the whole report is here;

Ship Structure Committee: Case Study: Carla

[PaulinOz]

Quote "designed by a legendary race designer" the implication being it must be good I guess.
Also designed by a very legendary race designer, did not hit anything either just pure structural failure.

[minaret]

Originally Posted by PaulinOz

Quote "designed by a legendary race designer" the implication being it must be good I guess.
Also designed by a very legendary race designer, did not hit anything either just pure structural failure.

No, the implication being that it's probably light not heavy.

[noelex 77]

Ben Lexcen, the designer of the winning America Cup yacht Australia II, is reported to have said words to the effect "If it doesn't break it was too heavy"

The cynical might suggest "If it doesn't break it was too expensive" might also be applicable to some modern consumer products .

We need to be careful that this thinking doesn't spread to cruising yachts.

[jimbunyard]

Originally Posted by noelex 77

Ben Lexcen, the designer of the winning America Cup yacht Australia II, is reported to have said words to the effect "If it doesn't break it was too heavy"

The cynical might suggest "If it doesn't break it was too expensive" might also be applicable to some modern consumer products .

We need to be careful that this thinking doesn't spread to cruising yachts.

I could find surprisingly little about the boat, it's designer or it's construction.

I saw a passing reference to it being carbon fiber, or at least had a carbon fiber component in the hull, but no word of if it were cored or not. The quality of the video is rather poor, but at one point you can see a section of the hull, just below the rail and just aft of the crack, spall off, which could be a sign of cored construction or an incompetent repair...

There are also a couple of reports that the vessel hit something previously, was repaired, and then stress bearing items (winches? chainplates?) were installed at or in the vicinity of the repairs.

Hardly the fault of the designer (who, by the way, often times has little say or control in the actual construction), if true...

[Stumble]

Originally Posted by jimbunyard

I could find surprisingly little about the boat, it's designer or it's construction.

I saw a passing reference to it being carbon fiber, or at least had a carbon fiber component in the hull, but no word of if it were cored or not. The quality of the video is rather poor, but at one point you can see a section of the hull, just below the rail and just aft of the crack, spall off, which could be a sign of cored construction or an incompetent repair...

There are also a couple of reports that the vessel hit something previously, was repaired, and then stress bearing items (winches? chainplates?) were installed at or in the vicinity of the repairs.

Hardly the fault of the designer (who, by the way, often times has little say or control in the actual construction), if true...

For the 95 Americans cup all of the boats were carbon, and weirdly enough they all had the same skin and hull thickness (dictated by rule), but there was no rule dictating the internal framing structure. My theory is at they spaced the frames to far apart, the hull hit a wave and the lack of stiffness caused the hull to collapse.

This was in early days of FEA, and the use of large carbon structures. If I remember correctly the same cup they'd had two masts break, and a couple of smaller breakages.

[Redreuben]

If it doesn't break it's too heavy,
If it breaks it was too light.

So we are now at the point where owners after driving down the European quality to a Chinese price, now want their floating Condos to be idiot proof so they can survive reef groundings ?