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Old 12-07-2008, 09:21   #16
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seven tons of bouyancy, 6.5 of displacement -

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Originally Posted by Whimsical View Post
Depends on what it is made out of.
Take mine for example. The cored panels alone displace over 7 ton while the loaded displacement is only 6.5 ton. This is without taking into account any sealed boyancy chambers of which there are many.

Mike
Yes, but that means that your boat structure has to be 92+% under water to float. Doesn't leave you much to hang on to-
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Old 12-07-2008, 09:41   #17
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Floating holed catamarans

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Originally Posted by cat man do View Post
There was a 40 ft Brisbane cruising cat that flew a hull and the leverage on the daggerboard tore a large section of hull away,

That hull filled with water and drowned the motor on that side, but they still got her back to port under her own power.

Dave
Yes, if your boat is right-side-up, there is tremendous bouyancy in one hull because cats have very high freeboard. If you also have a crash bulkhead and a watertight bulkhead aft to isolate an inboard motor, you might not even float all that lopsided.

When the Kiele V lost its mast and was holed, reporterd described it as sunk, but photos lots show it floating though down by the stern. See:

Catamaran Accident Off Maui Continues Run of Hawaii Visitor Fatalities
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Old 12-07-2008, 10:43   #18
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Huricane Isabel lifted my 34' Simpson onto 2 pilings, lodging against the starboard keel. Isabel then jack-hammered the boat on the pilings until they broke thru the hull. As the water receded, the boat lowered onto the pilings until they supported her from the inside overhead/deck, but eventually they tore out a 12 by 5 foot section of the starboard side. When we got her off , she floated starboard stern down 16 inches because the airtank was compromised, however: The engine was never submerged. There was no water in the fuel. Both berths dried out, and the mast remained standing. When we hauled her out, I returned 2 live crabs to their preferred environment. Three enterprising canadians patched up the 'indavertant bay window' and sailed north.
Post Mortem: Cedar strip under fiberglass with baltek core above the waterline floats good. The horrible event was survivable, and it would have been a helluva ride, but staying aboard would have been much safer than boarding a liferaft. Besides you can't catch crabs with a liferaft.
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Old 12-07-2008, 10:46   #19
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Any pictures?

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Originally Posted by sandy daugherty View Post
Huricane Isabel lifted my 34' Simpson onto 2 pilings, lodging against the starboard keel. Isabel then jack-hammered the boat on the pilings until they broke thru the hull. As the water receded, the boat lowered onto the pilings until they supported her from the inside overhead/deck, but eventually they tore out a 12 by 5 foot section of the starboard side. When we got her off , she floated starboard stern down 16 inches because the airtank was compromised, however: The engine was never submerged. There was no water in the fuel. Both berths dried out, and the mast remained standing. When we hauled her out, I returned 2 live crabs to their preferred environment. Three enterprising canadians patched up the 'indavertant bay window' and sailed north.
Post Mortem: Cedar strip under fiberglass with baltek core above the waterline floats good. The horrible event was survivable, and it would have been a helluva ride, but staying aboard would have been much safer than boarding a liferaft. Besides you can't catch crabs with a lifeboat.
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Old 12-07-2008, 11:43   #20
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Quote:
Originally Posted by BigCat View Post
Yes, but that means that your boat structure has to be 92+% under water to float. Doesn't leave you much to hang on to-
That was the hull material only without the displacement of all the other components or the bit you obviously missed the many sealed boyancy chambers. As the materials used in your own are the same I would have thought you would have realised that.
I was responding to the idea that the boat was unsinkable not how it would float inverted. Even broken into a million pieces they wont sink

Mike
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Old 12-07-2008, 12:36   #21
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New ones are unsinkable

This is from standard ISO 12217-2. Nowadays, the catamarans on European market must be unsinkable:

"Because multihull sailing boats may capsize, it shall be shown by calculation that, when inverted and/or fully flooded, the volume of buoyancy, expressed in cubic metres (m3), in the hull, fittings and equipment is greater than the number represented by (mLDC/850), thus ensuring that it is sufficient to support the mass of the loaded boat by a margin. Allowance for trapped bubbles of air (apart from dedicated air tanks and watertight compartments) shall not be included."

Terho
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Old 12-07-2008, 13:33   #22
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Quote:
Originally Posted by Whimsical View Post

Even broken into a million pieces they wont sink

Mike
Exactly. I can't understand why people find this concept so dificult. If your boat is built of bouyant material it won't sink. It CANT sink. Even if you smash it into matchsticks, the matchsticks will float.

Obviously, certain items such as batteries, engines, rig, etc will reduce the overall bouyancy, but as you said, the materials alone for my boat, like yours, displace more than their weight in water, even before they are built into a boat, with numerous (more than 50) sealed bouyancy chambers.

It simply can't sink.
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Old 12-07-2008, 14:16   #23
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Quote:
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All interesting stuff but how do you find out if the cat you are looking at can be sunk other than asking for comments from the dealer?
Just ask the complete CE certification report , it states the actual empty weight , max loaded weight, and all the buoyancy abours including enclosed bulkheads but including watertight compartments etc
In other words
Ig a boat has 6 cubic meters of H 80 foam , that creates 5 tons of buoyancy
If that same cat has another 12 compartments with 6000 liters of air inside you can add another 6 tons of buoyancy , than take all the structural items in the boat that weight less than water like wood, vinylfoam etc , take the weight and the weight of these items and this also ads buoyancy.
If all this buoyancy ads up to 13000 kilo,s and the total loaded weight of this cat is 10000 kilo it will never sink.
Examples of these boats are for instance the Boston Whaler, The Belgium Etap , and all FastCats
That is another reason why lightweight boats are safer than heavy boats.
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Old 12-07-2008, 14:49   #24
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I think that asuming that a sealed compartment or group of them will keep your boat afloat is not the best idea, the Titanic used that idea.
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Old 12-07-2008, 15:03   #25
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I think that asuming that a sealed compartment or group of them will keep your boat afloat is not the best idea, the Titanic used that idea.
If the Foam and other positively floating materials used on board already give over 100 percent buoyancy there should never be a danger and in case of the Titanic that would have saved well over 1000 lives since she did sink.
If a positive bouyancy exists a boat will never sink , if added to that another 125 % buoyancy is present in sealed chambers not connected the chances of survival by the passengers are 1000 % better than with the titanic where no foam , or any other light weight materials were used, there lightest material on board was oak wood and compared with all the inferior steel used and the fact that there watertight bulkheads where not watetight at all was a recipe for disaster, ad to that that while in conditions where icebergs where present and the speed of 22 knots was maintained for prestige how could she ever have survived. ???
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Old 12-07-2008, 15:26   #26
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I think that asuming that a sealed compartment or group of them will keep your boat afloat is not the best idea, the Titanic used that idea.

Actually the Titanic did NOT have sealed compartments. She had bulkheads which did not seal against the deck - given that more than one compartment was holed initially, the compartments could fill, and overflow into the next compartment. If the compartments had been truly sealed, she wouldn't have sunk. (Unless every compartment had been holed.)

But the real point is, she was made of STEEL. Steel doesn't float. boat built of steel can sink, no two ways about it. A catamaran built of steel could sink. A cat built of aluminium could sink. But a cat, or a monohull for that matter, built of BOUYANT material - with enough bouyancy to support the non floating parts - that can't sink. Boston whalers, or Etap yachts don't sink. Modern composite cored multihulls don't sink. They can't.
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Old 12-07-2008, 17:50   #27
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But the real point is, she was made of STEEL. Steel doesn't float. .
Neither does LEAD

Dave
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Old 12-07-2008, 17:55   #28
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Cat man Do has presented the ultimate closing arguement. The fat lady has sung. We all have entirely too much free time.
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Old 13-07-2008, 07:09   #29
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Hello Paul,

All seems a bit more civilised over here doesnt it.
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Old 13-07-2008, 07:25   #30
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Yes - its great over here and I am allowed to discuss and learn from a lot of people who know a lot!

What name were you under on the other forum?
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