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Old 09-09-2014, 15:21   #46
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Re: Catamaran Sinking

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Originally Posted by yeloya View Post
Being an engineer, I have an idea on buoyancy calculations. Remember though that Archimedes had found this principal in a bathtub and the things are somewhat different on the sea; unpredicted hydro dynamic/aerodynamic forces may prove Achimedes wrong ..
That's why I said all boats can sink.

But this really doesn't matter, if YOU believe that YOUR boat will not sink under any condition, good for you..

Cheers

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Please explain to me how a 6.5 tonne solid object that displaces 12 m3 of seawater can sink?
Ok you're going to say the boat isn't a solid object. But the materials in it's construction, not including any sealed compartments, displace at least 12 cubic metres. And weigh (less than) 6.5 tonnes.

How can it sink?

I suppose ultimately given long enough, all the core materials could break down and become waterlogged, but that could take years. I'm talking about a reasonable length of time, not years.
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Old 10-09-2014, 01:07   #47
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Re: Catamaran Sinking

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Originally Posted by StuM View Post
That conflicts with the links in my previous post showing it was in charter in Croatia and was being advertised for future charter in Phuket.

Based on those, it was a delivery - not just a borrowed boat on a cruise.

I wonder if the conflicting story has something to do with the crew and insurance?
It may have also been something to do with Google Translate since I can't read Swedish!
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Old 10-09-2014, 07:01   #48
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Re: Catamaran Sinking

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Originally Posted by 44'cruisingcat View Post
Please explain to me how a 6.5 tonne solid object that displaces 12 m3 of seawater can sink?
Ok you're going to say the boat isn't a solid object. But the materials in it's construction, not including any sealed compartments, displace at least 12 cubic metres. And weigh (less than) 6.5 tonnes.

How can it sink?

I suppose ultimately given long enough, all the core materials could break down and become waterlogged, but that could take years. I'm talking about a reasonable length of time, not years.
Dude, that's like asking how can a steel ship float. Steel is denser than water by a lot. How does it float?

The question is...is the sum of a ships parts more or less boyant than water. Most wood is boyant. Many items are near neutral boyancy when soaked. They either sink slowly or float slowly (I.e stay just under the surface).

In order for a boat to be unsinkable the sum total of the material itself needs to be less dense than water.
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Old 10-09-2014, 07:54   #49
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Re: Catamaran Sinking

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Originally Posted by 44'cruisingcat View Post
Please explain to me how a 6.5 tonne solid object that displaces 12 m3 of seawater can sink?
Ok you're going to say the boat isn't a solid object. But the materials in it's construction, not including any sealed compartments, displace at least 12 cubic metres. And weigh (less than) 6.5 tonnes.

How can it sink?

I suppose ultimately given long enough, all the core materials could break down and become waterlogged, but that could take years. I'm talking about a reasonable length of time, not years.
Quote:
Originally Posted by Scot McPherson View Post
Dude, that's like asking how can a steel ship float. Steel is denser than water by a lot. How does it float?

The question is...is the sum of a ships parts more or less boyant than water. Most wood is boyant. Many items are near neutral boyancy when soaked. They either sink slowly or float slowly (I.e stay just under the surface).

In order for a boat to be unsinkable the sum total of the material itself needs to be less dense than water.
Lets settle this disagreement with the Boston Whaler test. We'll get an old cat of 44' cruising cats choosing and then shoot it full of holes and see if it sinks. I for one am curious which way it will go
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Old 10-09-2014, 08:16   #50
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Re: Catamaran Sinking

Right a Boston whaler has no voids. Or more correctly the voids are segmented into tiny pockets with foam. The boat itself is less dense than the water.
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Old 10-09-2014, 08:43   #51
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Re: Catamaran Sinking

I know. I really just wanted to see if someone wanted to do a boat shoot. You know kind of like a red neck car shoot just on the water.
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Old 10-09-2014, 08:57   #52
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Re: Catamaran Sinking

I had a hatch incident going from Grenada to Trinidad about fifteen years ago. The aft latch on my starboard escape hatch failed and I took on about 20 gallons of water. Fortunately the hatch on my Fountaine Pajot Fidji is relatively high on the inboard hull and shielded somewhat by a splashguard. I was in the usual 6 to 8 ft seas and had both latches failed the hull would have quickly flooded and I might even have capsized before getting the hatch closed and the hull drained. It turned out that the aluminum rivets holding the portion of the latch attached to the hatch corroded out and failed. I drilled out and replaced the rivets with machine screws and self-locking nuts. This is a common problem with Lewmar hatches and I ended up replacing the rivets on both escape hatches and six deck hatches. Have you checked your hatches lately?
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Old 10-09-2014, 09:25   #53
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Re: Catamaran Sinking

How much of the hulls are solid glass? Maybe only foam in the decks and cabin top? Add engines, batteries, mast. fill with water and it would sink.

Most overturned cats will trap some air in the bilges but if you entirely flooded most production cats, I bet most will sink.
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Old 10-09-2014, 09:31   #54
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Re: Catamaran Sinking

I'm thinking maybe this should be a Myth Busters episode!

Maybe if we all write in real nice they will test the theory.

44 Crusing Cat, tell us what your exact boat is and we can see if they'll take the challenge. It'll be a hoot!

Then afterwards we can all argue that they did the experiment wrong
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Old 10-09-2014, 09:53   #55
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Re: Catamaran Sinking

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Originally Posted by ontherocks83 View Post
I'm thinking maybe this should be a Myth Busters episode!

Maybe if we all write in real nice they will test the theory.

44 Crusing Cat, tell us what your exact boat is and we can see if they'll take the challenge. It'll be a hoot!

Then afterwards we can all argue that they did the experiment wrong
We should send the boys out looking for "Too Good to be True"
Er... I meant "Be Good Too"
soon to be

"Be Good II"
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Old 10-09-2014, 15:37   #56
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Re: Catamaran Sinking

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Originally Posted by Scot McPherson View Post
Dude, that's like asking how can a steel ship float. Steel is denser than water by a lot. How does it float?

The question is...is the sum of a ships parts more or less boyant than water. Most wood is boyant. Many items are near neutral boyancy when soaked. They either sink slowly or float slowly (I.e stay just under the surface).

In order for a boat to be unsinkable the sum total of the material itself needs to be less dense than water.
Which mine is, or were my previous posts to difficult to understand. Once again, the material in my boat occupies about 12m3, we cruise at less than 6.5 tonnes. So as I say, we can't sink.
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Old 10-09-2014, 15:40   #57
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Re: Catamaran Sinking

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Originally Posted by Boatguy30 View Post
How much of the hulls are solid glass? Maybe only foam in the decks and cabin top? Add engines, batteries, mast. fill with water and it would sink.

Most overturned cats will trap some air in the bilges but if you entirely flooded most production cats, I bet most will sink.
Most catamarans have coring down to the waterline. Many, including mine, have coring throughout. Every bit of my boat is cored. That's how you launch a 44 foot boat at less than 5 tonnes.
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Old 10-09-2014, 15:58   #58
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Re: Catamaran Sinking

Cats don't sink. But they may fly upside down
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Old 10-09-2014, 15:58   #59
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Re: Catamaran Sinking

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Originally Posted by 44'cruisingcat View Post
Which mine is, or were my previous posts to difficult to understand. Once again, the material in my boat occupies about 12m3, we cruise at less than 6.5 tonnes. So as I say, we can't sink.
Unfortunately that doesn't mean anything. I could build a steel hull that displaces 6.5 tonnes with a volume of 12m3. And it'll float until you fill it with 5.5 tonnes of water. That's less than half full.
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Old 10-09-2014, 16:03   #60
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Re: Catamaran Sinking

Scott, the overall hulls do not have a volume of 12 m3. The hull material has a volume of 12 m3.

There is a difference and Archimedes rules.
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