Whats the reason for the huge differences in displacements in similar sized boats? - Page 2 - SailNet Community
Old 08-27-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

Quote:
Originally Posted by bobperry View Post
That's what I had in mind.
I like that, "design matrix" I'd like to use that. May I?
Thanks Jeff.
Bob,

I would be truely honored if you find anything useful to you in anything that I write. Please feel free to quote at will.

Jeff

Zeehag,

I would respectfully suggest that you are missing a few words if you want your statements to be clearer and more useful. "Displacement is the weight of the water displaced by the hull of the boat and the weight of the water displaced by the hull at rest is equal to the weight of the boat on a scale."

See, isn't that clearer.....

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Old 08-27-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

So if the boat sinks, does it weigh more...??

A lb of lead sinks...displaces "X" amount of water...

A lb of Gold sinks....Displaces "Y" amount of water...

"X" and "Y" don't weigh the same....

So how can a lb of weight be the same as an lb of displaced water...???

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Old 08-27-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

Displacement, as used in naval architecture, implies that the vessel floats. The weight of water that a vessel displaces while floating is equal to the weight of the vessel. Once it sinks, all bets are off.

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Old 08-27-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

Squidd:
Archimedes Principle
That will explain what is going on.

If you build a boat in your backyard and it weighs 10,000 lbs. it will sink into the water until it displaces a volume of water equal in weight to 10,000 lbs., 156.25 cu. ft. of salt water.

If you add 2,000 lbs. to your boat it will now weigh 12,000 lbs. and sink in the water until it displaces 187.5 cu. ft. of salt water.

Displacement measured in cubic feet times 64 ( salt water weighs 64 lbs. per cubic foot) will always tell you the weight of the boat.

Displacement is usually given in lbs. or tons .
Displacement and weight are the same thing.

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Old 08-27-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

OK, but as above Archemides put a one lb crown that was supposed to be "pure gold" in the water it should have displaced "X" amount of water...(but it had lead in it...)

So it only displaced "Y" amount of water....Be it cubic foot or tare weight...

Different densitys displace differing "displacements" even at the same weight...

So you should be able to have different displacement rated boats at the same weight and/or different weight boats with the same displacement...

(assuming they float)....but what if you hang/weigh them in a sling...?

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Last edited by Squidd; 08-27-2012 at 07:33 PM.
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Old 08-27-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

Squidd:
To help you ponder: Maybe get your self a copy of Steve Killing's book YACHT DESIGN EXPLAINED and do a little reading. Study up on Archimedes Principle.

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Old 08-27-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

Squidd:

The weight of a boat hanging in a sling will be exactly the same as the weight of the water that boat displaces when it is launched.

I'll give you a tip. This is not a "theory". This is not up for debate. This is a fact of the physical universe and referred to as Archimedes Principle. You want to argue it? Call Archimedes.

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Re: Whats the reason for the huge differences in displacements in similar sized boats

I'm not arguing.... just having a hard time wraping my head around it...

I thought Archemides said "different densitys have different displacements at the same weight..." If that's not what he said, then I am mistaken and apologize for stressing you out...

On the other hand...If the world really is round....wouldn't all the boats slide off to one side or the other (unless they were perfectly balanced on top...?)

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Re: Whats the reason for the huge differences in displacements in similar sized boats

Squidd:
I'm not stressed out. I have done my best to explain this to you and that's all I can do. Now it's up to you. I think your understanding of Archimedes Principle is less than accurate.

Now it's off to my Tai Chi Chuan class where I will once again try not to tip over.

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Old 08-27-2012
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Re: Whats the reason for the huge differences in displacements in similar sized boats

Quote:
Originally Posted by bobperry View Post
...

Now it's off to my Tai Chi Chuan class where I will once again try not to tip over.
This image just made my night. Then I remembered how lazy I am and I stopped chuckling. Raising a glass to you.

Donna

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