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Old 20-06-2013, 23:25   #46
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

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Originally Posted by TeddyDiver View Post
With a hole below WL the sea is both sides of the hull, in and out, so evidently the only weight matters is the weight of the boat. Displacement diminishes a bit during the process...
This is only correct if water ceases to enter the hull when the weight of the vessel plus the weight of the water inside the hull and the weight of the water displaced by the hull are equal. If the hull continues to take on water, though, eventually the weight of the vessel and the water inside the hull will exceed the weight of the displaced water and the vessel will sink.

Stated another way - if a vessel with a hole in the hull below the waterline doesn't sink, then the weight of the water displaced by the hull is still greater than the weight of the vessel plus the water inside the hull.

You are correct, though, TeddyDriver, that the mass of the vessel and everything it contains is an important component of the calculation, as well. The reason a vessel floats is because the weight of that mass is less than the weight of the water displaced by the hull.

And I'm sorry my typo in your user name, daddle, touched a nerve. Innocent error.

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Old 20-06-2013, 23:44   #47
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

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What about a boat with positive floatation?
A vessel with positive flotation can still sink, minaret, if it takes on enough water such that the weight of the vessel and the water now inside the hull exceeds the weight of the water displaced by the hull. If the boat has taken on all the water it possibly can and still remains afloat, then the vessel is truly unsinkable.

It isn't that an unsinkable vessel can't be made, it's that an unsinkable cruising sailboat (our focus here) is highly unlikely, given the way the typical sailor tends to pack heavy stuff in every conceivable nook and cranny. If, instead of bringing heavy, dense objects aboard and putting them in every available storage space, a sailor filled those same spaces with foam, or even just left them filled with trapped air, he would greatly improve his odds of not sinking.

In most cases, though, taking such precautions only slows the sinking process, it doesn't defeat it.

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Old 21-06-2013, 00:10   #48
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

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Originally Posted by TaoJones View Post
A vessel with positive flotation can still sink, minaret, if it takes on enough water such that the weight of the vessel and the water now inside the hull exceeds the weight of the water displaced by the hull. If the boat has taken on all the water it possibly can and still remains afloat, then the vessel is truly unsinkable.

It isn't that an unsinkable vessel can't be made, it's that an unsinkable cruising sailboat (our focus here) is highly unlikely, given the way the typical sailor tends to pack heavy stuff in every conceivable nook and cranny. If, instead of bringing heavy, dense objects aboard and putting them in every available storage space, a sailor filled those same spaces with foam, or even just left them filled with trapped air, he would greatly improve his odds of not sinking.

In most cases, though, taking such precautions only slows the sinking process, it doesn't defeat it.

TaoJones

There are certainly cruising sailboats with positive floatation. The FD12, for instance.
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Old 21-06-2013, 00:15   #49
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

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Originally Posted by TaoJones View Post
A vessel with positive flotation can still sink, minaret, if it takes on enough water such that the weight of the vessel and the water now inside the hull exceeds the weight of the water displaced by the hull. If the boat has taken on all the water it possibly can and still remains afloat, then the vessel is truly unsinkable.

It isn't that an unsinkable vessel can't be made, it's that an unsinkable cruising sailboat (our focus here) is highly unlikely,.......


TaoJones
Actually, it's quite easy to build a truly unsinkable cruising sailboat. I've done it, several friends of mine have done it, there are plenty of them around.

It's just that having several tonnes of lead hanging underneath it makes it that much more difficult. But certainly not impossible.
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Old 21-06-2013, 01:04   #50
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

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Actually, it's quite easy to build a truly unsinkable cruising sailboat. I've done it, several friends of mine have done it, there are plenty of them around.

It's just that having several tonnes of lead hanging underneath it makes it that much more difficult. But certainly not impossible.
That's a fair point, 44cc, and I'm guilty of approaching the question with a ballasted monohull in mind. But monohull or multihull, the science of what I'm saying doesn't change: If the mass of a vessel and all it contains, including seawater, exceeds the weight of the water displaced by that mass, the vessel is going to sink - whether or not it has several hundred, or thousand, pounds of ballast attached.

To my contention about sailors placing more and more heavy items aboard their vessels, it's as true for mulithullers as monohullers, I'm afraid. Granted, the absence of ballast is a bonus for the multihuller, but the overloading of his vessel with too much heavy "stuff" is a major cause of compromised performance.

I think that's more a cruiser problem, though, than a design or construction problem.

But while it's theoretically possible to load enough weight into a multihull to sink it, it's probably not going to happen. Not too many gold smugglers using catamarans, I suspect.

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Old 21-06-2013, 02:44   #51
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TaoJones - Thanks for correcting your explanation of sinking ... Heh.

TeddyDiver makes an interesting semantic point about whether a vessel with a hole in it "contains" water that adds to its "weight", but it makes no difference so long as it is applied consistently. The end result is sinking.

There's another semantic point about whether "displacement" refers to the design displacement, or the increasing displacement of your thinking, or the decreasing displacement of TeddyDiver's model.

Personally I think a boats sinks when the downward forces, gravity and such, exceed the force of buoyancy. Avoids the confusion of mass, weight, and displacement. Seems simpler. A boat filling with water is losing buoyancy. Boats underway, towed perhaps, sink from hydrodynamic forces without achieving an excess mass.

No vessel can contain more water than its displacement. Always significantly less.

Embellishing writing with Latin *always* indicates that some BS is nearby. Nunc est bibendum.
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Old 21-06-2013, 02:53   #52
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

No one has mentioned U Boats.
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Old 21-06-2013, 03:21   #53
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

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Originally Posted by TaoJones View Post
A vessel with positive flotation can still sink, minaret, if it takes on enough water such that the weight of the vessel and the water now inside the hull exceeds the weight of the water displaced by the hull. If the boat has taken on all the water it possibly can and still remains afloat, then the vessel is truly unsinkable.

It isn't that an unsinkable vessel can't be made, it's that an unsinkable cruising sailboat (our focus here) is highly unlikely, given the way the typical sailor tends to pack heavy stuff in every conceivable nook and cranny. If, instead of bringing heavy, dense objects aboard and putting them in every available storage space, a sailor filled those same spaces with foam, or even just left them filled with trapped air, he would greatly improve his odds of not sinking.

In most cases, though, taking such precautions only slows the sinking process, it doesn't defeat it.

TaoJones

The posifive flotation can be compromised in whatever else is causing the boat to ship water.
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Old 21-06-2013, 03:30   #54
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Old 21-06-2013, 10:02   #55
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

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Originally Posted by daddle View Post
TaoJones - Thanks for correcting your explanation of sinking ... Heh.

<snip>

No vessel can contain more water than its displacement. Always significantly less.

Embellishing writing with Latin *always* indicates that some BS is nearby. Nunc est bibendum.
I wouldn't agree that I corrected my explanation, daddle, but hopefully I made it clearer.

Your statement that "no vessel can contain more water than its displacement" is a nice, brief summation. I like it.

As to embellishing writing with Latin, I believe you must be referring to my use of the term ceteris paribus, which apparently set off your BS detector. Your interpretation of the term as "always," however, is not what it means to me.

I've come to understand the term as "other things being equal," so in this context I was trying to say that if nothing else changes except that the amount of water inside the vessel now exceeds the water displaced by the vessel, sinking is inevitable.

"Nunc est bibendum." I'll drink to that, daddle . . . it's on me!

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Old 21-06-2013, 10:42   #56
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Re: What Can Cause the Sinking of a Sailboat on Open Seas?

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The posifive flotation can be compromised in whatever else is causing the boat to ship water.
Yep!

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