At work and bored

[thewetone]

If you sail out into a lake with a 1 ton anchor on board and then throw it overboard wil the level of water in the lake go up, go down or remain the same?

<hr width=100% size=1>Randy

Once the avalanche has started, it's too late for the pebbles to vote

 

[zephyrsailor]

should thing it depends on the mass of the anchor and displacement of boat with anchor on board or something like that.

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[mikewilkes]

Does that depend on the level of bordem and whether said anchor warp is around your kneck? If it is then perhaps it may not matter.
Be positive, cos the paycheck at the end of the month pays for your "toys", and it sure beats the hell out of going to the pub every night or watching what they call "entertainment " on British TV!!!
Mike

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[StugeronSteve]

Quick whisper in ear, "mass of anchor is 1 ton surely, as the anchor is more massive than an equal volume of sea water it is the volume of the anchor that matters". But yes, the sea level will rise and you will have to lay out a little more chain, which in turn will lift the sea level and, oh b****r it I'm going for a cup of coffee. Whoops, sorry, same thing applies for freshwater though.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by StugeronSteve on 30/11/2003 10:04 (server time).</FONT></P>

 

[Seafort]

Nah! it will go down.

With the anchor on the boat "The boat" will displace a volume of water equal in weight to that of the anchor.

Hoof the anchor over the side and (providing the anchor rests on the bottom) the boat will no longer displace 1 ton of water. The water level will therefore go down.

If we now consider the anchor......The density of iron (or any anchor material) is much higher than water. The anchor will therefore displace much less than its own weight of water, thats why it sinks. (ie the anchor displaces a smaller volume of water when it is immersed than when sitting on the boat)

The net change causes the water level to go down.

Have you considered what happens if you just dangle the anchor over the side not touching bottom? /forums/images/icons/wink.gif


Dave.

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[jimi]

stay the same .. elementary my dear Archimedes

<hr width=100% size=1>O wad some Power the giftie gie us
To see oursels as ithers see us!

 

[john_morris_uk]

First reaction - it stays the same because the same water is displaced by the anchor whether its on the boat or in the water- but actually it doesn't displace exactly the same because obviously the anchor sinks!
Therefore as the water is not displaced as much when the anchor and chain is thrown overboard, the lake level goes down.

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[jimi]

But the boat rises a bit out the water ..

<hr width=100% size=1>O wad some Power the giftie gie us
To see oursels as ithers see us!

 

[trevor_loveday]

The lake level will go down when the anchor is thrown overboard.

This is because one ton of anchor on the boat will make the boat sit lower in the water, so the boat is displacing its underwater volume. If you imagine a half-full bath of water and then place a heavy bucket in the middle, the water will rise around the edge of the bath because the volume available for the water has been reduced.

When the anchor goes in the water, it will displace its own volume in water but that is assumed to be less volume than the boat was displacing because of the anchor on board (i.e. the difference between the boat displacement with and without the anchor on).

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[jimi]

Hi Trev, think your right. Initially a tone of water will be displaced and then when the anchor is put in the water a weight of water eqivalent to the volume of the anchor will be displaced which will be less than a ton so the water level will drop

<hr width=100% size=1>O wad some Power the giftie gie us
To see oursels as ithers see us!

 

[PhilF]

Thats a bit like whether a bird cage is heavier if the bird sits on the perch or is flying in the cage - - have another drink!

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[BlueSkyNick]

WOn't it depend on the size of the boat on which you take the anchor, and its relative buoyancy?

If it was something like a GP14, or a Beneteau 331, it would lie significantly lower in the water, and displace more than if you took the anchor on the QE2 which would hardly be affected.

(PS I know this is bollocks, but can't be bothered to think about it too deeply!)

<hr width=100% size=1>People who think they know it all are very annoying to those of us that do.

 

[Seafort]

Nope.

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[StugeronSteve]

>PS. I Know this is B******s but I can't be bothered to think about it too deeply<

Just how I felt this morning and look at the mess I got myself into, forgetting that the b****y thing was already afloat and displacing a ton of water when dropped.
I know what you're thinking but a ton of displacement is a ton of displacement, QE2. GP14 (unless it sinks under the weight) or beloved 331. Steve.

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[BrendanS]

The shape and size of the boat is irrelevant.

Archimedes' principle says that an object which is floating displaces an amount of water which weighs the same as the object. . In the first case, the boat with the cannonball pushes aside water that has the same weight as the boat + anchor. In the second case, the boat displaces only enough water to keep it afloat, and the anchor is resting on the bottom, not floating. The anchor then displaces only as much water as its volume, which will be less than one ton (making a few assumptions about what the anchor is made of).


If the anchor is heavier than water, then the amount of water the anchor displaces when it sits on the bottom is less than that when it is responsible for when it is in the floating boat, and the total level in the lake will go down.

It doesn't matter how big or what shape the boat is. It will displaces a set amount of water (before some one comments, as long as nothing changes!). Put a one ton anchor on any boat, and it will displace one ton more water than before.

<hr width=100% size=1>Any sufficiently advanced technology is indistinguishable from a rigged demo

 

[VicS]

Yes Brendan is right. When the anchor is on the boat it will be responsible for displacing one ton of water (about 36cu ft.) but once in the water and sitting on the bottom it will only displace its own volume (about 4.6cu ft if it's a cast steel anchor)) so the water level will drop by about 0.0087 inches for a 1 acre lake.

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.I think
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It would have been easier to have stated with a 1tonne anchor and done the calculations in cu metres


<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>

 

[BrendanS]

Trevor posted correctly first. I was just clarifying that boat size and shape don't make a difference

<hr width=100% size=1>Any sufficiently advanced technology is indistinguishable from a rigged demo

 

[Cactus]

Surely the boat only displaces an amount in relation to the weight of the anchor spread over the cross section of the hull in the water. Therefore the boat additional displaces the same volume of water with the anchor as the anchor would on it's own..

.. so the level stays the same. I win.


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[jimi]

My first answer was based on the boat in question being a submerged submarine when it anchored

<hr width=100% size=1>O wad some Power the giftie gie us
To see oursels as ithers see us!

 

[BlueSkyNick]

Nah - with the anchor on board, the boat displaces an amount of water equal to the anchor's weight. But when its in the water the anchor displaces an amount of water equal to its own volume which is a lot less than its own weight. If it was the same, the anchor would just about float.

<hr width=100% size=1>People who think they know it all are very annoying to those of us that do.