Ship on a Conveyor Belt...

[navier_stokes]

Well not quite, but I read this problem in an article and thought it was quite interesting.

You have a ship floating in the open ocean.

Now a second hull is gradually built around the original ships hull within a very close proximity... say 250mm.

The construction of the new hull starts at say deck height and finishes around the base of the original hull.

The outer hull is fixed.

Once construction is complete, the ocean surrounding the second hull is removed

So eventually, you have a ship, and a "second skin" hull, separated with a layer of water that has been enclosed between the two as the second hull has been built.

The question:

Is the ship still floating or has it sunk? If it has sunk, at what point does it sink?

[TheEnd]

still floats.

[mybrainhurts]

It'll never take off...

[thinfourth2]

I believe it is basically how floating dry docks work

[Gargamel]

if the water is sealed in then it will float, if the water could escape over the top of the second hull then it will displace the water and sink

[sadako]

TheEnd said:

still floats.

As long as the weight of the hulls does not exceed the weight of the water displaced it will float.

[robinhood21]

Gargamel said:

if the water is sealed in then it will float, if the water could escape over the top of the second hull then it will displace the water and sink

[navier_stokes]

sadako said:

TheEnd said:

still floats.

As long as the weight of the hulls does not exceed the weight of the water displaced it will float.

Yes, but is the amount of water sealed between the two enough to be displaced and the ship to float?

[Jasandjules]

navier_stokes said:

Well not quite, but I read this problem in an article and thought it was quite interesting.

You have a ship floating in the open ocean.

Now a second hull is gradually built around the original ships hull within a very close proximity... say 250mm.

The construction of the new hull starts at say deck height and finishes around the base of the original hull.

The outer hull is fixed.

Once construction is complete, the ocean surrounding the second hull is removed

So eventually, you have a ship, and a "second skin" hull, separated with a layer of water that has been enclosed between the two as the second hull has been built.

The question:

Is the ship still floating or has it sunk? If it has sunk, at what point does it sink?

Well, when you remove the ocean, it'll sit on the ground......

[navier_stokes]

robinhood21 said:

Gargamel said:

if the water is sealed in then it will float, if the water could escape over the top of the second hull then it will displace the water and sink

Yes, but this would assume that more water flows into the gap between the two hulls - how does this happen?

I.e. the ship obviously cant float on just a 250mm gap of water.

Assuming infinitely tall sides for the second hull.

[navier_stokes]

Jasandjules said:

Well, when you remove the ocean, it'll sit on the ground......

The original hull, not the second one :P

[AJS-]

Try it and see.

[s2art]

it floats. Nothing significant has changed.

[hugoagogo]

still floats, gap is still 250mm, water level on original boat is unchanged, amount of water displaced is the same

am i missing something?

If you took the boat out of the water, then refilled the outer hull with water, then plonked the boat back in, it would displaced the volume of water equal to it's weight - back to a 250mm gap all round

[Gargamel]

navier_stokes said:

robinhood21 said:

Gargamel said:

if the water is sealed in then it will float, if the water could escape over the top of the second hull then it will displace the water and sink

Yes, but this would assume that more water flows into the gap between the two hulls - how does this happen?

I.e. the ship obviously cant float on just a 250mm gap of water.

Assuming infinitely tall sides for the second hull.

For clarity - if you started at deck height (no water) and worked down to the water line - then it would sink as the inner ship would displace the water from 250mm thickness into the upper areas. if you sealed the two hulls and filled the compartment with water to the full height then it would float.

[hugoagogo]

nope, doesn't need to be sealed

think of it this way, you have a tiny toy boat floating in a bath

you get a saucepan and scoop out the boat and the water surrounding it, boat doesn't sink at all then, does it?

[esselte]

hugoagogo said:

nope, doesn't need to be sealed

think of it this way, you have a tiny toy boat floating in a bath

you get a saucepan and scoop out the boat and the water surrounding it, boat doesn't sink at all then, does it?

Bet relatively there's still enough water in the saucepan for the ship to displace enough to float......

[AJS-]

Well it definitely hasn't sunk anyway. It's just wet.

[TheEnd]

if you had a tight enough second hull, you could float it in a teaspoon of water

[hugoagogo]

esselte said:

hugoagogo said:

nope, doesn't need to be sealed

think of it this way, you have a tiny toy boat floating in a bath

you get a saucepan and scoop out the boat and the water surrounding it, boat doesn't sink at all then, does it?

Bet relatively there's still enough water in the saucepan for the ship to displace enough to float......

it's already displaced the water, it's not an ongoing process