How can one determine the weight of a boat submerged in water?

[alister718]

if i tell you that water displaced in terms of (Volume initial and Vfinal ) is Vf how would i be able (if you can) to calculate the weight of the boat?

 

[mgb_phys]

If the boat is floating it's weight is equal to the weigth of the volume of water displaced.
If you know the volume and density of the water you have the weight of the boat.

 

[alister718]

Buoyancy has nothing to do with it?

 

[Math Jeans]

V_f would not allow you to know the weight of the boat, It would only allow you to know the volume of the boat. You must also know the material that the boat is made from in order to find the weight.

The displaced water dictates how much upward force is exerted on the boat.

 

[russ_watters]

Buoyancy has nothing to do with it?

That is buoyancy. That's what buoyancy is!

In physics, buoyancy is the upward force on an object produced by the surrounding fluid (i.e., a liquid or a gas) in which it is fully, or partially immersed, due to the pressure difference of the fluid between the top and bottom of the object. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body.

http://en.wikipedia.org/wiki/Buoyancy

 

[russ_watters]

V_f would not allow you to know the weight of the boat, It would only allow you to know the volume of the boat. You must also know the material that the boat is made from in order to find the weight.

No. Think about that a little more. Why would this tell you the volume of the boat? Most of the boat is not submerged! So the volume of water displaced is only the volume of the submerged portion of the boat...

The displaced water dictates how much upward force is exerted on the boat.

Yes, and...? How much upward force does the floor exert on you...?

 

[alister718]

if order to do this we would need to find the height of the boat that is not submerged

 

[Math Jeans]

Sorry, I thougt that the implication was the the boat was fully submerged. My mistake.

 

[russ_watters]

if order to do this we would need to find the height of the boat that is not submerged

No, no, no, no, no.

Look at the equation for buoyant force! You only need to know one thing (that isn't a constant) and you gave it in your opening post!

 

[russ_watters]

Sorry, I thougt that the implication was the the boat was fully submerged. My mistake.

A boat designed to run fully-submerged is called a "submarine"...

A boat that is not designed to run fully-submerged but is must have a hole (or holes) in it, so it's sunken displacement tells you nothing about its weight or volume.