Displacement of Scooters at Depth - Spun off from the A&I Discussion about Nothernone

[johndiver999]

Any volume only generates buoyancy when it is filled with something lighter than the surrounding medium that is displaced. When the cylinder is flooded, the light stuff (air) is lost and replaced by the same type of matter that is displaced (water). The buoyancy of the volume that is flooded thus goes to zero.

Incorrect, a solid lead brick will experience a bouyant force when placed in a liquid. Re-read Archimedes principal. Any object wholly or partially.....

I checked boulder Jon’s answer using the density of aluminum without any consideration of the tank volume and generated the same numerical result. His computation of 11 liter capacity is easier, and more direct and correct within rounding errors/assumptions.

 

[dmaziuk]

I would think completely flooded or nose off it would be 20lbs or so negative because of batteries and motor but i dont know my maths is weak

But is its water-displacing volume now the sum total of volumes of the motor and the batteries and the shell walls minus the nose, or the same as before minus the nose?

 

[Dominik_E]

Incorrect, a solid lead brick will experience a bouyant force when placed in a liquid. Re-read Archimedes principal. Any object wholly or partially.....

I checked boulder Jon’s answer using the density of aluminum without any consideration of the tank volume and generated the same numerical result. His computation of 11 liter capacity is easier, and more direct and correct within rounding errors/assumptions.

Sigh. I left out "net", for simplicity. Yes, a lead brick will generate buoyancy, but this will be smaller than the antiparallel vector of gravity that inevitably results from the mutual attraction of the Earth and the lead brick. It will thus sink. A water brick will generate buoyancy in water, but the scalar value will be identical with that of the antiparallel vector of gravity that inevitably results from the mutual attraction of the Earth and the water brick. It will thus not move. I run out of options of phrasing it in simpler terms: if you take a scuba tank and fill it completely with water, it will have the exact same negativity in water as when you rip it open.

 

[johndiver999]

Sigh. I left out "net", for simplicity. Yes, a lead brick will generate buoyancy, but this will be smaller than the antiparallel vector of gravity that inevitably results from the mutual attraction of the Earth and the lead brick. It will thus sink. I run out of options of phrasing it in simpler terms: if you take a scuba tank and fill it completely with water, it will have the exact same negativity in water as when you rip it open.

Yes a ripped open tank or scooter (or imploded) will be identical to one that is flooded completely. Pretty simple concept really. For an 80 tank the swing is around 24 lbs.

 

[Dominik_E]

Yes a ripped open tank or scooter (or imploded) will be identical to one that is flooded completely. Pretty simple concept really. For an 80 tank the swing is around 24 lbs.

Yes, it is trivial. But it really is the point of debate it seems

 

[Jiminy]

But is its water-displacing volume now the sum total of volumes of the motor and the batteries and the shell walls minus the nose, or the same as before minus the nose?

I dont think it matters if the water can go where it wants there would be no air cavities left and the only difference would be the mass of the shell which is something but i dont think the shell weighs much. They are plastic arent they?

 

[Jiminy]

Yes, it is trivial. But it really is the point of debate it seems

Its an interesting thought experiment like

What would ones descent rate be if you suddenly became 15lbs negative?

 

[johndiver999]

Depends on the drag you generate.

 

[Dominik_E]

Indeed, and as I wrote already hours ago, the drag is the one thing that really may be different between total flooding and total implosion. But as a scooter would anyhow have to drag down a diver, the absolute difference would still be small...

 

[Jiminy]

I found this from submerge scooters. Does anyone know what scooter he was diving?

Always be prepared to cut away from the scooter in any emergency, for example flooded or stuck on scooter. (A flooded scooter may be 50 pounds/25Kg negative or more.)

http://www.silent-submersion.com/Instructions/Instruction manual 2009.pdf