Tinman the conversation has been interesting.  In order to change the buoyant state of a submersible the density has to change.  So, something gives:  mass and/or the fluid volume that the submersible displaces.  If we change the density but not not total mass of material inside a sealed and constant volume container, that container's buoyancy does not change.  That is why I speculated that maybe you were hoping to develop enough pressure in whatever contains the phase change material to change that container's volume, expelling sea water ballast.

From the: "It can't produce free energy." camp,  what you have cycling a submersible up and down are the UP and DOWN states.  We can pretty much ignore everything in between.  In the up state the system including the surrounding fluid is at its potential energy minimum, even though the submersible is at its potential energy maximum.  When the submersible is at the bottom of the travel, the system energy is at its maximum.  Before your submersible can rise you need to change its density.  You can either eject mass, or increase the submersible's volume, or a bit of both.  To do either you must expend work.  Since rising removes energy from the system, expending additional work at the bottom only aggravates the energy loss going from the down to up state.  On the way from the top to the bottom you have to be able to get all the energy that the system lost just to break even.  Sinking the submersible requires increasing its density.  That lowers the center of gravity of the system at the top without changing mass, so system energy is again lost.  The bottom line:  A submersible only moves up or down by expending energy from the system that includes the submersible.  The submersible moves up or down because the end position represents a lower energy state than the starting position.

You do know ofcourse Mark,that the mass of an object can be changed without changing it's size,and also without ejecting any material.

Energy is collected on the way up,once the vessle has surfaced, and on the way down.
I can take a sealed steel sphere and make it sink or rise as i see fit-no ejected mass,no ballast intake or exausting-->nothing enters or leaves the steel sphere.

No that is a new one on me.  If I have some quantity of some material then it has a fixed mass.This is where we are at odds.  I contend based on state analysis that you have to put energy into the system in order to make the submersible fall from its elevated state, or to make it rise from its more submerged state.Are you claiming that you can make that sphere rise or fall without changing either the volume it displaces or the total mass of the sphere and its contents?

Unless you change the state of that material.
Energy is used to convert the liquid to gas, 75% of which is returned when the gas is converted back to liquid. This leaves the onboard turbines a task of generating the remaining25%

Unless you change the state of that material.
Energy is used to convert the liquid to gas, 75% of which is returned when the gas is converted back to liquid. This leaves the onboard turbines a task of generating the remaining25%

No, a thousand times no.    A mole is a mole is a mole is a mole.  Material state is related to the volume a given mass occupies.  It does not change the material's mass.  The mass is determined by how many molecules of the material there are, and what elements compose those molecules.

Mark-what is mass?
Is it the weigbt an object weighs?

First: mass is not weight.  Mass determines:  1) Resistance to acceleration, and 2) Force of acceleration towards other mass separated by a distance.  In proximity to a dominant mass, IE such as anything here on earth relative to the earth, mass will relate to weight:  equivalent force acting on the mass from the acceleration due to gravity by a nearly uniform scalar.  For instance on earth we use Ge as ~9.8 m/s/s.

Second: The weight of a particular number of moles of a given material does not change with phase.  A mole of: ice, water, or steam all have the same mass.  And barring locations with radical gravitational gradients: at any given location they experience the same gravitational force that we describe as weight.

My understanding of what Tinman is saying is that he does need external energy to condense the gas to liquid.  If one has a heat sink below the phase change temperature for the pressure one is at, then simply cooling the gas and in the process giving up stored energy to the heat sink will condense the gas to liquid.

My understanding of what Tinman is saying is that he does need external energy to condense the gas to liquid.  If one has a heat sink below the phase change temperature for the pressure one is at, then simply cooling the gas and in the process giving up stored energy to the heat sink will condense the gas to liquid.

I see. We need to present him to the Nobel Prize.   For the courage of presenting new theories.

No
Energy is needed to turn the liquid into gas-this I have said many times already. Energy is returned when the gas is converted back to liquid.
Mark-what is mass?

We agree that it takes energy to convert material from liquid phase to gas phase.  We agree that gas can be converted to liquid by removing heat.  We agree that heat can be removed without adding energy when one has a heat sink that is below the phase change temperature for the pressure.

I answered you on mass a couple of posts back.  It is a property of matter.  That property establishes both resistance to acceleration (inertia) and force attributable to acceleration towards other masses commonly referred to as gravitational force.