Great, i ordered 3. So 6 pieces left. It is backorder, so its up to 6 weeks deliver time.
Flo and Jan, are you the same person?
Flo, do you have a photo of this arrangement? How do you prevent electric current flow through the cooling water?
I gave up water cooling in an open circuit when i realized that i created a pole to the battery via the cooling hoses, rinsing water through copper pipes which were soldered to the Fets Drain. In combination with my unperfect isolation of phase wires at the motor, this could lead to eletrical shock. So be aware of the consequences.
Jan, are you testing some vesc or what is it?.
Under which cooling conditions do you reach 80A continuously (lets say 5-10minutes).
Can we see some photo?
I ordered these heatpipes: https://www.voelkner.de/products/238849/Heatpipe-Qg-Shp-D6-100gn-6mm-100-Lang.html
I was testing 300 Alien esc with watercooling together with C80100 Outrunner brushless motor 80KV 7000W
Since it was a 300A esc and watercooled I did not expect heating problems. I run it for about 5min.
The reason for testing was that the esc had cut off a few times in sea trials. I belive the problem was some leak between the cables in the mast that maybe gave wrong pulses bac to the esc.
Hey @Jan, was the cutoff you experienced like an on/off pulsing? I had that recently and I also assumed is came because of a leak in my motor pod. Everything ran smooth without load but in the water I got that pulsing. I would like to understand what exactly caused that. I am thinking that the leak shorted the phases and at a certain current the ESC would cut off and restart after a second. Not sure.
I like your heatpipes @PowerGlider , but I don’t know how to keep them electically isolated.
My current approach is to solder copper plates to the fets and dump the heat to the rectangular aluminum pipe around it. Please excuse the crude looks, this is only a test 
Between the copper plates and the aluminum pipe there will be electrically insulating but heat conducting foil.
The problem I have found so far is that its labour intensive. I have been sanding copper for an hour as the fit determines the contact pressure.
I’m not @Jan. Thanks Jan for the suggestion on loading the motor. I will look into that when the vesc is ready.
Thanks for sharing Pacificmeister. My last esc, a 200A boat without cooling, was running ok for a few times with high amps (+ 100A) then I got the pulsing you are talking about, and after a minute or so it burned. I changed to a 300A with cooling and no pulsing, but it still cuts of in the water at 45A, but can run in air with load of 80A. So I meassured the cables, unconnected, with a megger at 250V and it showed 23 Mohm dry (not perfect). So I suppose under water it will be less and this is causing the problem. My cables are a tight fit in the fuselage so I belive I made is a crack in the silicone when pulling them tru.
Is it battery current or motor phase current?
If it is battery current i would assume, the motor is overloaded in water, the phase current too high and the ESC limits the current due to temperature or other overload protection.
Try to reduce the torque demand by making your paddles smaller.
Once I recieve the new Powerglider motor I will change the cables and try again.
Looks good, what you plan to do with the pipe? Where is the heat going further? Where are the electrical
connections going?
The pipe will be my mast. I will add an airfoil shape to it. The short motor wires will leave at the bottom, the battery wires leave the pipe/mast at the top. Because of the long wires I have 8 x 470uF low esr capacitors close to the esc, probably overkill. I have tested this long battery wire setup last summer without problems. The cooling solution is still untested 
I’m currnetly reprogramming the esc software to show all fet temperatures.
Hi @Jan, I rode this morning again after overhauling the pod, now runs super smooth with the additional bearing to stabilize the prop. No more pulsing and I am now pretty sure it was the moisture that cause it. Hope you find your cracks.
Can i help you? You want to implement some model?
I know a bit about polishing metals. Is best to use flat sandpaper on a sheet of glass. Start with 120 grit and work your way up to 1000. This ensures that the base material is flat. After that you can use a polishing wheel on the angle grinder. This gives you a mirror finish in a few seconds. Polishing wheels look like cotton and cost 10€. You need a polishing compound too.
@PowerGlider, thank you! I have a working code with the old Vesc firmware of a year ago. It already displays the temperatures, unfortunately I rushed the soldering job and pulled an smd pad. Now I can only mount two temperature sensors or reassemble a new vesc with my spare PCB. Two sensors will have to do for testing 
I just assume that the copper bar soldered to the fet’s cooling tab has the same temp. The Sensor is currently clamped to the copper bar. I want to keep it simple right now and will leave a larger margin during testruns. A model with junction temperature calculation will have to wait for a future version
@MaxMaker Thanks for the ideas. I have it somehow fitting right now and insultated. Maybe i will even use an endmill in my lathe next time and get both copper planes aligned and then polished like you described.
I’m now working on compiling the new vesc tool software, just this evening.
Thanks again for the support.
First we need to remove the heat from the fets. Massive copper parts are a must. From there several options exist. Lets see how they perform.
What do you think about the hand vacuum mashine which is low cost and looks promising to provide appropriate vacuum for waterproofing motor:
I have that pump and like it. But I use it for a different purpose. I use it for checking if my boxes are watertight. I have 1/4 inch pipe fittings in each box and this gives me great piece of mind before I go out (I killed a VESC when water got in the box)
I am using a very simple venturi-pump which I found in my dad’s lab. Similar to this one:
Very cheap and even 3D printable - a waste of water though.
If you don’t want to waste water you can just use a bucket and circulate the water with a pump. But i is not much simpler than a vakuum pump then, depends on what approach you prefer.
How do you seal the pipe fittings?
I put quarter inch plugs in. And some teflon tape.