Thrust to water flow rate question.

I am not a scientist, engineer or anything close so please forgive my ignorance. Just looking for some expert advice. If I have an electric tunnel thruster with a 185mm propeller mounted inside a tube of roughly the same diameter as the propeller. and the tube forms a loop with a circumference of about 2 meters. If the tube is filled with water and the thruster is rated to have 211lbs of thrust. Is there a way to determine the flow rate of the water in the tube based on the thrust or do i need more info on the propeller size and rpm and such to determine the waters speed.

What you are calling an "electric tunnel thruster" is basically a pump, and your pump is pumping water around a loop of piping. Pumps are supplied by their manufacturer with a pump characteristic curve or "head-flow" curve, and each pump design is different.
Centrifugal Pump Characteristic Curve - Engineers Edge
The flow resistance of a pipe can be found in a handbook or a water flow calculator like this one.
Water Flow Rate Calculator
What would happen is that an equilibrium flow rate would be reached where the output pressure, or head, of your pump is equal to the resistance of the loop of piping.
For such a short length of pipe, the flow resistance would not be very great. Your pump may very well be running near "runout" condition as shown on the curve in the first web site link posted above in which case it would not develop anywhere near its rated pressure.

Edit: Never mind all that. A thruster is a different kind of thing.
These thrusters have a thrust rating at a certain flow rate.
http://www.thrustmastertexas.com/pro...hitePaper.html
If you know the thrust, and the flow rate in gpm, you can find the velocity from the flow rate.