Today on YouTube I was looking through video from RCModelReviews and found one titled “How ducting a propeller increases efficiency and thrust".
What really caught my attention is when the discussion of what I am calling a "coanda ducted fan”. This starts around 11:15 into the video.
It seems to me that the BlueRobotics thrusters might be using this principle to improve efficiency. Is my assumption correct?
Why this is important to me is that I am using “weed guards” on my thrusters and it seems to me that the weed guards might have a negative effect on a “Coanda ducted fan” design.
Also part of me thinks BlueRobotics thrusters might NOT be using a “Coanda ducted fan” design. The reason is that the propeller blades are not all that close to the sides of the duct. In the above video, the distance between the propeller tips and the duct must be very close to avoid "prop tip vortices” which from my understanding, have a negative effect on efficiency. The "prop tip vortices” issue may be addressed through BlueRobotics design of their props. Also in this video, it is mentioned that any ducting should be very light because any efficiency gained by the ducting can be reduced or eliminated if the ducting is too heavy.
Assuming that air and water are both fluids, I am guessing that even though all the information described above were for propellers and ducting in air, that the same principles apply in water.
I am planning on building a simple load-cell test setup to measure the thrust of a T200 in water, with and without the weed guard, but if BlueRobotics can tells me my weed guards should not make a difference in performance. I will bag my tests.