Which 700bb turbo do you have 8.4v or 9.6v? I used to race these motors on 12 NiCad cells, in a mono we would use up to an X445 on the 8.4v or up to an X450 on the 9.6v, our boats back then were about 26-27" so likely lighter than yours, and thus I would probably chose a prop one size down from those. I think a 48mm 3 blade would be too much for it on 12 cells (if that is what you are using) unless it is of lower than 1.4 pitch or of a low blade area design.
I have a different viewpoint to Fluid on the watercooling, likely due to my experience being with 3 and 4 minute timed races and I believe Fluid was mainly sprint racing for a shorter duration. We found them to respond reasonably well to can cooling especially in monos with their longer 4 minute duration races (averaging about 30A with speeds in the mid 30s, than hydros that ran for 3 minutes averaging about 40A with speeds in the high 30s. The way to cool the cans was with a water cooling coil made from thin walled alloy tube, these are still available from CEM, but you could get better results making your own, as putting tension on the tube as you wrap it around the mandrel can with care result in deforming the round tube into a flat bottomed "D" section that has a LOT more surface area in contact with the can, and you then slather the inside of the can with thermal compound to fill what is left of the gaps before sliding it on the motor. The best method to wind a cooling coil is to wind it around an undersized mandrel so its own spring tension grips the motor can securely, but you can also form it around the motor, and put thick heat shrink around it, wind it up tight and then heat it up, the shrink once shrunk will hold it tight.
Whilst cooling coils did lower motor temperature, it did not significantly increase their lifespan when racing or stop us burning them up in SAWs, the weak spot of the 700BB turbo is the thin brass brush springs that have to carry all the current to the brushes, when these get hot they weaken and dont apply as much pressure to the brushes resulting in more arking and increased heat which weakens them further in a viscious cycle till they fail completely. We started soldering about an inch of copper tube to the brass motor terminals and that vastly improved the lifespan of the motors when racing, and increased the current we could put through them when running SAWs. While I would say a cooling coil while good is optional, cooling the terminals is mandatory.
I know you have the motor already, and maybe the ESC, but I agree with Fluid brushless doesn't have to be faster, a 3650 motor with 1350kv will spin the same prop as a 9.6v 700bb turbo at the same RPM, but with much better electrical efficiency and will weigh a lot less, giving you longer run time, and it will run cooler, and last forever.
Paul Upton-Taylor, Greased Weasel Racing.
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