ORIGINAL: peterpella
Some guy wrote that 12v 700 motor was too slow. Funny.
Some guy who has been there done that. First of all, that motor won't even wake up until 16 cells are used.
THIS IS MY FIRST RULE: EVERYTHING DEPENDS ON COMBINATION OF MOTOR, PROP, AND HULL.
What about the absolute most important component of an RC FE boat, the cells? Something that controls everything and you fail to include that in your lecture. Not to mention the ESC, type of drive, and setup.
THE SECOND RULE IS: A PROP DIAMETER MUSTN'T BE BIGGER THAN ANKER ( ROTOR ) DIAMETER, if we talk about direct drive.
How can you possibly come to the conclusion of this? First of all a DC motor does not have a rotor, it is called an armature. The size of prop has very little to do with the Diameter of the armature. Depending on how many cells are used drastically changes the prop you may run. I have ran upwards of a 55mm prop with a 700 motor direct drive which is 10mm larger than the CAN of the motor.
Drill a hole below the water line. The distance between a hole and water surface should be equal to the prop diameter. That means that if the boat doesn't run, the edges of prop touch the water surface.
Where have you ever heard of any one doing this on a surface drive hull? So if my hull is heavier my prop shaft will be higher up as the water level increases? This is the exact opposite of what you want considering when on plane you will have no prop in the water.
My boat may be lighter or heavier than yours, this should NOT play any difference in where the prop shaft transom hole is placed!
On my old 24” and 27” mono, the prop shaft holes center was placed about 1/8 to 3/16” above the bottom of the vee. On my 46” mono, the prop shaft hole is place a little higher than ¼” above the bottom of the vee.
The edge of the prop touches the surface? So if I increase the number of cells used, drop in prop diameter, the hole must be higher up on the transom. You are going to end up with a hull that will not plane!
Also, you will only have the radius of the prop above the prop shaft center line.
Ryan