I need help with my props

[hallsboats]

hi
i have a brushless set up the motor is Brushless Watercooled Motor 3650. 3300 rpm per volt.
i have a problem and wondering if anyone can help
when i got half speed it goes at a constent speed. when i got up
too full throttle it dose the same speed.

any ideas what prop with help me

size on the hull is 1metter(40inch)

thanks james

[NativePaul]

My guess is that your prop is cavitating when it gets over half speed and not giving any further thrust, the 3300kv motor suggests that you may be running 3s on a fairly small prop around 40mm, you dont say what type of hull it is, but if your trying to go fast a 36x50mm motor is much to small to give the required power and a 1m hull will probably need a 50mm+ prop to push it requiring a much physically bigger Lower KV motor to swing it and more voltage to get the needed power and the RPM back up. I would suggest a motor at least 45x70mm and under 1000kv with 10 or 12s.

[hallsboats]

oh. so i should get a 50mm prop ?
if so . can u send me the link to the one u reckondmend ?

[NativePaul]

No. Well yes and no, it sounds like you need a bigger prop but the motor you have at the moment wont swing it unless you use it at a low voltage, and that will make what is already a very low power setup for the hull size even lower power, How many cells are you running? a 50mm prop with more than 2s on that motor will burn up the motor and ESC in no time, and on 2s it will be massively underpowered, whether dropping voltage and propping up to get rid of the cavitation will increase the speed despite it having less power is debatable, but it won't be a huge improvement if it helps at all, you need a bigger prop AND a lot more power to spin it fast.

[hallsboats]

oh well im using a makita 18v battery 3.0Ah .
and im using a 45mm prop

[sailr]

Your prop is too big for that KV! Try a 40mm prop.

[hallsboats]

what pitch ?

[sailr]

Get an Octura X440. It is 40mm diameter, 56mm pitch. The first four means 1.4. multiply the diameter by 1.4 = 56. How many cells are you running?

what pitch ?

[hallsboats]

no sure im using a Makita 18v Battery Makita 3.0Ah. but what cell would you, use ?

[NativePaul]

3300 kv on 18v is trying to spin near 60,000 rpm the power system would prefer a much smaller prop maybe an x431 but a prop that small wont push a 1m hull, yo need at least a new motor, around 1500kv would be much better for 18v but that is still not a lot of power for a 1m hull although it would be much better than what you have now (which wont last long by the way) , 800kv and 32v would be better still but will your ESC handle the voltage? I dont know Makita cells but with 3Ah it might be a good idea to parallel them, as I am guessing that thier massive voltage drop under load is the only thing that is keeping your motor and ESC alive with the hundreds of amps your setup must be trying to pull at the moment, in it's efforts to spin a 45mm prop an 60,000 on 18v.

[hallsboats]

ive got a graunper 700bb motor. do you think that will be anybetter to use ??. and ive got a Brushless watercooled 70Amp Speed control (ESC) i get my stuff from PMB models.

http://www.prestwich.ndirect.co.uk/brushless.htm

that is the website . if that helps