prop and rudder help

[Robdog600]

Hi guys, im a bit of a newbie to rc boats. i need a bit of help. i am building myself a scale replica of a aluminium trailer boat its going about 53" inches long and roughly 19" wide and 21" high at the cab. i am planning on pulling my mamba monster 2200kv brushless motor and esc out of my rc truck and putting in it. i will probably be running 6s and 4s set up in it, my question is what size rudder should i be putting on it , prop, etc i am not wanting any crazy speeds just a bit of fun , and reliable, cheers Rob



this is a couple of pics of what im building and progress so far!

[Robdog600]

any help plz guys

[Peter A]

To be fair the motor you have would be a tad small in a boat that size and heavy. What sort of drive system were you thinking of, submerged or surface?

[Robdog600]

Not sure yet maybe submerged. its either that brushless motor set up or I go with a 50cc 2 stroke motor I have. im not out to break any speed records just something fun to play with?
any help would be much appreciated
Cheers Rob

[DiveR_James]

Hi Rob I am also building a boat similar size, was planning on using a 50cc 3HP engine, what prop did you end up using? a 74mm 4"P?

[Dr. Jet]

If a 3 hp motor will work in that application, let's try reverse-engineering an electric system. 1hp is roughly 750 Watts, so 3 hp = 2250 Watts. Watts are Volts times Amps. A 6S battery will be about 22 Volts, so you need a motor that is happy at a tad more than 100 amps continuous to have similar power. Perhaps two geared motors running 50 amps each would work.

[Peter A]

Or if you go to 10s then you can reduce your current draw further. I have a 45" boat with a TP 4070 440 kv motor. On a Prather 245 it will pull around 50-60 A at around 65kph. I can run on 12s also and prop up for more speed (ABC 2314/4) to bring me up around 80kph. The motor is paired with a Seaking 130 HV esc. I would expect if were to run this setup submerged you would be running props in the 47-50 mm size but low pitch.
So as a suggestion, the seaking 130 hv esc with a leopard 5692 540 kv in either surface or submerged drive, prop to suit. Bear in mind that you have a large and heavy boat, but if you peed expectations are in the scale speed range then current draws should be reasonably low and run times good. 10s 2p could give you 10 mins or so.