Proboat Rockstar 48 - Prop for FE

[Jbarber4]

I changed out the stock motor for a 1900KV set up for 6s so that my nephew could run the boat, problem is that I think the stock prop that worked with the gas motor is probably way too big. I need some advice on prop selection. The boat has the 1/4" flex shaft set up that it came with stock. The plan is to run somewhere between 25 and 40mph, nephew is 5 years old so as long as it gets up on plane and goes, he will be happy.

IMG_20241123_223441699.jpg

[fweasel]

1900kV is too much RPM on 6S for a boat that size. What you can do is wire your "presumably" two 3S packs in parallel to maintain the 3S voltage, cutting the RPM in half, and allowing you to still run the same stock prop.

Two conditions, #1, not sure if your ESC can run on 3S, so check that. #2, the ESC is likely wired with two battery connectors in series. To run 3S packs in parallel, you'll either need to do some soldering, OR, put a shunt plug in one connector, then plug a parallel harness in to the other connector allowing you to run two 3S packs.

[Jbarber4]

Took it to the lake today for a test, was using a prop off a sonic wave that was drilled out to fit the 1/4" shaft. The boat looked fast, I don't have gps but it looked like 40-45 mph. This was on 6s, the problem is that it won't go to full throttle. It cuts out about 70% the esc also gets pretty warm after 2 mins or so. I am gonna try 3s as mentioned with stock rockstar prop. Any other options?

[fweasel]

I wouldn't recommend running a 3/16" bore prop drilled out to fit a 1/4" propshaft. More likely than not, the hole will be off center and cause vibration in the strut, causing premature wear or worse. Also, the diameter of that prop was likely too small to push a 48" hull from a stop and will cavitate badly. Then, because of the high RPM, it will spin way too fast producing way too much load on the ESC. 1900kv is at the limit of RPM for the majority of 6S sport boating setups in an appropriately sized hull. 48" is way too big for that setup. If you're going to stick with what you've got, cutting the voltage in half (to 3S) is your best bet.

[Jbarber4]

Took it out to test 3s today and it runs nice and stable with the stock prop (70mmx1.4 estimated size) looks to be running around 30 or 35mph. One issue I was noticing was the motor wires and esc wires are getting real hot. The esc itself and motor didn't feel hot at all but the wires attached to them would be too hot to touch after 30 seconds of run time or so. Additionally It seems that the esc is cutting power when I give it full throttle. Any suggestions for improvement, or time for a better esc?

[fweasel]

Are the wires getting hot, or the bullet connectors under the colored shrink wrap? Cool motor and ESC's temps seem to indicate the components are happy from a load standpoint and cooling appears to be adequate. Heat in motor wire connectors can be from high resistance caused by undersized connectors or poor quality solder joints. You can replace them with a set of Castle 6.5mm bullet connectors.

[Bande1]

you need 8s for that boat with a 600-700kv motor. and the motor needs to be at least a 5692. I have a high voltage esc for $120.

[tbonemcniel]

You've just got the wrong motor, and possibly wrong ESC, in a boat that size. It's all just undersized. What you're running are electronics that are meant for a 36" boat max, in a 48" boat. Everything is getting hot because it's pulling too many amps. To make the same power and lower the amps, you need to up the voltage. And to keep the rpm in check, that means lowering the kv rating of the motor. An easy thing to do with little guess work, is just buy the motor/ESC combo for a Black Jack 42. It would probably work decently on 8S in that hull.

If it were me, I'd be putting a Castle XLX2 and a 2028 or similar sized/kv motor in that hull, but that's a large expense for something for your nephew.

[Bande1]

$100 motor

https://www.amazon.com/Surpass-Hobby...s%2C161&sr=8-1

$120 esc