Daz1701

[&o]I have a 6ft model bismarck that was purchased on Ebay and it only has 1 prop and a very old looking motor the prop has the number 60 on it its is very slow is one prop enough for this model???? I have a 600 motor out of a plane is this big enough spins well fast but not sure it it will be to fast???

Also got 5ft MTB with 4v motor also single prop but looks like you can fit a lot bigger prop that the Bismarck is 4v enough???

If anyone can help i would be greatfull as Im lost and the model shops were nI live dont seem to cater or know about larger models???

mfr02

For your Bismark you need about 60 watts. Thats 5 amps on 12volts. The requirements between a plane and a boat are totally different. A high revving motor trying to drive a large prop in water will be working in stall conditions, it will just flatten the battery and smoke. Visit a vehicle dismantler and get a heater fan motor. Nothing like as fast revving, but plenty of torque to turn a big prop so that a lot of water will go backwards at the right speed. You didn't mention size and number of blades.
An MTB, on the other hand, needs to go fast. This means the water shoved by the prop has to go fast, which in turn means high revs. Consider your ex-plane 600 here, with a small prop. This will give a narrow, but fast stream of water.

Daz1701

Thanks for the info! What sort of prop would you suggest for the bismark 3,4,5 Blade 60 is the largest size that will fit but No of blades
Pitch etc is a mystery to me I looked on the Deans Marine web site so many props to choose from plastic metal 2-7 blades again any help would be apreciated

mfr02

3 or 4 blade, diameter about the same as or smaller than the motor diameter. As long as the motor is using the power reasonably efficiently, the prop will act as a slipping clutch/torque converter much like an automatic gearbox in an intermediate gear. The hull has a theoretical maximum speed, once you get to get beyond that there is a lot of power wasted added to which it will look silly.
You only need to start worrying about pitch when you are looking for ultimate performance, i.e. racing.

cyclops2

I used the large plastic props on a 5' Missouri and a 3' wood PTB. Missouri had a 6 volt Dumas motor on 6 volt battery. PTB had a 05 sized motor from a electric car on a 8 cell car pack.
Both had great scale speeds.