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[stringer]

the boat im working on is a 2 ft fibreglass hull it has a mount i fitted for a 540.wish to know if a brushless comes in that size to fit the mount.also seen some graupner motors with high revs.would they compare to brushless or does nothing compare to brushless.i know nothing about brushless sizes and dont really know what is suitable for £30 price range.seen some £15 from hong kong but dont trust their quality.i also dont know a great deal about electric any advice on brushless power sizes greatly appreciated.thanks  

[gwa84]

for brush less motors and speed controllers check out the giant cod website they have some very good prices

[nick_75au]

Hi Stinger,
What do you want out of the motor, is the boat a high speed planing hull(surface drive or submerged prop) or a displacement hull.
Do you know the prop size you are going to use?
What voltage do you intend to use?

There are 540 sized  brush-less motors that will it your mount, and in a good range of Kv ratings (Kv = RPM per volt).

High RPM does not necessary mean high speed, as if you overload the motor with too large a prop it can not achieve its efficient range and draws too much current.

The comparison of brushed and brush-less is not easy to answer, however comparing each with equivalent specs the brush-less will be somewhat more efficient under the same load.

Nick

[Aeronut4]

Basically, what Nick said.    However, it's worth bearing in mind that brushless controllers with reverse that are suited for marine use seem to be somewhat of a rarity at the moment.  There's plenty available for cars though, if you can find the right one.

[stringer]

thanks,its quite a heavy boat submerged prop size 35 off the top of my head 3 blade and i am looking for speed
i never thought about the reverse thats a good point that i didnt know about.thanks

[nick_75au]

For submerged drive and 35 mm prop planing hull, you need about 15-20000 RPM loaded speed, so on say 3 cell li-po or 10 cell Ni-XX a 2200 Kv motor is about right. Slightly less as prop size goes up and more if prop is smaller. A 540 brushless should have no problem with a 35 mm prop, if its bigger a 540 Xl might be worth getting. Look at Hobbyking.com, they have a range of reversing controllers, but if its a racing boat I wouldn't worry about reverse.

Cheers
Nick