tomhugill

Hey all,

Sorry that this is kind of a cross post from the nitro forum but its still relevant! I recently purchased a pair of Atlantic challengers off eBay for a decent price. One of them is the graupner electric version which is kitted out. The other is the same boat built from the graupner plans but with a single cast jet drive unit (this seems to be a graupner jet propulsion unit 5). It has come with no other fittings. I was initially looking at a Gas power plant but I've read that this can work with electric power which I am more familiar with. The jet unit recommends a minimum 800W motor. I'm not sure what sort of RPM these jet units require. So my question is can anyone recommend a suitable brushless setup for this boat?

785boats

What voltage do you intend to run. This will affect the Kv of the motor you need.
Most impellers start to cavitate at around 25- 28 thousand revs. So over revving them just wastes power for no speed gain.

Also, what size IC engine do they recommend.

785boats

If it were mine I'd be using something like this on 6s. Just need a water cooled motor mount.
http://www.hobbyking.com/hobbyking/s...ass_Heli_.html
http://www.hobbyking.com/hobbyking/s..._Boat_ESC.html

tomhugill

I was thinking possibly 4s as I have 2 10mah 2s I could run in parallel. But maybe I could get a third for 6s? Would something like this work? http://www.hobbyking.com/hobbyking/s...arehouse_.html with this:

http://www.hobbyking.com/hobbyking/s...arehouse_.html

785boats

Hi Tom. And Merry Christmas.

Unfortunately a 1400kv motor on 4s might be a bit slow. that's about 21000 revs. Maybe 18000 under load.
For 4s, something around the 1800kv range would be better. Perhaps this one.
http://www.hobbyking.com/hobbyking/s...er_1760kv.html
But I see you would like to buy from the UK warehouse & it's not available there.
This one is available there. I've used them with great success in monos before, but not on a pump. Pumps take about 20% more power than props for the same speed.
http://www.hobbyking.com/hobbyking/s...otor_90mm.html

Of course it doesn't have to be an outrunner. Any inrunner of the 3674 or 40mm size with a kv from 1800 -2000 would do. as long as it can make a power output of 1500W or more on 4s.

The ESC you picked would be fine for any of them

I think there is a typo on the batteries you noted on your previous post. You need more than 10mah.
You will need at least 4s 5000mah 40c packs. Preferably 2 in parallel for any decent run time.

tomhugill

Hey yeah, I meant 10Ah!

785boats

I Thought so.

I see the guys over on R/C groups are giving you some good advice. I didn't realise it was the larger impeller size.
I didn't see the 'Unit 5' reference in your first post. Stupid me. So yes a lower KV rasting than I was thinking of woulbe better.
That 1400kv 600 size outrunner you linked in post # 4 would be ideal on 6s in my opinion. And they sound great too.

Cheers.
Paul.