Paul
I have no experience of these but I know a man that does. Have a word with Alan Shillito at ASTEC; he specialises in fast electrics and has a very nice range of brushless motors and speed controllers, including some real monsters. **LINK**
Dave M

Paul,

First I should say that I have not used i/c motors nor have I used brushless.

Looking at the specs of the motors given in Dave's link above I note that many of the motors are rated at 1 kWatt (1 HP = 746 watts). Consequently the currents drawn are very high – many tens of amps.

You will need some heavy guage wire for your connections in order to avoid wasted voltage drops. Also you will need to locate power components (ESC, Motors, Fuse, Battery) as close together as feasible. Wire connections need to be heavy duty connectors (gold plated). Switches are a problem at this level of current and often not used (remember that at 100 amps even 20 milliohms resistance will give rise to a 2 volt drop). As I have had no experience of this level of current in a model boat I don't know whether radio frequency interference (RFI) is a big issue.

The pursuit of speed brings with it some limitations – time on the water will be relatively short limited by the battery capacity (ampere hours Ah).

Ian

I dont think that RFI is a problem with brushless, however much the current is…however, I notice that a lot of brushless ESC come with a the reciever lead wrapped around a ferrite core?

I would think that you will need a watercooled ESC as well, given the likely high current involved.

Ashley

It's an interesting comparison. The Electrics won't develop the same power as the I/C but the power versus speed equation is not linear so they may well come quite close speedwise given the right setup. But I agree, could be a bit expensive on the battery side though.

Colin

I thought I would have one last look at this subject. I found this :

**LINK**

Apparently 4000 Watt continuous operation is feasible ! …. though I bet you would need forced water/pumped water cooling with a good flow rate. It is designed for model helicopter useage with a Kv of 520 rpm/volt (so for example if you had 5 LiPo cells = 5 x 3.7 = 18.5 volts the no load rpm would be a bit less than 10000) – inevitably the current would be high = about 200 amps in my example for an approx 4000 Watt output (it would be about 10% less due to losses) !!

A few points to note – a. I haven't looked for a compatible ESC b. I haven't looked at the feasibility of suitable LiPo battery and in particular safety issues (prevention of possibility of short circuit of battery would be essential because of the large stored energy and ultra low internal resistance of that type of battery) c. aircraft don't need to reverse the motor rotation so you would either live with just forwards or you would require a mechanism for going astern.

If you wanted to go further with this my recommendation would be to get in contact with Scorpion and discuss your requirements.

Regards.

Ian

Paul,

I had a look at the motors suggested by Francisco – they are aimed at cars, helis and planes. I don't know who stocks/sells these products in uk. Nevertheless, I did find 1 motor and 1 esc on their excellent website that might be of interest :

Motor (outrunner) C6354-KV250 which can be supplied at up to 10 LiPo cells (= 37 volts) with a max continuous current rating of 90 amps and at 37 volts the no load rpm would be about 9000. Rated at 2450 watts max.

Suitable ESC is Aeolian-100A (no reverse).

See **LINK**

Also found 10 cell LiPo battery (advertised on a us website for $160 :

Turnigy nano-tech 5000 mAh 10S 45 ~ 90 C LiPo Pack

Another issue that I can't answer is whether it is permissible/feasible to operate LiPO battery packs in parallel (you would need many battery packs to give any reasonable duration on the water). It is also now evident that the brushless motor for high powers is an expensive approach !!

Ian

the bigger has got a descomunal power!!