Hi,
Thanks to everyone for your help it is much appreciated I have learnt quite a bit, I didn't realize the power these small motors have, I'm now going to go with a 3542/05 1250Kv on 8.4v NiMh a Mtronik G2 Hydra 50 amp ESC and a 35m 3 blade Brass Prop

Also I had a look at a very useful site explaining all about Kv =Turns of wire on these Brushless motors.

www.ateamboatyard.co.uk/understanding-brushless-motors/

Zippy

HI Zippy, long time no speak, we last met two years ago at a fireboat funday, and discussed brushless applications at length.

I currently have a turnigy T600 outrunner, 800kv, in my 3 footer. Last time you saw this boat it was a 700bb turbo brushed set up, 2 x 9.6v nimhs with a 1.5:1 gearbox. it went well, but now is way more efficient. The brushless is direct drive, propshop 3 blade Cleaver after your suggestion, turnigy 60 amp esc (watercooled boat version) running on two 7.2v lipos.

This same motor in my big Huntsman with 1.25:1 ratio on two 11.1v lipos and "x" prop 52.5mm was good for 23mph, 7kg boat, and didn't need cooling, but was a bit amp hungry spiking at 70amps!!!! so the esc had to handle it.

Maybe not the best set up, but tried and tested, didn't you have a brushless setup in your Huntsman?

Higher kv motors will struggle on larger heavier boats, as they need some torque. A very successful direct drive brushless motor was an align 1200kv, BL something or other! 52.5mm "x" prop, but it did get hot and needed water cooling. its an outrunner, but with a can on the outside, so you can fit a water jacket

Both motors are common with rc helI peeps, and come up on ebay in helicopter section, when testing they are worth a punt.

Make sure you buy one with the shaft the right way around for boat use, as the shafts are grooved for circlips usually and cannot be reversed on most of them. They are usually intended for aircraft which have all manner of adapters depending on the props to be used

Good luck,

Paul

HI Zippy, welcome to the site.
Just had a look at the Mtroniks site and see their ad says "The Genesis Hydra30 is best suited to small scale RC boats to be used at scale speeds."
If this is the combo set, the rating is 1000Kv which at 7.2 volts will give you 7200 revs. This seems a little on the low side if you want a really fast model that planes easily.
My 34" Fireboat uses a RC-Smart 3480 outrunner and a EZRun-60A-SL 60A Constant ESC. I use an 11.1v LiPo but it works well with a 7.2 NiMh.
Prop is a brass 35mm 3 blade.
My model weighs in at 1900gms all up so is fairly light. Weight is the biggest problem and you need to get the heavy bits (battery) towards the rear.
You could use a 8.4 or 9.6v Nimh if the speed is too slow but this will come at the cost of extra weight so its a bit of a balancing act.
Brushless motors like to run at high revs so avoid using too big or coarse a prop. The fast racing type 2 blade props will place too heavy a load for your purpose.
Ideally you should invest in or borrow a Wattmeter to measure the current draw on your chosen set up. This will avoid you running the motor and ESC above their rated value.
I have no experience of Mtronik brushless ESC's but use their brushed ESVs in many of my models and find them excellent value. Giant Shark have a large selection of brushless motors and setups and if you search the web you will find many more suppliers both in the UK and abroad.
There is a section on this site Photo Gallery with a whole section relating to Fireboats and I suggest you have a browse to see what set up other use so you can have a better idea when searching.
Good luck and do please post details and pics of your model. 😀

HI Zippy you need to go to a web site called Giant Shark that is were I get my brushless motors from you will need special speed controllers for brushless motors hope this helps

HI Zippy, I have no experience of the Mtonics for brushless motors, so I can't comment. I suggest that you decide on a motor first, find out the amps it will pull and then match a speed controller to it.

I think there are people on here that have brushless motors in a 34" crash tender, perhaps they will help you to choose.

Alan