Spearfish motor?

[Andrew Martin 3Participant @andrewmartin3]

I have acquired a MFA Spearfish which currently has a Torpedo 850 motor in it with a X50 prop. The Torpedo motor is shot and was wondering if anyone can give some advice on a brushless solution using a similar size of prop please? Secondly would I need to change to Lipos and presumambly speed controller all of which seems to be getting expensive compared to getting a replacement motor. Does anyone have experience with a Spearfish with a Torpedo 850 motor and what was it like speed wise? I had a Spearfish many years ago with a Irvine 61 engine it and it went very well. I dont want a boat that is totally uncontrollable though.

[Andrew Martin 3Participant @andrewmartin3]

[ashley needhamParticipant @ashleyneedham69188]

Andrew. If you have the esc and some 12v Nimh's then a replacement 850 at 25 quid or so is the way to go.

​HOWEVER as almost ANYONE ELSE will tell you that only a 25Kw brushless will give you the performance that you so crave….BUT on the other hand, how much are you going to use it and how fast do you want to go??? Yes you would need a brushless ESC as well.

The 850 gives a reasonable performance for a boat used twice a year….

​Ashley

[Dave MilbournParticipant @davemilbourn48782]

Andrew

I'm a little puzzled at the answer you seem to want to hear. Your question changes tack halfway through. Here are a few indisputable facts:

Yes – replacing the motor with a brushless one will mean you having to replace the speed controller as well.

Yes – that is going to be more expensive than simply replacing the motor with another Torpedo 850.

No – the model will not be 'totally uncontrollable' provided that you choose the right combination of brushless motor, speed controller and batteries.

A good Irvine 61ABC 'on song' puts out around 1.7 BHP (1.25Kw). Ashley is exaggerating with his 25Kw value (33.5BHP), but I think we all know that already.

Suit yourself – it's your money, m'duck. IMHO the only use for a Torpedo 850 is as ballast…

DM

Edited By Dave Milbourn on 03/01/2017 17:37:16

[Andrew Martin 3Participant @andrewmartin3]

Thank you, OK well the brushless route seems the way to go. Ill happily scrap the old 850! So what should I be looking at? Giving me an explanation that I need 1.25kw motor sort of helps but does not give me known motor makes/models and speed controllers that are known to work and are actually available to buy and that is what I am actually looking for.

I should explain I am used to Brushless motors for Aircraft but seem to have got lost when applying this to marine usage. I am not averse to spending the money either as have had plenty of experience with that flying electric I have plenty of Lipos ranging from small 1100 to 4400 in both 2s and 3 s and some 4s configs. Obviously aircraft speed controls and programming cards will probably be different as no reverse.

[harry smith 1Participant @harrysmith1]

Hi Andrew

One of our club member's runs a Spearfish with a Hobbyking 35mm 3639-1100kv brushless motor with a 5800mah 3S Lipo Battery, ESC is the Hobbyking car 60 Amp, prop 2 blade 45mm.

Good turn of speed without getting insane.

If your wish more speed change to 4S battery with all the other bits the same.

Or more speed the 3648-1450kv motor.

[Andrew Martin 3Participant @andrewmartin3]

Hi Many thanks, Harry and all

I do have the following motor on my workbench https://hobbyking.com/en_us/turnigy-d3548-4-1100kv-brushless-outrunner-motor.html which is 910w compared to the 800w of the 3639-1100kv. Ill use that first and revert to the 3639-1100kv if no good.

I'll try different props as well. I'm assuming Xtype is the way to go?

Andrew

[harry smith 1Participant @harrysmith1]

Hi Andrew

The D3548-4-1100kv is a far better motor, I am running one in my Sea Commander.

Harry

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