Model Boat Mayhem

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: Motor comparison advice  (Read 830 times)

colin-stevens

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 730
  • Location: Southwater
Motor comparison advice
« on: July 04, 2020, 06:49:52 pm »


Hello all, Been away from the hobby for a few years now, (my previous model being a total failure on the water), and have just seen a kit of a 55ft Coastal Motor boat. Had a yearning for one of these for many a year so..........

The motors they say they have have used are:
Turns: 6, 1350 KV (rpm/V), Suitable for 2-3S Lipo, Max Current: 32A, Max Power 322W, Weight: 68g.
Useful piece of information, saves the guess work.
However I happen to have:
Overlander BM400 V3-  motor poles 4, 2100 KV (rpm/V)  , LiPo Voltage Range  2 - 4S, Maximum Amp Draw  42A, Power 220W, This is 12mm longer than the one above.
My question is, being a cheap skate would my motors power the boat as well as the ones recommended.
Thank you

Colin

Logged
grumpy old XXX

ChrisF

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 973
  • What's my favourite cake!
  • Location: Warwick
Re: Motor comparison advice
« Reply #1 on: July 04, 2020, 07:21:59 pm »

You don't say how big the model is, what type of hull and what the size of the recommended motor is which we need to offer advice.


For the type of boat I would say that the kV of the motor you have is too high, something in the 900 to 1100 kV range would be more suitable if a planing hull and even lower if a displacement hull.


Having Googled your motor it definitely isn't suitable being an inrunner. They are less torquey than outrunner motors and will give too high a revs for the type of boat - more suited to light race boats.


Chris
Logged
Building Fairey Marine boats: River Cruiser 23, Huntress 23, Huntsman 28, Huntsman 31 and Swordsman 33 and two more to come! All to a scale of 1:12

colin-stevens

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 730
  • Location: Southwater
Re: Motor comparison advice
« Reply #2 on: July 04, 2020, 07:26:14 pm »

I thought by quoting the reckomended motor specs and the specs of the ones I have someone may be able to tell if they are comparable.
[/size]
[/size]Its Mountfleet 55ft Coastal Motor Boat, model spec
[/size]Length 43", (1092mm)Beam 8.75" (210mm)Height 18.5" (470mm)Displacement 6.6lb (3kg)
[/size]I dont know the prop size.
Logged
grumpy old XXX

ChrisF

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 973
  • What's my favourite cake!
  • Location: Warwick
Re: Motor comparison advice
« Reply #3 on: July 04, 2020, 07:41:37 pm »

Hi Colin

Had a look at the Mountfleet site and can't identify your model - what's it called? What you have said though confirms my initial thoughts that your Overlander is not suitable.

Chris
Logged
Building Fairey Marine boats: River Cruiser 23, Huntress 23, Huntsman 28, Huntsman 31 and Swordsman 33 and two more to come! All to a scale of 1:12

Stan

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,213
  • Location: West Yorks
Re: Motor comparison advice
« Reply #4 on: July 04, 2020, 08:13:12 pm »

My thoughts only. You may purchase other motors and should they not give the performance you wish for you may end up buying the motors recommended by the kit maker.  But you pays your money and makes your choice good luck with the build.


Stan.
Logged

colin-stevens

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 730
  • Location: Southwater
Re: Motor comparison advice
« Reply #5 on: July 04, 2020, 08:18:12 pm »

My thoughts only. You may purchase other motors and should they not give the performance you wish for you may end up buying the motors recommended by the kit maker.  But you pays your money and makes your choice good luck with the build.


Stan.
More or less where I was going, and its not as if the cost a fortune. Thank you.
Logged
grumpy old XXX

john44

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,634
  • member of the Potteries Model boat club
Re: Motor comparison advice
« Reply #6 on: July 05, 2020, 08:44:45 am »

Hi guys, according to the Mountfleet spec the 55 ft coastal motor boats were developed by Thorneycroft
For WW11 to be used as a MTB boat, so it says.
PS,I would use the recommended motors


John



Logged

chas

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 502
  • now in los montesinos Spain.
Re: Motor comparison advice
« Reply #7 on: July 05, 2020, 09:49:23 am »

The Thornycroft CMB is an unusual hull, with unusual handling characteristics. Definitely best to stick with what is proven to work with this one, and stick to the recommended c of g. It's 30 plus years since I made one, but it took a lot of sorting out.
Chas

Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,023
  • Location: Blackpool, Lancs, UK
Re: Motor comparison advice
« Reply #8 on: July 05, 2020, 10:24:57 am »

According to Wiki, the original coughed out 670KW.  A about 1:15 scale this indicates aroud 200 watts out of the motor, which is very close to the original reccomendation of 220W into the motor.
Picking the right motor to give the needed RPM at an apprpriate power level, and to then pick the right prop to convert that power and RPM into moving water is the tricky bit.  The best way for a modeller to do this is to either find one that works and copy it, or follow the guidelines in the original instructions.  If the originally specified brushed motors do the job, and have known speed/ power/ torque figures, it becomes a case of picking brushless numbers that most closely match that.
Logged
"With the right tool, you can break anything" - Garfield

colin-stevens

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 730
  • Location: Southwater
Re: Motor comparison advice
« Reply #9 on: July 06, 2020, 05:45:59 pm »

The Thornycroft CMB is an unusual hull, with unusual handling characteristics. Definitely best to stick with what is proven to work with this one, and stick to the recommended c of g. It's 30 plus years since I made one, but it took a lot of sorting out.
Chas


Did yours have working torpedoes?
Logged
grumpy old XXX
Pages: [1]   Go Up