Model Boat Mayhem

Please login or register.

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

Author Topic: Optimum prop shaft angle  (Read 4123 times)

ChrisF

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,316
  • What's my favourite cake!
  • Location: Warwick
Optimum prop shaft angle
« on: September 08, 2017, 06:09:53 pm »

The plans I have for various Fairey Marine boats were designed for IC engine use and I'm going to use brushless.


The angle of the prop shafts shown aren't too steep but I take it is better to get the angle as shallow as possible?


I have room to move the motor forward which will lesson the angle but appreciate that the size of the prop which needs to be accommodated will have a bearing.


What angle should I ideally be aiming for, around 10 or 12 degrees?


Chris
Logged
Building Fairey Marine boats: River Cruiser 23 prototype, Huntress 23 Long Cabin with stern-drive, Huntsman 28, Huntsman 31 and Swordsman 33 and two more to come! All scratch built and to a scale of 1:12

canabus

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,347
  • Boats a hole in the water you pour money into!!!
  • Location: Tasmania,Australia
Re: Optimum prop shaft angle
« Reply #1 on: September 10, 2017, 12:27:46 pm »

Hi Chris
I have a Precedent Huntsman which I removed the IC motor and driveline out of and replacing with a 35mm brushless motor, 60Amp ESC, 3S 5800mah Lipo battery and 40mm 2 blade prop.
This is the same setup for the Swordsman and works very well with good turn of speed and run time.

Canabus
Logged

ChrisF

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,316
  • What's my favourite cake!
  • Location: Warwick
Re: Optimum prop shaft angle
« Reply #2 on: September 10, 2017, 05:15:09 pm »


Thanks Canabus


Did you alter the angle of the prop shaft or leave as it was?


Chris
Logged
Building Fairey Marine boats: River Cruiser 23 prototype, Huntress 23 Long Cabin with stern-drive, Huntsman 28, Huntsman 31 and Swordsman 33 and two more to come! All scratch built and to a scale of 1:12

canabus

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,347
  • Boats a hole in the water you pour money into!!!
  • Location: Tasmania,Australia
Re: Optimum prop shaft angle
« Reply #3 on: September 11, 2017, 07:36:58 am »

Hi Chris

I changed the prop angle to 6 degrees and with a 45mm prop, 4mm clearance to the bottom of the boat.

Canabus
Logged

ChrisF

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,316
  • What's my favourite cake!
  • Location: Warwick
Re: Optimum prop shaft angle
« Reply #4 on: September 11, 2017, 09:48:01 am »


Thanks Canabus


That's a pretty low angle isn't it.


My drawing shows 12 degrees, which isn't bad, but I might reduce it a bit.


Chris
Logged
Building Fairey Marine boats: River Cruiser 23 prototype, Huntress 23 Long Cabin with stern-drive, Huntsman 28, Huntsman 31 and Swordsman 33 and two more to come! All scratch built and to a scale of 1:12

canabus

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,347
  • Boats a hole in the water you pour money into!!!
  • Location: Tasmania,Australia
Re: Optimum prop shaft angle
« Reply #5 on: September 11, 2017, 10:06:38 am »

Hi Chris

The plan is to run a 3648-1450kv, 60 Amp Hobbyking car ESC with a 2 blade 40mm prop.

I will see what it's like on 3S, but, I can up it to 4S.

I seen a MFA Spearfish on EBay cheap, these are a stable rocket with a brushless motor.

My mate has one, great in rough water!!!

Canabus
Logged

pompebled

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 588
  • Location: Sneek, Netherlands
Re: Optimum prop shaft angle
« Reply #6 on: September 15, 2017, 11:31:19 am »

My drawing shows 12 degrees, which isn't bad, but I might reduce it a bit.
Hi Chris,

Rule of thumb is not to exceed 7°, a steeper angle definately has an impact on the running attitude, specially if the prop is on the large side.

On my 110 cm M.A.S., the propshaft is 50 cm long, allowing a low angle, which is a good thing, as I'm running a Ø58 mm high pitched prop.
I'll put up a picture tonight when I'm home.

Regards, Jan.
Logged
Boaters are nice people

pompebled

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 588
  • Location: Sneek, Netherlands
Re: Optimum prop shaft angle
« Reply #7 on: September 18, 2017, 05:23:18 pm »

Hi Chris,

A bit later, but here are the pictures I promised...

Regards, Jan.
Logged
Boaters are nice people

dreadnought72

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,892
  • Wood butcher with ten thumbs
  • Location: Airdrie, Scotland
Re: Optimum prop shaft angle
« Reply #8 on: September 18, 2017, 08:24:24 pm »

The cosine is our mate here!

A 0° propshaft angle obviously puts out 100% of the prop power directly astern.

It's maybe a bit of a surprise, but a propshaft angle of eight degrees leads us to cosine(8°) = 99%. 18 degrees is over 95% efficient. Even a fairly absurd 25° propshaft angle is still over 90% efficient.

But by then, of course, the other 10% is spent trying to bury the bow.

Conclusion? Less is best, but I wouldn't be sweating over a couple of percent when that sort of loss is negligible compared to correct prop size, rpm/'cavitation', hull form, etc.

Andy
Logged
Enjoying every minute sailing W9465 Mertensia

pompebled

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 588
  • Location: Sneek, Netherlands
Re: Optimum prop shaft angle
« Reply #9 on: September 18, 2017, 09:33:43 pm »

Hi Andy,

Do these figures also apply on our models, where the water isn't scaled down and appears 'thicker'...?

In my experience with fast(ish) semi scale models, too steep a propangle makes the model uncontrolable when exceeding a certain speed making it impossible to get a stable running model at the desired topspeed.
In a model it is indeed 'the flatter the better'.

Regards, Jan.
Logged
Boaters are nice people

ChrisF

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,316
  • What's my favourite cake!
  • Location: Warwick
Re: Optimum prop shaft angle
« Reply #10 on: September 23, 2017, 02:34:56 pm »

Sorry for the delay in replying, been away for a few days in the sun.

Thanks for the information, will get it as low as I can but won't worry too much about it.

Chris
Logged
Building Fairey Marine boats: River Cruiser 23 prototype, Huntress 23 Long Cabin with stern-drive, Huntsman 28, Huntsman 31 and Swordsman 33 and two more to come! All scratch built and to a scale of 1:12
Pages: [1]   Go Up
 

Page created in 0.098 seconds with 21 queries.