Saturday, February 20, 2010

Re: [Electric Boats] Trolling Motor Question

 

Denny,


In regards propeller efficiency, I have at least one reference that says that the choice of number of blades is dependent on rpm. Let me quote from Delta Propeller http://www.deltaprop.com :

Q. Shall I use 2-, 3-, 4-, or 5-blade propellers?
A. Excessive horsepower, direct drive and high advanced speeds indicate that propellers of high pitch-diameter ratio be employed.Generally 2-blade propellers are used. At somewhat lower advanced speeds and shaft speeds, 3-blade propellers with pitch-diameter ratios of approximately 1.0 are required for best propeller efficiency. It is in this category that most pleasure boas lie. At even lower advanced speeds and shaft speeds, 4-blade propellers with pitch-diameter ratios of .8 or less are required for optimum propeller efficiency. On large cruisers and commercial applications such as trawlers, shrimpers, tugs and work boats, 4 blades are generally used. If excessive vibration is a problem, 5-blade propellers are used.

Some of the electric motors operate in the 1000 rpm range which is half to a third of diesels and might indicate a three or four blade for max. efficiency. Torqeedo runs at about a 1000 rpm and uses three blades.

Ned


On Feb 20, 2010, at 2:23 PM, dennis wolfe wrote:

 



The more blades, the less efficient.  2 and 3 blade designs are the best compromise between strength, diameter and efficiency.  The desire for small diameter leads to larger number of blades.  If you are OK with the diameter of a 2 blade prop that loads your motor properly that is the best option.
 
Denny
 
 
----- Original Message -----
Sent: Friday, February 19, 2010 11:00 PM
Subject: RE: [Electric Boats] Trolling Motor Question

 

Denny –

Thanks for the input.  I didn't think about the thrust bearings if I ran it in Tractor mode for prolonged periods.  Once the water gets back to liquid form, I'll bolt on the prop and let you know how it all works. 

Can anyone tell me about area of the prop & aspect ratio.  How would say a 6 blade prop (two three-blades) compare to the standard trolling prop?

Kevin

From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of dennis wolfe
Sent: Friday, February 19, 2010 9:02 AM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Trolling Motor Question

 



Kevin,

He has a reverse pitch prop so needs to run the motor backwards to produce thrust in the originally intended direction.  The motors are designed to take reverse thrust for some time but I agree it's better to use it as a pusher, as the designers intended.

Denny

----- Original Message -----

Sent: Thursday, February 18, 2010 5:01 PM

Subject: Re: [Electric Boats] Trolling Motor Question

 

I would like to say yes, but.
If the thrust bearing fails to support in reverse, the long term failure
will be high. I would have to see the engineering drawing for the motor
in question before I would be quick to answer yes. Reversing the leads
will make the motor run in reverse but there is more to the question.

Kevin
>
>
>
>
> From: dwolfe@dropsheet.com <dwolfe@dropsheet.com>
> Subject: Re: [Electric Boats] Trolling Motor Question
> To: electricboats@yahoogroups.com
> Date: Thursday, February 18, 2010, 3:22 AM
>
>
> Yes, you just switch the leads to reverse rotation. Put the prop
> on backwards so the "airfoil" is oriented the right way. BTW, APC
> has a 10x6 pusher design.
> Denny Wolfe
>




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