Re: [Electric Boats] modification of the propeller

 

Balance will be a problem even with the use of CNC machinery. The problem is that all material has imperfections. Best prop design for a nozzle has clearance as close as you can so no rounded edges on the tip is standard. I would look into model airplane props and trim the ends to fit in nozzle. The props are cheap as props go and you can play with pitch till you find optimum.  Using a knife blade to balance the prop on will help you balance the prop after trimming is done. That is how vintage props were balanced.

Kevin Pemberton

On 06/09/2013 08:27 AM, Dimitrije wrote:

 

back in 2004 I made two types of cheap, small, homemade, trolling motors.
Small type used propeller Sevylor SMB 12V, diameter of 128mm and ~ 100W 24V/3600 RPM (no load) dc motor. At full speed dc motor pulling 6.5Amp. It was sucessful for 9 fit inflatabble canoe and one to 2 people. Then I made and bigger trolling motor, but since I could not find the propeller diameter or approximately 150mm, I used for the test propeller (Mercury 2 HP) of 178mm. With this prop this dc motor, 24V (3000 RPM, no load) is on test gave a strong thrust (pushing a rigid 12 fit boat with 3 people), but the engine pulled too much power, about 30Amp, and I must finished test after 3 minutes .
  Now I would like to finished the bigger type trolling motor, so I decreased propeller diameter to 155mm. The question is whether it is necessary to profiled wings ends ? (It's expensive to work on a CNC milling machine, but if processed wings manually, I'm afraid it will get imbalance).
I want made nozzle tube around the propeller, with an internal diameter about 165 to 170mm; whether anyone has experience with that?
best regards
first ~100w trolling motor 18V/24V on Sevylor canoe ...2004
http://imageshack.us/a/img43/6905/canoetrollmotjpgw180h18.jpg

second ~200w trolling motor, (not in use) ... tested 2006
http://imageshack.us/a/img542/9368/200wtroll.jpg
propellers, sevylor 128mm dia, mercury 178mm and reduced mercury propeller (155mm)
http://imageshack.us/a/img196/3476/propsj.jpg

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