Re: [Electric Boats] Trolling Motor Question

 

Denny,

We are taking delivery in the next ten days or so on a new 16'4" Stuart Reid designed "Piwakawaka." http://www.jwboatdesigns.co.nz/plans/piwakawaka/index.htm With batteries and motor (but without passengers), it should weigh in just over 300 lbs. Instead of the inboard shown on the plans, we have had a fiberglass tube build into where the rudder post would normally go. The tube has an ID of 1.25" to allow the MK Endura (or a larger Endura if we decide we need it) to fit in it and rotate. The MK will have the shaft cut off and a wooden tiller attached to the head of the shaft, so, in the water, it will look like the original plans (but without the steam stack). We will steer with the tiller turning the MK. This should open up the floor of this fairly small launch, be quieter, and allow a bit more manuverability.

We are installing a 30 MK Endura powered by two 12v AGM Series 31 batteries in series with a 24v controller. My calculations suggest that we will need, on a dead calm lake with no wind early in the morning, a 8" pitch prop to move the boat at hull speed at 1200 rpm. (I am anticipating being able to run the motor at 1400 or more rpm with the 24v and stay under 30 amps.) My hp calculations with my wife and me aboard also suggest that we should get the necessary hp to reach hull spead in those ideal conditions.

After reading your posts on this and other sites, I bought a number of the airplane props (9" and 10" with 6", 7" and 8" pitches), but I wonder if the blade area will be too small for the boat if we need to move through some tide or wind. I am also considering the new Torqeedo two-blade kayak prop (8" x 8"). The Torqeedo kayak prop is designed for the Torqeedo motor turning at 1200 rpm, which is the rpm that I am hoping to get at just under 30 amps. I would appreciate any thoughts you or anyone else might have on whether we should worry about not having enough blade area with those airplane props for this little boat. The airplane props just don't look like boat props.

Greg

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