the better choice is larger than the original prop. square prop most likely would be most efficient (14x14 as an example of square). What you are after is least slip, translation better efficiency. the slower the prop turns the less friction in the water. Design considerations for slower RPM larger prop, include larger prop shaft to handle the torque. Many have found a gear reduction produces higher efficiency. This may be due to locked rotor conditions at low RPM, that is my guess. Just because a prop will fit in the hole is not all that has to be considered, clearance is a must. prop wash can become a problem without enough clearance..
back to the subject on this thread.
no one I know of has found regen to be worth the effort in any way. Folding props are only good to reduce drag when not motoring, same with feathering props. Efficiency is not that great, but 2 blade is most efficient as far as blade design is concerned. In and out of port and setting anchor does not require efficiency. If you sail and want the same power generation under way you will likely find 1hr of genset running will equal your 24 hr of regen without the drag. Daytime solar from a solar canopy over the cockpit will produce more power. At anchor regen with high tidal current will produce fairly well but a folding prop will likely fold. Another issue that may come up in high currents trying to regen is anchor drag.
As a FYI, small drive controllers without regen can be obtained with small hp motors, brush-less and brushed as kits for e-bikes. for canoes this is a great option for 1 hp to maybe 2hp applications.
Kevin
On Thu, Jun 6, 2019 at 6:50 PM elcapitanbrown@gmail.com [electricboats] <electricboats@yahoogroups.com> wrote:
From what I've been told the gear reduction is the better option to retain a typical diesel prop and that it gives you a more likely case to keep the one you already have. It allows the motor to spin faster, since its top speed is 5k rpm, while delivering half that speed to the prop which was designed to have its top speed around 2500 rpm or at least cruising speed there. That's my understanding of it.
Can anyone confirm this is accurate and does anyone here use their motor without the gear reduction and simply avoid pushing the motor higher than the 2500 rpm the prop works best at?Also, is there any efficiency gains by running the motor at the slower rpm vs the higher rpm with the gear reduction?Lastly, I also read that without a gear reduction you need a linkage of some kind that will help reduce the torque load the motor produces. So going without the gear reduction there is probably another component you will need.Just my 2 cents and really interested to see if I got it right and learn something with you.
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Posted by: Kevin Pemberton <pembertonkevin@gmail.com>
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