John Blazy
10-26-2004, 12:23 AM
It just dawned on me to share what I think is a valuable development in propulsion systems for small boats.
Obviously, many want the romance of sail power, or many like to plane, but for those considering clean (green), silent, initial low-cost, and extremely low fuel cost propulsion, I seemed to stumble upon a fairly radical bridge between the low end of trolling motors and the high-cost of permanent magnet, primary power electric drive systems - using aftermarket parts on high-power trolling motors.
Based on a couple years of research, I've discovered that there is a great chasm in the electric primary power propulsion world - the chasm between super cheap trolling motors (less than 500-600 bucks) and the permanent magnet motors (2 grand and wayy way up to 6 grand).
The great thing about trolling motors - thanks to all the bass fishermen out there - is that they are cheap, easy to get, and very reliable.
The problem with the trolling motor is that the props are all low pitch (4")- designed to push a heavy boat with quick response, kindof like driving in first gear only. So for primary drive, or auxiliary power, many simply shoot for the Briggs E-tek or its equivalants and pay through the nose for fittings (+labor), or complete systems like Ray electric outboards, and consequently , many electric drive dreams are dashed and never get on the water. The E-boat forum is full of posts on both extremes - cheap drives for very small boats, or very complicated drives for pretty much anything larger.
This has been solved, thanks to a couple guys on the e-boat forum, and kort nozzle fabrication (a thrust enhancing, flow maximizing, power-reducing "hoop" that fits around a prop). One guy suggested using the stainless steel E-drive prop (6-3/4" pitch) from the Minn Kota E-drive motor (a new, MK motor for constant use on pontoon boats, but close to three grand) and fitting it onto the lower cost, 36 V, 101 lb thrust MK Riptide.
He ran two 101's in tandem, which didn't torque each motor that much, which is why he got away with it without burning out the motors (I tried the E-drive prop on one motor only, and the prop way over-torqued the motor, resulting in a shrill schreeching sound - but considerably faster :D ).
I decided to put the stainless E-drive prop on my 24V 65 lb MK Maxxum, and used a kort nozzle to decrease the torque on the motor (no schreeching :cool: ). I now easily get the equivalent of over 100 lbs of thrust with the new prop, and hit hull speed at less than full power for a 14 foot boat.
Extrapolating from this experience, less than a grand (101 lb thrust motor with E-drive prop + nozzle) will easily power a 20 - 25 footer with the same performance that three to six grand got you before with the higher power perm. magnet motors. And a lot less hassle - way easier through-hull fittings if you choose, or you can simply transom mount.
So in conclusion, this info might be valuable to those considering building a small to medium displacement hull boat and don't want to foot the cost of rigging for sail, or simply want the quiet whisper drive. Or want auxiliary power for their sailboat.
In my electric drive boat, I can go close to hull speed (6-8 knots) for about 1-1/2 hours constant throttle on each battery bank (two banks of two 105 Amp/hr deep cycle marine batts) to the point of 50% depth of discharge. Or three hrs round trip, covering ten to twelve miles total (yes, I check the maps with a compass after each trip). In reality, without constant throttle, most of my summer boating trips have been 5-7 hrs on the water, and only a few times did I dip into my second battery bank (one bank on Port side, and one on Starboard).
The catch to all this, is that one must fabricate a kort nozzle. Do a search on kort nozzles, and you'll find lots of info, or I'll explain further. I may make a mold from mine and cast a few someday.
I'm a little biased, of course, but open to issues
http://www.imagestation.com/picture/sraid144/p8b235bfb5da08e165457d85b3e538087/f6807950.jpg
Obviously, many want the romance of sail power, or many like to plane, but for those considering clean (green), silent, initial low-cost, and extremely low fuel cost propulsion, I seemed to stumble upon a fairly radical bridge between the low end of trolling motors and the high-cost of permanent magnet, primary power electric drive systems - using aftermarket parts on high-power trolling motors.
Based on a couple years of research, I've discovered that there is a great chasm in the electric primary power propulsion world - the chasm between super cheap trolling motors (less than 500-600 bucks) and the permanent magnet motors (2 grand and wayy way up to 6 grand).
The great thing about trolling motors - thanks to all the bass fishermen out there - is that they are cheap, easy to get, and very reliable.
The problem with the trolling motor is that the props are all low pitch (4")- designed to push a heavy boat with quick response, kindof like driving in first gear only. So for primary drive, or auxiliary power, many simply shoot for the Briggs E-tek or its equivalants and pay through the nose for fittings (+labor), or complete systems like Ray electric outboards, and consequently , many electric drive dreams are dashed and never get on the water. The E-boat forum is full of posts on both extremes - cheap drives for very small boats, or very complicated drives for pretty much anything larger.
This has been solved, thanks to a couple guys on the e-boat forum, and kort nozzle fabrication (a thrust enhancing, flow maximizing, power-reducing "hoop" that fits around a prop). One guy suggested using the stainless steel E-drive prop (6-3/4" pitch) from the Minn Kota E-drive motor (a new, MK motor for constant use on pontoon boats, but close to three grand) and fitting it onto the lower cost, 36 V, 101 lb thrust MK Riptide.
He ran two 101's in tandem, which didn't torque each motor that much, which is why he got away with it without burning out the motors (I tried the E-drive prop on one motor only, and the prop way over-torqued the motor, resulting in a shrill schreeching sound - but considerably faster :D ).
I decided to put the stainless E-drive prop on my 24V 65 lb MK Maxxum, and used a kort nozzle to decrease the torque on the motor (no schreeching :cool: ). I now easily get the equivalent of over 100 lbs of thrust with the new prop, and hit hull speed at less than full power for a 14 foot boat.
Extrapolating from this experience, less than a grand (101 lb thrust motor with E-drive prop + nozzle) will easily power a 20 - 25 footer with the same performance that three to six grand got you before with the higher power perm. magnet motors. And a lot less hassle - way easier through-hull fittings if you choose, or you can simply transom mount.
So in conclusion, this info might be valuable to those considering building a small to medium displacement hull boat and don't want to foot the cost of rigging for sail, or simply want the quiet whisper drive. Or want auxiliary power for their sailboat.
In my electric drive boat, I can go close to hull speed (6-8 knots) for about 1-1/2 hours constant throttle on each battery bank (two banks of two 105 Amp/hr deep cycle marine batts) to the point of 50% depth of discharge. Or three hrs round trip, covering ten to twelve miles total (yes, I check the maps with a compass after each trip). In reality, without constant throttle, most of my summer boating trips have been 5-7 hrs on the water, and only a few times did I dip into my second battery bank (one bank on Port side, and one on Starboard).
The catch to all this, is that one must fabricate a kort nozzle. Do a search on kort nozzles, and you'll find lots of info, or I'll explain further. I may make a mold from mine and cast a few someday.
I'm a little biased, of course, but open to issues
http://www.imagestation.com/picture/sraid144/p8b235bfb5da08e165457d85b3e538087/f6807950.jpg