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Prop torque question
On Fri, 30 Oct 2009 17:13:13 -0500, cavelamb
wrote: Joe wrote: I'm hoping someone might have a refference site for free wheeling prop torque produced by a prop around the size of a 20X20 sailing at hull speed. (9kts) One goal on the boat we are designing and building will be an electric drive system and we are leaning towards a power phase 150 drive. http://www.uqm.com/propulsion_specs.php It's a 200 HP perm magnet motor, so as you sail and the prop turns it will generate power for the battery banks. These motors are now being used in electric hummers in the Army. They need 420 volt DC using two banks of batterys (35 batteries each bank) and will require 75 LBS or torque to generate electricity. Now I'm pretty sure the torque on a prop around the 22" size will be way over 75 lbs but do not know exactly. Im hoping it's twice that at least for gear reduction. So I'm hoping someone might have, or know where I can get data on prop torque. If not.... I guess I'm going to have to get a monkey wrench and a scale and find a boat of the proper size to test. Any suggestions? Joe As a starting point, it will probably make about the same amount of torque as it uses under power - for the same prop rpm. Probably a good starting place. I've seen at least one 40 ft. sailboat with an auto alternator belted to the prop shaft, the theory was that one could generator electricity while sailing. Another point is that there isn't a free lunch and I suspect that the force necessary to turn a propeller generating X amount of power has to come from somewhere. Probably in drag on the boat which will have to be overcome by larger sails. By the way, the statement "will require 75 LBS or torque to generate electricity" is quite simply wrong as RPM of the generator also enters into the equation. First because torque is not measured in pounds, it is measured in force at some specified arm length - Foot Pounds, Inch Ounces, etc. Secondly because movement of the electrical generating fields is required. The specification should have been some amount of horsepower, which is really another way to specify speed and torque. Cheers, Bruce (bruceinbangkokatgmaildotcom) |
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