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#11
posted to rec.boats.cruising
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Prop torque question
On Fri, 30 Oct 2009 10:36:32 -0700 (PDT), 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? That drag just seems counterproductive to moving along. Since you're designing a new boat, maybe solar arrays and wind generators charging those batteries would work better. The cost reduction of using simple electric propulsion might offset some of the solar and wind generator costs. The generating screw is an elegant idea, but that drag? Just don't seem right. --Vic |
#12
posted to rec.boats.cruising
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Prop torque question
Joe wrote:
On Oct 30, 7:12 pm, Bruce wrote: 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. Hello Bruce, Did you check out the spec sheet? And you are right, drag will be produced but overcomed by larger sails. You have seen alt drives on shafts ect this is the same deal except this generator is a state of the art high temp NdFeB permanent magnet motor generator. Might need a big ass variable pitch prop to max the input but overcoming it's drag with canvas can be done. The pitch required for driving the boat verse driving the generator are nearly identical opposites. A variable pitch prop - providing it can "feather" (or turn to zero pitch relative to the free stream) would indeed be better. Answering Cavelamb the motor produces 475 lbs of torque at full power. After strapping down a few shafts on crewboats, I know damn well a 32X32 will produce well over 475 lbs torque at the end of a 36 " monkey with little speed. That's full power, though, and way higher RPM than the prop will turn the shaft when not under power. If possible, drag the prop and not the RPM. Then refer to the engine's documentation (hopefully) to read how much power the engine WOULD BE producing at that RPM. You have me thinking that a cool setup would be an "outboard generator". A modified long shaft outboard leg, with the correct pitch prop installed and a big alternator in place of the motor... |
#13
posted to rec.boats.cruising
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Prop torque question
cavelamb wrote:
The pitch required for driving the boat verse driving the generator are nearly identical opposites. A variable pitch prop - providing it can "feather" (or turn to zero pitch relative to the free stream) would indeed be better. Answering Cavelamb the motor produces 475 lbs of torque at full power. After strapping down a few shafts on crewboats, I know damn well a 32X32 will produce well over 475 lbs torque at the end of a 36 " monkey with little speed. That's full power, though, and way higher RPM than the prop will turn the shaft when not under power. If possible, drag the prop and *NOTE* the RPM. Then refer to the engine's documentation (hopefully) to read how much power the engine WOULD BE producing at that RPM. |
#14
posted to rec.boats.cruising
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Prop torque question
On Fri, 30 Oct 2009 22:41:50 -0500, cavelamb
wrote: Joe wrote: On Oct 30, 7:12 pm, Bruce wrote: 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. Hello Bruce, Did you check out the spec sheet? Yes And you are right, drag will be produced but overcomed by larger sails. You have seen alt drives on shafts ect this is the same deal except this generator is a state of the art high temp NdFeB permanent magnet motor generator. Might need a big ass variable pitch prop to max the input but overcoming it's drag with canvas can be done. The type of fields is really immaterial other then that permanent magnet fields do not require exciting current and are therefore more efficient, within limits. To run your motor at maximum torque output you will need to run it at about 1,000. If you design a fixed pitch prop for that RPM then you have no flexibility as the torque required to turn it at a higher RPM would be more then your motor can provide at increased RPM.Thus as you say, you will need a variable pitch propeller. However, as the motor provided maximum torque at low RPM (max at stalled speed) you have to design for some intermediate RPM. and I'm not too shore how efficient this is going to be as normal propeller design is that a large diameter prop with low pitch produces high pulling forces and lower speeds while a smaller diameter and higher pitch produces high speed but lower bollard pull. This is not necessarily reason to scrap the idea rather you will need to look into propeller RPMs versus Torque and probably end up using only part of the total range. From the chart you appear to be able to get between 400 and 350 Nm torque (296 - 260 Ft. Lbs.) in a range of 1,000 - 3,000 rpm, or about 56 HP to 148 HP. However, to actually generator that torque you are going to have to use a really high pitch at low RPM, or have an over large diameter prop at high speed. I suggest that you probably will never actually generate maximum torque. even with a variable propeller. According to the chart you will generate about 40 KW at 1,700 RPM and 120 KW at 3,000 RPM which is 53 HP to 160 HP of input power. It would appear that there is going to be considerable drag created here. I have use "rule of thumb" for these calcs as they are only intended to show approximate values but they do show the general conditions that you will be operating under. The pitch required for driving the boat verse driving the generator are nearly identical opposites. A variable pitch prop - providing it can "feather" (or turn to zero pitch relative to the free stream) would indeed be better. Answering Cavelamb the motor produces 475 lbs of torque at full power. After strapping down a few shafts on crewboats, I know damn well a 32X32 will produce well over 475 lbs torque at the end of a 36 " monkey with little speed. That's full power, though, and way higher RPM than the prop will turn the shaft when not under power. If possible, drag the prop and not the RPM. Then refer to the engine's documentation (hopefully) to read how much power the engine WOULD BE producing at that RPM. You have me thinking that a cool setup would be an "outboard generator". A modified long shaft outboard leg, with the correct pitch prop installed and a big alternator in place of the motor... Again Cavelamb, sorry to high jack your post but I never saw his original reply. Cheers, Bruce (bruceinbangkokatgmaildotcom) |
#15
posted to rec.boats.cruising
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Prop torque question
Joe wrote:
I'm hoping someone might have a reference site for free wheeling prop torque produced by a prop around the size of a 20X20 sailing at hull speed. (9kts) It's a 200 HP perm magnet motor... 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. A SWAG for you: the MOST efficient a fluid mill gets, is to extract the kinetic energy represented by halving the fluid's speed. The energy in question is given by prop area (diam 20 inches) and effective speed 4.5 kts. Now: reduce the units to easy SI units: 4.5 kts = 2.3 m/s diameter of water column: 20 ins = 0.51 m volume of water/sec = 2.3 X pi X 0.51^2 / 4 = 0.47 cu meters density of water 1050 kg /m^3 (for salt water say...) Mass flow rate: 0.47 X 1050 kg/sec = 489 kg/sec Force times speed = power So power = 489 kg/sec X 9.8 N/kg = 4797 watts. Let's suppose 50% transfer efficiency and we end up with 2.4 kW to play with, at hull speed. Finding a prop speed 10 % less than the no slip speed of a 20 /20 prop, and knowing the available power from above, leads easily to the torque available... Brian W |
#16
posted to rec.boats.cruising
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Prop torque question
cavelamb wrote:
You have me thinking that a cool setup would be an "outboard generator". A modified long shaft outboard leg, with the correct pitch prop installed and a big alternator in place of the motor... That's called a trolling motor! Brian W |
#17
posted to rec.boats.cruising
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Prop torque question
brian whatcott wrote:
cavelamb wrote: You have me thinking that a cool setup would be an "outboard generator". A modified long shaft outboard leg, with the correct pitch prop installed and a big alternator in place of the motor... That's called a trolling motor! Brian W Wrong prop pitch |
#18
posted to rec.boats.cruising
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Prop torque question
On Oct 31, 3:08*pm, cavelamb wrote:
brian whatcott wrote: cavelamb wrote: You have me thinking that a cool setup would be an "outboard generator". A modified long shaft outboard leg, with the correct pitch prop installed and a big alternator in place of the motor... That's called a trolling motor! Brian W Wrong prop pitch you would do better building a tow generator. Get a 5 ft long stainless bar that will fit a low pitch prop at the trailing end. The bar has a ring to tie to a towing line. That line is attached to an perm. magnet motor/generator. One of the best sources for a cheap perm magnet motor is in old reel to reel recorders. Or just buy one off the shelf. http://www.onpassage.com/Alternative...generators.htm Joe |
#19
posted to rec.boats.cruising
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Prop torque question
"Joe" wrote in message
... you would do better building a tow generator. Get a 5 ft long stainless bar that will fit a low pitch prop at the trailing end. The bar has a ring to tie to a towing line. That line is attached to an perm. magnet motor/generator. One of the best sources for a cheap perm magnet motor is in old reel to reel recorders. Or just buy one off the shelf. http://www.onpassage.com/Alternative...generators.htm Joe Or get the hybrid d400 and have the best of both worlds - water towed, and wind generator.... No, I've never seen one or had any direct feedback about its use. Just an interesting concept... L8R Skip -- Morgan 461 #2 SV Flying Pig KI4MPC See our galleries at www.justpickone.org/skip/gallery ! Follow us at http://groups.yahoo.com/group/TheFlyingPigLog and/or http://groups.google.com/group/flyingpiglog "You are never given a wish without also being given the power to make it come true. You may have to work for it however." (and) "There is no such thing as a problem without a gift for you in its hand (Richard Bach) |
#20
posted to rec.boats.cruising
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Prop torque question
On Oct 31, 12:10*pm, brian whatcott wrote:
Joe wrote: I'm hoping someone might have a reference site for free wheeling prop torque produced by a prop around the size of a 20X20 sailing at hull speed. (9kts) It's a 200 HP perm magnet motor... 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. A SWAG for you: the MOST efficient a fluid mill gets, is to extract the kinetic energy represented by halving the fluid's speed. The energy in question is given by prop area (diam 20 inches) and effective speed 4.5 kts. Now: reduce the units to easy SI units: 4.5 kts *= 2.3 m/s diameter of water column: 20 ins = 0.51 m volume of water/sec = 2.3 X pi X 0.51^2 / 4 = 0.47 cu meters density of water *1050 kg /m^3 (for *salt water say...) Mass flow rate: 0.47 X 1050 kg/sec = 489 kg/sec Force times speed = power So power = 489 kg/sec X 9.8 N/kg = 4797 watts. Let's suppose 50% transfer efficiency and we end up with 2.4 kW to play with, at hull speed. Finding a prop speed 10 % less than the no slip speed of a 20 /20 prop, and knowing the available power from above, leads easily to the torque available... Brian W Thanks Brian, I can use this data and go back to the company and talk to an applications engineer. Joe |
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