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Electric drive for Sailboats
http://members.cox.net/sholley1/electric.htm
"A few years back I was impressed when I saw a "dock maintainance barge" tooling around the cove in our Marina under the power of a little 12 volt trolling motor. It was small, old, but the persistance of the little thing moved the barge around quite well. I proceeded down to my boat, and embarked on the following procedure to go sailing." "NOTE: There is no neat formula or correlation between thrust and horsepower. However, I read a comparison that measured a 6 hp gas outboard produced just over 130 lbs of thrust, so that would class the 107 Motorguide in the realm of a 5 hp gas (give or take a little). Thats not a lot of power, but ample for my needs. I don't know how I'd fare towing in another boat, but I'll include towing in "tests to come"." http://www.geocities.com/Yosemite/Fo..._outboard.html Auxilliary Power Requirements with Electricity "A typical trolling motor is designed to push a displacement hull at a maximum of about 2 to 3 miles per hour. Therefore, I determined to use the highest thrust 12 volt electric trolling motor that I could purchase and see where that would lead. In this case, a Motorguide model T47 motor with a 36 inch shaft length was commonly available at the local Kmart stores. This motor draws about 50 amps at maximum speed and is rated to produce 47 pounds of thrust. Replacing the propeller with a two blade (power) design from the three blade (weed free design) included with the motor should result in the required combination of low shaft speed and high thrust. This motor, combined with a bank of two new fully charged group 27 deep cycle batteries, could operate at maximum thrust for about 2.5 hours. In theory, the calculations said that this combination would propel my Com-Pac at just under three knots. This would meet my stated goal of a 5 mile range under power with some safety margin." |
For whatever it is worth to you, I can drive my 16 ft sailing skiff at 3.6
mph using an Endura 30 drawing 30 amps. BS "Mic" wrote in message ... http://members.cox.net/sholley1/electric.htm "A few years back I was impressed when I saw a "dock maintainance barge" tooling around the cove in our Marina under the power of a little 12 volt trolling motor. It was small, old, but the persistance of the little thing moved the barge around quite well. I proceeded down to my boat, and embarked on the following procedure to go sailing." "NOTE: There is no neat formula or correlation between thrust and horsepower. However, I read a comparison that measured a 6 hp gas outboard produced just over 130 lbs of thrust, so that would class the 107 Motorguide in the realm of a 5 hp gas (give or take a little). Thats not a lot of power, but ample for my needs. I don't know how I'd fare towing in another boat, but I'll include towing in "tests to come"." http://www.geocities.com/Yosemite/Fo..._outboard.html Auxilliary Power Requirements with Electricity "A typical trolling motor is designed to push a displacement hull at a maximum of about 2 to 3 miles per hour. Therefore, I determined to use the highest thrust 12 volt electric trolling motor that I could purchase and see where that would lead. In this case, a Motorguide model T47 motor with a 36 inch shaft length was commonly available at the local Kmart stores. This motor draws about 50 amps at maximum speed and is rated to produce 47 pounds of thrust. Replacing the propeller with a two blade (power) design from the three blade (weed free design) included with the motor should result in the required combination of low shaft speed and high thrust. This motor, combined with a bank of two new fully charged group 27 deep cycle batteries, could operate at maximum thrust for about 2.5 hours. In theory, the calculations said that this combination would propel my Com-Pac at just under three knots. This would meet my stated goal of a 5 mile range under power with some safety margin." |
On Mon, 30 May 2005 04:07:00 -0400, tedwilliams wrote:
On Sun, 29 May 2005 21:32:39 GMT, skddjl (Mic) wrote: /// "NOTE: There is no neat formula or correlation between thrust and horsepower./// There is in fact a formula which relates thrust to horse-power and water speed. Simply put: thrust in lb. = ( power in watts / speed through water in MPH ) X 0.1 scaling constant Example: 1/2 HP = 373 watts, water speed 1 MPH thrust = 373watts /1 mph X 0.1 = 37 lbs water speed 2 MPH: thrust = 373watts / 2 mph X 0.1 = 18 lb thrust Notice that the big unknown is the water speed. Even if a boat is anchored, the propeller will push water at 1 mph or 2 mph depending on its size, pitch etc. You can take 1 mph as a lower limit - usually higher. This is higher than the other unmentioned losses - motor efficiency 90%? prop efficiency 80%?? Brian Whatcott Altus OK |
Ted wrote: Hmmm, the math is pretty simple. We measure the output power of motors or engines in Hp. 1 Hp = 746 watts. 5 Hp = 3730 watts. To produce 5 Hp at 12 volts would require 310.8 amps. (Assuming no IR, friction, and windage losses) That requires some pretty heavy duty wiring. I doubt that I could lift a true 5 Hp 12 volt motor. Ted, See http://www.electricmotorsport.com/PA...pecs.htm#Page5 This motor (ETEK) is capable of 9HP continuous, and only weighs 21 lbs. Of course, it only puts out about 2HP max at 12V, but you can get over 9HP at 48V. You are right about the amp draw at 12V of course. I remember reading in a recent "cruising world" about a new production day sailer in the 36-40ft range that relies on electric propulsion and a genset to charge the rather large battery bank. For a day sailer that is typically connected to dock power every night, electric seems like an interesting way to go. A genset and a large house battery bank are pretty nice things to have on a sailboat anyway, and you have eliminated a bulky and heavy diesel inboard that is only good for propulsion and charging batteries. If you start google searching you'll find that there is a lot of interest in hybrid/electric conversions for autos and boats. There is a lot of info available and quite a few people experimenting. Now if we could only get someone to produce a 2,400 lb keel which was also a huge battery bank (sigh). Either that, or a really affordable large fuel cell (sigh again). YMMV Don W. (Who is toying with the idea of converting a Catalina 27 to electric and getting rid of the 9.9HP Yamaha 4-stroke) |
On Mon, 30 May 2005 11:49:12 -0400, ted williams wrote:
[bw] There is in fact a formula which relates thrust to horse-power and water speed. Simply put: thrust in lb. = ( power in watts / speed through water in MPH ) X 0.1 scaling constant [tw] You are 100% correct in the theoretical thrust relative to speed. /// Using your example, at a thrust which produces 37 lbs at 1 MPH could be easily overcome by a modest breeze against the surface of the vessel that produced more than the 37 lbs of force provided by the motor. If the net effect of the breeze against the vessel surface produced 74 lbs, the vessel would travel backward at 1 MPH. Regards, Ted Hmmmm... the formula gives a value for thrust, given some water speed and input power. What it DOESN'T give, is a value for boat speed given thrust at a given input power. That would need knowledge of air drag and hull drag which do not enter here. However, if you could find the drag at given hull speeds, e.g by towing the hull and measuring the force required, THEN you could say how much thrust would be needed ( = drag) at that speed and hence what power would be needed at that speed, ignoring the losses I mentioned earlier. Sincerely Brian Whatcott |
snip I had a look at the page and found a few odd things. The math for a motor has not changed since they were invented. Only the efficiency in which they convert input power to mechanical energy has improved. Take a look at the 24 volt motor shown on: http://www.electricmotorsport.com/PA...pecs.htm#Page5 Motor output is 15Hp max and 8 Hp continuous. Well, this is *not* a 24V motor. It can be operated on 24VDC, but will not reach its maximum rated output. It is a 50VDC motor, look at the specifications box. To get 15 Hp at 24 vdc assuming no losses, you would need 466.25 amps. The motor is rated at a maximum motor current of 330 amps for 60 sec. You might get the equivalent of 15 Hp for 5 seconds before it was toasted. 8 Hp would require 248.67 amps continuous at 24 vdc. brush life for that current rating isn't given. What would it be? I don't know, maybe 24 hours or less. It appears that brush life drops exponentially with current Take another look at the page. The charts are for the same 50VDC motor operated at three different voltages. The charts basically give you the performance characteristics at the stated voltage - you can't extrapolate from them. The chart looks correct as it takes into account the losses in motor efficiency. But the chart does not jive with the text below it. Notice the chart only shows up to a tad over 4 Hp for a motor that the text below the chart clearly states 15 Hp max, 8 Hp continuous. The motor is rated for 150A continous. At 48VDC, that's 8HP at about 3100 RPM. That 150A continuous input would net you 4HP at about 1350 RPM. Half the voltage, half the VA, half the horsepower. The 48 vdc motor is similar. A claimed maximum Hp of 15 Hp which would require only 233 amps within the stated rating of the current limit for the motor but think about the brush life, it is off the chart. When you look at the chart, again it appears that brush life drops exponentially with current. 8 Hp would require 124.3 amps. Still lots of amps. Per the chart, it requires 150A. You're right, that's a lot! Keith Hughes |
Ted,
There was another page somewhere with brush life vs input current. Its basically an inverse exponential, which is why the motor is rated at 9HP at 50V. It is capable of putting out higher power outputs, or of putting out 9HP at a lower voltage, but the brush life drops dramatically at the higher currents. Looking at the 48V chart, it appears that the motor makes 9HP at about 155A. Now looking at the bottom of the chart is says that the brush life at 150A continuous is 500 hours. Now if we drop back to 5HP at 48V, we need about 90A. The chart says that the brush life at 100A continuous is 2000 hours. That is about the same as the TBO of a gasoline engine. Another interesting feature of this motor is that the brushes are removable as snap out unit, and can be changed in about a minute according to the literature. A Yamaha 9.9hp is capable of making about ten HP on the max throttle setting, but I almost never run it wide open because it makes too much noise, and things start vibrating. Also, the higher power settings just result in the nose of the boat rising further in the air, and the outboard trying to bury itself in the water with an increase of only a knot or so. I'd bet that the average power setting is more like 4-5HP. So, for a _day_ sailer, with 15 minutes of motoring to get out of the slip, and another 15 minutes of motoring to put it away, it appears you would need about 45AH at 48V, (180AH of 12V), X 3 for battery life, or 4 ~120AH batteries. As you noted that is a BIG house bank. Also, as you noted, you are discharging them at a pretty fast rate during the discharge cycle. However, if you have a DC genset that is capable of producing 3-5KW, you can start the genset, and use it to power the motor continuously. Also, with that big house bank, and a 3-5KW inverter you can have some pretty snazzy AC appliances on the boat meaning that you can do away with the alcohol stove, and power a microwave and an AC fridge. If you run the genset, you can probably even power a small AC unit some of the time. Oh, and another nice feature is that the motor can be driven as a generator by the prop while you are sailing, although you may need a pretty fancy switcher circuit to take advantage of the variable voltage. Of course, all of this is going to weigh more than a 99Lb outboard, but you hever get something for nothing. Just thinking online, Don W. Ted wrote: On Mon, 30 May 2005 15:35:59 -0700, Keith Hughes wrote: To get 15 Hp at 24 vdc assuming no losses, you would need 466.25 amps. The motor is rated at a maximum motor current of 330 amps for 60 sec. You might get the equivalent of 15 Hp for 5 seconds before it was toasted. 8 Hp would require 248.67 amps continuous at 24 vdc. brush life for that current rating isn't given. What would it be? I don't know, maybe 24 hours or less. It appears that brush life drops exponentially with current Take another look at the page. The charts are for the same 50VDC motor operated at three different voltages. The charts basically give you the performance characteristics at the stated voltage - you can't extrapolate from them. Ahhh, thanks. What threw me were the same Hp readings for all 3. I thought I was looking at 3 different motors. Normally, when a motor specification is given (such as for say an MD408), it is given ratings at 250 VDC. I thought I was looking at 3 motor specs. I only gave it a quick look and assumed it would was like all the other motor specs I have read but for different motors. Didn't realize it was the same motor. The article was a far different method of presenting motor specs than those by GE, Westinghouse, Reliance, etc. I am accustomed to reading industrial motor specs and they all follow a similar format. For instance older older MD type motors are ususally rated at 250 VDC. You have to know they are rated to withstand 500 VDC and extrapolate the Hp and RPM at 500 VDC. Today, motors are rated typically at 500 VDC. The typical AC source to the drive is 3 phase 460 VAC at 60Hz. Now when you go overseas to say China, their standard voltage is 380 VAC at 50Hz. You won't get much over 400 VDC from a 380 VAC source. In this case, we take the standard motor speed and KW ratings and derate them for the 380 VAC source. What might require a standard 50 Hp motor for an application here may require a standard 75 Hp motor in China. Older CD motors are rated at 250 VDC and can't commutate 500 VDC. They are what they are and you can't exceed the specs. Same thing applies to the type of AC motors. To place an AC motor on an IGBPT drive, the motor has to be able to withstand the PWM power to the drive. Unless the motor is built to withstand variable frequency and voltage by Pulse Width Modulation, you can heat one up real fast. VM Star is a great Reliance built motor designed for that pupose. My error. Thanks for clearing it up. It had me going around in circles for a bit. My warmest regards, Ted |
Hey, Weeb...
Are you still on Lanier? I've got an option contract on the house but they've not exercised, just paying the renewals, as yet, so I'm still here while I'm not on the boat refitting (which means I get about a week a month at home).... L8R Skip, near the Habersham Condos -- Morgan 461 #2 SV Flying Pig http://tinyurl.com/384p2 "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain wrote in message ... On Sun, 29 May 2005 21:32:39 GMT, (Mic) wrote: http://members.cox.net/sholley1/electric.htm "A few years back I was impressed when I saw a "dock maintainance barge" tooling around the cove in our Marina under the power of a little 12 volt trolling motor. It was small, old, but the persistance of the little thing moved the barge around quite well. I proceeded down to my boat, and embarked on the following procedure to go sailing." "NOTE: There is no neat formula or correlation between thrust and horsepower. However, I read a comparison that measured a 6 hp gas outboard produced just over 130 lbs of thrust, so that would class the 107 Motorguide in the realm of a 5 hp gas (give or take a little). Thats not a lot of power, but ample for my needs. I don't know how I'd fare towing in another boat, but I'll include towing in "tests to come"." http://www.geocities.com/Yosemite/Fo..._outboard.html Auxilliary Power Requirements with Electricity "A typical trolling motor is designed to push a displacement hull at a maximum of about 2 to 3 miles per hour. Therefore, I determined to use the highest thrust 12 volt electric trolling motor that I could purchase and see where that would lead. In this case, a Motorguide model T47 motor with a 36 inch shaft length was commonly available at the local Kmart stores. This motor draws about 50 amps at maximum speed and is rated to produce 47 pounds of thrust. Replacing the propeller with a two blade (power) design from the three blade (weed free design) included with the motor should result in the required combination of low shaft speed and high thrust. This motor, combined with a bank of two new fully charged group 27 deep cycle batteries, could operate at maximum thrust for about 2.5 hours. In theory, the calculations said that this combination would propel my Com-Pac at just under three knots. This would meet my stated goal of a 5 mile range under power with some safety margin." A number of years ago I replaced the gas outboard on an Irwin 24 with the cheapest trolling motor at the local Walmart. This was on Lake Lanier, not in the ocean, but it was more than sufficient for driving this boat in and out of the marina. I am not sure what the thrust rating was, but I paid $150 for both the motor and a deep cycle trolling motor battery. With a solar panel on the cabin roof I never needed shore power to keep it charged up enough for going in and out of the marina 2 or 3 times a week. The boat I am building now (a 7 meter Eco7 catamaran) will have two electric trolling motors for auxilliary. Weebles Wobble (but they don't fall down) |
On Tue, 31 May 2005 15:37:05 -0400, "Skip Gundlach on wifi"
skipgundlach.sez.remove.this.part@earthlink.(fish catcher)net wrote: Hey, Weeb... Are you still on Lanier? I've got an option contract on the house but they've not exercised, just paying the renewals, as yet, so I'm still here while I'm not on the boat refitting (which means I get about a week a month at home).... L8R Skip, near the Habersham Condos I live in Lilburn, but have no boat currently (building one as we speak) Weebles Wobble (but they don't fall down) |
Perpetuated Motion
Electric propulsion for boats: A century-old technology may just be the wave of the future LINK: http://www.cruisingworld.com/article...ID=396&catID=0 " Advocates for diesel-electric propulsion list among its virtues that it's clean, quiet, efficient, and requires very little maintenance. Another advantage frequently noted in connection with the STI system is the ability to make electricity--to "regenerate"--when the boat is under sail." "While internal-combustion engines are typically described by their horsepower rating, STI's motors are named for the torque they develop. An ST 37 puts out 37 foot-pounds of torque or 6 horsepower; Tether recommends using it on monohulls up to 32 feet and 10 tons or to replace diesel engines of up to 24 horsepower. An ST 74 puts out 74 foot-pounds of torque or 12 horsepower; Tether recommends using it on monohulls up to 50 feet and 16 tons or to replace diesel engines of up to 48 horsepower." |
On Thu, 02 Jun 2005 12:43:35 GMT, (Mic) wrote:
Perpetuated Motion Electric propulsion for boats: A century-old technology may just be the wave of the future LINK: http://www.cruisingworld.com/article...ID=396&catID=0 " Advocates for diesel-electric propulsion list among its virtues that it's clean, quiet, efficient, and requires very little maintenance. Another advantage frequently noted in connection with the STI system is the ability to make electricity--to "regenerate"--when the boat is under sail." "While internal-combustion engines are typically described by their horsepower rating, STI's motors are named for the torque they develop. An ST 37 puts out 37 foot-pounds of torque or 6 horsepower; Tether recommends using it on monohulls up to 32 feet and 10 tons or to replace diesel engines of up to 24 horsepower. An ST 74 puts out 74 foot-pounds of torque or 12 horsepower; Tether recommends using it on monohulls up to 50 feet and 16 tons or to replace diesel engines of up to 48 horsepower." The ST37 is right in the range for my current light cruiser, and the ganged ST74 is appropriate for my anticipated next boat, which would be a modified full-keeler. I'm watching this technology like a hawk. It makes a lot of sense on a number of levels, but of course, it isn't for everyone. In the meantime, I'm replacing the exhaust end of my old Atomic 4.... R. |
On Thu, 02 Jun 2005 10:13:43 -0400, rhys wrote:
On Thu, 02 Jun 2005 12:43:35 GMT, (Mic) wrote: Perpetuated Motion Electric propulsion for boats: A century-old technology may just be the wave of the future LINK: http://www.cruisingworld.com/article...ID=396&catID=0 " Advocates for diesel-electric propulsion list among its virtues that it's clean, quiet, efficient, and requires very little maintenance. Another advantage frequently noted in connection with the STI system is the ability to make electricity--to "regenerate"--when the boat is under sail." "While internal-combustion engines are typically described by their horsepower rating, STI's motors are named for the torque they develop. An ST 37 puts out 37 foot-pounds of torque or 6 horsepower; Tether recommends using it on monohulls up to 32 feet and 10 tons or to replace diesel engines of up to 24 horsepower. An ST 74 puts out 74 foot-pounds of torque or 12 horsepower; Tether recommends using it on monohulls up to 50 feet and 16 tons or to replace diesel engines of up to 48 horsepower." The ST37 is right in the range for my current light cruiser, and the ganged ST74 is appropriate for my anticipated next boat, which would be a modified full-keeler. I'm watching this technology like a hawk. It makes a lot of sense on a number of levels, but of course, it isn't for everyone. In the meantime, I'm replacing the exhaust end of my old Atomic 4.... R. The problem with the STI system is the size of the battery pack required for the 144 volt system. It takes up a lot of space and adds a lot of weight. There are a lot of advantages to their system as well, especially as was already noted the regeneration under sail appeals for long passagemaking. Hopefully as the technology evolves a better and lighter battery system will be brought online. As a lover of multihulls, the current battery system takes their system off the table for me. Weebles Wobble (but they don't fall down) |
I look for the 'pertinent omission' in marketing data and hype.
Sure one can argue the 'green' attributes of such a system; but, one surely HAS to look at the all that additional weight for the batteries and control systems. With such a boat much deeper in the water and dragging a three bladed fixed prop .... it HAS to take MORE overall energy to move such a boat. The boat is now much deeper in the water and freewheeling a gigantic prop ...... of course you now need a bigger boat that goes slower. As far that the 'energy balance' ..... I'll bet its a 'wash' thus no clear advantage. Batteries dont last forever and I wouldnt want the replacement bill for such 'monsters' added to my cruising kitty. I'm more keen on the Pardeys 'engine' choice when it comes down to 'efficiency'. In article , Mic wrote: Perpetuated Motion Electric propulsion for boats: A century-old technology may just be the wave of the future LINK: http://www.cruisingworld.com/article...ID=396&catID=0 " Advocates for diesel-electric propulsion list among its virtues that it's clean, quiet, efficient, and requires very little maintenance. Another advantage frequently noted in connection with the STI system is the ability to make electricity--to "regenerate"--when the boat is under sail." "While internal-combustion engines are typically described by their horsepower rating, STI's motors are named for the torque they develop. An ST 37 puts out 37 foot-pounds of torque or 6 horsepower; Tether recommends using it on monohulls up to 32 feet and 10 tons or to replace diesel engines of up to 24 horsepower. An ST 74 puts out 74 foot-pounds of torque or 12 horsepower; Tether recommends using it on monohulls up to 50 feet and 16 tons or to replace diesel engines of up to 48 horsepower." |
On Thu, 02 Jun 2005 10:13:43 -0400, rhys wrote:
On Thu, 02 Jun 2005 12:43:35 GMT, (Mic) wrote: Perpetuated Motion Electric propulsion for boats: A century-old technology may just be the wave of the future LINK: http://www.cruisingworld.com/article...ID=396&catID=0 " Advocates for diesel-electric propulsion list among its virtues that it's clean, quiet, efficient, and requires very little maintenance. Another advantage frequently noted in connection with the STI system is the ability to make electricity--to "regenerate"--when the boat is under sail." "While internal-combustion engines are typically described by their horsepower rating, STI's motors are named for the torque they develop. An ST 37 puts out 37 foot-pounds of torque or 6 horsepower; Tether recommends using it on monohulls up to 32 feet and 10 tons or to replace diesel engines of up to 24 horsepower. An ST 74 puts out 74 foot-pounds of torque or 12 horsepower; Tether recommends using it on monohulls up to 50 feet and 16 tons or to replace diesel engines of up to 48 horsepower." The ST37 is right in the range for my current light cruiser, and the ganged ST74 is appropriate for my anticipated next boat, which would be a modified full-keeler. I'm watching this technology like a hawk. It makes a lot of sense on a number of levels, but of course, it isn't for everyone. In the meantime, I'm replacing the exhaust end of my old Atomic 4.... http://www.soundingsonline.com/stories.html?story=2 "Waypoint carries twin 12-hp Solomons Technology ST 74 electric motors powered by a dozen batteries. The batteries' charge is renewed by leaving the power plants running when the boat is sailing so the props turn in the water, transforming the electric motors into an electric generator. If there's no wind, a 15-kw diesel generator recharges the batteries, says Mike Stevens, Catamaran Company's Annapolis salesman. Stevens says Waypoint can run four hours at 8 knots on batteries, or 6 to 10 hours at 5 or 6 knots. He says the electric-powered cat appeals to the company's most environmentally conscious customers. "They want to sail with a green wake," he says." R. |
Mic wrote:
.... http://www.soundingsonline.com/stories.html?story=2 "Waypoint carries twin 12-hp Solomons Technology ST 74 electric motors powered by a dozen batteries. The batteries' charge is renewed by leaving the power plants running when the boat is sailing so the props turn in the water, transforming the electric motors into an electric generator. If there's no wind, a 15-kw diesel generator recharges the batteries, says Mike Stevens, Catamaran Company's Annapolis salesman. Stevens says Waypoint can run four hours at 8 knots on batteries, or 6 to 10 hours at 5 or 6 knots. He says the electric-powered cat appeals to the company's most environmentally conscious customers. "They want to sail with a green wake," he says." R. This isn't a bad setup for a charter boat that takes short hops, but a 32 mile range on the battery charge is a bit limiting. I'm guessing that the genset doesn't come close to keeping up with the drain, so this really isn't a "diesel electric." However, on a lighter catamaran, the number might workout better. |
Rich Hampel wrote in
: Batteries dont last forever and I wouldnt want the replacement bill for such 'monsters' added to my cruising kitty. Although they are VERY quick to point out to you that a Toyota Prius battery pack is still under a long warranty to sell the cars....If you wander back into the parts department and ask, you'll find out WHY they are VERY quick to point out to you that a Toyota Prius battery pack is still under a long warranty....................to sell the cars...... Bring out SEVERAL other thousand! Waste Marine and your local brokers must be very jealous....The markup on Ni-MH battery packs must be MOST impressive.... If you factor in battery pack replacement, operating cost is about the same as a Cadillac Escalade with a Northstar Beastie. |
Mic wrote:
Perpetuated Motion Electric propulsion for boats: A century-old technology may just be the wave of the future LINK: http://www.cruisingworld.com/article...ID=396&catID=0 " Advocates for diesel-electric propulsion list among its virtues that it's clean, quiet, efficient, and requires very little maintenance. Another advantage frequently noted in connection with the STI system is the ability to make electricity--to "regenerate"--when the boat is under sail." "While internal-combustion engines are typically described by their horsepower rating, STI's motors are named for the torque they develop. An ST 37 puts out 37 foot-pounds of torque or 6 horsepower; Tether recommends using it on monohulls up to 32 feet and 10 tons or to replace diesel engines of up to 24 horsepower. An ST 74 puts out 74 foot-pounds of torque or 12 horsepower; Tether recommends using it on monohulls up to 50 feet and 16 tons or to replace diesel engines of up to 48 horsepower." This is cool. But, lead acid batteries and high voltage DC and salt water are like rocket fuel, deadly as chlorine. A Canadian (British) submarines had a fire recently that seems to point to the biggest drawback. Lithium iron batteries are way dear, yet. The steam idea; now what if, when you made hydrogen electrically from water, instead of throwing away the pure oxygen, you stored it and then introduced it into an I.C. engine that burned hydrogen? Would that be a steam engine? How efficient and how large or small could such an engine be? I know, we haven't figured out how to corral big lumps of H2, yet, but who knows what will come along. Isn' it unfortunate that we cannot yet efficiently derive electrolyzed O2 as a liquid? Can hydrolysis occur at very cold temperatures, under pressure? Seems to me it shouldn't matter too much, as the atomic bond of water might not be bothered much by ambient considerations. The nicest thing about all that is that if you spring a leak in the system, the water around the boat might get cold enough to walk on. 'Gorra, If gasoline is dangerous on boats, how about pressurised supercold O2? Oh, and sails inflated with H2? On subject, the balance in such a subj. electrical system, it seems to me, would be a 5 hp charger and a 20 hp, 20 minute battery drive, or about that. In a blow at sea, no self respecting sailor would prefer to rely much on the engine, when the wind is so free, if wild. Any sailboat that cannot sail might never expect to be able to power out of a storm. I still want to know how an engine would work if it dispensed cold instead of heat. Liquid nitrogen is more benine than gasoline, and could be used to suck heat through an engine if the heat source is, let's say, relatively infinite, being represented by the enormous heat stored in the liquid water of the sea. It's heat would vapourize the LN2, providing gas volume to be harnessed in an "external combustion" steam type engine, leaving in it's wake only cold water, perhaps even ice, and still cool nitrogen gas. Just think, free air conditioning as a side effect! All that is lacking is a cold temperature LN2 low volume injection pump of some sort, to introduce LN2 to a heat exchanger, boiling the LN2, providing overpressure and volume to drive a piston. A small bore, cold environment injection pump could generate a large volume of cold gas in a heat exchanger which would gain power from being warmed by the sea. A leaking LN2 tank (dewar) could asphixyate cabin occupants, so must vent overboard. Anyone being asphixyated by evaporated liquid nitrogen would likely wake up from the increasing cold before expiring. If half of the nitrogen and oxygen in a cabin were replaced by pure cold nitrogen, the ambient temperature would freeze the nose and the water in the exhalations passing through your nose. When it gets that cold, all your nasal hairs freeze together and pull on one another, causing pain, and that should wake you up before more than half of the oxygen is displaced from the room. Ask any musher about that cold effect. You can make your own liquid nitrogen. All you need is a good compressor and a heat exchanger, which stores potential energy in the form of a temperature differential, in the environment and an insulated cold tank until you want it back. Using a windmill to pump air to provide storable LN2 might even work. Terry K |
This post presents an interesting concept illustrated in diesel locomotive
drive train description. There multiple methods of converting and transmitting energy but they all have one thing in common you never get out as much energy as you put in. The difference between energy in and energy our is energy converted to some other form that is not useable by the system (such as heat from friction). System efficiency is a mathematical description of the amount of lost energy compared to input energy. The object of any sailboat drive is to move it through the water without the use of the sails and wind. The typical drive system converts chemical energy (in the form of fuel) into rotary motion to spin the propeller. The most efficient drive system is a direct drive (such as directly attaching the propeller to the rotary motive device's output shaft). Unfortunately, most motive devices such as diesel engines do not produce an output a form of energy that is directly useable by a propeller and also they do not operate well when submerged. Hence the need/existence of some type of transmission and shafting which introduce drive system losses. A gear box type transmission has the least amount of losses. a hydraulic transmission (either in a single case [like found in modern automobiles] or separate pump/motor drive) have greater losses. The electric drive systems have more losses that a gear box but depending upon design can be more or less efficient that a hydraulic drive. Electric drive losses come from wire line losses expressed as voltage drop, battery losses in both charging and discharging, electric energy generation be it through a solar cell or engine, wind, water driven generator, motor losses converting all that electricity into rotary motion to spin the propeller, and depending upon the size and style of electric motor used, shafting and associated bearing, coupling and seal losses. My bottom line is that there are many ways to move the boat but none are perfect with no losses. The final design for each individual is a compromise based upon how much the owner/builder is willing to spend and how much energy loss "he" is willing to accept. Done right each design has its good points and its bad points but none give a free ride. Two pluses in favor of an electric drive are; 1. the electric power can be derived from both combustion (such as a diesel gen-set) and non-combustion (such as solar panels or wind mills) sources. 2. The stored electrical energy can be used for "hotel" related boat uses freeing up space and the cost of a second generator set. "Ted" tedwilliams@nospam wrote in message ... On Fri, 03 Jun 2005 14:33:22 -0300, Terry Spragg wrote: Mic wrote: Perpetuated Motion Electric propulsion for boats: A century-old technology may just be the wave of the future LINK: http://www.cruisingworld.com/article...ID=396&catID=0 " Advocates for diesel-electric propulsion list among its virtues that it's clean, quiet, efficient, and requires very little maintenance. Another advantage frequently noted in connection with the STI system is the ability to make electricity--to "regenerate"--when the boat is under sail." "While internal-combustion engines are typically described by their horsepower rating, STI's motors are named for the torque they develop. An ST 37 puts out 37 foot-pounds of torque or 6 horsepower; Tether recommends using it on monohulls up to 32 feet and 10 tons or to replace diesel engines of up to 24 horsepower. An ST 74 puts out 74 foot-pounds of torque or 12 horsepower; Tether recommends using it on monohulls up to 50 feet and 16 tons or to replace diesel engines of up to 48 horsepower." The statement above "STI's motors are named for the torque they develop" is absolutely meaningless without rotational speed. Torque is force at zero speed and is measured in foot pounds or inch pounds. Torgue is simply the force exerted in pounds at a given distance from the center of the motor shaft. For example: 12 lbs-in of torque means that imagining a lever arm connected to the shaft, at 1 inch up on the lever shaft you would measure 12 lbs of force. At 12 inches up, you would measure 1 lb of force. No rotational speed is considered. To propel a boat, the propellor has to turn. A million lbs-ft with no propellor speed won't move a toy boat. I could take a toy motor that produces .001 lbs-ft of torque and connect it through a reducer of say 10,000:1. At the output shaft of the reducer (assuming no losses) I would measure 10 lbs-ft of torque. If my toy motor top speed was 1,000 rpm, the rpm at the output shaft of the reducer would be 0.1 rpm. So, bearing that in mind, I could tell people that my electric motor and gear combination that runs on a common D cell can produce 10 lbs-ft of torque and I wouldn't be lying. In essence, torque produced by a motor without factoring in speed and time is meaningless. It cannot be equated to horsepower. The following formuala is used to convert a known (speed in rpm) and (torque in lbs-ft) into HP. HP = (rpm x T(torque))/(( 5252(constant)) For the example of my toy motor and gear combination I can easily calculate the HP. HP = (.1x10)/5252 HP = 0.000190403655750 Not much HP is it? But I get 10 lbs-ft of torque! Thrust is similar. Assume no boat or other losses have an effect on the motor/prop combination. . For an example we'll use a trolling motor rated at 40 lbs of thrust at .25 mph at the motor's maximum speed. Changing the prop to get 1 mph for the motor maximum speed, the thrust would be 10 pounds. Change the prop again to get 2 mph at the motor maximum speed would result in 5 pounds of thrust. Once again, thrust like torque must be related to speed to be meaningfull. I am well aware of electric motors being used on submarines and such. I have worked on a submarine motor that was salvaged and is in use today on a cold rolling mill. The motor is rated at 2500 hp at 600 volts at 2650 amps. That would take a lot of battery power to operate it in a submarine. The diesal powered locomotives you see are not driven directly by the engine as in an automobile. There is no gear train to the wheels. The diesal engine turns a generator. The diesal engine is known as the Prime Mover and runs at a constant speed. The field of the generator is electrically excited producing flux in the generator fields. That in turn produces volts at the output of the generature. The generator is wired to electric traction motors that turn the wheels. To change the speed, the amount of generator field excitation is varied and thus the generator output volts going to the traction motors. There is a lot more to motors, thrust, torque, hp, and batteries than I can possibly describe here. I just wanted to throw this in so nobody gets confused and thinks they are getting something for nothing. Oh, and by the way, if you had an electric trolling motor on your sailboat, and the you were sailing faster than the trolling motor's theoretical maximum speed with the given prop, the motor would turn faster and regenerate putting power back into the battery. Of course you are converting the energy produced by the wind in the sails and thus motion into electrical energy so unfortunately no perpetual motion. grin Ted |
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On Mon, 06 Jun 2005 13:41:50 -0400, rhys wrote:
On Thu, 02 Jun 2005 13:27:27 -0400, wrote: The problem with the STI system is the size of the battery pack required for the 144 volt system. It takes up a lot of space and adds a lot of weight. There are a lot of advantages to their system as well, especially as was already noted the regeneration under sail appeals for long passagemaking. Hopefully as the technology evolves a better and lighter battery system will be brought online. As a lover of multihulls, the current battery system takes their system off the table for me. I can see that with a multihull. My current boat wouldn't enjoy 12 batteries, all that copper and the required charger, either, But certainly there are passagemakers and full keelers that could have the batteries low and in return shrink the size of the diesel tanks to whatever would reasonably cope with the genset's occasional use. I also anticipate a lot of competition in this area, which I hope will spur further savings in weight and complexity. R. I agree. I think STI is a good first offering that will be built on by others in the near future. I am not sure what the benefits are of using the 144 volt motor vs a 24 or 48 volt system. I use an electric truck at work that does quite well on a 48 volt system and have wondered if someone will follow up and offer a system that can use a more practical sized battery system. Weebles Wobble (but they don't fall down) |
Well. I am a real fan of eletric motors for boats. And while the distance I
travel on the lake the to and from my cabin is not that great (about 2.5 kilometers per trip) I got sick and tried of the old two stroke and the work needed to get it going. On very cold days, it could be murder to start - and let's not mention the mess-ups in oil ratios when my brother tried to use it a few times. The four stroke honda works great as long as I don't do something stupid and end up flooding the engine, then it takes up to 15 minutes before it will start. Atleast I finally learnt how to flush the water filter. The electric motors - perfect first, perfect always. Generally I get about 4 trips out of the main battery (I have a smaller backup incase) and if I remember to plug in the main batteries from the cabin to recharge boat's battery before I go to sleep, it is always ready in the morning. To me however the biggest advantage is the quiet. Set at lower speeds the motors as so quiet that even beavers which are in the water and would notice an loud sound do not hear me coming. I can visit the loon's nest without driving the parent birds away, I get far closer to animals on shore with the electric than even with paddles. ----------------------------------------------------------------------------------------------------------------------------------------------------- When talking about long distance travel well designed electric systems have an advantage I did not see mentioned here. The ability to instantly switch between motor vs generator lets you do a special type of cruising called ‘regenerative motor sailing'. Basicy, you set the controller for a fixed speed and start sailing. If the speed is even a small faction below the average speed your boat would in the wind conditions then the batteries are almost always in a charging state - more importantly. If the wind increase/gusts the energy is shuttled to the batteries instead of trying to speed up the boat to a speed it can not keep - so you sail on at a steady rate. The wind dies a bit and the motor mode instantly keeps your speed up - so you sail on at a steady rate. Your boat starts to surf down a wave - again the generator mode kicks in and the extra energy goes into the battries - so you sail on at a steady rate. You hit the face of the wave and you start to climb up and once again the motor mode kicks in - so you sail on at a steady rate. Get the idea :) Infact Multihull magazine reports on once setting the right speed for ‘regenerative motor sailing' all day, enjoying it because it was so smooth and quiet and still ending the day with more of a charge in the batteries than when they started out. Earl Colby Pottinger http://www.multihull-maven.com/article.php?id=40 http://www.multihull.com/elec_wheel.html http://www.solomontechnologies.com/news.htm -- I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos, SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to the time? http://webhome.idirect.com/~earlcp |
Ted tedwilliams@nospam :
Hmmm, the math is pretty simple. We measure the output power of motors or engines in Hp. 1 Hp = 746 watts. 5 Hp = 3730 watts. To produce 5 Hp at 12 volts would require 310.8 amps. (Assuming no IR, friction, and windage losses) That requires some pretty heavy duty wiring. I doubt that I could lift a true 5 Hp 12 volt motor. 50 amps at 12 volts = 600 watts or 0.804 Hp. That is the maximum Hp produced by the T47. Again, no IR, friction, and windage losses which is impossible to achieve. With a good motor, you might get 90% out of what you put in. I think you made a mistake, don't ST motors run at 144 volts? That makes a big diffirence. check out: http://www.solomontechnologies.com/S...%20system.html Earl Colby Pottinger -- I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos, SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to the time? http://webhome.idirect.com/~earlcp |
On Fri, 10 Jun 2005 01:58:55 -0500,
Earl Colby Pottinger wrote: When talking about long distance travel well designed electric systems have an advantage I did not see mentioned here. The ability to instantly switch between motor vs generator lets you do a special type of cruising called ‘regenerative motor sailing'. Basicy, you set the controller for a fixed speed and start sailing. If the speed is even a small faction below the average speed your boat would in the wind conditions then the batteries are almost always in a charging state - more importantly. If the wind increase/gusts the energy is shuttled to the batteries instead of trying to speed up the boat to a speed it can not keep - so you sail on at a steady rate. The wind dies a bit and the motor mode instantly keeps your speed up - so you sail on at a steady rate. Your boat starts to surf down a wave - again the generator mode kicks in and the extra energy goes into the battries - so you sail on at a steady rate. You hit the face of the wave and you start to climb up and once again the motor mode kicks in - so you sail on at a steady rate. Get the idea :) Infact Multihull magazine reports on once setting the right speed for ‘regenerative motor sailing' all day, enjoying it because it was so smooth and quiet and still ending the day with more of a charge in the batteries than when they started out. Earl Colby Pottinger http://www.multihull-maven.com/article.php?id=40 http://www.multihull.com/elec_wheel.html http://www.solomontechnologies.com/news.htm Thanks for the links. We are looking at having to repower Windwalker (aging Perkins 107) in the next couple of years. I don't think that electric is *quite* there yet, for us, but it's not as far off as it used to be, that's for sure. If the fuel cells using diesel or methanol were available at a decent price, that would tip it over the edge for me. I'd dearly love to get rid of the stinky "iron genny" and getting quiet, and a good recharger for house batteries whilst underway is a bonus. Plus, even with the weight of the batteries, I'd likely wind up losing weight by dumping the diesel engine. Solomon has some nice rigs, but a bit pricey at the moment. Getting there though. -- Jim Richardson http://www.eskimo.com/~warlock Gun exchange programs would work great if they gave you a gun when you handed in a criminal |
Ted tedwilliams@nospam :
Every motor becomes a generator when the motor is turned faster than the rated speed at the rated EMF. This is commonly known as regeneration. The point is that ST motors are designed to be efficent generators when used in that mode, and that the circuits that are to be included are design to use those motors as a source of power when the motor goes into generator mode. Secondly, if the motor is running in extended range (not possible with permanent magnet motors) you increase the motor speed by holding armature volts constant and decreasing the motor field flux. This is known as the constant Hp mode of operation since as speed increase, the resultant torque decrease proportionatly thus constant Hp. Yes, but ST's circuits that they use take gotcha's like this into account, no matter what speed the motors are used at as generator and not matter what the voltage/ampage output of the motor/generator the invertor in designed to convert it to the best range for recharging the batteries. The motors are not directly connected to the batteries which could result in the type of problem you relate above. Rather a very intelligent speed controller with feedback from the motors. If the motors are spinning too slow indicating that the boat moving slowly the power to the motors are ramped up. If the motors are spinning too fast thus indicating the boat is also moving faster than the set speed the motors are used as generators the resulting power is *conditioned* to the best values to recharge the batteries. Earl Colby Pottinger -- I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos, SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to the time? http://webhome.idirect.com/~earlcp |
Jim Richardson :
If the fuel cells using diesel or methanol were available at a decent price, that would tip it over the edge for me. I'd dearly love to get rid of the stinky "iron genny" and getting quiet, and a good recharger for house batteries whilst underway is a bonus. Plus, even with the weight of the batteries, I'd likely wind up losing weight by dumping the diesel engine. Have you looked at Honda's generators with invertor output? For the power out, those machine are very quiet. While the largest model I have used is only 2.5KW it is my understanding that all the models are very quiet in operation. More than once I had to personally go and check my unit to see if it ran out of gas because I could not hear it running. And that is another thing, depending on your needs the ecomo mode uses very little gas to run. Let's me set my charger to slow charge the batteries (best for life and completeness of charge) without wasting gas producing more power than is used. Earl Colby Pottinger -- I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos, SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to the time? http://webhome.idirect.com/~earlcp |
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