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Electric motor to power a dinghy revisited
Hi,
I want to put a motor on an 8' inflatable dinghy. A big question is whether I should use a conventional gasoline/oil based motor or go with electric. The situation is as follows: I plan to take the boat out to a complete wilderness (in a car/SUV) and use it there for, say, a week to explore lakes and streams. There will be no AC outlets out there. This creates a problem---how do I recharge the battery/batteries if I decide to go with electric motor? Is it possible to do it through the running car in some way? Is this a realistic approach anyway? Solar power(likely, unrealistic)/other alternatives? I would not have asked unless electric motor was not so nicely quiet and environmentally friendly and thus appeal to me. Using electric motor has its value, but it is not clear if it holds it in the above set up. Thanks |
Electric motor to power a dinghy revisited
A big question is
whether I should use a conventional gasoline/oil based motor or go with electric. Easy to calculate running times for any given trolling motor and battery combination. Now calculate or observe your hull speed. Now you know your best possible range. Derate that for possible problems. My bet is a battery does not store enough energy to do what you want. The energy density of a lead storage battery vs gasoline is ludicrous. Think of that 50-pound trolling battery as a gas tank that holds (the equivalent energy of) a pint of fuel, takes all day to "fill" (recharge), costs $$$, and wears out in a few years. |
Electric motor to power a dinghy revisited
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Electric motor to power a dinghy revisited
When you move to the wilderness, and disconnect from the artificial
urban environment, you come face-to-face with the key issue: Electric vehicles require electric generators... somewhere. When you can just plug your charger into the wall, that nasty generating plant is out of sight and out of mind. But when YOU have to supply the electricity, you end up with the same conclusion: burn fossil fuel. But if you are going to burn fossil fuel, next you need to ask yourself if burning the fuel in an engine in the generator is an improvement over burning the fuel in an engine and using the power output directly, thus eliminating the need to carry (and indirectly, to manufacture) the battery and the electric motor, and eliminating the inefficiencies of turning shaft horsepower into electircity, electricity into stored chemical energy in the battery, stored chemical energy in the battery into electricity again, and finally converting electricity back into shaft horsepower. TAANSTAFL bob wrote: Hi, I want to put a motor on an 8' inflatable dinghy. A big question is whether I should use a conventional gasoline/oil based motor or go with electric. The situation is as follows: I plan to take the boat out to a complete wilderness (in a car/SUV) and use it there for, say, a week to explore lakes and streams. There will be no AC outlets out there. This creates a problem---how do I recharge the battery/batteries if I decide to go with electric motor? Is it possible to do it through the running car in some way? Is this a realistic approach anyway? Solar power(likely, unrealistic)/other alternatives? I would not have asked unless electric motor was not so nicely quiet and environmentally friendly and thus appeal to me. Using electric motor has its value, but it is not clear if it holds it in the above set up. Thanks |
Electric motor to power a dinghy revisited
wrote:
I want to put a motor on an 8' inflatable dinghy. A big question is whether I should use a conventional gasoline/oil based motor or go with electric. The situation is as follows: I plan to take the boat out to a complete wilderness (in a car/SUV) and use it there for, say, a week to explore lakes and streams. Why not get a canoe & paddle? Or a boat which can be rowed? Likely to be almost as fast as a small outboard motor, or electric motor, much more reliable, good healthy exercise. ... how do I recharge the battery/batteries if I decide to go with electric motor? Is it possible to do it through the running car in some way? Sure, you could just connect the batteries to your car's start battery with jumper cables. It might take a couple hours of running at RPM above idle to recharge though. ... Is this a realistic approach anyway? Solar power(likely, unrealistic)/other alternatives? That depends on what the math of battery life vs recharge times, and the speed/range of your chosen motor with the numbers you get. Years ago, I went fishing and frog gigging regularly with a neighbor of mine who used an electric trolling motor on a small (10' or so) aluminum jon boat. We went ten miles or so on a plain old car battery, but then we could take a few days to get it charged again vie household 120VAC current. And went noticably slower at the end of the trip than at the beginning. ... I would not have asked unless electric motor was not so nicely quiet and environmentally friendly and thus appeal to me. Using electric motor has its value, but it is not clear if it holds it in the above set up. Richard J Kinch wrote: Easy to calculate running times for any given trolling motor and battery combination. Now calculate or observe your hull speed. Now you know your best possible range. Derate that for possible problems. Also remember you don't want to run the motor at over 3/4 throttle for best range. I don't think hull speed will be an issue. My bet is a battery does not store enough energy to do what you want. The energy density of a lead storage battery vs gasoline is ludicrous. True but the battery does offer some advantages. It's quiet and you can place the weight of it anywhere in the boat you want. Think of that 50-pound trolling battery as a gas tank that holds (the equivalent energy of) a pint of fuel, takes all day to "fill" (recharge), costs $$$, and wears out in a few years. That seems rather pessimistic. A plain old lead-acid battery can easily run thousands of charge-discharge cycles if it's treated properly. And the power equivalent is much more than a pint of gasoline, especially if you factor in the woeful inefficiency of internal combustion engines. Fresh Breezes- Doug King |
Electric motor to power a dinghy revisited
Thanks everybody for the replies :)
I guess the best decision would be to go with a gasoline outboard. Since there is going to be no easy access to AC, recharging will be available through the alternator only. Meaning the following flow of energy: fuel - alternator - battery - motion with multiple transition of energy back and forth from/to chemical (2 types), electric (2 times), and motion (2 times) type forms. This cycle just does not seem as efficient as a simple fuel - motion. Plus, the time required to recharge---I don't think I'll have it. I'll start looking for some 4-stroke outboard like Honda now. Why not get a canoe & paddle? This is a good idea. But, for a person who spends all most of the time at his job just sitting on a chair this might too much of an exercise. Plus, I want to have some energy left to build a camp/cook a descent (hot) meal. |
Electric motor to power a dinghy revisited
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Electric motor to power a dinghy revisited
To complex for my poor brain..........
Borrow a canoe and two paddles from your neighbor. Fast, quiet, cheep, light, easy. Why are you set on a rubber raft? Bob |
Electric motor to power a dinghy revisited
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Electric motor to power a dinghy revisited
Why are you set on a rubber raft?
Easy to transport, easy to store (does not take much space, and I don't have a house), light weight, fits into a backpack (a heavy backpack, but could easily carry it a couple of kilometers). Does this sound convincing? |
Electric motor to power a dinghy revisited
DSK writes:
Think of that 50-pound trolling battery as a gas tank that holds (the equivalent energy of) a pint of fuel, takes all day to "fill" (recharge), costs $$$, and wears out in a few years. And the power equivalent is much more than a pint of gasoline, especially if you factor in the woeful inefficiency of internal combustion engines. Nope. Here's the analysis: My Group-27 deep-cycle trolling battery weighs 53 lbs and provides 115 Ah x 12 volts = 1.4 KWh. Divide by 746 watts/hp and multiply by 80 percent trolling motor efficiency, you get about 1.5 hp-hours at the prop, from a full charge to full discharge. How much gasoline is 1.5 hp-hours? My 25 hp Tohatsu burns about 2 gal/hour. So 2 gals for 25 hp-hour, or 12.5 hp-hour/gal, or 0.08 gal/hp-hour, times 1.5 hp-hours, is 0.12 gal, which is to say, 1 GROUP 27 TROLLING BATTERY = 1 PINT GASOLINE Gasoline has over 50 TIMES the energy density of lead storage batteries. A plain old lead-acid battery can easily run thousands of charge-discharge cycles if it's treated properly. Huh? They're good for about 200 cycles, assuming you can log that many before 3 or 4 years of aging works its harm. Then they degrade rapidly, holding less charge, and self-discharging faster. Think of it as a gas tank that starts shrinking and leaking after a few hundred fills, or a few years of just getting old. Unless you mean by "treated properly" that you don't fully discharge, in which case, your realized energy density is even less favorable. |
Electric motor to power a dinghy revisited
8' ... have you ever heard of ... oars?
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Electric motor to power a dinghy revisited
Richard J Kinch wrote:
My Group-27 deep-cycle trolling battery weighs 53 lbs and provides 115 Ah x 12 volts = 1.4 KWh. Divide by 746 watts/hp and multiply by 80 percent trolling motor efficiency, you get about 1.5 hp-hours at the prop, from a full charge to full discharge. How much gasoline is 1.5 hp-hours? My 25 hp Tohatsu burns about 2 gal/hour. So 2 gals for 25 hp-hour, or 12.5 hp-hour/gal, or 0.08 gal/hp-hour, times 1.5 hp-hours, is 0.12 gal, which is to say, 1 GROUP 27 TROLLING BATTERY = 1 PINT GASOLINE Gasoline has over 50 TIMES the energy density of lead storage batteries. I still think that's a large exaggeration. And your math is skewed. Why not multiply your gas outboard's power output by it's theoretical efficiency of about 40% or less? FWIW I agree that gasoline is very much more bang for the buck than any other type of stored energy, that's why it's so hard to find "alternative fuels." A better way to compare would be to measure how many ton/miles each power plant could move at a given speed in a given hull form. For moving a slow efficient hull, the trolling motor would be better than you think. And for moving a light load fast, it won't do anything. A plain old lead-acid battery can easily run thousands of charge-discharge cycles if it's treated properly. Huh? They're good for about 200 cycles Baloney. Even the advanced metals batteries go for over 1,000 ycles if properly cared for, and old fashioned lead-acid batteries are limited only by how they're treated. Their life is theoretically infinite. If you're only getting 200 cycles out of your deep-cycle battery, then you're doing something wrong. Maybe you need a proper 3-stage charger with a desulphating function? They're not expensive these days. I know of many people getting 8+ years of heavy (practically continuous) use out of traction or golf-cart type batteries. Unless you mean by "treated properly" that you don't fully discharge, in which case, your realized energy density is even less favorable. Sure. But if you discharge it 100% and get to use it less than 200 times, vs discharging it 50% and using it over 2,000 times, what does that do to the energy density averaged over the life span? Fresh Breezes- Doug King |
Electric motor to power a dinghy revisited
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Electric motor to power a dinghy revisited
On Wed, 12 Apr 2006 20:08:25 -0700, dmitri.maslov wrote:
Hi, I want to put a motor on an 8' inflatable dinghy. A big question is whether I should use a conventional gasoline/oil based motor or go with electric. The situation is as follows: I plan to take the boat out to a complete wilderness (in a car/SUV) and use it there for, say, a week to explore lakes and streams. There will be no AC outlets out there. This creates a problem---how do I recharge the battery/batteries if I decide to go with electric motor? Is it possible to do it through the running car in some way? Is this a realistic approach anyway? Solar power(likely, unrealistic)/other alternatives? I would not have asked unless electric motor was not so nicely quiet and environmentally friendly and thus appeal to me. Using electric motor has its value, but it is not clear if it holds it in the above set up. Batteries for trolling motors are heavy and take a long time to charge. Even if you had a portable generator or oversized alternator on your car, you'd have to run it for quite awhile. There goes your peace and quiet. As others have mentioned, a canoe or kayak with paddles might be the ultimate solution. Or a small rowboat. Inflatable dinghies don't row well enough for anything but short distances. We've been very happy with the 2hp Honda BF2D we use for our dinghy. It's completely self contained, with no external tank, and weighs only 28lb. It runs well over an hour on a quart of fuel. It's dead reliable, and not too loud. I recommend it. Don't get me wrong, I love electric motors. Matt O. |
Electric motor to power a dinghy revisited
oh oh oh. gotta an idea! Yellow "bannana boats." The are inflatable kayaks. Very light Very portable.. just roll them up reasonably fast much cheeper than all the other stuff. Besides trying to compute BTU to KW to BHP, SHP, Jules, moles, etc can be rather confusing for someone llike myself who still has 1200 flashing on my VCR. Bob |
Electric motor to power a dinghy revisited
DSK writes:
old fashioned lead-acid batteries are limited only by how they're treated. Their life is theoretically infinite. You couldn't be more wrong. Sure. But if you discharge it 100% and get to use it less than 200 times, vs discharging it 50% and using it over 2,000 times, what does that do to the energy density averaged over the life span? Nothing. Learn what "energy density" means. |
Electric motor to power a dinghy revisited
On Thu, 13 Apr 2006 23:09:15 -0700, Mark Borgerson wrote:
As for power equivalent: a 100AH,12V battery at a reasonable discharge level is equivalent to about 1.3HP for one hour. That's a pretty big, heavy battery, not easy to carry around! My own experience with a battery of about that size and a trolling motor is that you can propel a very light boat for about two hours at perhaps 1-3 knots on one battery. That's probably about right. How long does it take to charge though? And how do you charge it? It's one thing if you have shore power or a heavy duty alternator or genset aboard your yacht, but... I think I would get about the same speed with my 4HP Johnson OB at a fast idle. Whether that would take more than a pint of fuel is a good question. You don't need that much power. A .5 HP electric motor is probably good enough. A small dinghy has a really low hull speed anyway, so running your gas outboard at full throttle isn't much faster than at 1/3 or 1/4. This translates to a smaller electric motor. IME a pint of fuel an hour seems about right. A big difference between charging a battery and driving an OB is that the pollution from the motor goes directly into the water. That can be a problem on some lakes. This is true. In fact electric is all that's allowed on some lakes. http://www.windsun.com/Batteries/Battery_FAQ.htm I haven't read this page, but be careful about battery websites. They contain more old wives' tales, mechanics' folklore, myth, and marketing drivel than just about anything else. I'm actually intrigued by small electric outboards. I'd like to have a self-contained unit with a built-in Li-ion or NiMH battery. It could weigh no more than a small gas outboard, run for two hours, and charge in 15 minutes off the generator in the "mother ship." Even if it were very expensive, the quiet and cleanliness would appeal to a lot of people. Matt O. |
Electric motor to power a dinghy revisited
Here are some more details. There expected to be 2 people aboard, still
water, the total travel distance of 200-250 km (covered over a period of few days), and we have to carry all our equipment (including tent, sleeping bags, etc.) and food supply with us. Would have to carry too much stuff for a canoe, so it is unlikely that a canoe will offer as much speed and comfort as you suggest. Plus, I'd hate to find my palms grind to meat some 50 km from the starting point of the trip. |
Electric motor to power a dinghy revisited
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Electric motor to power a dinghy revisited
Did not mean to do this with the electric motor anyway. With the
electric, one would have to stick to the vehicle and make short trips only, and it was initially proposed to be done this way. However, based on the discussions, I got convinced that even that is not going to work. Since electric does not seem to be an option anyway, why not try to extend plans? |
Electric motor to power a dinghy revisited
In article ,
says... On Thu, 13 Apr 2006 23:09:15 -0700, Mark Borgerson wrote: As for power equivalent: a 100AH,12V battery at a reasonable discharge level is equivalent to about 1.3HP for one hour. That's a pretty big, heavy battery, not easy to carry around! My own experience with a battery of about that size and a trolling motor is that you can propel a very light boat for about two hours at perhaps 1-3 knots on one battery. That's probably about right. How long does it take to charge though? And how do you charge it? It's one thing if you have shore power or a heavy duty alternator or genset aboard your yacht, but... I think I would get about the same speed with my 4HP Johnson OB at a fast idle. Whether that would take more than a pint of fuel is a good question. You don't need that much power. A .5 HP electric motor is probably good enough. A small dinghy has a really low hull speed anyway, so running your gas outboard at full throttle isn't much faster than at 1/3 or 1/4. This translates to a smaller electric motor. IME a pint of fuel an hour seems about right. A big difference between charging a battery and driving an OB is that the pollution from the motor goes directly into the water. That can be a problem on some lakes. This is true. In fact electric is all that's allowed on some lakes. http://www.windsun.com/Batteries/Battery_FAQ.htm I haven't read this page, but be careful about battery websites. They contain more old wives' tales, mechanics' folklore, myth, and marketing drivel than just about anything else. I'm actually intrigued by small electric outboards. I'd like to have a self-contained unit with a built-in Li-ion or NiMH battery. It could weigh no more than a small gas outboard, run for two hours, and charge in 15 minutes off the generator in the "mother ship." Even if it were very expensive, the quiet and cleanliness would appeal to a lot of people. As a device to get you from your anchored yacht to the shore, this might be an attractive alternative. In most NW anchorages, you are seldom more than a few hundred yards from the beach, so rowing isn't a big problem---unless you have to cope with a few kids and a dog and an inflatable that rows with all the directional stability of a soup bowl! At times like that, a 1/2hp OB with an hour's endurance might be useful. With resonable efficiency 1/2Hp for one hour would need about 1200Watt hours to recharge. That's about 100 Amp hours at 12V---or about 4 hours at 25 Amps. Not an unreasonable load for a husky alternator on a diesel trawler running 4 to 5 hours between anchorages. (Friday night--11:30PM, good wine with dinner--- check my math!) Mark Borgerson |
Electric motor to power a dinghy revisited
On Wed, 12 Apr 2006 20:08:25 -0700, dmitri.maslov wrote:
Hi, I want to put a motor on an 8' inflatable dinghy. A big question is whether I should use a conventional gasoline/oil based motor or go with electric. I'm surprised at all the negative responses to this. My "other" hobby (apart from sailing) is flyfishing, and at least here in BC, electric motors are de regeur (ok, my French isn't that good - I SAID I was from BC! ;) ). In fact, a lot of lakes do not ALLOW gas engines. A decent electric motor/battery will push you at hull speed for around 2 hrs, or trolling speed for at least a day. Hell, mine will push my 9.5ft inflatable over 5 knots for 1.5hrs. Charging IS an issue: Even a fairly decent panel (60-80W) will take a day (more or less) to charge a Group 24 battery. But why not get a decent AC charger like a Statpower and run it off a small Honda genset? (The DC output off those gensets is WAY too wimpy!) That way, you're not polluting the lake, you're getting the super-quiet Electric Experience, and an hr or so running at dinnertime would set you up for the next day. I'd say go with a Minn Kota Max40T and a deep-cycle Group 24 battery. Lloyd Sumpter http://www.bcboatnet.org |
Electric motor to power a dinghy revisited
On Sun, 23 Jul 2006 21:36:53 -0700, Lloyd Sumpter
wrote: Charging IS an issue: Even a fairly decent panel (60-80W) will take a day (more or less) to charge a Group 24 battery. But why not get a decent AC charger like a Statpower and run it off a small Honda genset? (The DC output off those gensets is WAY too wimpy!) That way, you're not polluting the lake, you're getting the super-quiet Electric Experience, and an hr or so running at dinnertime would set you up for the next day. I'd say go with a Minn Kota Max40T and a deep-cycle Group 24 battery. Lloyd Sumpter http://www.bcboatnet.org Yes, small outboards spew pollution, stink, and are too damn loud. Why can't they make an aircooled model with a real good muffler? I hate polluting. |
Electric motor to power a dinghy revisited
Lloyd Sumpter wrote in
: run it off a small Honda genset? (The DC output off those gensets is WAY too wimpy!) My Honda EU3000i puts out 12 amps on its charging output jack. Of course, that won't compare to plugging the big Vector autocharger into the AC plug and getting 40 amps...(c; |
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