What do you think of a 12 volt trolling motor for a dinghy? I would not be anchored more than one night but would make several trips to shore. I would not need to operate at top speed. How many hours could I expect out of a fully charged battery.
Electric trolling motor
- Thread starter Don K.
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Electrics . . .
I get about 2-3 hours from a full size battery, (110 amp/hr) on my Sea Eagle 11 inflatable. The time depends upon how fast you go - and since these are not real fast, I use 4 or 5 on my 5 position throttle most of the time. I have a 44 lb MinnKota, it works well for the inflatable, but I have only ever used mine on very flat water. Many electrics are not salt water compatible, so check that out as well, if you are on the ocean. I have seen some folks using a jump starter battery - it works & is lighter and easier to carry, but probably has 1/4 to 1/3 the run time. Several folks moored at a local lake do it this way to get out to the mooring. Remember - even a 2hp outboard will outperform almost any electric. I think the equivalence is about 75 lbs thrust per HP. IMHO, An electric won't work at all well against much wind and chop. Hope this helps!
I get about 2-3 hours from a full size battery, (110 amp/hr) on my Sea Eagle 11 inflatable. The time depends upon how fast you go - and since these are not real fast, I use 4 or 5 on my 5 position throttle most of the time. I have a 44 lb MinnKota, it works well for the inflatable, but I have only ever used mine on very flat water. Many electrics are not salt water compatible, so check that out as well, if you are on the ocean. I have seen some folks using a jump starter battery - it works & is lighter and easier to carry, but probably has 1/4 to 1/3 the run time. Several folks moored at a local lake do it this way to get out to the mooring. Remember - even a 2hp outboard will outperform almost any electric. I think the equivalence is about 75 lbs thrust per HP. IMHO, An electric won't work at all well against much wind and chop. Hope this helps!
that cant be right..
A 6hp outboard has a still-thrust rate of 133lbs. A 9.9hp has a still-thrust of 218lbs. Here is an outboard electric that is made to be primary thrust, its about 11 net HP at full voltage.. http://www.outboardelectric.org/brochure.pdf#search='thrust%20per%20HP%20outboard%20motor'
A 6hp outboard has a still-thrust rate of 133lbs. A 9.9hp has a still-thrust of 218lbs. Here is an outboard electric that is made to be primary thrust, its about 11 net HP at full voltage.. http://www.outboardelectric.org/brochure.pdf#search='thrust%20per%20HP%20outboard%20motor'
Don K.
Don, I can't tell you much about powering a dinghy, but I have a trolling motor on a 17' bay boat (fishing boat with 90 hp outboard) This is what I can tell you. You are better off to get a trolling motor with a little more power (# of thrust) and be able to run it at a lower power number than to get a low powered motor and have to run it at or near full output. Also, the battery lasts a LOT longer when not used continually. If you are making several trips of relatively short duration 15-20 minutes or so, and there is some time interval between trips, I'd guess that you would be able to make quite a few trips (say 10-15) before you had any trouble. The worst case scenario would mean an extra fully charged battery kept on the sailboat, just in case, and there is nothing wrong with an extra fully charged battery lying around if you need it.
Don, I can't tell you much about powering a dinghy, but I have a trolling motor on a 17' bay boat (fishing boat with 90 hp outboard) This is what I can tell you. You are better off to get a trolling motor with a little more power (# of thrust) and be able to run it at a lower power number than to get a low powered motor and have to run it at or near full output. Also, the battery lasts a LOT longer when not used continually. If you are making several trips of relatively short duration 15-20 minutes or so, and there is some time interval between trips, I'd guess that you would be able to make quite a few trips (say 10-15) before you had any trouble. The worst case scenario would mean an extra fully charged battery kept on the sailboat, just in case, and there is nothing wrong with an extra fully charged battery lying around if you need it.
We have an inflatable dingy with a minkota trolling motor on it and used it to get from anchorage to shore for a 10 day trip and it worked out great. We kept an extra battery for it and I never had to recharge it during the trip. We weren't real far from shore but made several trips per day and I spent some time just poking around the bays. The water was flat when we were using it so I don't know how it would do with some wind or chop. I plan on setting it up this year so I can use the solar charger on it. Rob Morton
That Can't Be Right . . .
I saw your link - still wonder where the truch is on thrust vs. HP. For example: Minn Kota rates their 2hp E Drive electric as drawing 40A @ 48V. Their Endura 46 (46 lbs thrust) draws 42A @ 12V. If input power relates to output power in a linear fashion, then an Endura 46 is about .525 HP. This would equate to around 87 lbs thrust = 1 HP. Based upon Minn Kota's numbers - I would be real skeptical of a 6hp gas only delivering 138 lbs thrust. That would make the Endura 46 a ~2hp motor - and Minn Kota clearly does not claim that. Maybe we can find a better, or confirming source of information? The 75 lb number is something I remember from a catalog, but I don't know if I can find it - it seems at least moderatly close from Minn Kota's input power numbers & their E Drive rating.
I saw your link - still wonder where the truch is on thrust vs. HP. For example: Minn Kota rates their 2hp E Drive electric as drawing 40A @ 48V. Their Endura 46 (46 lbs thrust) draws 42A @ 12V. If input power relates to output power in a linear fashion, then an Endura 46 is about .525 HP. This would equate to around 87 lbs thrust = 1 HP. Based upon Minn Kota's numbers - I would be real skeptical of a 6hp gas only delivering 138 lbs thrust. That would make the Endura 46 a ~2hp motor - and Minn Kota clearly does not claim that. Maybe we can find a better, or confirming source of information? The 75 lb number is something I remember from a catalog, but I don't know if I can find it - it seems at least moderatly close from Minn Kota's input power numbers & their E Drive rating.
Basics
One HP is equal to 1341 watts. At 12V 1341 watts is 112A. At 48V 1341 watts is 28A. This all assumes 100% efficiency, but that is the best you can get. In other words you would not get one hp at the prop. As a rule of thumb, one pound of thrust will require about 10 watt. The Endura 46 consumes 42A at 12V for 46# of thrust. That is equal to 10.9 watts/pound of thrust and is consuming .38hp of electricty. As a further rule of thumb a trolling motor requires about half the hp of a OB. Therefore to get equivalent thrust out of an OB, roughly .76hp is required. Except that a hp is equal to 1341W, all of these relationships are rough.
One HP is equal to 1341 watts. At 12V 1341 watts is 112A. At 48V 1341 watts is 28A. This all assumes 100% efficiency, but that is the best you can get. In other words you would not get one hp at the prop. As a rule of thumb, one pound of thrust will require about 10 watt. The Endura 46 consumes 42A at 12V for 46# of thrust. That is equal to 10.9 watts/pound of thrust and is consuming .38hp of electricty. As a further rule of thumb a trolling motor requires about half the hp of a OB. Therefore to get equivalent thrust out of an OB, roughly .76hp is required. Except that a hp is equal to 1341W, all of these relationships are rough.
lets get the basics right
Watts = Volts x Amps One Horsepower is equal to 747 Watts. H.P. = (V x A) ÷ 747 Thrust is a function of the propeller efficiency, propeller RPM, boat speed, & etc. - not the driving machinery (H.P.). Determining thrust requires a complex set of calculations [sorry cannot help you here
]. It must be remembered that hp is absorbed by the prop as torque, and some driving machinery is better suited to delivering torque, at the required rpm, than others - including the generalization that electric motors are better at delivering thrust than are internal combustion engines. I am unaware of any universal Horse Power to Thrust constant equivalent.
Watts = Volts x Amps One Horsepower is equal to 747 Watts. H.P. = (V x A) ÷ 747 Thrust is a function of the propeller efficiency, propeller RPM, boat speed, & etc. - not the driving machinery (H.P.). Determining thrust requires a complex set of calculations [sorry cannot help you here
]. It must be remembered that hp is absorbed by the prop as torque, and some driving machinery is better suited to delivering torque, at the required rpm, than others - including the generalization that electric motors are better at delivering thrust than are internal combustion engines. I am unaware of any universal Horse Power to Thrust constant equivalent.Rule of thumb - lbs thrust per 200lb load
One of the mfr(can't remember which...maybe Minnekota) gives the following rules of thumb for figuring thrust needed and amps needed. You need 5# thrust for every 200 lbs gross weight of boat(thats including your weight etc) and you will draw ~1 Amp per lb of thrust on 12VDC and about half that with 24VDC. The thrust estimations are for normal semi-Vee fishing boat hulls at normal(whatever that is) trolling speeds. I put a 36# Minnekota on my 18' 1200lbgross daysailor and it pushes it 2.5 knts into a 12 knot wind. So the figures given seem conservative and safe.
One of the mfr(can't remember which...maybe Minnekota) gives the following rules of thumb for figuring thrust needed and amps needed. You need 5# thrust for every 200 lbs gross weight of boat(thats including your weight etc) and you will draw ~1 Amp per lb of thrust on 12VDC and about half that with 24VDC. The thrust estimations are for normal semi-Vee fishing boat hulls at normal(whatever that is) trolling speeds. I put a 36# Minnekota on my 18' 1200lbgross daysailor and it pushes it 2.5 knts into a 12 knot wind. So the figures given seem conservative and safe.
used one two season's now
Usually get about 2-3 weeks until i have to charge. Thinking about going to 1 or 2 motorcycle batt. 1 big battery weighs down stern to much.usually take 5 to six trips a week to and fro. I like it. no fuels, Pray for Wind, Lugeman
Usually get about 2-3 weeks until i have to charge. Thinking about going to 1 or 2 motorcycle batt. 1 big battery weighs down stern to much.usually take 5 to six trips a week to and fro. I like it. no fuels, Pray for Wind, Lugeman
motorcycle batteries loose ability to
charge after a few discharges. A couple of 6V sealed lead acid rechargeable batteries would work, however..
charge after a few discharges. A couple of 6V sealed lead acid rechargeable batteries would work, however..
deep cycle
You need deep cycle marine batteries to operate a trolling motor properly. Regular batteries (such as auto or motorcycle batteries) are not designed to go through the constant discharge/charge all of the time, they are designed to stay charged all of the time, and will not stand up to the cycling that deep cycle batteries are designed for. 4. What does deep cycle mean, and how are deep cycle batteries different? Deep Cycle refers to applications that typically discharge 60 to 70% or more of the battery capacity. An automotive battery is an SLI battery (Starting, Lighting & Ignition.) Its plates are designed to deliver maximum power for a short duration. Starting an engine typically discharges an SLI battery 3% or less. When an SLI battery is used in a deep-cycle application or in a vehicle with heavy accessory loads, the battery life will be shortened proportionally to how deeply and frequently it is discharged.
You need deep cycle marine batteries to operate a trolling motor properly. Regular batteries (such as auto or motorcycle batteries) are not designed to go through the constant discharge/charge all of the time, they are designed to stay charged all of the time, and will not stand up to the cycling that deep cycle batteries are designed for. 4. What does deep cycle mean, and how are deep cycle batteries different? Deep Cycle refers to applications that typically discharge 60 to 70% or more of the battery capacity. An automotive battery is an SLI battery (Starting, Lighting & Ignition.) Its plates are designed to deliver maximum power for a short duration. Starting an engine typically discharges an SLI battery 3% or less. When an SLI battery is used in a deep-cycle application or in a vehicle with heavy accessory loads, the battery life will be shortened proportionally to how deeply and frequently it is discharged.
John Payne
I don’t find this particularly helpful, but FWIW: Trolling Motors - How much thrust is required? from John C. Payne (Author ~ “The Fisherman's Electrical Manual” & “The Marine Electrical and Electronics Bible”) “... The general rule of thumb in choosing the required thrust is to take the total weight of the loaded boat and divide it by 70. For example, if your boat with people and gear weighs a total of 3500 lbs (1700 kg) you divide this by 70. That means that a motor with at least 50 lbs (215 kg) of thrust is required. Another method is 5 lbs thrust for every 200-350 lbs of boat weight. Depending on your fishing the wind and current should be factored in. The draft of a boat affects the drift rate, and shallow draft or high freeboard cabin type fishing boats tend to have a greater wind (sail plane) effect than deeper draft low freeboard ones. Where strong river or tidal flows will be involved greater thrust will be required ...”
I don’t find this particularly helpful, but FWIW: Trolling Motors - How much thrust is required? from John C. Payne (Author ~ “The Fisherman's Electrical Manual” & “The Marine Electrical and Electronics Bible”) “... The general rule of thumb in choosing the required thrust is to take the total weight of the loaded boat and divide it by 70. For example, if your boat with people and gear weighs a total of 3500 lbs (1700 kg) you divide this by 70. That means that a motor with at least 50 lbs (215 kg) of thrust is required. Another method is 5 lbs thrust for every 200-350 lbs of boat weight. Depending on your fishing the wind and current should be factored in. The draft of a boat affects the drift rate, and shallow draft or high freeboard cabin type fishing boats tend to have a greater wind (sail plane) effect than deeper draft low freeboard ones. Where strong river or tidal flows will be involved greater thrust will be required ...”
My dad uses one on his inflatable
My dad uses a cheapo little trolling motor on his inflatable. The battery is a little one that normally goes in an electric wheelchair. It's maybe 10"x6"x8" and I'm guessing it weighs 15 pounds. He didn't spend a lot of money on it since he wasn't sure how it would work out. The trolling motor was very inexpensive - I think it was maybe $100. It's only for fresh water but he uses it in salt and figures he'll replace it a few years down the road and still be ahead. The battery is physically small but it's good for well over an hour of operation before pooping out. I've used his setup. It works very well. Obviously, it's nice and quiet. His trolling motor has speeds from 1 to 5 and 3 works great. It's comparable to a leisurely rowing pace and really saves on the battery. It doesn't have the juice to power into a 20 knot headwind and three foot waves, but neither do I. I'd get the cheapest motor you can find to see if you really like the setup. Get a little battery and see if it has enough juice. You can always upgrade to a deep-cycle batt if you need more power. Deep-cycles are nice but I'd figure that you'd drop one in the drink about every other time you use it - they weigh a ton. Chris I. Clearwater, FL
My dad uses a cheapo little trolling motor on his inflatable. The battery is a little one that normally goes in an electric wheelchair. It's maybe 10"x6"x8" and I'm guessing it weighs 15 pounds. He didn't spend a lot of money on it since he wasn't sure how it would work out. The trolling motor was very inexpensive - I think it was maybe $100. It's only for fresh water but he uses it in salt and figures he'll replace it a few years down the road and still be ahead. The battery is physically small but it's good for well over an hour of operation before pooping out. I've used his setup. It works very well. Obviously, it's nice and quiet. His trolling motor has speeds from 1 to 5 and 3 works great. It's comparable to a leisurely rowing pace and really saves on the battery. It doesn't have the juice to power into a 20 knot headwind and three foot waves, but neither do I. I'd get the cheapest motor you can find to see if you really like the setup. Get a little battery and see if it has enough juice. You can always upgrade to a deep-cycle batt if you need more power. Deep-cycles are nice but I'd figure that you'd drop one in the drink about every other time you use it - they weigh a ton. Chris I. Clearwater, FL
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