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Old 14-06-2014, 21:39   #151
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Re: Electric Propulsion on Catamarans

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Originally Posted by 44'cruisingcat View Post
They didn't match in any respect. Put the Yamaha's in gear and you get an instant response. The boat moves. Open the throttles and there is push. Much more than the Torqeedo's. Maybe the electrics have far more torque at 1 RPM, but so what? The Yamaha's don't stall when you put them in gear. But when you put them in gear the boat moves. When you're moving forward and you hit reverse the boat stops. Quickly. More quickly than with the Torqeedo's. (Actually their reverse thrust is pretty poor.)

And the Torqeedo's (The 4000's I experienced) aren't low-revving high torque motors. They have a 10:1 reduction gearbox. So at 1000 RPM of the prop, the motor is spinning at 10,000. Actually the motor looks more like it belongs in a model aeroplane than in boat.
Sounds like the wrong size propellers may have been chosen for the Torqeedos.
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Old 14-06-2014, 22:47   #152
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Re: Electric Propulsion on Catamarans

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It is not nonsense. It is quite correct. The rated power is at whatever rpm yields max power. What matters is thrust at the propeller. That requires torque at low speeds. Electric motors generate very high torque at low speeds. Diesel engines generate very low torque at low speeds. So, to get the needed torque, one can either choose a low-power electric motor or a high-power diesel engine.

With the single-speed gearbox found on boats, a diesel engine needs to be at least twice as powerful as an electric motor to avoid stalling.
It is nonsense. Horsepower is a measure of work done. That's it. By definition a horsepower is the amount of wrk done by lifting 33,000lbs one foot in one minute. That's it, that's all horsepower is, and there is no allowance for where the power comes from. Wether by gas, diesel, electric, or hamster wheel it is all the same. Alternatively HP can be defined as 745.7 watts.

Again it doesn't matter what method of power delivery is used, they are all the same. In fact the whole point of creating the original definition of horsepower was to be able to fairly compare different ways of generating the power.

It is fundamentally dishonest and wrong to argue that electric motors provide more HP than their rated output.
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Old 14-06-2014, 23:03   #153
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Re: Electric Propulsion on Catamarans

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It is fundamentally dishonest and wrong to argue that electric motors provide more HP than their rated output.
You are deeply confused. No one is making that argument.
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Old 14-06-2014, 23:07   #154
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Re: Electric Propulsion on Catamarans

HP is HP, but gasoline engine HP ratings are PEAK.
whereas an electric motor is rated as CONTINUOUS, and can have a PEAK HP that is double, triple, even quadruple the continuous rating,
so a 100HP electric motor can output 400hp..for a short time.
A 100HP engine can output 100HP for a short time until it blows up.

However, electric motor ratings are changing when they compete with engines, and boat engines are generally rated less peaky,
so the above difference may not be so dramatic today.

Quote:
Originally Posted by Stumble View Post
It is nonsense. Horsepower is a measure of work done. That's it. By definition a horsepower is the amount of wrk done by lifting 33,000lbs one foot in one minute. That's it, that's all horsepower is, and there is no allowance for where the power comes from. Wether by gas, diesel, electric, or hamster wheel it is all the same. Alternatively HP can be defined as 745.7 watts.

Again it doesn't matter what method of power delivery is used, they are all the same. In fact the whole point of creating the original definition of horsepower was to be able to fairly compare different ways of generating the power.

It is fundamentally dishonest and wrong to argue that electric motors provide more HP than their rated output.
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Old 15-06-2014, 10:28   #155
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Re: Electric Propulsion on Catamarans

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You are deeply confused. No one is making that argument.
Actually they are.

The argument was 13hp electric is equivalent to 40hp diesel. That is flat out wrong. What they appear to be confusing is the HP needs of a typical automobile and the HP needs of a boat.
- Electric cars often are equipped with much lower HP than the equivalent gas/diesel powered car. The reason they can do this is once at freeway speed, it may only take 20-30hp to maintain 70mph. This means you are using a small fraction of the typical 100-200hp gas/diesel motors power. The reason they provide such large motors is to accelerate more effectively. At the lower RMP just starting out, the motor is only putting out a small percentage of the rated HP & torque, so in order to get brisk acceleration the gas/diesel needs an engine rated for higher HP.
- Electric boats have far different needs, especially slow displacement vessels. Unless something has gone wrong, no one uses full throttle while docking and anchoring, so that doesn't really factor in. The difference in 7 vs 15 seconds to go from zero to 6kts, is not relevant to a cruiser who will get up to speed and leave it there for hours. The result is boat motors are sized to handle cruising speed while fighting wind and waves. In this scenario, the motor should be up around it's ideal RPM, so you do have the rated HP & torque available and can put it to use. If you try and use an electric motor of 1/4 the diesel HP suggested, it's competing on equal terms and will lose out because it brings far less HP to the party.
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Old 15-06-2014, 10:39   #156
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Re: Electric Propulsion on Catamarans

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- Electric cars often are equipped with much lower HP than the equivalent gas/diesel powered car. The reason they can do this is once at freeway speed, it may only take 20-30hp to maintain 70mph. This means you are using a small fraction of the typical 100-200hp gas/diesel motors power. The reason they provide such large motors is to accelerate more effectively. At the lower RMP just starting out, the motor is only putting out a small percentage of the rated HP & torque, so in order to get brisk acceleration the gas/diesel needs an engine rated for higher HP.
- Electric boats have far different needs, especially slow displacement vessels. Unless something has gone wrong, no one uses full throttle while docking and anchoring, so that doesn't really factor in. The difference in 7 vs 15 seconds to go from zero to 6kts, is not relevant to a cruiser who will get up to speed and leave it there for hours. The result is boat motors are sized to handle cruising speed while fighting wind and waves. In this scenario, the motor should be up around it's ideal RPM, so you do have the rated HP & torque available and can put it to use. If you try and use an electric motor of 1/4 the diesel HP suggested, it's competing on equal terms and will lose out because it brings far less HP to the party.
Electric cars have only slightly less powerful electric motors than hydrocarbon engines in conventional cars. The reason is that cars with reciprocating hydrocarbon engines have multi-speed gearboxes to compensate for the lack of low-end torque. Boat engines are sized to avoid stalling. If one were willing to put a multi-speed gearbox on a boat, then it could do fine with less power, as it can with an electric motor, which doesn't need a multi-speed gearbox because electric motors have relatively flat torque curves and so are much less prone to stalling.
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Old 15-06-2014, 12:25   #157
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Re: Electric Propulsion on Catamarans

All I know is typical cruising lends itself more to solar electric than cars, yet we have the electric cars now. In a car you need the ability to climb mountain grades, hold a minimum speed that is fast and consumes a lot of energy.

In cruising (not crossing oceans) slow speed is acceptable and doesn't hold up traffic. While at anchor the solar array is collecting more energy than domestic needs require, thus slowly filling "the tank" for the next short passage. With solar arrays sized for this service, one can enjoy an electric galley, electric dinghy, AC, etc while on the hook. Best of both worlds in my opinion.

The last time I was cruising, typically I would enjoy an anchorage for a week and move on, and repeat. Rather perfect scenario for solar electric propulsion.
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Old 15-06-2014, 13:15   #158
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Re: Electric Propulsion on Catamarans

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Originally Posted by nimblemotors View Post
HP is HP, but gasoline engine HP ratings are PEAK.
whereas an electric motor is rated as CONTINUOUS, and can have a PEAK HP that is double, triple, even quadruple the continuous rating,
so a 100HP electric motor can output 400hp..for a short time.
A 100HP engine can output 100HP for a short time until it blows up.
Lots of misinformation in this thread.

CONTINUOUS power rating of an engine is just that, continuous. All it says is that a given motor (be it electric or combustion), under specified environmental conditions (temperature, pressure, etc.), can supply stated power continuously = 100% duty cycle. A 100HP car combustion engine can deliver FULL continuous power (100HP) continuously. If in doubt look at German highways and German cars designed to go 'pedal to the metal' on those highways. They do not blow up.

PEAK power is an area for manipulating numbers (aka marketing). Both electric and combustion engines can be overdriven - be it overvoltage or injecting nitro and boosting pressure - for a limited time. Now, this is hardly useful when one is faced with opposing wind/current/waves for any length of time - right? Especially when stated peak power numbers are given, but a corresponding duty cycle is not.

Finally, and most importantly, engine output power is a linear function of troque and rotations per minute:

Engine Output PWR = Torque * RPM

so stating that electric engines have 'full power' from 0 RPM is incorrect. They may have full torque right from the start, but to deliver actual power they need rotational speed too.
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Old 15-06-2014, 13:26   #159
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Re: Electric Propulsion on Catamarans

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All I know is typical cruising lends itself more to solar electric than cars, yet we have the electric cars now. In a car you need the ability to climb mountain grades, hold a minimum speed that is fast and consumes a lot of energy.

In cruising (not crossing oceans) slow speed is acceptable and doesn't hold up traffic. While at anchor the solar array is collecting more energy than domestic needs require, thus slowly filling "the tank" for the next short passage. With solar arrays sized for this service, one can enjoy an electric galley, electric dinghy, AC, etc while on the hook. Best of both worlds in my opinion.

The last time I was cruising, typically I would enjoy an anchorage for a week and move on, and repeat. Rather perfect scenario for solar electric propulsion.
Then what you know is wrong.

Cars in general need very little power to a maintain speed, and most driving is done in start and stop traffic, which allows electric vehicles to take advantage of regenerative braking. Boats require high power at operating speeds, since boats spend very little time accelerating. Even an ev in the mountains will spend roughly half it's time braking as it comes down the back side of the mountain.


If you are ok averaging a hundred miles a week that's fine. It meets the capability of today's PV panels, means you don't have to worry about weather windows, and can wait for glassy calm days to leave. Most if not all cruisers like to cruise further, go faster, and while keeping an eye out for weather, don't require a <2kn breeze before they depart.

If there is better equipment out there, fine. Give the the name of it, a manufacturer spec sheet, and some real world testing to justify it. Otherwise it's just vapor wear. PV panels can't provide enough electricity for motive power, and the engines you have mentioned don't have the HP to make cruising possible. Add in a large diesel generator and lots of fuel, with bigger electric motors, and it's certainly possible. But then you are right back to diesel movers, but less efficiency.
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Old 15-06-2014, 14:32   #160
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Re: Electric Propulsion on Catamarans

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Then what you know is wrong.

Cars in general need very little power to a maintain speed, and most driving is done in start and stop traffic, which allows electric vehicles to take advantage of regenerative braking. Boats require high power at operating speeds, since boats spend very little time accelerating. Even an ev in the mountains will spend roughly half it's time braking as it comes down the back side of the mountain.


If you are ok averaging a hundred miles a week that's fine. It meets the capability of today's PV panels, means you don't have to worry about weather windows, and can wait for glassy calm days to leave. Most if not all cruisers like to cruise further, go faster, and while keeping an eye out for weather, don't require a <2kn breeze before they depart.

If there is better equipment out there, fine. Give the the name of it, a manufacturer spec sheet, and some real world testing to justify it. Otherwise it's just vapor wear. PV panels can't provide enough electricity for motive power, and the engines you have mentioned don't have the HP to make cruising possible. Add in a large diesel generator and lots of fuel, with bigger electric motors, and it's certainly possible. But then you are right back to diesel movers, but less efficiency.
This is getting a bit nuts. You just like to argue. I've given this example before and here it is again. First the catamaran chosen was a heavy, commercial vessel, so not ideal. Then lead acid batteries were used, also heavy and lower energy density than the LiFePO4 cells that I am currently using. The solar panels aren't light either and about 14% efficient. Even with all these negatives it crossed the Atlantic on just 10 kw of solar.

transatlantic21: The world's first crossing of the Atlantic on a solar boat

My plans are a cat of 1/3 the weight and a more efficient hull. The solar panels are 20% efficient and each 180 watt panel weighs 6 lbs, not 50 lbs. LiFePO4 rounds out the package and I have no intention of crossing oceans. 30 to 40 miles per day is fine by me, with the battery storage for 120 miles in 24 hours.

Greg,

What part of the Atlantic 21 are you having a hard time wrapping your mind around?
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Old 15-06-2014, 14:37   #161
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Re: Electric Propulsion on Catamarans

deckofficer is quite correct that boats can go slow which makes electric power more viable for propulsion. One just has to live with reduced range.
Or a hybrid with additional propulsion, sails or engines.

The same view can be said regarding solar panels for house loads. If they can't provide enough power for the Air Conditioning, then you would say they are useless since you need a generator anyway.

Because something doesn't meet YOUR needs does NOT mean it doesn't meet the needs of OTHERS. What gives Mr. Stumble the authority to speak for 'MOST IF NOT ALL'? Don't think they can think for themselves?
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Old 15-06-2014, 14:50   #162
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Re: Electric Propulsion on Catamarans

I'd love to drop two of these in and keep one slightly bigger genset.



Synchronous permanent magnet electric motor
Saildrive with 1,93:1 reduction
Lightweight: Weighs only 46.5 kg (motor & saildrive)
The only complete electric inboard propulsion system with
Closed circulation liquid cooling, provides both cooling and lubrication
EMC-certification
Technical Data:
Nominal power: 15 kW
Nominal torque: 65 Nm
Speed: 2200 rpm
Reduction ratio: 1,93:1
Nominal battery voltage: 48 V
Weight: 46.5 kg / 102.5 lb



And people still say electric cars wont works... Well that view is finally getting destroyed. Still held on by old folks


Oh after 2 1/2 years of my Nissan Leaf... No oil no maint. at all.. I did just buy new tires..

And I use 70% of the battery capacity every day, always wonder why people say only 50% of a battery is available..??
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Old 15-06-2014, 14:54   #163
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Re: Electric Propulsion on Catamarans

Jack,

Besides that, what has Stumble shown as to his expertise in this arena? At least I have a background in both electric vehicles and off grid home power. I've given examples of others successfully doing the same thing, i.e., SolarWave, Atlantic 21, Ra doing the Loop, and Reuben Trane's Island Pilot DSe cat. Not to mention the monster PlanetSolar.

Also in my electric kayak I'm getting 80 miles from 62 lbs of lithium cells.
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Old 15-06-2014, 15:44   #164
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Re: Electric Propulsion on Catamarans

Getting back to the Torqeedo Cruise 4.0 vs a 10 hp outboard......

Check out the specs - even Torqeedo only claim 1800 Watts "Propulsive power" and ">45%" efficiency.

http://www.torqeedoaustralia.com/Tor...e%20Remote.pdf

Whereas a 10 hp outboard produces 10 hp - 7400 Watts AT THE PROPSHAFT.

Also compare props and rpm - the cruise 4 spins a 12 x 10 prop at 1000 rpm. The Yam 9.9 HT spins a 12 x 9 prop at around double that.

They're far from equal.
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Old 15-06-2014, 16:26   #165
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Re: Electric Propulsion on Catamarans

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Getting back to the Torqeedo Cruise 4.0 vs a 10 hp outboard......

Check out the specs - even Torqeedo only claim 1800 Watts "Propulsive power" and ">45%" efficiency.

http://www.torqeedoaustralia.com/Tor...e%20Remote.pdf

Whereas a 10 hp outboard produces 10 hp - 7400 Watts AT THE PROPSHAFT.

Also compare props and rpm - the cruise 4 spins a 12 x 10 prop at 1000 rpm. The Yam 9.9 HT spins a 12 x 9 prop at around double that.

They're far from equal.
2240 watts of propulsive power and 56% efficiency.
http://www.torqeedo.com/us/electric-...ata-dimensions

A slower turning prop at a higher pitch is more efficient than a faster turning prop at a lower pitch. As you increase the prop speed, slip and cavitation increase. The main reason you can't run a high pitch prop on an ICE is it would stall it. This is where the low rpm torque of an electric motor allows the use of a slower turning prop of a higher pitch. To drive this point home, on large ships the prop is pitched for the design speed (say 20 kt) at 112 rpm. Our slip percentage is lower than any recreational vessel, it has to be for that service.

I'm not defending Torqeedo, they are overpriced IMHO but their design and power would give me the most distance per watt of anything else that is commercially available.
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