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Old 13-06-2014, 16:21   #136
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Re: Electric Propulsion on Catamarans

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Originally Posted by deckofficer View Post
Sounds like you are defeating your own argument. You say electric boats are underpowered but then state your 54' 32 ton boat could run at 8 kt on 1 gallon per hour. 1 gallon per hour works out to about 13hp.
For someone with so much offshore experience you seem to be capable of massive amounts of wishful thinking. The 1gal/hr was on glassy water in dead calm conditions. When powering into 8' chop and 40 kn winds we needed every bit of the 120hp we had to maintain 4kn ahead. Trying to design a boat with just enough power for the best possible conditions eliminates the entire history of boating... That storms happen, and if you are going to be out in them, be prepared.


Secondly,

I frankly doubt that your design specs will work as intended. The numbers just don't work. At least not according to the numbers I could find on the internet. If you believe them, then publish what you are planning on using (model numbers included). I am always willing to be proven wrong, but none of the boat designers or builders I have talked to, and the largest catamaran builder in the world, think electric propulsion is realistic for prime time.

Sure the entire boat building industry could be wrong (have been a lot in the past), but it takes more than just throwing out some guesstimates to justify it. Particularly when those who have tried it have ended up right back where the numbers indicate. Not failures exactly since it was what was predicted, but certainly not something suitable for most peoples use.
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Old 13-06-2014, 17:39   #137
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Re: Electric Propulsion on Catamarans

Greg,

As an attorney I'm sure you posses good comprehension skills, so here goes.

On a displacement hull, power requirements stay linear over the speed range, i.e. no change in wetted surface as in a planing hull that produces lift as speed increases. Up to hull speed, a double in speed requires an 8X increase in power.

As you search the market for a suitable candidate for low power propulsion, you won't find coefficient of drag specs on the boats but you will find top end speed for a given power. When you find a offshore capable powerboat that can run at 25 kt on 100 hp, you have a winner. Bond in Poland makes such a boat called the Motorcat 30. Larry Graf the designer of the popular Glacier Bay powercats hangs a pair of 250 hp outboards to achieve that same speed of 25 kt. Larry has now moved on to a more efficient proa design with his new company Aspen. I have drifted, but what I'm getting at is what was considered a very efficient hull design just a decade ago has been usurped by new designs driven by market forces demanding less fuel usage.

So if a boat can run in the calm at 25 kts on 100 hp, it will run at 12.5 kt on 12.5 hp. At 6.25 kt the power requirement drops to 1.56 hp.

The designers at Bond are starting early tests using a single Minn-kota e-drive and top speed is 5.5 kt. This is a 1500 watt electric outboard. Torqeedo makes outboards up to 80 hp, but the Cruise 4.0 at 4000 watts is suitable, a pair for the Motorcat, total 8000 watts. As you can see from the power requirements at lower speeds, 1500 watts is good for cruise, the remaining 6500 watts would be for conditions that warrant, like tidal currents entering a breakwater, etc. For normal passages, that is the reason for weather routing, to avoid conditions that push your vessel's capabilities.

For determining range you have to know how many whr per mile at your cruise speed is required. Tests show the Motorcat 30 at a cruise speed of 5.5 kt is consuming 1500 watts which gives you <300 whr per mile. The rest is just math.
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Old 13-06-2014, 22:58   #138
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Re: Electric Propulsion on Catamarans

Bob,

I don't know that the Glacier Bay was ever considered all that efficient compared to other power cats. The Twin Vee for instance was always much more fuel efficient than the Glacier Bay. Certainly they are more efficient than a deep Vee hull, but so what? The boats aren't really that comparable. And while the Motorcat 30 is impressive for what it is, it isn't any more fuel efficient than my Twin Vee 26. Excepting that I have bigger engines for higher speed runs.

As for the electric Motorcat test. They have reported nothing. Until they publish what the test conditions were, and give the raw data as far as I am concerned it is a publicity stunt done by people financially motivated to report good numbers.

For instance, they never mentioned if the test was done with all 1600lbs of expected batteries. Which on a 2600lbs boat is a massive increase in displacement.

The nonsense that 8hp electric is the same as 20hp diesel is just wrong. It is a flat out lie, and any engineer of any stripe knows better. Which raises major validity questions about the rest of the data they report. 20hp is 20hp regardless of the source, wether it is produced by electric motors, diesel motors, or hamsters on a wheel. HP by definition is a measure of work done and has nothing to do with the source of the power.

Secondly, the power demand is not quite that linear, but even if it is so what? 8kw leaving the batteries every hour, takes X amount of batteries, and Y amount of solar panels to recharge the batteries. Figuring out what those numbers is really simple. And they don't look good for electric propulsion.

Which is probably why the E-MC is planning on carrying a generator to recharge the batteries. Which of course further increases the weight, and requires all the complexity of an installed engine. Except instead of converting rotational energy to drive power the E-MC concerts rotation energy - electricity - chemical storage - electricity - rotational power. With progressive power losses at each step.

Like I keep saying, if you are ok with the range limitations that electric demands, go for it. I did and was very happy with my electric sailboat. But I certainly don't think it is reasonable for most people under most situations.
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Old 14-06-2014, 00:03   #139
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Re: Electric Propulsion on Catamarans

The power claims is not a stretch like you suggest. They say the thrust of the 4.0 matches that of a 9.9 hp ICE outboard. Propulsion power is that of a 8 hp ICE. Running two means the thrust of 19.8 hp ICE. You can't allow a 0.2 hp promotional fudge factor? Boy your hard core.

I can't answer why Motorcat is even considering a lead acid bank and I do agree with you that lugging 1600 lbs of lead for just 19.2 kwhr is a waste. And since it is LA with a 50% DOD, you only have 9600 whr usable. By going with LiFePO4 you have 29,120 usable whr for 736 lbs.

The gen set they plan on using is DC, which for any given output weighs much less than an AC gen set. The inefficiencies you mention with multiple conversions is true for a fully loaded scenario but isn't for any power level less than full power. If cruise speed requires 2 hp and you want the safety margin of 20 hp, it is in fact more efficient to size the electric at 20 hp and the DC gen set at 2 hp. You burn more fuel running a 20 hp ICE at the 2 hp level than a 2 hp ICE. It takes more energy to spin the rotational mass of a larger engine at a 1/10 throttle setting than a smaller engine at full throttle for the same output. Many years ago I tested this on the Noble Paul Wolff that I mentioned in an earlier post. In benign conditions where the ship only needed 2 mw of power from the generators we would run (2) of the 4.7 mw gen sets for safety if one shut down unexpectedly. I asked the engineer to run just one gen set and measure fuel burn. After that I requested all 7 gen sets to be brought on line to produce the shared load of 2 mw. You would be surprised of the increase in fuel burn spinning all those engines at such a low setting.
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Old 14-06-2014, 02:45   #140
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Re: Electric Propulsion on Catamarans

Bob,

quite frankly, I would love to carry a battery with the equivalent of a can of Diesel around in my pocket - but that's pipe dreams. And since I am cruising now and not in the - hopefully not too - distant future, I have to live with today's technology.

Greg has already mentioned it, as I have - in "lake" conditions all electric propulsion may have benefits. But in ocean conditions it's a different ball game. I second his statement that in shitty weather I have both engines running well above 50% power - and that sucks up fuel at an alarming rate. And today's batteries simply won't sustain this kind of draw. 29 kWh? Would have lasted about 20 minutes. Allow for 50% inefficiencies - ok, then it lasts 40 minutes. This does not address the issue! When you're at the stage where all sails are tucked away as best as possible and you're trying to keep your boat steady with its butt facing the waves, it's usually a condition that will last for quite a few hours, if not days. And if you're going against it, it is worse because the power required to do so is much bigger.

And even if you are discounting bad weather: At the beginning of our cruise we went through the strait of Gibraltar - due to time constraints against a force 6 on the nose. The tide was not in our favor (our mistake - coming from the Med it takes some practice to work with tides) and at the bottleneck we were inching forward with about 2.5 knots with both engines running at 80%. And that went on for hours! And no, this is not just the bad luck of bad sailors, this is real world. Situations like this will arise, and with a tiny battery pack I would be scared to death of finding myself slowly drifting backwards towards something that I would much rather avoid.

End of my rant - I am bailing out of this thread. It is too much theory, too much wishful thinking, not enough realism for me. And yes, I will continue to watch technology - I love my solar and wind power, as stated above. But for propulsion in situations where the "normal" wind power won't cut it - no way.

I wish you light winds and flat seas...

Oliver
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Old 14-06-2014, 04:27   #141
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Re: Electric Propulsion on Catamarans

perhaps we have to wait until TESLA MOTORS, the electric car maker, perfects it's technlogy to a point where we will be able to use it on cats......tesla electric cars are amazing, totally and fully electric
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Old 14-06-2014, 07:14   #142
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Re: Electric Propulsion on Catamarans

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Bob,

quite frankly, I would love to carry a battery with the equivalent of a can of Diesel around in my pocket - but that's pipe dreams. And since I am cruising now and not in the - hopefully not too - distant future, I have to live with today's technology.

Greg has already mentioned it, as I have - in "lake" conditions all electric propulsion may have benefits. But in ocean conditions it's a different ball game. I second his statement that in shitty weather I have both engines running well above 50% power - and that sucks up fuel at an alarming rate. And today's batteries simply won't sustain this kind of draw. 29 kWh? Would have lasted about 20 minutes. Allow for 50% inefficiencies - ok, then it lasts 40 minutes. This does not address the issue! When you're at the stage where all sails are tucked away as best as possible and you're trying to keep your boat steady with its butt facing the waves, it's usually a condition that will last for quite a few hours, if not days. And if you're going against it, it is worse because the power required to do so is much bigger.

And even if you are discounting bad weather: At the beginning of our cruise we went through the strait of Gibraltar - due to time constraints against a force 6 on the nose. The tide was not in our favor (our mistake - coming from the Med it takes some practice to work with tides) and at the bottleneck we were inching forward with about 2.5 knots with both engines running at 80%. And that went on for hours! And no, this is not just the bad luck of bad sailors, this is real world. Situations like this will arise, and with a tiny battery pack I would be scared to death of finding myself slowly drifting backwards towards something that I would much rather avoid.

End of my rant - I am bailing out of this thread. It is too much theory, too much wishful thinking, not enough realism for me. And yes, I will continue to watch technology - I love my solar and wind power, as stated above. But for propulsion in situations where the "normal" wind power won't cut it - no way.

I wish you light winds and flat seas...

Oliver
I don't understand this need to plow into head seas for hours. Even though I have plowed out of harbors into 25 knots of head winds when I had too. But, for the most part I avoided it even when I had a diesel and still avoid it with electric propulsion. It was never fun and you and the boat takes a pounding. As the sign in the Navel Academy says:
"“You can out-think the ocean, but you can’t out-slug the ocean.”
As was pointed out you waste a lot of energy doing so no matter what propulsion system you have. I also don't go up down escalators for the same reason.
But, I can and have used EP to tweak things so I make it past a buoy after the wind and currents stopped being friendly or I wanted to avoid another tack to make it under the Verrazano Bridge in gale conditions. Don't forget a lot of ferries and ocean liners like the QM2 also use electric propulsion and they are not built for just calm conditions. Even this former NYC Fireboat uses electric propulsion and has done so for over eighty years. So EP has been here for awhile but, it's just starting to makes it's way into smaller boats.
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Old 14-06-2014, 10:52   #143
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Re: Electric Propulsion on Catamarans

Mike,

I have followed your blog for a while, and am jealous of the system you have created. If I ever need to repower my boat I am going to shamelessly copy it. So let me be clear, I am not against electric power. What I am against is putting up insainly optomistic numbers and just hoping people will buy them.


Bob,

They are claiming that twin 5.3hp electric motors are the same as twin 10hp diesel motors. It's nonsense. If they were replacing one diesel with two electric motors then fine. Which means the boat needs four torquedos to replace her two diesels.
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Old 14-06-2014, 10:56   #144
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Re: Electric Propulsion on Catamarans

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They are claiming that twin 5.3hp electric motors are the same as twin 10hp diesel motors. It's nonsense.
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.
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Old 14-06-2014, 12:06   #145
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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.
Thank you for that post, I was starting to feel like the lone rider on this. You reminded Greg of the very important fact of torque. On an ICE both peak hp and torque happens at a single rpm, whereas peak torque on an electric motor is available at 1 rpm. The other thing the Greg doesn't seem to understand is the hp rating for a motor is given for continuous duty and all electric motors have a much higher peak rating. The ICE just gives the peak rating at whatever rpm that happens at.

Case in point, my Etek motor is rated at 4 hp @ 48 volts. Could a 4 hp ICE accelerate my 250 lb mass along with the scooter's 100 lb to 45 mph in 2 seconds? Not hardly. For an electric motor like my Etek if I feed it 48 volts and my controller can only muster 200 amps that would be 12.8 peak hp. My current controller is capable of 400 amps, thus a peak of 25.6 hp, and that is why it can accelerate like it does.


This is a scooter I built, if it was a rodeo bull it would have a perfect record. 5 friends/family have tried to ride it, all have flipped it on take off and landed on their butts. I give a good preflight but they still don't comprehend that 1 rpm torque potential. As an attorney you can understand product liability and the reason you can't purchase a little monster like this off the shelf. For long range I have a 490 lb battery trailer that it has no problems towing, and that is a total of 840 lbs. Lets see a 4 hp ICE pull that off.

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Old 14-06-2014, 15:49   #146
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Re: Electric Propulsion on Catamarans

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It is not nonsense. It is quite correct..

I've been on boats powered by Torqeedo's and by Yamaha 9.9hp High thrust motors. The Torqeedos do NOT match the Yamaha's.
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Old 14-06-2014, 16:00   #147
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Re: Electric Propulsion on Catamarans

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I've been on boats powered by Torqeedo's and by Yamaha 9.9hp High thrust motors. The Torqeedos do NOT match the Yamaha's.
In what respect, top end speed or static thrust?

I'm sure it is a match in thrust unless Torqeedo skimps on what the controller can produce in amps. My Etek spins 76 rpm per volt. When you just crack the throttle for say 5 volts, the amps will quickly ramp up to get the motor to 380 rpm. If the controller is capable of 400 amps like the one I'm using, that is 5 volts X 400 amps = 2000 watts / 746 = 2.6 hp almost immediately and if your not ready, well, plop. I doubt the controller on the Cruise 4.0 is anywhere near 400 amps, but it is high enough to match a 9.9 hp on thrust.
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Old 14-06-2014, 16:21   #148
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Re: Electric Propulsion on Catamarans

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In what respect, top end speed or static thrust?

I'm sure it is a match in thrust unless Torqeedo skimps on what the controller can produce in amps. My Etek spins 76 rpm per volt. When you just crack the throttle for say 5 volts, the amps will quickly ramp up to get the motor to 380 rpm. If the controller is capable of 400 amps like the one I'm using, that is 5 volts X 400 amps = 2000 watts / 746 = 2.6 hp almost immediately and if your not ready, well, plop. I doubt the controller on the Cruise 4.0 is anywhere near 400 amps, but it is high enough to match a 9.9 hp on thrust.
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.
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Old 14-06-2014, 17:04   #149
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Re: Electric Propulsion on Catamarans

Sounds like you were in a position to A B the two outboards. Could you elaborate as to the type of boat and were you using the Torqeedo LiPO battery? Anything else you can remember about the test would be appreciated.
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Old 14-06-2014, 19:36   #150
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Re: Electric Propulsion on Catamarans

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Sounds like you were in a position to A B the two outboards. Could you elaborate as to the type of boat and were you using the Torqeedo LiPO battery? Anything else you can remember about the test would be appreciated.
i believe it was a 44ft Bob Oram designed sailing catamaran similar to 44C own vessel.
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