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Old 08-01-2007, 06:18   #1
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Electric and Diesel comparison

Hi guys.
I have been lurking here for some time but now must open my mouth.
I have started construction of a Schioning 12.3 Wilderness. Hope to launch early next year.
There are threads here and at other sites that I have been following with great enthusiasm for the obvious reasons. What I have not yet been able to develop however is a sense of equivalency between electric and diesel motors.

In my case twin 20 Hp diesels are appropriate, which equates to 6.5 Hp/ton, so I will work from this.
Fey on their site suggest diesel Hp x .7 or 14 Hp (10 kW). http://www.feys.org/System/our_system.htm
This seems to be the high end with Re-e-power at the other http://www.re-e-power.com . The 4000 to be equivalent to 40 Hp thus the 3000 is equivalent to 20Hp which is 3800 w continuous. Quite a large variation.
The Lagoon is using 10 kW motors but this weighs "Max displacement (EEC) 12,800 kg / 31,800 lbs" (from the site Lagoon 420 - New Catamarans - The Catamaran Company ). An error here, is it 12,800 kg and 28,000 lb or 14,454 kg and 31,800 lb. Take the middle ground and say 13,600 kg with 20 kW or 680 kg/kW. Equate this to my max displacement of 6350 kg and we have 9.3 kW. Twin Re-e-power 3000s is 7.6 kW, a bit short of the lagoon but a lot closer than the 20 kW suggested by Fey’s formulae. Given Lagoon’s research and development with Solomon I would doubt they would be severely under powered so I have used this as the starting point for an existing vessel. Information on other vessels that actually exist seems sketchy at best.

If the Lagoon was powered conventionally at 6.5 Hp/T we get 88 Hp or say twin 40’s. Does this seem reasonable?
Are there any reports on the electric Lagoons performance in various sea states?
Are there any reports on other vessels where enough data is available to further my comparison?
Any more manufacturer sites that may help fill in my blanks, either motor suppliers or boat manufacturers.

Most of the info is splattered around so maybe this thread could form a point of focus.
Mods how about a specific forum for electric prop and related equipment as it will end up across several poorly related places.
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Old 08-01-2007, 09:54   #2
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I happened to 'drag race' a Lagoon 440 to a mooring field in Waypoint, an electric 410 s2. He had about a knot more boat speed than me at cruise on calm water. I also had a drag race with a 38' something or other cat, and we were about equal at cruise, with me having a slight edge. On average, I'd say she cruised at 6.5 kts.

As for sea states, they have an unexpected effect. The max amperage you can draw is 100A, split between two shafts. Cruise is 40A per shaft. As the sea state rises, the amperage fluctuates more. The engine controls are constant speed, not constant power like diesels. As the boat surges into a wave, the motors draw more current. On the back side, amperage falls off as the scews unload. Why they designed for constant speed vs constant power, I can only guess. You probably get finer control when docking.

In sum, I really liked the electric power. It completely changes your sailing experience. You must always have your electric motors energized and throttles bumped forward (you get less drag and more charging current with throttles bumped forward). While I avoid like the plague starting diesels under sail, motor sailing with electric is no different from being under sail alone, save for an extra couple of knots of boat speed. You also have engines immediately available in case of MOB or tacking through light air. I'm sold on the technology. I can't wait for new owners to report back once they cover some miles. It really is a different (and better) way of sailing.

Brett
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Old 08-01-2007, 10:48   #3
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Better until the salt air or, heaven forbid, a dollop of sea water gets to it. Must admit, the quietness of electric is great, the battery capacity or having to run the motor(s) or an engine to supply the juice isn't so enticing.

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Old 08-01-2007, 10:57   #4
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Quote:
Originally Posted by LtBrett
Why they designed for constant speed vs constant power, I can only guess. You probably get finer control when docking.
On of the benefits of the Solomon system (as well as the L420 system I understand) which I believe is related to the constant speed aspect is that you can get additional speed with no net consumption in energy. On the downside of swells/wave you generate and on the upside you assist. I've heard it quoted that this adds .5 to a full knot.
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Old 08-01-2007, 11:09   #5
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I wish I had more to add. Great thread. I'm eager to hear more, as I have loved the "electric wheel" since Solomon came out with it. Another principal advantage would be the weight. To get the same HP, you end up with less weight, including batts, genset, etc... At least that's what the marketing said a while back. If my Perkins 4-108 ever kicks it, I'd look into converting.
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Old 08-01-2007, 13:11   #6
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ESS,
I played with the throttles quite a bit while underway, and while I could get the amperage to flip from positive to negative in swells, the swing was quite small, biased towards the negative. To add .5kts, you need something like 7A per shaft, far more than you get from regenerating. No way are you getting a knot for free. Remember, you are basically down 1kt from propeller drag in neutral, .5kts when bumping the throttles forward to the max recharge point. If you set the throttles so amperage flips positive to negative, you get a miniscule charging current. Perhaps it would be different in a following sea.

Sean,
As far as weight goes, I think you are comparing the weight of 12 8D batteries at about 150 lbs each (1800 lbs) plus perhaps two hundred lbs of motor (conservatively) versus Yanmar 3YM30's which weigh about 300lbs each. I really think the marketing hype for these hybrids is a bit optimistic. I can see the technology developing in two paths, for two different types of sailors: 1. plenty of battery power and full recharge capability and 2. minimal battery weight onboard with reliance on the genny for regeneration or extended motoring. I'm betting the latter takes off. One type of sailing is good for regenerating--10x ratio of sailing to motoring. Most sailors don't have that ratio and would be better served by a simplified (cheaper) system that gives them enough power to clear the mooring field under electric power and return, foregoing the drag and complexities of recharging underway. I can see this type of system being lighter, cheaper, and more reliable than twin diesel. By the way, I estimated the 10x ratio by estimating how much sailing time it would take me to regenerate the amp hours I used motoring out of the harbor. Or you could think about a discharge rate of 80A vs a charging rate (in very favorable conditions) of 8A.

Brett
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Old 08-01-2007, 13:54   #7
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Lithium Ion batteries weigh a lot less!
See the data sheets.
Valence - U-Charge™ Power System – Kilowatts of safe Lithium-ion Power

Link won't post.
valence dot com ucharge
I have no affiliation with the company.
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Old 08-01-2007, 18:24   #8
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Bret 50 amps per motor but at what voltage - need to convert back to kW. What is the top speed in substantial chop and the weight of the vessel? need these to form some sort of comparison.

Valence batteries are not perfect but I will start another thread for this
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Old 08-01-2007, 18:53   #9
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The Valance *claims* are impressive, but is there any outside confirmation of them? I've heard a lot of folks saying that lithium batteries are problematic because of delicate recharging, fire dangers, and low life cycles (i.e. 500 cycles "period) and for these folks to have beaten all the problems in one shot...That's either incredibly good, or too good to be true.

Whenever I see a home page with an "Investor Info" button on it...I wonder if the main purpose isn't selling stock shares to investors.
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Old 08-01-2007, 20:25   #10
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Whimsical,

Waypoint had a motoring voltage of 146. You cannot use 50A per motor to convert to KW as 100A is the maximum current of both shafts combined. As I mentioned, current fluctuates and you cannot operate close to your ceiling without blowing a breaker. I expect the new 420's will have roughly twice the amperage and half the voltage.

As far as Waypoint's displacement, listed at about 8 tons (I don't believe this #), check out Used Lagoon 410 catamaran for sale - Magic for a sister ship, or Catamarans for Sale, Sailing Vacations and Catamaran services. For her performance in chop, I motored her into 6-8 foot seas with 25kts of wind on the bow making about 4 kts on GPS. Her power seemed satisfactory. Keep in mind that conventionally powered Lagoon 410's have, if I am reading correctly, the Yanmar 3YM30's, rated at 30hp. The "area under the torque curve" is much greater for electric motors, so a 12hp electric motor will likely outperform a 30hp diesel until it reaches higher RPM's. I don't know if the conversion factor should be .4 or .7, and I'm not sure anyone else has a rock solid answer on that, either. I recommend putting the theory aside for a moment and baseline your electric motor comparison on a vessel that works in practice. Lagoon 410S2's have both propulsion options.

Brett
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Old 08-01-2007, 20:54   #11
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Quote:
Originally Posted by LtBrett
Whimsical,

I recommend putting the theory aside for a moment and baseline your electric motor comparison on a vessel that works in practice. Lagoon 410S2's have both propulsion options.

Brett
Which is basically what I am trying to do over a range of diferent vessels. The comparison of one type of vessel with both power sources is good to make some determination of equivalency along the lines of kg/kW much like the old hp/ton. I don't think you can translate power requirements from a 10 ton cat to a 5 ton one without it. The claims of manufactures varies widely and it is only through looking at a number of real world situations that the understanding will develop. I don't have the time or inclination to build one of each type and then select the best one so I must do it through theory.
Thanks for a bit more data. I didn't realise the 410 came from the factory with electric, more research.
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Old 08-01-2007, 21:13   #12
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Bret
"Waypoint had a motoring voltage of 146. You cannot use 50A per motor to convert to KW as 100A is the maximum current of both shafts combined."
But you can say that Waypoint has a total power of 14 kW or 570 kg/kW, if the weight is correct. The diesel 410 has 60 hp which suggests 20 hp equates to about 4.5 kW. This adds credence to Re-e-powers claims and detracts from Frey.
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Old 09-01-2007, 08:57   #13
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I guess my point is that there are a number of factors that come across in practice that don't seem to be well captured in a theoretical analysis. First, look at power output at cruising speed vs. maximum power when considering which engine to purchase. I think this concept is especially important when comparing diesel to electric. Check out Yanmar's site and their ratings for the 3YM30. It puts out about 12KW at the propeller at 80% of maximum throttle. Waypoint puts out about 6kw at 80% throttle at the propeller.
Second, voltage and therefore power changes whether on generator or battery. Use 168v to get max power available when the generator is running.
Third, Waypoint is powered by 2 motors rated at 6hp per shaft. Running the numbers I observed, the max HP she is capable of producing is 22.5.
Fourth, you can run a diesel at full throttle. You cannot run Waypoint's electric motors close to full throttle or you will blow a breaker due to the surges in current caused by waves.
Finally, I do not understand why an electric motor putting out roughly half the power of a diesel at the propeller is sufficient. You need to get your arms around this issue by contacting owners of both types of boats. I would like to know how fast a diesel 410 goes at 80% throttle in calm seas. My theory is that a diesel will go faster, and the electric is significantly less powerful. However, the power difference is not noticeable at low speed and all you are giving up is top end. The electric probably has a more aggressive prop pitch so she feels more responsive than the diesel at maneuvering speeds.

I am in no way saying to abandon the theory--just look at the case study first in some detail so you can establish a baseline for your theoretical analysis. And please keep posting your results.

Brett
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Old 09-01-2007, 20:00   #14
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Bret
"Finally, I do not understand why an electric motor putting out roughly half the power of a diesel at the propeller is sufficient."
This was exactly my initial reaction to claims of lower hp for electric and I am still far from being convinced. It is still ultimately about turning a prop regardless of the motor behind it.

I suppose the Fey site being oriented toward stink boats highlights the max power end and a factor of .7 becomes appropriate for their situation. Utilising empirical data from a power boat probably only confuses the issue.

Getting a grasp on the effect of having max torque available at all rpm's underpins this discussion. The question now becomes what max level of thrust is required in a cat. I, and I think most others, equate this to making forward progress in adverse conditions. Given sufficient power to achive this then motoring speed while becalmed in smooth seas becomes minor as most conventionally powered vessels motor to conserve fuel.

"her performance in chop, I motored her into 6-8 foot seas with 25kts of wind on the bow making about 4 kts on GPS"
Was this the maximum power (80% due to current surges) ?
"I would like to know how fast a diesel 410 goes at 80% throttle in calm seas." This would probably add significantly to the discussion, any diesel 410 owners here that could do a couple of tests for us.

I am beginning to think diesels would have more and electric installations are sized around minimum functional levels. After all a watt is still a watt. Size becomes dependent on what one considers to be a safe minimum in conditions likely to be encounterd. Most electric and diesel comparisons are essentially smoke and mirrors because we are not comparing apples with apples. What was that old joke about 2 hp/ton for normal people and 4 hp/ton for americans.

Still I am not counting out electric due to the many other benefits.
Mike
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Old 09-01-2007, 20:05   #15
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Mike, I suspect the confusion comes from the fact that both hp and torque are needed, and the output curves for each are different for each engine/motor type. No doubt a prop needs a certain amount of both and that will vary with the conditions, i.e. speed and sea state. If running an electric motor at full throttle causes it to overheat when forcing against rough wx, that tells me the electric motor (in that situation) just doesn't have enough power compared to another engine (diesel or electric) which could continue to overcome the resistance.
Which goes back to why the USN used to require engines to be rated at 1/3 of their full output, i.e. continuous duty rating /vs/ combat rating. Running engines flat out seems to encourage all of them to go back to the great engine factory in the sky. Sometimes, more dramatically than others.<G>
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