Electric and Diesel comparison

[LtBrett]

This is kind of fun. The more I think about this issue, the clearer the answers become. Ok, first, the performance I quoted in chop was at 80% throttle. Second, I'm making progress figuring out the difference between electric and diesel drive application. Confine the discussion to kw to keep it clear. Look at the kw curve of the diesel engine:

http://www.yanmarmarine.com/products...0_TechData.pdf
Remember the curve indicates a performance envelope, or the MAXIMUM power available at any given rpm. The actual power put out by the motor at cruise will be less. You set cruise by adjusting throttles until you get the desired rpm. If it only takes 6kw in calm seas to maintain 3000 RPM, that's all the engine will put out, and you'll never know exactly how much power you are using. Under this somewhat contrived example, you would have 6 additional kw at 3000 rpm available if you need to accelerate or if you are pushing against weather. Compare this with the electric motor that defines cruise not as an rpm but as a power setting. It just spins the shaft as fast as it can using all its 6kw. The propeller is probably pitched to give a 6.5 kt cruise (whatever rpm that may be) with 6kw of motor power.

This is a difficult explanation for me to make clearly and briefly. Here's a real world example on a diesel boat to illustrate. Your fuel consumption in gph is higher when heading into weather vs. running with weather, even though your cruising rpm may be the same. This is because your engine is more heavily loaded in the former case. In other words, it is operating closer to its max power curve seen in the literature. Now think of an electric motor as always operating on its max power curve, like a fully loaded diesel.

This corroborates my theory that electric boats are, in fact, underpowered on the top end. But the bottom line stands: Waypoint had enough power in the conditions under which I operated her. Heavier seas/wind might be an issue. You need more owner feedback.

Brett

[Whimsical]

Brett
Give the man a cigar! and yes it is fun.
The output of the diesel can be measured if the fuel flow can be ascertained. Many people would know their cruising fuel consumption in calm conditions given all the stories of needing to motor in no wind. Few would have reliable data on fuel consumption in heavy seas I would think, especially as the definition of heavy sea is variable. 1 Ltr/Hr is roughly 5hp or 4kW and if I remember correctly there have been a few accounts of 1.5-2 Ltr/Hr at 5-6 Knts on a heavy cat in calm conditions. 6-8 kW This doesn't tie in well with your experience (80 A @ 140v = 11kW). More confusion.

It sounds as if you would be happy to have some more power just in case. What would you think from your experience - 20kW ?
You don't believe the claimed weight of 8T? so what would you think fair 10T?

At this point in time if I was to commit to electric it would probably be thinking along the lines of your power 14 kW in my weight boat 6.5t max loaded. About 12 kW for the genset and 12kW Hr of batts. This would give maybe 30-40 mins of operation with a discharge to 20% in an emergency and a good house bank at anchor. If the weights don't work out at this power level then they won't work at higher and my participation ceases.
I realy liked the Re-e-power pods but at this power level I would need two model 4000 and am not keen on 4 props, although it would sure give some redundancy.
More research (fun). Keep you all posted
Mike

[gosstyla]

OSSA has a technical paper on their site that discusses some of what you are getting into although more from the comparision of efficiency between diesel and diesel/electric. See:

Diesel-electric marine propulsion systems and accessories.

[Whimsical]

A very interesting read - Good find Goss

[gosstyla]

"Good find Goss"
Not really, the 47Ft Crowther shown on that site is mine. I'm in Chile right now hope to have it ready to sail up to the Caribbean by end of next month.

Glacier Bay's engineers are schedule to get here on the 22nd to do final motor sea trials and sign off on the installation.

[Whimsical]

Very nice I'm sure your smile must be enormous about now.
50 kW of generators driving 12 Ton is a lot larger than any other example I have found so far. The block diag doesn't show propulsion batteries but then at these power levels probably pointless. I feel compelled to make a joke about being underpowered but I am speachless. You must have spent a lot of boat units for this, but then quality costs.
Hopefully you can find time to take some notes on the power levels used in various sea states for us.
Again fabulous

Note the conventional version had 2 x 75-100 hp, seems huge in comparison to most I have seen.

[LtBrett]

Mike,
You mentioned cruising at 1.5 to 2 l/hr in a heavy cat. Is that per engine? The math would make more sense that way. Also, fuel burn may rise exponentially with speed, so there is a big difference in fuel used at 5 vs 6.5kts. BTW, I don't own Waypoint. I chartered her. My boat sucks fuel a little faster, about 130 l/hr. So this discussion of engines burning in an hour what I go through in 30 seconds is kind of novel.

I did a back of the envelope calculation on the electric system you outlined, and it sounds like the size of your battery bank will be dictated by the voltage required by your motor supplier, unless you add a transformer. Re e power seems to run a whole lot of amps (only 36 v). I guess you buy starting batteries vs. deep cycle batteries! Neat solution, though.

Brett

[Whimsical]

Brett
The 1.5-2 l/hr comes from my memory of reading some thread discussing range under power, can't find it again. It stuck in my mind because it seemed to optomistic. I would agree per engine would make more sense which is what I thought at the time but it had to be both to fit the numbers claimed. Might be a typical fishing story, the fish is always bigger than the scales show, so I am not taking much notice of it.
"fuel burn may rise exponentially with speed" Most certainly but most seem to motor slow to conserve fuel but this is so variable as to be meaningless. This is where it would be great to find 2 people with matching boats to do the comparison.
So far my research is not looking good weight wise but I haven't done much yet. Generators seem to be a big hurdle.
The re-e-power 3 and 4,000 models are 48v but still some hefty currents. I emailed them but no response. Each motor seems a little small for me so I would need 4 which ends up expensive and 4 props. I liked the pod arrangement for several reasons including space and cooling. The others need a shaft and speed reduction.
Some have very impressive efficiency claims over 90% Agnimotors.com - Manufacturers of high efficiency D.C. motors - Home
I could approach some of the suppliers of turnkey systems but I wont do this untill I am comfortable with my understanding of the power requirements.
Mike

[LtBrett]

I think typical diesel engines in the 30HP (22kw) range burn around 4l/hr, so perhaps the statistic you remember should have read in gallons per hr? I took a look at the Agni motors, but I don't understand why they would need a reduction. Waypoint's motors were twinned 6hp on each shaft, direct drive. Should be comparable, unless they are reducing because they said to run 24vdc. At 60vdc, you've got plenty of torque.

Sometimes I really miss being an engineer. Then I remember that I sleep nowadays.

Brett

[Whimsical]

Bret
From fuel consumption graphs of numerous manufacturers it seems 5 hp per litre/hour is about right so 30 hp would be 6 ltr/hr. The question becomes what is the fuel consumpion at cruise then this can be translated back to hp or kW used. If data from matching boats were available for the same speed and conditions it would be easy to determine the equivalence between the two. Then if accurate consumption data was available in heavy going it would be a lot easier to translate this to electric motor size. Difficult with diesel as few cats would have flow monitors, easy going the other way from electric to diesel.

Your earlier post triggered the realisation that the graphs show what the engine CAN put out but not what is used in the real world. I'm now convinced that the Feys factor of .7 is probably correct when considering equivalence. A watt is still a watt but I think the .7 factor takes into account the electric motors can be run continuously near full power but the diesels continuous is less maybe 80% then there seems to be some efficiency gains so down 10% to .7. Diesel boats are probably specd around the 80% power level required then the next motor up, so may be a little over powered given the large jumps in engine sizes. In my case this then becomes two 10 kW electric but I am feeling more comfortable with 14 kW total. The gen size of 12 kW could be augmented by the batts for about 5 hours to max power of course.

I think it will only be through real world experiences that the answer will eventually be confirmed. I have never read a story of a mono being forced back against the diesel that had enough info such as weight, power and sea state so I won't be holding my breath for a story about a cat.
I do believe that eventually there will be some generic rule of thumb about power to weight requirements for cats as there is for monos. I suspect there will be little difference in this regard. This is why I was amazed at the crowther 47 having between 12 and 16 hp/ton in diesel form. Can't wait to hear Goss's acount of the trials.
Mike

[gosstyla]

This may be a repeat response - but I think believe the first try was lost.

Mike:
No propulsion batteries - went through the numbers and decided it didn't make sense for me. Actually when I started this project I specified Solomon Tech. assuming their 20 hp motors would be ready in time. They weren't and on reconsidering thought they would still be a little under powered anyway. For my purposes I always expected a genset would have to be the primary power source for the motors. I only wanted the prop charging and battery propulsion to help eliminate the prop drag and smooth out velocity in a swell.

I should have a lot of data available. I agree to let Glacier Bay install a data collection system which they plan to do while here at the end of the month. They are interested in seeing how the systems perform in "real life" during my passage up to Panama and living aboard and cruising the Caribbean over the next couple of years.

[Whimsical]

Goss
I agree at 52 kW the batt bank to buffer the gen would be heavy, I realised that when I saw the block diag. What is the batt voltage? Even at 140 v the discharge rate would be 370 amps.
It will be interesting to see some concrete numbers for power used, especially if they set it up to record wind and sea state. I think the data needed to ultimately decide on motor size, for me and others, will only come from operation in very adverse conditions. Lets hope you never have the opportunity to collect this for me.
Mike

[gosstyla]

Mike:
Batteries are just for house - 12VDC. The gensets produce 240VDC.

[mikereed100]

Mike,

I have a roughly similarly sized cat to yours and have been looking with deep interest into installing electric propulsion. I have been in contact with the folks at e-re-power and they suggest the epod 3000 (2) for my cat (45' 9 tons). I believe they are preparing for the boat show in Philly so are hard to contact just now but are normally very responsive and helpfull. Check out the electric propulsion group at Yahoo for mor info. Other similar sized motors are the Lynch 200 and Perm PMG. There is a genlteman with a Lavezzi 43 in Washington that is using the Thoosa 9000 system (2 Lynch 200's). He gets 6.5 knots at 100 amps, 48v and 7.4 knots at 350 amps. Google "Gato Verde Orcashere" for a good article on his intallation (sorry, don't know how to include links)

Mike

[Whimsical]

Mike
I'm not realy into pc's very much and have never seen a "group". Just did a search and found an "electric boating group". Signed up so I will have a look. Thanks. Did a search for the Gato and no results. I post a link by opening two explorers, one in the thread and the other of the link then highlight, copy and paste the address. Works for me. Ive found many motors including those but not much real world data on performance, hope the groups will provide this.
Mike