# Sizing electric motors

Discussion in 'Hybrid' started by ted655, Apr 28, 2008.

1. ### lazeyjackGuest

our new boat has 18sq/m roof, , it will be livaboard, in Europe, It will have 230, and 24 vdc, inverter and 800 approx amp hr batt
how would you see solar cells upon this craft?
In Germany I have seen whole vast supermarket roofes, feeding juice into the system, , as you walk in, there is a big tube, with the kw/h output changing as the sun peeps in and out

2. ### Guest625101138Previous Member

You might find this map of interest. In a way it shows the new energy rich and you have to wonder why Australia does not have solar plants scattered around Alice Springs:
http://www.soda-is.com/img/carte_Ed_13_world.pdf

So one answer to your question is about as good as 9sq.m in Melbourne or 5sq.m in central Australia or mid Atlantic.

The map suggests Europe gets about 80W/sq.m average. This is over 24 hours per day and, I believe, on a horizontal surface. So in one day each sq.m would yield 80 x 24Wh = 1920Wh. Now a good solar cell will yield 18% of incident energy in electrical energy. So each sq.m will give you 345Wh in a day. With 18sq.m you can recover 6.2kWh on average each day. The charge/discharge efficiency will reduce that to about 5.5kWh. This can be improved if you do most of the running through the peak of the day and sit at night.

So this is what you have to work with. If you set up tracking you could expect quite a lot more but this is more complexity.

Your 800Ah batteries will give you heaps of storage at 24V. I would go up to 48V as this seems to be a more common voltage level and keeps wiring a bit smaller. Having big batteries give you lots of grunt in an emergency but they cost in having to carry them around.

To get reasonable performance I had to add the wind turbine. This has the advantage over sails that you can charge when at rest. If you have good tidal flow you could charge from the water when anchored. It gets down to operating efficiently. All these things are getting better and I think are practical now.

So if you are happy to mooch along then you might have something that is practical. Post a bit more detail on the boat.

Rick W.

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### alan whiteSenior Member

Thanks. I'll check it out when I get back from work.

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### ted655Senior Member

http://users.wirefire.com/gemort/the hull.htm
http://www.waterwheelfactory.com/
And, as usual, there is plenty right here on this forum
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A project can always get upside-down in costs, but an attempt to lower overhead is also important in a commercial venture.
Almost certainly is an aluminum hull, with some type of nostalgic superstructure.. 45' is short, as is a 12' beam. A excursion boat could manage, but a dinner boat will need around 60' X 15' beam.Suitable galley, storage,heads for both sexes, dancing area & "romantic" walkways, etc.. To preserve the "look" of vintage riverboat, the hull can't have much deck overhang. Most of these diminutions would need to be waterline.
Tilting roof panels, port/strbd could be hydraulically operated to achieve optimum angle, in relation to boat position.
People, (and insurance companies), are afraid to go out in strong currents, I see no need to design for a Mississippi class boat, (8-16 knot currents). However, the ability to quickly return to port in case of health or weather emergency's should be designed for. To obtain certifications & insurance coverage, such power WILL be required.
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5. ### Guest625101138Previous Member

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### alan whiteSenior Member

Guessing a displacement of at least 50-60,000 lbs. Not to say you couldn't be lighter, but you've got a substantial vessel there.
I would suggest you size the motors to make hull speed plus 50% reserve but others may have better info. You can always have a big-prop 100 hp outboard on standby, and also use that for maneuvering in some instances by setting it up to steer a full 180 degrees.
At that size, steel is probably the cheapest material to build with.
The roof collectors (in LA) will be pretty flat during the summer season so there's the question of what you anticipate your active season to be.
I see no reason to size to Missisippi standards (16 kts? wow!) but the additional outboard would probably make the difference when conditions were adverse.
Keeping your cruise speed down to six knots will use a fraction of the power needed to do 10 knots. Once you have your displacement and general hukk shape, your waterline beam and length and depth will determine your "sweet spot", the speed that uses the least power to achieve. Every hull has a best speed. Higher speeds favor a longer waterline and lower speeds favor a wider beam in general. This has to do with wetted surface area to displacement ratios, where extremely low speeds require the least power as the hull shape approaches a spherical shape (wider and deeper). Higher speeds (short of planing) like long lean hulls with less frontal area (narrow and shoal).

Alan

7. ### Guest625101138Previous Member

Here is a good site for solar radiation in the USA:
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/

It looks like that April will give say 5kWh/Sq.m/day in the south for a horizontal panel. Allowing 18% conversion efficiency results in 900W/sq.m/day.

If the boat is used primarily for dinner cruises then it could be moored in a particular way to maximise advantage of tilted panels.

Rick W.

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### ted655Senior Member

People just want to move & look. 5knts will do that. More speed or power might be a requirement by others. I think the shallow scow shape of the tradistional riverboat must be part of the "package" Cats are for California.
The outboard (s) is a new thought. I was thinking of 2 more electric motors & under hull shafts/props, discreetly housed.
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Are 2 or more motors ever belted to 1 gearbox, to add HP?
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Looking at the solar pattern on that world map, makes me ask if overcast skies are figured in to the ratings? We have many cloudy, rainy days here in Louisiana. Those #s look high for this state, but I really don't know.

9. ### Guest625101138Previous Member

This is the way to get beam overall with a narrow hull:
http://www.slv.vic.gov.au/pictoria/b/3/5/doc/b35771.shtml

Also it has really only been in modern times with cheap fuel that we have not needed to be concerned about overall efficiency. In the early days of ship design they had to work with much less power to achieve their ends. Here is a good story.
http://www.pabook.libraries.psu.edu/palitmap/bios/Fulton__Robert.html

I will see what Godzilla produces for a 60ft boat displacing 15t optimised for 10kts.

Rick W.

10. ### Guest625101138Previous Member

From looking at other maps I believe the world map does not figure overcast conditions. I think the one I posted on the US does. I have one for Australia that certainly allows for clouds and it is lower than the world map.

Rick W.

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### alan whiteSenior Member

IT shouldn't make any difference whether there's a single large motor or two motors belted or geared to a single output. The additional motor adds its power to the first.
Any transfer through parallel shafts (gears, chain, or belts) means a certain percentage of power is lost in friction. gears and chains are generally most efficient, and gears last longest by far (and are not subject to catastrophic failure like chains or belts).
There should be no need to connect motors together though. Better to use a higher rated motor to begin with. Otherwise, there's too much complication and parts to maintain.
Having two motors to drive seperate paddles is ideal. Any other powerplant should either be a genset or an auxilliary diesel for an alternate propulsion source, or both. The auxilliary engine could be a shafted prop or an outboard. Running the paddles from it could be done, but would make for unneeded complication.
If the shafted prop setup is connected parallel to the generator, the generator could serve as an electric motor as well. A single prop should be fine.
Then you would have three electric motors, all of which can generate, and one diesel engine, which either provides extra thrust, or makes kilowatts when the sun isn't shining.

12. ### Guest625101138Previous Member

I looked at the 60 footer displacing 15t. I have attached a rough rendering and a performance calculator for a paddle wheeler shown. The dimensions of the wheel in the calculator are the same as in the image but you can play with it to see how efficiency changes. The efficiency with wheels as shown is a bit over 60%.

You would do better with props but you get slightly better pulling power with the wheels despite the lower efficiency at speed. The wide set wheels also give good steering in tight spots at low speed.

If you go for a couple of these compact pancake motors:
http://www.perm-motor.de/pm_pdf/pmg_132_e.pdf
you could expect around 8kts with the big wheels shown using rated motor torque.

The nominated gearing provides the following performance:
Burst speed at twice rated torque, motors at 3300rpm, is 10.1kts.
Rated speed at rated torque, motors at 2500rpm, is 8kts.
Economic cruise at 1600rpm gives 5kts with combined motor output of 2.8kW.

All the performance figures are for clean hull in calm conditions.

Rick W.

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### ted655Senior Member

Wow! Thanks so much, You've done things I could never do, & everyone has enlightened me! Thank you all.
The reason I started this inquiry, was a TV commercial. They show a gallon of "fuel" & say how a efficient automobile MAY get 40 miles from that amount. Then, they show a diesel-electric locomotive/train, and claim that same gallon will go 240 miles.
I realize there is velocity & mass, etc., involved in their claim, & they probably get no where near that when switching & making the train, but still...., diesel-electric seems the future. You fellows take it even further with the hybrid approach. AHH, if the storage technology would ever catch up, and/or, come down in price.
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While the hull you created is more modern than what I was thinking, it is very close & gives me a ton of information.
I would only have 4 degrees deadrise, a wider, rounder bow & straighter sides. I also had thougt a 5M wheel diameter, might give more power with less motor. Also allow for a narrower width, giving more deck/cabin width.. I did want the wheels set into the sides of the boat. I had no clue as to the location of the wheels. I "guessed" they needed to be past amidship. I had no idea how far.
It's taking a bit for this Yank to work in metric, but it good exercise for my brain. Thanks again.

14. ### Guest625101138Previous Member

The hull shown is actually optimised for 10kts and a stability criteria with KMT at 2.5m above the keel. It just happened that the waterline beam ends up at 3.5m. It does not matter much what is done above the waterline as long as it can be built practically. If you load the hull with a tonne or so of lead batteries along the keel it will make it very stable. This would give ample cruising range on batteries alone.

Going to bigger diameter wheels will improve their efficiency providing width is not reduced. The gearing needs to be 99:1 and power for 5kts drops to 2.4kW.

You can play with the yellow cells in the Excel spreadsheet to see how changing the wheel size affects performance of the boat. The hull data is accurate for calm conditions and unfouled. I have never personally tested my paddlewheel calculator but It aligns with data provided by others. You need big wheels to get the efficiency up.

The Perm 132 motor spins to 3300rpm. Each motor has rated torque of 20Nm and they can be pushed to twice that in bursts. The duration will depend on motor cooling. You would need thermal protection if you planned to run for long periods at full power. Cell b24 in the spreadsheet gives the combined motor torque. This can be 40Nm at rated load and 80Nm for peak conditions.

Rick W.

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