Electric motors

Discussion in 'Propulsion' started by Manie B, Apr 15, 2008.

  1. Manie B
    Joined: Sep 2006
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    Location: Cape Town South Africa

    Manie B Senior Member

    Gentemen, at what point does an electrical drive system become a waste of time and money? I am refering to the Re-E power e-pods

    Assuming you install 2 of these on a 36 ply epoxy cat. If you want to run both motors at say 30% throttle for many = 12 / 24 / 36 / 48 hours continiuosly how many solar panels would be necessary if you also had 2 wind vane generators, and how many batteries.

    When i look at the cost of 2x Yanmar sail drives - plus fuel and tanks ( and weight ) and ever rising fuel costs, surely with modern technology and reliability we could find a reasonable electrical system? At US$ 8400 per pair their pricing seems ok??? When i read how sailors battle with fuel supplies and quality at remote spots it seems another problem.

    For me a huge attraction is self sufficiency, imagine NO SHORE POWER. Also imagine not buying diesel and the stink!

    So the question is what is a middle of the road system and what performance could you expect??

    Attached Files:

  2. Guest625101138

    Guest625101138 Previous Member

    I have been developing the concept of a solar-wind powered boat for about 1 year now. It is my retirement project. It originally began as a self-righting sailing cat but after learning about hull efficiency with a string of 15 pedal boats to gain design experience I now have a reasonably firm concept that is with a NA for detail design.

    The boat is 40ft long, BWL is 5ft with 6ft overall beam. The KMT is 1.5m. It has a 20ft long cabin with standing head room. There are two 10ft long bolt on ends meaning the boat can be reduced 20ft for trailering and storage.

    It has overall dislacement of 1100kg with helmsman. There is 260kg of VRLA batteries sitting in a long shalow keel to provide outstanding righting moment for beam. It will take 6 x 220W solar panels on the cabin roof and a 1.5kW turbine on the aft deck. Batteries have a capacity of 11kWh and nominal voltage of 48V.

    The cruising speed is 7.5kts at 1.5kW. It will get to 10.5kts with full motor power of 4.5kW. For overnight cruising in restricted energy recovery (no wind) it will do 5kts with 500W.

    I have purchased two Mars PMDC motors and two compatible 4-quadrant Kelly controllers for USD1538 including postage from China and USA. One motor will be used for the water prop and the other for the air tubine. The drives allow me to reverse the system such that I can propel from the air and generate from the water.

    I have off-the-shelf right angle drives for both the turbine and the prop. I will make interconnecting parts predominantly from aluminium to keep weight down.

    Both the drive leg and the turbine will weigh around 18kg.

    OK - so my view is, if you have an efficient hull and drive design, then you can look forward to good performance from an electric power system using relatively moderate energy collection from both solar and wind. The boat is not the roomiest ever built but adequate for extended coastal cruising for one or two and completely autonomous. (Excluding crew provisions)

    I have attached an image of one of the more recent design development. There are other threads with earlier versions but not radically different.

    Rick W.

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  3. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    The problem is regeneration of watt hours. Current technology (affordable) means solar panels covering your boat (and depleting your bank account).
    Wind power is another choice. Expensive to set up too, and anything with real power could not remain set up when under way, since the blades would be too big.
    A shore-based wind power generator would work well if you remained in one harbor.
    Then too. batteries are anathema to multihulls because of weight. My feeling is that all of these things will become cheaper and lighter as time goes on, but right now one has to consider that initial cost might be too high to make such a system pay in most cases.
    And if a big enough windmill could successfully remain up in any kind of weather, that would be nice. But then it's as if you're sailing anyway, what with the big rig orienting to the wind all the time.
    An efficient diesel or lightweight gas engine running a genset is a great option, allowing two motor/props, one on each hull.
    This does away with gearing and is possibly slightly more efficient than a regular motor/shaft set-up, also allowing the genset to be placed anywhere. also, there's no need for huge banks of batteries.

  4. StrandedMariner
    Joined: Sep 2007
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    Location: Shanghai, China

    StrandedMariner Steelboatsailor

    I had a look at the web site, and had a look at the E-POD 2000 system, the smaller one. I assume you have two of them, so at recommended cruising (let's assume an amperage of 50A at 24VDC, with max continuous at 170 A as per specification) you look at 2 x 50 x 24 = 2400W output. If I only look at replenishing consumption, you would need a minimum of this in total generating capacity. If it's only solar, with a typical panel of 70W peak production at 24V, and a cost of about R 10,000 per panel, and with dimensions of 800 x 500mm for a typical panel, you would need in solar panels alone about 34 panels. If you would put up two wind generators of 200W each at 24VDC (which is high end), you still would need 28 solar panels.

    This all assuming that you only use cruising speed, not taking into account storing extra for hours that there is no wind and/or sun, and also assuming that everything is producing at maximum capacity.

    Apart from the cost, you are looking at a solar panel surface of minimum 11.2 m2, or for solar only 13.6m2. And that is only to compensate for actual use, not building up a reserve.

    And than I did not even look at the required storage capacity of the batteries you would need.

    Just my two cents,

    Best regards,
  5. Manie B
    Joined: Sep 2006
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    Location: Cape Town South Africa

    Manie B Senior Member

    I love this forum, ask a question, get a straight answer, game over, thank you, thank you to all

    As we say in south Africa "ja well no fine"
    So we are not there yet.
    once again thanks to all
  6. JustBusiness
    Joined: Jul 2008
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    Location: Buffalo, NY, USA

    JustBusiness New Member

    This is the most on topic of any discussion I have found for a hypothetical project I am starting for a college business class. All and any response is greatly appreciated.

    The project: Design a complete business plan for a start up company.

    My chosen topic: A company that specializes in replacing marine engines, specifically Mercruiser 5.7 litres (200-260 hp) with ALL electric drive systems. A diesel generator may be considered for emergencies, however not a top priority.

    Where I need help: The boats are powerboats (I'm no sailor, unfortunately). My goal is to have a top speed of about 25 knots, cruising around 20 (if possible!) for maybe 4-8 hours of continuous operation. I need help selecting electric motors. From my calculations they will need to be about 160-300 kw's per motor. One I have considered is the ACPropulsion AC-150, however, I have not recieved any feed back from the compnay, and am looking elsewhere (remember, this is hypothetical). For batteries I plan on using EEStor ceramic powder ultra capacitors. They are supposed to be ready for commercial use any time now.....but they have been saying that for a year. Any reccomendations on alternatives, other than LiIon? I feel like 6000 LiIon cells is probably a bad idea.

    Finally, I need to either adapt the motor to run with the current ones on most 5.7 litre mercs, which is the Mercruiser Alpha One, however if there is a more reliable, and more efficient option I am all ears! Thank you for everyones help, I am reading more and more about this everyday.


    Justin Sanderson
  7. Guest625101138

    Guest625101138 Previous Member

    Can you give me the basis of this calculation?

    Rick W
  8. JustBusiness
    Joined: Jul 2008
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    Location: Buffalo, NY, USA

    JustBusiness New Member

    calc basis

    I used a basic converter (found via google), at converter

    After using it again, the numbers came back slightly more conservative, 148-193 KW, via 200-260 hp input.

    How about some opinions? Anywhere to source the motor from? How about batteries? And the drive, can I adapt to use current alpha ones, or will I need new outdrives?
  9. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    JustBusiness, my 2 cents,

    Get a new boat designed for efficiency - refer to the effort and analysis Rick Willoughby has put in.... I am heading along a similar path with a skinny hulled 39ft POWERcat (600mm hull beam at w/l) and 24 ft beam overall but the problems are electric-motors - to get efficiency up means higher voltage - - means more batteries (weight is bad), and max area I want to solar panels is just under 3000 watts potential, so 2 light weight "Polar Power, marine gen-sets using the Lombardini LDW1003 diesel engine and the 6255-DC-generator" - - ALL have problems and issues - just the best match I can find so far------- The propeller will be a slow turning (1000rpm) 550mm dia. 2 blade, (like an aircraft prop), wheel to get MAXIMUM efficiency and give co-gen when I have the 2 Genoas (hitch-hiker rig) giving a good run...... All the technology is new and could not be considered "mature" and I expect improvements before launch date.... the hulls will be optimized for somewhere in the 10 to 20 knot performance bracket (cruise at up to 10 and not be a ***** if I get favorable breezes & add a bit of power :D)

    Pushing a hull designed to take advantage of LOTS of horsepower from thirsty engines is not a logical way to proceed for fuel efficiency... Fix the cause of the problem instead of tinker around the edges..... Go for a sea kindly hull that is VERY easily driven, then figure out the minimum power needed to get you there comfortably....
  10. Guest625101138

    Guest625101138 Previous Member

    You need to do more than just the conversion from HP to kW.

    The power required for a planning hull for a particular speed is almost a linear function of weight.

    A first pass power estimate:
    1. Lets say boat actually only needs 100kW to do 20kts.
    2. You want to run for 4 hours so you need 400kWh of battery capacity - lets say 450kWh so it is not completely spent (most makers prefer only 50% discharge to avoid damage)
    3. You have a choice of VRLA or NiMH. VRLA will be cheapest. A 6V 300Ah battery will weigh 50kg. Allowing for controller and motor losses you will need 300 batteries giving total weight of 15000kg.
    4. THe boat to carry these and a couple of passengers that is intended to plane will weigh a minimum of 25000kg.
    5. A rough approximation of drag will be 1/8th of the mass. So lets say 3000kgf or 30000N.
    6. Power is force by velocity so at 20kts (10m/s) you will need 300kW at the hull.
    7. A heavily loaded prop will give around 50% efficiency so motor power is really more like 600kW.
    8. If we iterate again it will never get better. Hence what you ask is impossible with VRLA batteries.

    Going to NiMH you can maybe double the energy density. The outcome will be the same - IMPOSSIBLE.

    Going to li-ion you can get about tripple the energy density. The big feature of these though is that they have very high power density. Lets see what might be possible. They give good cycle life at 1C and even higher
    1. Lets target the 100kW for 1 hour as a first iteration. So need 100kWh.
    2. A battery pack of 37V and 40Ah weighs 15kg. You will need about 70 batteries with total weight 1050kg.
    3. A boat to carry these, motor and a few people will come in around 4000kg.
    4. Drag will be 5000N.
    5. Power at the prop for 10m/s will be 50kW. Required motor is say 80kW as you may have a moderately loaded prop.

    So the 1 hour rate is practical with these in a technical sense. Hitch is that each battery costs USD1740 with volume discount. So 70 will be a cost of USD120k - just for batteries. So while technically feasible I think the business plan is flawed for the time being. Maybe when oil hits USD500bl and you can find people who have deep pockets and want to keep boating.

    Rick W.

  11. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    Thanks Rick, Well I suppose that almost answers my question too, Not quite viable yet? - I will work a bit more on my end first, then would like to be able to PM you with my request for help..... Thanks

    Your answer would be worthy of publishing on the net and I would be happy to see that happen when it does..... Just I have to refine my thoughts and ideas a bit yet....
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