electric powered boats

Discussion in 'The Projects Forum' started by Jay Bliss, Jan 24, 2015.

  1. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0
    In the Fall of the year there's a 24 mile electric boat marathon held on the Wye river on the eastern shore of MD. All kinds of boats and electrical systems show up. Of late, lithium batteries have been used, although the second place overall went to AGM batteries. Motors of 8kW and over are classified in the extreme category.

    I'd like to compete in the under 8kW category. Efficiency is king, and there are many areas to consider efficiency: hull design, prop design, prop drive, and motor and controller. My question to you all: what specification of motor yields the highest energy output per kW input?

    Weight is an important criteria also. Lighter is better.

    And finally, what are the sources for lightweight highly efficient motors; who makes them? Thanks in advance for your input.
     
  2. John P

    AAC Fanatic!

    Oct 14, 2008
    1,632
    224
    Most likely you'd want a brushless d.c. motor, and you would endeavor to use a combination of gearing and load that would cause it to run somewhere between 80% and 90% of the no-load speed. If you look at graphs showing the operating characteristics of a motor, that's typically where the highest efficiency occurs.
     
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    I would be looking at 400hz ac induction motors.
     
  4. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0
    Thank you John P. I think I'd like to try to eliminate gearing. Energy losses inherent make me shy away. I came across this listing of motors, with choices that more than befuddles this mind:
    http://www.directindustry.com/industrial-manufacturer/motor-62956-_8.html
    After p. 8 the listings seem to repeat themselves.

    I've looked on Youtube also, and I've been astounded at how noisy some of these motors can be.
    In the marathon listed above, the first three finishers sported Torqeedo electric outboards, the Cruise 4.0 specifically. That unit has the motor and some electronics fully submerged, thus solving both cooling and noise problems. Because the bulb of the motor is indeed large--an elongated grapefruit--it has to require extra energy. My search for the most efficient motor is only the first step in trying to be competitive. And now I'm introducing the requirement of quietness.

    Clearly the energy requirement to push water aside and back for 24 miles is extremely large. So the motor is the first of many key ingredients to finesse.

    On that site www.directindustry.com they list categories technologies and type and electrical characteristics and controls... Is brushless DC the best choice?
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    I would think you want multiple motors on the same shaft, so that you can get a lot of power in a small diameter shaped liked a torpedo. Most motors are not built with much concern to minimizing diameter.
     
  6. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0
    Thanks Strantor. I plugged "400 Hz" into ebay, and got an interesting array. At first glance, these motors appear one-directional? Their high rpm is a downer. I reckon their controllers might be pricey too. I didn't see anything that accomodated 100-200volts dc.

    My thinking is that the motor(s) get mounted inboard and get cooled with a separate water system; low friction seal and bearing off the stern. Or the motor(s) get mounted like an outboard in which case there is more loss from a gear arrangement.
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,672
    899
  8. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0
    DSC04139.jpg
    There's a variety of boats that compete. I've experimented with outrunner motors; I've smoked two 6374's and countless ESC's. Somewhere in the industrial or EV world there has to be an efficient and quiet and bi-directional and long-lived motor (the requirements always grow). I'm studying: brushless DC, 400Hz.
     
  9. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,281
    1,232
    What RPM are you looking for?
     
  10. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0
    4000 or less. There's a huge selection of props out there, and prop selection is going to be the one demanding most detail and time and attention. The Torqeedo philosophy limits rpm to 1300 with a planetary gear reduction and a large (13" as I recall) prop. The direct drive Thai Longtail operations are running about 3600. I'd like to incorporate one of those, I think from my armchair.....
     
  11. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,281
    1,232
  12. John P

    AAC Fanatic!

    Oct 14, 2008
    1,632
    224
    My instinct is to say that if cooling is a concern, you've already failed. Lost heat implies inefficiency, energy you're laboriously bringing with you in a battery just to throw it away. But maybe if the motor is in an underwater housing, the heat would build up and you'd have to cool it.

    When I said "gearing" I was thinking maybe a belt reduction, but in general a motor will probably spin at a speed much greater than you'd want on the propeller shaft. Or can some motors be run with electronic drives so as to be slow and efficient at the same time?

    This is the event:
    http://www.electricboats.org/2010-Wye-Island.html

    Someone made a video. It looks as if that Torqeedo thing is very successful.
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Not sure what you saw, but the 400hz induction motors I'm referring to are bidirectional just like any other induction motor.
    Yes this is true. There is a downer to every type of motor. The upper to the 400Hz motor is that it packs the same power into a frame roughly 1/7 the size of its 60Hz equivalent. If you're talking a few HP, the 60Hz motor (or DC motor) will be of substantial size. The 400Hz motor will look substantially undersized in its stead, but will prove itself in performance. Back to the downer; while the 400Hz motor will be 1/7 the size, it will spin 7X faster @ max speed. This will require down-gearing to get the RPM you want. BUT, mechanical speed reduction with a gearbox can be more efficient than electrical speed reduction by adding motor poles. An efficient 400Hz motor with an efficient gear box that weighs some fraction of a 60Hz motor with no gearbox, is probably a more efficient overall system (taking into account weight, drag, etc) than the 60Hz larger motor.
    Most standard industrial VFDs will go up to 400Hz.
    Many standard industrial VFDs accept a DC input. The VFD typically takes in 50/60Hz AC, rectifies it to DC, and then chops it back up into AC at the desired frequency. VFDs which accommodate a DC input, simply skip the first step of rectifying incoming AC. They accept the incoming DC and chop it up into AC at the desired frequency.

    Any AC motor (including DLDC -AKA- brushless DC -AKA- PMAC -AKA- permanent magnet AC -AKA- synchronous AC) is going to require a variable frequency drive of some sort. The motors labeled BLDC, typically come with the variable frequency electronics built into the motor housing. they are not "DC" motors actually. Just permanent magnet AC motors that come with a VFD built in.

    The downside to anything with permanent magnets in it, is that it is not at all tolerant of overheating. Overheat the magnets and they demagnetize. Your expensive motor turns into a boat anchor. An induction motor can run until it's literally smoking, and still have a fighting chance of finishing a race.

    If you're looking for something fluid cooled, you are off the beaten path. Good luck. Look into EV motors. You may be better off going with the off-the-shelf electric outboard solutions your competitors use.
     
  14. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    I completely misjudged what we were talking about! (A common occurrence around here.) I was picturing RC boats, not "real" boats! I guess the length of the race should have tipped me off.

    That video was helpful. It said that particular boat needed 2000W to maintain ~9mph. That means it needed about 6kW•hr of energy to complete the race. One way to save weight is to shave your battery capacity down to "just enough", like an Indy car driver hoping to cross the finish line with a gas tank near - but not quite - empty.

    My hunch is that a drag analysis would show that air resistance is dominant. That's where I'd put my efforts. It's the limiting factor on a bicycle, with air drag increasing steeply with the square of speed. That means power going to air drag goes with the cube of speed.

    That's true of water drag as well, but the "configuration" changes as the boat comes up and planes. So it's complicated, but of course it's been studied to death. Longer hulls are faster, but planing beats all. (I'm a windsurfer, and we scoff at the 'bathtubs in the water" boaters.)

    I have a Seadoo jet boat and I know one thing the guys that are really into it talk about is prop pitch. The point is, you want the pitch to be optimal for the conditions where you want peak performance. So top end speed with engines at 7000rpm is a different goal than the "hole shot", where they use an aggressive pitch to get acceleration at lower engine rpm. You can't have both. Since your race is a couple hours, I would think you want a prop that is optimal at flat out. You need to know the motor rpm when it's loaded.
     
  15. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0

    MUCH to digest here. The details you provide are illuminating. Thanks Strantor.
     
  16. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Yes sir, you are looking into a rabbit hole. I have been down this rabbit hole as a hobbyist looking for the most efficient motor technology for small EVs, and industrial motor controls are part of my job.

    If your boat were my project, I would start here:
    Do I really need fluid cooling?
    If so:
    • That is a very limiting factor, and my choice of motor technology will be decided by what I can find with fluid cooling. Start here; find any and all motors that have fluid cooling, and then choose the most efficient available motor/drive technology that I can afford.
    • Some electric vehicle motors have fluid cooling, check these out
    • Some submersible motors (ROV thrusters, subsea pumps, submbersible sump pumps, etc.) are oil-filled sealed types. Perhaps if I can get one of these, I can drill ports into it and circulate oil for cooling - would require a heat exchanger and that's additional components that I might not be able to justify.
    if not:
     
  17. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0
    THAT's a stack of information. Thank you. It'll take a week to digest! I'm on to it.
    In the best of all possible worlds this is what I'd opt for--at this point, with no budget limits. Yes, its liquid cooled.
    http://www.evrdr.com/ktm-freeride-e-hi-voltage-trail-bike/
     
  18. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0
     
  19. Jay Bliss

    Thread Starter New Member

    Jan 24, 2015
    19
    0
    Yup I wondered if you weren't in RC mode, wayneh....
    Those numbers in the video are accurate: I used Nissan Leaf modules powering a borrowed torqeedo. I had 7000 watts aboard, and ran out of the spec'd juice requirements of the Torqeedo within yards of the finish line. (Five minutes of breather time and the Leaf batteries were back into acceptable range for the Torqeedo metrics). So I'm here now looking for a power plant under 8kw, light, reversible, and so efficient that I might shed some battery weight (9lbs = 500W), or better yet halve the elapsed time.
     
  20. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    I believe your challenge is to cut drag - air and water - enough to get planing. Probably 12 mph or so. Being a windsurfer, I'd get a big long floaty board, lay down on it with aerodynamic faring over myself and rocket to the finish! It's conceivable that a "submarine" configuration with very little above the water line - your face, to breath - might be really good, to.
     
Loading...