Electric Boat Data

Discussion in 'Boat Design' started by Guest625101138, Nov 30, 2007.

  1. Guest625101138

    Guest625101138 Previous Member

    I have been doing some performance testing of electric boat components.

    I am using one of my more stable pedal boats and scooter electrics.

    The boat is a 6.6m long catamaran made from two length of 142mm aluminium irrigation pipe. It is stable and unsinkable but a bit wet once it gets into waves. It is a good platform for testing propulsion systems.

    The drive is a geared 300W scooter motor swinging a 380mm 3-bladed high aspect prop. I have been fiddling with the prop pitch so not exactly sure what efficiency now but it used to be better than 80% in its original application. I use a little scooter variable speed controller with potentiomater speed adjustment. The batteries are two 12V, 10Ah gel VRLA.

    I did a 40 minute run today at different speeds into, across and downwind a reasonable breeze in protected water. Distance covered was 3.2km at average of 5.7kph. Top speed recorded was 9.4kph. This was produced downwind with 240W from the battery. The boat would get this speed or better in dead-calm conditions. Attached pdf chart shows speed during test.

    I have attached a video showing the boat at 120W giving 6kph and 240W giving just above 9kph.

    The 3.2km used approximately 20% of the battery charge so range between 12-15km at 6kph. Less than one hour running at 9kph.

    Michlet gives me a power requirement of 110W for 9.4kph on this boat. So overall efficiency is 46%. Motor 78%, prop say 80%, controller 95% - so some unaccounted losses. The testing needs to be done in calm conditions to get more precise data on the hull.

    Rick W.

    Attached Files:

  2. JonathanCole
    Joined: May 2005
    Posts: 442
    Likes: 8, Points: 18, Legacy Rep: 58
    Location: Hawaii

    JonathanCole imagineer

    Hi Rick,

    How did you rate the efficiency of your batteries? VRLA batteries tend to be good for short duration power bursts, but may be less efficient otherwise.
  3. Guest625101138

    Guest625101138 Previous Member

    The batteries are rated at 10Ah. I have not checked what rate of discharge this applies to. I think it is normally given at the 10 hour rate. I was operating much higher than this and was pleasantly surprised to find that the on-load voltage was 12.4V when I got home, indicating still 80% of charge left.

    The batteries have now only been used a few times and not deep cycled yet. I plan to do one or two longer runs to get deeper discharge although I will not be doing any extended testing of cycle life.

    For my coastal cruiser (see attached) I have homed in on 8 X 12V gel VRLA in series parallel for 48V system. These will fit end-to-end in a shallow keel to ensure adequate stability.

    The cruiser is still undergoing development. Displacement has now gone up to 1100kg, length down to 12m and overall beam is now 1.8m. Cruising speed down from 8 to 7.5kts and top speed from 12 to 10.5kts.

    I have homed in on Sanyo HIT 205W panels but am having difficulty finding a supplier in Australia. I am currently looking for one to test out on the little electric boat.

    Rick W.

    Attached Files:

  4. Guest625101138

    Guest625101138 Previous Member

    I did a full discharge test on the test boat today.

    Weather basically calm but some breeze now and then to 20kph.

    I set the motor at 7A for most of the run. This produced just over 7kph with the wind and around 6kph against the wind. There was a bit of weed so I stopped a few times to clean weed from the prop.

    At this speed useful range is 7.5km. The average speed over about 80 minutes was 5.8kph. I got approximately 9Ah out of the 10Ah batteries before the controller started to cut-out on low voltage. I was still able to do 4kph but I would not regard it as useable.

    The batteries are Fullriver HGL 10-12 having a capacity of 10Ah at the 20hr rate. Getting 9Ah at 1 hour rate is reasonably good I believe for a 10Ah rated battery.

    The batteries are AGM type not gel. They weigh 3.3kg each so the pack of 2 contributes about 5% of the total displacement.

    I am quite happy with these results. It would be interesting to see how far you could get if everything was optimised for a particular speed.

    If I dropped speed to 5kph I would get a range of around 10kph but it is boring just doing loops of the lake.

    Rick W.

    Attached Files:

  5. Guest625101138

    Guest625101138 Previous Member

    I did my first test using the Mars Motor/Kelly Controller drive leg today. I used the old tubular aluminium cat as the test boat.

    I used the same 2 x 10Ah batteries as before in series to give 24V. The boat got to 11kph before the batteries reached their limit. That was around 500W.

    The drive leg weighs 19kg plus 7kg in batteries so the boat was a bit lower than design in the water. There was extra drag from the cross braces ploughing through the water once speed got above 7kph.

    I have attached a speed versus battery power plot and there is a video clip (3.6Mb) of the drive accelerating. It is nice and smooth and not particularly noisy although you can hear it picking up speed.

    The motor and controller are quite nice. The combination is rated at 4.5kW on a 48V system and will peak to 9kW if required.

    Rick W.

    Attached Files:

  6. Quietboats
    Joined: Feb 2004
    Posts: 32
    Likes: 1, Points: 0, Legacy Rep: 20
    Location: Marshallberg, North Carolina

    Quietboats Junior Member

    Rick, thanks for positng this. One question--what kind of a belt are you using between the motor and shaft? Is it a cogged belt or a V belt? The reason for asking is the motor sounds pretty loud and I'm wondering if I am hearing motor noise compounded by the aluminum housing or belt noise. I am considering the Mars brushless motor myself for an electric boat project and quiet is the utmost importance. Thanks much. Tom
  7. Javaid Hosany
    Joined: Apr 2008
    Posts: 20
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mauritius

    Javaid Hosany Junior Member

    Ship loading type Michlet

    Dear Rick,

    I heard that you are the one who can help me with my project.

    I am an electric and electronic engineering student. And I am actually learning Michlet to predict the thrust needed for a solar boat that I am doing the electrical installation.

    Can you help me in understanding and calculating the ship loading type.

    Thank you lots.

    Best Regards
  8. Guest625101138

    Guest625101138 Previous Member

    The sound is the motor magnetic excitation due to the trapesoidal waveform. It is not dulled by the cover. If anything the aluminium amplifies it. I have it fully enclosed for a measure of water proofing but did not want to use any insulation as I wanted good thermal conmduction. The controller is mounted inside the cover. There is a potentiometer for speed control and a switch for reversing. It is a very simple outboard motor.

    I believe the Mars motors are quieter when mated to a sinusoidal controller such as a Sevcon but they cost more than the Kelly. I am very pleased with the combination. The controller only draws 60mA when connected and the motor turns over with 0.25A.

    I am using a 2:1 gearbox now and plan to eventually use a 3:1 box. There is no belt drive just a right angle box like a typical outboard.

    Rick W.
  9. Guest625101138

    Guest625101138 Previous Member

    Leave the setting at 3. This is the only valid value for the free version of Michlet according to the manual. All it means is that the GMT value produced for stability in the ship.mlt file is referenced to the waterline not the actual CofG. It has no bearing on the drag or power values derived.

    Rick W.
  10. Javaid Hosany
    Joined: Apr 2008
    Posts: 20
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Mauritius

    Javaid Hosany Junior Member

    Thanks lots Rick
  11. cookiesa
    Joined: Mar 2007
    Posts: 122
    Likes: 0, Points: 16, Legacy Rep: 10
    Location: Launceston, Tasmania

    cookiesa Senior Member

    Slightly Off Topic

    Hi Rick,

    Great work and thanks for the updates and videos!

    I am in the process of looking to build a Jarcat (5m Sailing Cruising Cat) and was contemplating looking at electric propulsion (thruster style) rather than a small outboard. The engine is not intended for long distance motoring, more on and off the ramp (even a smallish outbard on this size of vessel is limited unless you wish to carry lots of fuel)

    However I note the lack of efficiency on these. Are there alternatives or the other thought I considered is perhaps using the bottom of an outboard and using an electric motor atached... these seems like it would be less efficient than a thruster style though)
  12. Guest625101138

    Guest625101138 Previous Member

    The choices open to you really depend on your engineering capacity or access to such.

    I have a particular ambition with the outboard I made. The motor and controller are sized to drive quite a large boat from a 48V system collecting wind and solar energy. It is a long term project that I am slowly bringing together.

    A fundamental is that to get high thrust from low power you need to act on a large area of water. So props are big diameter.

    The little outboard I have will produce 9kW on 48V batteries capable of sustaining 200A. The test prop is 14" diameter with 2:1 gearing. My actual design is for 16" with 3:1 but I did not have a 3:1 box on hand. So this set up will be capable of high thrust.

    During the testing the little batteries ran out of grunt at 12A so power was limited to roughly 250W. The controller was cutting out on the 18V lower limit. So just a tiny fraction of what is possible from the unit.

    The electric outboards like Minn Kota are constrained by the size of prop. You could get higher thrust with a bigger prop but then motor bearings would likely fail. There is a German made Torqueedo electric outboard that has more grunt than the Minn Kota and is not ridiculously priced. Commercial outboards using the Mars motor I have or similar cost around USD5k without battery and still have a tiny prop.

    The prices I paid for what I have were:
    Mars BLDC motor USD400
    Kelly 4 quadrant controller USD250
    TEA DZ3 2:1 gearbox AUD420 (I priced a 3:1 box for AUD480 a few months ago)
    Prop home fabricated (would cost about AUD400 for cast 2-bladed)

    You then have to assemble it all. And buy a battery.

    You can get Lithium batteries that have very high power density which would be OK for high power short duration. Their power density is 10 to 20 times better than VRLA and energy density 2 to 3 times. They are expensive though. A 37V battery of useful capacity costs around USD400.

    So you go through all this and then look at what you get with 4HP IC outboard with high thrust prop and 10 litre fuel tank for maybe AUD600 second hand and conclude why bother.

    If you just want to sail then keep it simple. Look at a 4HP long shaft outboard with a big diameter prop with low pitch.

    If you have access to good engineering capability and enjoy that side of it then I can give you some pointers. Here are some things to look at:

  13. cookiesa
    Joined: Mar 2007
    Posts: 122
    Likes: 0, Points: 16, Legacy Rep: 10
    Location: Launceston, Tasmania

    cookiesa Senior Member

    Thanks for the information while interesting not practical in my application. Please continue with your work though as that is what has led to the development of so many new ideas, including electric propulsion now available on some production cats
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