Air bubble lubrication successful trials

Discussion in 'Boat Design' started by jakeeeef, Oct 22, 2021.

  1. jakeeeef
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    jakeeeef Senior Member

    I know they have, that's why I continue to come here. I just think that for some, what can be achieved with just 640 watts might be surprising and illuminating, if it is propped right.

    I ought to add in my defence that two windsurf boards and a power drill is not the extent of my boatbuilding experience either. As I said, it was just s quick and dirty solution to a challenge I had, and it worked OK.
     
  2. portacruise
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    portacruise Senior Member

    Jake, Curious to know if you measured the 640 watts while at your 9mph speed, or is that 640 watts based on the manufacturer ratings? Sometimes an electric motor can run for a short time at considerably over the rated power, depending on rated RPM and rated amps, some even have an instantaneous stall current rating. Of course, the opposite could also be true- maybe you were going 9 mph at well under 640 w, if you didn't measure it!

    One of the tricks I used for many years with a small cheap 12v Minn Kota trolling motor, was to run at twice the voltage (24v), while keeping the amps just below the maximum 12 volt amps by switching to a smaller and less aggressive propeller. I changed the wiring to bypass the resistor speed control while adding an external PWM , and Essentially got twice the power at 24 volts (but not double the boat speed). No damage whatsoever after many years of use at 24 volts, was verified when I disassembled the motor for examination. The minn kota ran at around 1,200 RPM underwater at 12v, so I had plenty of leeway on the RPM (maybe all the way to 3600 RPM) without blowing things up, even though the measured wattage was increased from 360 Watts at 12 volts to nearly double that wattage at 24 volts. So the point is that might be a way to increase the power of a drill motor that doesn't have to run at stock voltage, so long as the RPM specs and gearcase friction Heat allows for it.
     
  3. jakeeeef
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    jakeeeef Senior Member

    I'm basing it on manufacturers claims. They tend to overclaim not underclaim.

    But you're right to point out I don't know for sure without measuring it.

    It's one of the only drills on the market where the manufacturer states a Watts figure of any sort. Most 18 volt drills are about 350 watts by the way, where you can find out at all in the details.

    For that competition it was forbidden to alter the drills themselves, so no voltage changes.

    Outside of the context of that very particular competition, which is no longer running, powering a boat with a power drill is a very silly idea, and not something I've given much thought about since.

    Apart from anything else, power drills are designed to run for a minute or so at a time, even to drill a fairly big hole. The batteries overheat very quickly turning a large propeller, then they cut out, usually for half an hour at least until they have cooled down.

    Despite the fact that this boat did 9 mph ( in fact I think it might have even been 9 knots), it could only do so for a very short burst., Not much longer than shown on the video.

    The race was 2 or 3 minutes long, and was all about nursing the battery, about 6-7 knots if I recall, although I did burst over the finish line with a flourish of full power.

    The 24 volt minn Kota mod sounds like a great idea. I have a terrible 12 volt Sevylor motor in the shed that might benefit from similar treatment.
     
  4. Barry
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    Barry Senior Member

    Watts is not the unit to determine how much power that a battery can put out over an extended period of time so I am suspect of Makita's claim without the rest of the verbiage that went with this number

    A Watt is a Volt X Amp, I can take a Double A battery, the kind that you find in a tv remote and get it to probably produce 675 watts albeit for maybe a second or two, or some very short period. And I can take a 12 volt car battery and produce 675 watts for an extended period of time

    Pretty much all cordless batteries are rated in Amp Hours BUT with the unmentioned component which is the voltage

    So a 5 ah -18 volt battery, which are close to the median of cordless products would produce 5 amps x18 volt for 1 hour = 90 watts for 1 hour,, 10 amps x 18 volts for 1/2 hour 180 watts for 1/2 hour etc

    The point that I making is that any of the cordless batteries can produce 675 watts, the pertinent parameter is for how long and if you are buying a battery you need to compare amp hours

    (that being said, there can be different conditions at extreme discharge rates/temperatures that a battery may not attain its AH rating)

    Edited, did the math wrong the first post
     
  5. jakeeeef
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    jakeeeef Senior Member

    I don't know enough of the parameters I'm afraid.

    I do know it drilled a very large hole in my concrete front drive that no other cordless drill I own could touch!

    And if you take a bit of 10 mm threadbar, some bits of aluminium box section, and two old windsurf boards, you can do 9 knots with it ( for a very short time).
     
  6. alan craig
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    alan craig Senior Member

    You can "hack" a cordless drill and measure its parameters. As mentioned previously a power meter is essential for diagnosing and optimising electrical traction and for relatively low power systems a meter designed for model 'planes is fine. Picture shows a Bosch drill powering a 32" hand carved air propeller, modified to incorporate a power meter (this brand no longer available).
    The numbers on the meter show 16.85v, 25.5 A, 430W and 1350 rpm. The battery is 18v 3.0Ah or 54watt hours.
    These numbers tell me:
    The cells are at 3.37v for this load - fine for the fairly short duration.
    Discharge rate is 8.5C meaning 8.5 times the amp-hour rating and fine for most li-ion batteries.
    430watts is considerably more than half a horsepower of input power and means that I have about 7 minutes duration at this power level.
    This drill is rated 2050rpm no load so 1350rpm represents quite a big load for the whole system.
     
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  7. portacruise
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    portacruise Senior Member

    Hope the above comments help!
     
    Last edited: Nov 11, 2021
  8. portacruise
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    portacruise Senior Member

    Thanks Alan, I've also done similar measurements, with a different setup...

    One of the interesting (puzzling?) things I found out about drill motors is that their gearboxes(?) appear to be extremely wasteful! Even at no load, the Milwaukee cordless drill I recently tested draws 30 Watts at full speed, in comparison to my similar gearbox motor which draws 1 watt, no load. Also, the no load amp draw on the cordless drill drops as you slow the speed down with the PWM trigger, which appears to mean the gearbox is considerably less wasteful at low speeds, (if it is the gearbox that's responsible)! I've always presumed that gearboxes have fairly fixed losses throughout their design range, at least that appears to be the case for my other Gearhead Motors...

    I believe all batteries lose efficiency in delivering power under conditions of heavy current draws according to the Peukert equation, and also when operating at lower ambient temperatures. Lithium batteries are probably one of the best performers under those unfavorable conditions, though they might not deliver what they are rated ( stated at ideal conditions), sometimes the difference is significant.
     
    Last edited: Nov 11, 2021
  9. alan craig
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    alan craig Senior Member

    Portacruise, your Milwaukee is more efficient than my Bosch! I just measured its no load power at 58W at 19v. You might be drawing 300W to drill a big hole or turn a large prop so 30W losses is actually very good. My brushless outboard conversion on an Evinrude leg draws about 130W no load full speed, but will continue turning slowly right down to 4 or 5 watts.
     
  10. portacruise
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    portacruise Senior Member

    Alan, almost all of my sailing is done by packing in to long/ remote but small rivers or creeks, where the scenery can be breathtaking for me, compared to wide open Waters. Though there are usually long sections of clear and shallow water, I need to keep the speed down to avoid shallow rocks, boulders, and overhanging branches; most runnable River Rapids can be done quickly. So far, have not needed more than about 60 watts, which gives me about three knots added to whatever the river current flow may be. Because of the distances involved, I have to keep the efficiency, weight, reliability and other parameters as favorable as possible. I only have a couple of my discontinued super high efficiency propulsion Motors as spares, so I really don't want to use them. So I am thinking of packing a small cordless drill as an emergency backup, or leaving it as a hidden stash in route for emergency propulsion. A No Load draw of 30 W is just too much, and I am trying to find ways around it...

    Probably pretty crazy stuff for most people that would read this, but it's my thing, and I love it, haha!
     
    Last edited: Nov 12, 2021
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  11. fredrosse
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    fredrosse USACE Steam

    "What about boiling the water so the boat rides on a thin carpet of steam?"

    The heat transfer character of steam in contact with cooler water is fantastically high, the water will condense the steam at a fantastic rate. For example, maintaining a steam gas carpet under a hull, say 6 feet wide x 16 feet long would require well over 1 gallon per minute fuel oil burn. To say nothing of the space and weight for the gigantic burners directed to the hull bottom plating, or whatever type of boiler you would use to generate the steam. Non-condensing gasses, be it air, or IC engine exhaust is the only real possibility.

    Note that 60 gallons per hour fuel oil flow will provide enough oil to run a 1,000 horsepower Diesel engine continuously at full load.
     
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  12. S V
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    S V Junior Member

    portacruise, this looks like the topic to read, but I cannot get access to that pdf; it is behind paywall
     
  13. portacruise
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    portacruise Senior Member

    Yes, and maybe the paper has to be converted from the original language. Perhaps you can try contacting the authors, to see if they'll send you a free copy?
     
  14. portacruise
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    portacruise Senior Member

    I saw the other day that a Tesla generates more than 1000 horsepower in going from 0 to 60 at top speed. Curious to know how many times it could do something like that repeatedly on a drag strip, and what the drag race distance range would be when converted to miles, haha?
     

  15. fredrosse
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    fredrosse USACE Steam

    The Tesla Model 3 Automobile has an 82 kWh battery pack, and a good Diesel engine would need a little less than 7 US Gallons of Diesel Fuel to produce that much shaft energy. If the Tesla is producing 1000 horsepower, the battery capacity is greatly reduced, as the Amp-Hour capacity depends on the rate of discharge, faster discharge reduces available energy significantly.

    I don't know for the Tesla batteries, but if you have lead-acid batteries, the current standard is rating batteries on a 20 hour discharge rate, and if you discharge them more quickly, the total energy available goes way down, only about 20% of the rating is available. Giving Tesla a (probably generous) de-rating, say 50 kWh available at high power output. This is equivalent to the shaft energy of about 4 gallons of Diesel fuel.

    That 4 gallons of Diesel Fuel would power a 1000 horsepower Diesel for about 4 minutes, and that is about all one might expect from a Tesla automobile that is putting out the high horsepower mentioned previously.

    Please note that battery capacity is only one aspect of this imagined scenario. Putting enough amperage for 1000 horsepower thru the wires and motor windings would overheat that stuff quickly, and burnout everything long before the 4 minutes had passed.
     
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