Using compressed air on boats

Discussion in 'Boat Design' started by nick storm, Oct 17, 2006.

  1. nick storm
    Joined: Oct 2006
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    nick storm Junior Member

    I recently saw a program on TV here in Australia, called "The Inventors" on which a guy had designed a very efficient Fork Lift motor which was powered only by compressed air, whilst I cannot recall it's power and endurance, I remember it was good enough for commercial use in a factory.
    Naturally this caught my eye and I got to thinking about the possible uses of compressed air on boats, as a power source for winches, motors, tools,etc..
    Bearing in mind that air weighs a heck of a lot less than lead batteries, and that air lines are not subject to corrosion and shorting out.
    I would use excess solar or wind power to run 240v compressors thru inverters, and then store this "energy" in 3300 psi scuba tanks.
    Is this feasible ? Would it be better to use one big tank, or link several smaller ones?
    What would be the advantages, disadvantages and constraints of such a system ? Can anyone help?.........thanks, Nick
     
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  2. FAST FRED
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    FAST FRED Senior Member

    When air is used on trucks & busses it is about 125lbs , so the problem is the tanks get quite large to do any real work. An air for starting system will have a start tank the size of 2 garbage cans end to end, and you only get 1 chance at starting!

    The tried and true hydraulic system does far better than electric at things like anchor hauling. An electric motor relys on a circuit braker to pop when the motor gets overloaded and stalls.Hyd just stops till you incrase the supply pressure , smoke never pours out.

    Air is very wet so a complex system of dryers and multiple tanks to drain the water is required.

    On larger boats the future will be stolen from aircraft . Hydraulics , with an electric pump mounted on , is lighter than a main hyd sysyem and long runs of heavy pipe and fluid. Controlled with an ethernet , the only wiring will be power to all the individual pump motors.

    FAST FRED
     
  3. Poida
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    Poida Senior Member

    Hi there Nick

    I don't believe you would have a hope in hell of filling scuba tanks from wind or solar as the power supplied would only be enough to power very small pistons for compression and would take ages to fill. I assume you meant you were going to fill them on your boat. This means filltration and removing moisture, forget it.

    However you could fill them from a compressor the cost of which would be large or get your cylinders filled at a dive shop.

    How lo0ng will it last?

    Well find the power from a winch supplier, I just got a quote for an anchor winch for my 6m boat and it is 400w. Ring up Caps, Festo or Atlas Copco and ask them the cost and the air consumption of an air motor to suit what power you require. From this you can estimate how long your dive tank will last. Remember the air consumption given for the air motor will be stated as a volume at operating pressure. Air motors are hungry especially vane motors and you will find piston motors expensive.

    The result in my opinion, not worth it.

    The reason, although I didn't see the programme in question why a forklift powered by air would be feasable is in an explosive environment as a warehouse that stored flammible materials and where ventilation was limited so fumes from a gas engine would be unbearable for the employees.

    On a boat I see no advantage as you already have an engine and a generator so use an electric winch.
     
  4. MikeJohns
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    MikeJohns Senior Member

    Oddly enough I was just asked if I would like to join a think-tank on compressed air re-powering for coastal shipping.

    It is by all acoounts the energy storage of the future, it is receiving serious aclaim, it is a safe simple energy storage that can be utilised in many ways.

    The current proposed air powered cars are being designed around a 100km/hr 200km range, a prototype is to be demonstrated at the Paris roadshow this year. It takes 4 hrs to fill the tank using a home based plugin compressor or 3 minutes at a commercial station , a recharge would cost around $3 US .
    Most yacht aux motors are in a similar class and would benefit from trickle charging from excess elect energy since they have a lower use cycle.

    The higher you can store pressure the greater your energy storage density but they already appear to be eclipsing electric vehicle capability . One suggestion for coastal shipping is to compress the air to liquification (cooled)
    not suitable for smaller installations though.

    The big advantage is simple cheap energy storage, lower pressure air motors may prove to be a very good option for auxiliary marine use, they have been driving torpedoes for decades.

    Keep watching
     
  5. Jimbo1490
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    Jimbo1490 Senior Member

    Seems this might be a viable energy storage device if you stored above the vapor pressure of air, which, IIRC is quite high. Aircraft are beginnig to rely more and more on electric actuators BTW. The Boeing 787 is leading this trend.

    Jimbo
     
  6. Poida
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    Poida Senior Member

    Mike could you define the term re-powering for me please.

    You did mention safe - there are dangers with compressed air, one of the reasons why we now have to have a hydrostatic test done on scuba tanks every year instead of 5, due to a death. I've known others that have exploded, one instance wiping out a garden shed. They never found the valve out of the top of it.

    Remember filling a tank at home from a compressor takes energy either from a petrol engine or electricity = cost.

    It will be interesting to hear how your think tank progresses.

    Hydraulic and pneumatic characteristics are similar. Pneumatics provides a fast motion but not neccessarily an even motion due to its compressability.

    Hydraulics is slower and as a liquid can't be compressed providing a slower but even motion.

    Also if a hydraulic hose blows, it makes a mess, air doesn't. However by switching the hydraulic pump off you do not lose any more oil. If an air hose blows from a storage tank you could lose lots of air. Of course fitting a valve on the reserviour actuated by a loss of pressure sensor could be the answer. (I don't think that is how you spell reserviour, perhaps I should change it to the tank where all yer air is)

    Regards
    Poida
     
  7. Syed
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    Syed Member

    You are right Poida,

    Pressure vessels are amongst the highly hazardous installations in industrial plants. High pressure will require thicker tank walls that will make them very heavy, which is least desirable for boats.

    Regards,
    Syed
     
  8. ted655
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    ted655 Senior Member

    Someone in France is making a car that uses a compressed air motor. Unlike most of this "pie in the sky", low ranging, alternative prototype crap, This one is practical & in production. The darn thing works!
    Since it doesn't operate on a simple intake/exhaust cycle, I can't tell you the circutry. It IS a long range air engine that doesn't need large storage tanks.
    If your serious about this, I would learn more about this French car And it's engine (motor?).:idea:
     
  9. Richard Hillsid
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    Richard Hillsid Senior Member

    ted im interested
     
  10. MikeJohns
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    MikeJohns Senior Member

    Poida
    The "repowering" is the feasability of air driven motors for ship propulsion and the storage and regeneration of high pressure compressed air. I am not participating by the way, I don't get excited by committee processes, and I already suggested sail as a better alternative :).





    Ted
    I already mentioned that car in my prior post although I read that it was still only a prototype.

    Don’t knock prototypes and conceptual design, every mass produced machine started as a concept then a prototype, some work and go on to become mainstream. Large projects require team combined effort to ascertain feasibility. The latest oil price crisis has shaken enough people in high places for some money to start flowing into the investigation of alternatives. Air cars look very promising. Alternatives to fossil fuels are far from what you refer to as “crap” are you an oil man? :)


    High octane automotive fuels are I think around 10 times more explosive than TNT it is incredibly hazardous yet we manage these hazards. Pressure vessels properly engineered and tested are very safe these days.

    As for mass consider the mass of the fuel and equipment of a large oil engine, look outside the square …sailboats for example carry 30-40 % additional weight ………just for weight.



    Anyone who is interested I’ll attach a general regulation sheet for compressed air installations in boats this will give a general idea of regs pertaining to safe installation.
     

    Attached Files:

  11. ted655
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    ted655 Senior Member

    Sorry Mike, I missed your mention of the car. I don't knock prototypes. You are right, but I don't get excited by them. Too many have their 15 minutes of fame, too few come true.
    As far as more people getting serious about replacing fosssil fuel, ha. We've had the technoligys for years.
    Anyway, I first saw this car more than a year ago as a proto. Last month I saw another TV show and according to them it was in production. I admit, I haven't had one pass me on the road yet.
    My question is...., Is it cheaper to run a fossil fuel engine at a set rate (compressing air) Than running one through the RPM range at varying prop loads/speeds? Diesel/electric is widely used, what about diesel/pnumatic?
     
  12. Syed
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    Syed Member

    Found this interesting post on 'howstuffworks'. I think boats may be propelled more efficiently with direct 'air-jet' if air sourcing and storing arrangements can be made practical and feasible.
    Syed

    Quote:
    _________________________________________________________________
    "* Posted:
    June 22, 2006

    Storing air for powering a car may not be practical for a number of reasons, ask me for a better explanation if you need it, by a Hybrid makes more sense than ever.

    If the fuel is converted at a consistently high percentage of an Internal Combustion Engines efficiency, the tanks get topped off and the engine goes off-line waiting for the next charge cycle provided that the chassis is running at a rate that doesn't demand 100% of the compressor's output.

    A typical car, on the other hand, seldom reaches it's peak efficiency. A commonly produces car engine at peak efficiency is about 25% efficient: At full power. Seldom operated at that power setting, the net delivered efficiency is more like 0.5 to 1.0 percent.

    In simple terms, the compressors average 70% efficiency, a pneumatic motor is likely to be as efficient and the engine converting the fuel averages 25% efficiency. The average losses in a drive train are below 5% for gear interface and tire adhesion, so as the last 5% is common to both, it is factored in already.

    The sum is that the delivered efficiency if a compressed air Hybrive is 0.7 x 0.7 x 0.25 or about 12.25% vs an averaged 0.75% or about 16 times more efficient... A car that got 20 miles to the gallon could legitimately be expected to deliver 320 miles to the gallon.

    As a Hybrid, the acceleration comes from the stored volume. A SCUBA tank, (renound for it's capacity to take off like a rocket if mis-handled) delivered approximately 150 horsepower of energy when depleted over a one minute period. double that for a 30 second depletion period, double that again for 15 seconds, and double that AGAIN for the 7.5 seconds the average drive would accept to get to sixty miles an hour... Some 1,200hp in 7.5 seconds, certainly adequate for the common family sedan.

    In practice, half of all that is at least reasonable... 150 miles to the gallon and 600hp for acceleration...

    Kevin E. vonMoses
    Alternate Drive Systems, L.L.C.
    _________________________________________________________________
     
  13. MikeJohns
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    MikeJohns Senior Member

    Yes it is.
    And the air engines become highly efficient and can be designed with high torque low rpm direct drive becomes possible. The initial shoreside charge however and re-charge would be from an onboard electrical compressor or direct charging from a shore based installation.

    Electrical energy in these quantities is around 5-7c per kW.hr in Australia. As Fyed says air engines are a much more efficient energy conversion than combustion. The efficiency stakes will ultimately produce the winners.
     
  14. FAST FRED
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    FAST FRED Senior Member

    "The efficiency stakes will ultimately produce the winners."

    More likely the Liars for Hire will produce the winner.

    We already have very efficent flywheels , that can be powered up electrically & rapidly,
    but the concept of a 150,000+ rpm flywheel in a fancy vacume / epoxy case with air bearings being hit in an accident , and releasing 10 gallons of gasoline worth of energy , almost instantally, has the Trial Lawiers DROOLING!!

    Poke a hole in an air tank , & its lots safer.

    FAST FRED
     

  15. MikeJohns
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    MikeJohns Senior Member

    Fred
    Yes I'd forgotten them...

    The flywheel has some inertia problems on boats, bearing loads can be huge, the big problem you have to address is what happens if a bearing seizes, without very thick heavy armoured casings its very hard to guarantee a safe shutdown in an accident. Compressed air is easily released, non hazardous .

    I just heard that
    The new high efficiency air engines are triple expansion with a modified two part crank to suit the different expansion to combustion.

    Be easy enough to re-power any two stroke to run on compressed air you could inject the air into the spark plug hole using a simple sensor and electro pneumatics ..................anyone want to convert their outboard :)
     
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