Small inboard gas engine

Discussion in 'Gas Engines' started by dskira, Jun 6, 2008.

  1. dskira

    dskira Previous Member

    Good day
    It is sad we don't find small inboard engine anymore. they are smooth, easy to repair, do not need to run a long time to have the right temps like the diesel, they are light, and the risk of explosion almost inexistant if properly installed. (diesel get sometime in fire and that not fun eather)
    We put gaz bottle in boat and its far more dangerous than gasoline.
    I liked these gasoline engine for sail boat. I had one in the seventees a one cylinder Fita, realy smooth. They are less expensive to built than diesel, and the consumption as an auxiliary engine is not a real concern.
    Well it is what I think. is sombody else agree? Just curious :)
    Or perhaps somebody knows where to find a proper inboard gas engine in the 8 to 15 hp range :?:
     
  2. alan white
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    alan white Senior Member

    I agree. I've seen people switch to diesels and then of course they have a propane stove inside the cabin.
    Gas engines are smooth and I wonder why nobody ever designed a bilge blower whose flow prevented the engine from cutting out---- a simple switch activated by a flap. Then no gases could accumulate.
    I had a Vire from Denmark---- reliable and smooth and it would run on kerosene. Only moving parts were piston, crank, and rod. Period.

    Alan
     
  3. kengrome
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    kengrome Senior Member

    I think no one builds them anymore because they don't see a huge market for them, not with outboards being so easy to install, use, and remove in comparison. A resurgence in small inboard powered boats will have to occur before there's enough demand for a company to start making some good ones again.

    I have always wondered if I should be making such engines instead of boats. My dream would be a small horizontally opposed or v-twin with a dry exhaust stack, a built-in infinitely variable planetary gearbox, and some kind of mechanism that allows the prop shaft to be installed at any angle without changing the engine's position -- perhaps a CV joint or something similar. Then installation would be super-simple with all of the difficult alignment issues virtually eliminated.

    I think it is realistic to believe that such a design is possible, but it might take a lot of time and money before prototypes are built and tested then a factory setup and ready for production. Environmental regulations make designing simple engines 'more difficult' these days too, so they will never again be as simple as the old ones were. That's really too bad too, because the simpler they are the more reliable they are.
     
  4. alan white
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    alan white Senior Member

    Gas engines are very light in comparison with diesels. For this reason (and the current acceptance of outboards), it would be nice to see an electric motor like a Briggs and Stratton Etek as the driving motor and a small compact gas genset as the provider of electricity. The electric motor requires no gearbox, being reversing and high torque (the Etek R or RT model is a high torque version).
    The motor weighs 22 lbs or so.
    The genset could be a suitcase unit on deck, inside of a fiberglass or plastic case mounted in the rear of the cockpit. Its throttle could directly increase/decrease wattage and hence speed so batteries could be taken out of the loop if desired.
    The genset would be easily serviced or replaced while the electric motor would need little if any attention ever.
    88% efficiency, ultra reliable, constant 8 hp with 15-19 hp on tap for short spurts (using a battery), short trips without the genset running (using a few batteries), opportunity for solar and wind assist.

    Alan
     
  5. TollyWally
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    TollyWally Senior Member

    Ken,
    I would think that the gearbox is the challenge. . Our asian friends have filled the world with small well built motors, not so many gears. Built in has advantages but so has an independant installation when it comes to service and repair.
     
  6. TollyWally
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    TollyWally Senior Member

    Alan,
    The original premise of diesel electric was, I believe, just as you pointed out all about solving the gear problem. But, correct me if I'm wrong, won't you get less propulsion thrust per gallon of fuel consumed by running it through a genset and then an electric motor than burning it directly in an engine/gearbox setup ?
     
  7. alan white
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    alan white Senior Member

    No, as a matter of fact, the high efficiency of the electric motor, and in eliminating gears (running a straight shaft with a low RPM per volt motor) coupled with an efficient genset (which allows the gas engine to run at an optimum speed if using batteries) means a distinct advantage for the hybrid set-up.
    The hybrid would probably use less gas, in other words. Not only would solar and wind become options, but if there were a number of batteries, most maneuvering could be done in silence and if the gas engine broke down, there would still be ample stored power to get somewhere.
    The maintenence would be easier as well, as the electric motor needs none and the genset could be taken ashore. No water exhaust or cooling issues, no crawling into tiny spaces to fix things, no fire hazard.
    The electric motor would be about 8 inches around and maybe 4 inches thick--- therefore further back and allowing the engine area to become valuable storage space for example.
    Vibration would be lessened too, since the vibrating item (engine) isn't any longer transferring power through the hull.
    The "suitcase" genset could be of less hp than the electric if batteries were used. A 2500 watt unit putting out 72 volts would be ideal, allowing 92% efficiency from the motor. That would require only a small (3 1/2 hp) engine. The genset weight would be low, maybe 75 lbs. Being so light, it could be mounted off the stern as an outboard would be. It's generator could double as a starter. Retrofitting would be easy. Replacing the engine would be under $300.00. Overall costs would be no more than a diesel replacement and probably cheaper.

    Alan
     
  8. TollyWally
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    TollyWally Senior Member

    Discounting additional input from solar and wind generation, if I am understanding you correctly the suitcase genset and electric motor would be more efficient in providing propulsion?
     
  9. kengrome
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    kengrome Senior Member

    Ideally the electric motor would be engineered with a hollow tube type shaft instead of a solid shaft, with clamps on each end that tighten onto the prop shaft. Simply slide the motor onto the propeller shaft then clamp it on tightly (a spline would work too of course although at additional cost and probably not necessary). The motor's outer casing can then be secured to the hull via flexible mounts to cushion the starting and stopping torque and isolate vibration from the hull.
     
  10. Guest625101138

    Guest625101138 Previous Member

    Alan
    These motors spin too fast for best result with direct drive - something like 70rpm/V. The numbers for typical displacement speed favour at least 3:1 reduction to get good prop efficiency. The Perm PM132 might get away with 2:1 as it has higher rated torque.

    If you use a PMDC motor then the brushes will require maintenance. Typical brush life I can find is around 1000hrs based on automotive applications. You could expect better in a boat but I would not regard as maintenance free. The PMAC motors eliminate the brushes.


    Rick W.
     
  11. FAST FRED
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    FAST FRED Senior Member

    For the smaller boat GAS is ideal.

    Honda and others make Rototiller replacement engines (8 to 12hp) that hace a fine usually 6-1 reduction gear built right in.

    This will allow a tiny engine to replace a much larger engine.

    Nicest I have seen was an old atomic 4 replaced with the tiller unit , and it still did better than 5K!.

    At idle speeds the boat goes very slow , so the lack of neutral or reverse is OK.

    Cruise is at Full bore! , but these little Hondas don't seem to mind.

    A 4 inch duct with an inline fan did the cooling.

    Only downside is with an alternator mounted on the boat must be underway to charge the batset.

    FF
     
  12. alan white
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    alan white Senior Member

    Could be the Perm motor is higher torque (they claim 40% higher), Rick. B&S has the new high torque model as well, but I haven't researched it. I'm building an ultralight three-wheeled car right now so I'll very soon be choosing and buying a motor. Of course, I'd have a chain drive, so ratios are going to be easy to get.
    The B&S have brushes, yes, but 1000 hrs is practically a lifetime aboard a small cruiser and then when it's time, how long could the job take? I suppose it all depends on the architecture of the boat.

    Alan
     
  13. alan white
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    alan white Senior Member

    If you research state of the art technology in motors and generators, high voltage (72v) permanant magnet motors and generators are around 9o% efficient (90% x 90% = 81%, batteries account for a small variable depending on many factors).
    The real savings is in the engine controls. Every engine has an RPM range where it produces the most power relative to fuel consumed. The engine is run only at this specific RPM, and is not tuned to accellerate (soft start instead). No momentary loads need effect it.
    I can get amazing mileage out of a car by maintaining a steady 30 mph for hundreds of miles on level pavement. If I could lean out the fuel mixture while doing this, I could probably get over 50 mpg (or better) with my Toyota truck.
    The suitcase genset would have that dead level "road" and special tuning each time I turned it on.
    My guess is the efficiency of a well conceived hybrid is a bit better for those reasons. Costwise, I'd say economies of scale prevent the hybridization of small boats from competing fairly against the likes of Yanmar, for example, so while you could build your own system for about the same cost today, a manufactured system would be a lot cheaper down the road. Installation is knocked down to a fraction and parts and pieces such as controls and plumbing that would normally be required as part of a normal engine installation would be nonexistent (water intake, discharge, muffler, engine beds, cables, rods, fan, sensor for gas, through-hulls, etc.).
    Long term costs involve on-site work only with straight diesel/gas, but the suitcase would have a multi-pin connector and a fuel line (with fixed onboard tank).
    It could be delivered to a shop having guaranteed qualified personel. Or you could take it home, like a small outboard, and work on it there, running it at the bench.

    Alan
     
  14. alan white
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    alan white Senior Member

    That brings up another point. Since an electric motor drive can function as a generator while sailing, those who sail a lot more than motor need no genset at all. Just batteries and a controller. But imagine the flexibility using wind, solar, genset. and sail power (not to mention shore charging).
    Shore charging is underrated, but grid power is CHEAP. Electric cars, for example, cost a fraction to run (though lacking range).

    Alan


    Alan
     

  15. TollyWally
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    TollyWally Senior Member

    When I think of suitcase gensets I usually picture one of the Honda units, very quiet nice little units.

    Is this similar to what you are thinking about?

    I don't know the rating but I have twin 4D batteries, how much more capacity is needed for manuevering and in harbor work?
     
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