Why don't boats have gears?

Discussion in 'DIY Marinizing' started by jakefrith, Oct 28, 2008.

  1. dand0_4
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    dand0_4 Junior Member

    A modern 4 stroke outboard at a cost of about 10 grand and maybe 70 hp will get comparable mileage, but I have a good running chevy that I paid $500 for, parts are cheap and it will push far heavier loads at far greater speeds if needed. My old 60 hp outboardmotor at 5000 rpm,30 mph got about 2 mpg. The chevy 350 at 2000 rpm and 30mph should do much better. Its not just a matter of power, the outboard has to turn much higher rpms for the same speed because it has only 1 gear.
     
  2. gonzo
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    gonzo Senior Member

    The Chevy has no gears unless you bolt them to it. You could bolt the gears to your old 60HP too.
     
  3. nukisen
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    nukisen Senior Member

    Dand0-4
    Seems like a very interesting solution you have made there. :p

    As a little bit of redneck solution guy of course I do like alternative thinking.
    Specially when they seems to work well.

    Well done!
    :p
     
  4. dand0_4
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    dand0_4 Junior Member

    Gonzo, very true, but not very practical or easy. I am not disputing your point about power and efficiency, just relating a cheap and practical use for a very affordable, powerful and useful motor and auto trans combo. As nukisen has stated, I am a Texas redneck( I cannot deny it, although a fairly well educated one)We like big power and speed and it doesnt always make sense, but its fun!
     
  5. nukisen
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    nukisen Senior Member

    It doesn´t have to as long it is fun. hahaha
     
  6. gonzo
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    gonzo Senior Member

    I like Chevys. If the boat can take the weight it is OK. However, the thread is about why boats don't have gears. They usually have a single forward and reverse gear. Some applications do have a two speed gear to match the propeller curve to the HP curve at mid RPMs. In most applications it is not worth the expense.
     
  7. dand0_4
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    dand0_4 Junior Member

    If I get brave or crazy enough, a drag racer friend of mine will help me turn my 350 into a 383 stroker with aluminum heads and 450 reliable horsepower. This is what is in his everday drive to work car. Very dependable with thousands of miles and races under its belt. Should be good for 70mph or more!
     
  8. dand0_4
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    dand0_4 Junior Member

    Sorry if I am getting off track, Gonzo, you of course are correct in your assessment of the expense and complexity not being worth it in most applications. But the general idea of a cheap and plentiful auto transmission with gears for greater efficiency is a sound one.
     
  9. gonzo
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    gonzo Senior Member

    You have to add a thrust bearing to it but I've seen them installed. A marine transmission, with its cooler and already installed bearing is usually simpler. However, two speed marine transmissions are rare and really expensive. It starts becoming more attractive to modify something. 383s are the cheapest hotrod to build in the USA. Parts are all readily available. At 450HP, it will be revving pretty high and the overlap on the valve timing may make it ingest water at idle.
     
  10. will9000
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    will9000 Junior Member

    Most jet units dont require a gearbox because the engine is directly connected to the jet unit. They have gears in the sense, forward backwards. Hope this helps if your intrested in Jets.
     
  11. longtailboats
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    longtailboats Thai sean

    Props are designed to operate at certian RPM. Exceede that given RPM they lose performandse and are inefficient. So if you use gears you have to change props. HI, Thai Sean
     
  12. michael pierzga
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    michael pierzga Senior Member

  13. Brian@BNE
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    Brian@BNE Senior Member

    In case anyone remains interested in transmission efficiencies then here is something of interest:
    Manual - 97%
    Auto - 86%
    CVT belt - 88%
    CVT toroidal - 93%

    The article as it:
    http://www.zeroshift.com/pdf/Seamless AMT Offers Efficient Alternative To CVT.pdf

    Couple a toroidal tranny to a CPP and there would be a nice and flexible driveline. But it might also need a computer and diesel pyrometer to map the best combination of variables!

    But with a drop in efficiency of 4% means that you would have to have a lot of different speed requirements (towing/trolling at different speeds/hi or lo speed cruise settings) to get enough fuel saving to be worthwhile. I'm guessing that most folk will cruise at just one speed, and have a trolling valve or kicker for periods of fishing.
     
  14. graftonian
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    graftonian Junior Member

    Back in the day when "Day Cruiser" meant a V8 in back, a V drive, and a minamalist cabin (wall to wall naugahide)..... a few people tried 2 speed auto transmissions. Worked great, especially when we took the boats out of the low water and went to Lake tahoe for the week-end.
     

  15. claydog
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    claydog Junior Member

    Seeing as you brought up CVTs I might as well ask a question Ive had in the back of my mind for a while.

    Would running a CVT that's very tuneable, like on a snowmobile, allow you to run higher pitch prop so that the boat gets on plane in low range then shifts out to operate at the props intended max RPM in high range?
     
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