Why don't boats have gears?

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

  1. nukisen
    Joined: Aug 2009
    Posts: 440
    Likes: 8, Points: 0, Legacy Rep: 124
    Location: Sweden

    nukisen Senior Member

    For me who have a direct transmition from the engine to propaxle I have no prop with me when starting the engine. for those who uses a mechanical reverse gear will save the gears if they only change direction with idle speed. For hydraulic transmition it would be very unnesessary
     
  2. Myrtonos
    Joined: Jul 2012
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Melbourne, Victoria, Australia

    Myrtonos Junior Member

    Just as a boat is not a car, propellers are not wheels. When was the last time anyone here has seen a propeller turn as slowly as the wheels of a slow moving vehicle. Even on level ground and reguardless of the situation, the wheels of your car need to turn at a wider range of speeds than that of the engine, typicall four to seven times difference between the idle speed and redline. Propellers turn over a much narrower speed range, owing to the dynamic properties of water.
     
    Last edited: Dec 28, 2012
  3. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    maybe on a ship but a planning boat the prop operates at say 2:1 so the prop goes from idle to 3000+ rpm
    F1 race boat idle to 10,000 rpm at the prop
     
  4. Myrtonos
    Joined: Jul 2012
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Melbourne, Victoria, Australia

    Myrtonos Junior Member

    Any wheel always travels a fixed distance per revolution, this being proportional to the diameter. No matter what the ground speed, a wheel always spins at the same numbers of revolutions per mile, this depending on the diameter. But propellers don't seem to behave like that.
     
  5. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 109, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    A modern torque converter will have a lockup feature built in.

    Just figure out how to instruct the T converter to lock.
     
  6. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    yes they have slip so they can operate through a larger rpm range
     
  7. Frosty

    Frosty Previous Member

    Does it realy?
     
  8. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 145, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    No it doesn't.

    It was popular a few years ago when word spread around that automatic gearboxes wasted fuel and a lock-up mechanism could prevent that. But silently the feature disappeared: my Kia 4 wheel drive has a 5 speed box, automatic power distribution between front and rear wheels, but no lock-up.
     
  9. Frosty

    Frosty Previous Member

    Oh dear oh dear!!
     
  10. powerabout
    Joined: Nov 2007
    Posts: 2,901
    Likes: 61, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    Plenty of yank oz German and jap ( Camry, almost biggest seller in the world ) stuff have them
    I think everyone just stopped talking about them as its a standard feature?
     
  11. nimblemotors
    Joined: Jun 2009
    Posts: 244
    Likes: 3, Points: 0, Legacy Rep: 4
    Location: Sacramento

    nimblemotors Senior Member

    It seems to me there is difference in power requirements for a planing boat, where the torque needed to get on plane is much greater than needed to maintain it.
    So using a lower gear to get on plane would increase the torque, and shift once on plane.
     
  12. dinoa
    Joined: Oct 2007
    Posts: 229
    Likes: 18, Points: 18, Legacy Rep: 97
    Location: florida

    dinoa Senior Member

    Moon Craft runabouts circa mid sixties, about 14' length, made in England had Renault engine and manual transmission. I saw one used as a launch sitting on a converted Fermile yacht.

    Dino
     
    1 person likes this.
  13. jonr
    Joined: Sep 2008
    Posts: 721
    Likes: 11, Points: 0, Legacy Rep: 57
    Location: Great Lakes

    jonr Senior Member

    I agree, with the question being if it would pay for itself in fuel savings.
     
  14. WestVanHan
    Joined: Aug 2009
    Posts: 1,374
    Likes: 56, Points: 0, Legacy Rep: 746
    Location: Vancouver

    WestVanHan Not a Senior Member

    I can't imagine any automatic built in the last 20 years that does NOT have lock up. Maybe not in the first 2-3,but definitely in the top gears.
    If it's not locking up.something is wrong.

    CDK-maybe you are thinking about lock up betwixt the front and rear diffs?
     

  15. Myrtonos
    Joined: Jul 2012
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Melbourne, Victoria, Australia

    Myrtonos Junior Member

    In fact torque converter lockup was first introduced back in 1949 by Packard on their Ultramatic, but torque converter lockup didn't become more wiespread until thirty years later. Now I realise that fuel may have been very cheap at that time, but it was already known to be a finite resoucre, and the lack of torque converter lockup did mean that most automatic tranmissions were less efficient than manual ones, in spite of the latter interrputing torque with each shift. Packard's Ultramatic did have a highway efficienty comparable to a manual, while at the same time allowing smooth and continuous acceleration.
     
    Last edited: Jan 2, 2013
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.