Two RH props

Discussion in 'Props' started by Smarten, May 17, 2014.

  1. Smarten
    Joined: May 2004
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Rome

    Smarten Junior Member

    Hi,

    I found a couple of props good for my application but unfortunately both right hand. Now I know for sure that the boat's gears (it's a two screws boat) can manage full power load on both directions and maintain same ratio too.

    Now what about the efficiency of this odd arrangement versus a classic RH, LH pair? What will be the impact on boat maneuvering capabilities?

    Thank you for your support

    Linus
     
  2. powerabout
    Joined: Nov 2007
    Posts: 2,931
    Likes: 66, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    planning or displacement
     
  3. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    Use the props Linus, the advantages of counter rotating props are overrated. Think about all those boats with a single prop; there will be some "wheel effect" but you'll get used to it.

    I had a planing boat with twin RH props for nearly 20 years, then changed to counter rotation. Maneuvering in crowded spaces was always problematic and did not improve after the change, so I could not blame the props anymore.

    You're in Rome with the sea at your doorstep: return after dark when the spectators have gone home.
     
  4. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 117, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    In my limited experience with small (outboard) high rpm props it make little difference. With large low rpm props, its a different story and torque is a much larger factor.
     
  5. Yobarnacle
    Joined: Nov 2011
    Posts: 1,747
    Likes: 130, Points: 63, Legacy Rep: 851
    Location: Mexico, Florida

    Yobarnacle Senior Member holding true course

    With 2 RH wheels, reversing the port and ahead on starboard with full right rudder, the boat will slide bodily (walk) to port. Nice for port side landing. Noisy maneuver, takes a bit of throttle.
    But she won't walk to starboard reversing those settings.

    Reason is, the port wheel being RH, turns counter clockwise in reverse. The lower portion of wheel is deeper and gives more paddle wheel effect, paddling stern to port.
    Backing on the port pulls the bow to port, and the starboard wheel and full right rudder pushes you to port, so she walks to port.

    Trying to walk to starboard, backing on the starboard RH wheel, also paddles to port. Doesn't walk to starboard.

    I've run 3 engine boats with THREE RH wheels. Walks to port only.
     
  6. Smarten
    Joined: May 2004
    Posts: 10
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Rome

    Smarten Junior Member

    Hi All,

    Thank you for your comments.

    The boat is a semi-displacement one with a chine hull. Due the cost of diesel here (approaching 9$/gal) I rarely exceed hull speed (you are also much better to came back when Roma's football fans are already asleep!)

    Being today overpropped moving slowly with better matching props I will have probably more time to think ... and to use bow thruster. Frankly speaking never be really proficient in kicking throttle in such a way to have the boat walking.

    Regards

    Linus
     
  7. powerabout
    Joined: Nov 2007
    Posts: 2,931
    Likes: 66, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    its planing hulls with big vee where you notice it
     

  8. Yobarnacle
    Joined: Nov 2011
    Posts: 1,747
    Likes: 130, Points: 63, Legacy Rep: 851
    Location: Mexico, Florida

    Yobarnacle Senior Member holding true course

    Walking is a rocking movement with the two throttles. as you give more astern with one hand, you ease off the ahead engine with the other hand. Keep your hands, thus the throttles the same angle, distance apart. It's a constant play, rocking both hands in unison, back and forth, as you maintain your eye on a fixed point ashore, and stay abreast of it, as you close the distance.

    Only an idiot walks all the way to the dock from mid channel.
    Approach normally, stop a boat length from the dock, parallel to dock, then walk in those relatively few more feet. Helpful when you have to fit between two boats and just BARELY enough room. :)

    if dockside line handlers are available, you can T-bone the dock, get out some lines, and warp her in. But no line handlers ashore? Walk her in.

    Also, handy for mooring stern to dock, in a current; providing the current is on your port side, and you have enough power to walk against it and maintain lateral position as you creep astern into berth.

    Upshot is, two RH wheels ain't a BAD thing! :D
     
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.