Improving ship speed

Discussion in 'Propulsion' started by safaounaghi, Feb 15, 2015.

  1. safaounaghi
    Joined: Dec 2014
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Iran

    safaounaghi New Member

    Hi,
    I have a twin screw passenger ship with specs as bellow :
    L : 22.8 m
    B : 6.5 m
    D : 0.8 m
    Disp : 44.7 MT in full load
    Engines : 2*610 kw @1800 rpm
    Propellers Diameter : 30 inch
    Propellers Pitch : 37 inch
    No. of blades : 5

    with these specs, ship's speed is 15 knot that its so few with these engines.
    how can I increase my ship's speed?
    I just calculated a new propeller with B-Wageningen series for increasing propellers diameter, but not sure of its operation after producing and assembling that will cost a lot.
    What should I do for improving its speed except this way? what appendage should I add to hull for improving the speed?
    Is there any reference in this case?
    Some pics of the ship is attached
    Awaiting anyone's respond.
     

    Attached Files:

  2. TANSL
    Joined: Sep 2011
    Posts: 6,233
    Likes: 299, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Probably a bulbous bow will improve speed somewhat. A bulb, low volume, helps lifting the stem (changing the trim) and produces greater waterline length.
     
  3. baeckmo
    Joined: Jun 2009
    Posts: 1,189
    Likes: 143, Points: 63, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    You are right, the speed seems low, considering the available power, the displcement and length. What is the gear ratio (or is it 1:1?)?
     
  4. TANSL
    Joined: Sep 2011
    Posts: 6,233
    Likes: 299, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I hope not. At that speed propellers seem a fan.
     
  5. JSL
    Joined: Nov 2012
    Posts: 795
    Likes: 55, Points: 28, Legacy Rep: 41
    Location: Delta BC

    JSL Senior Member

    I did a quick check and with that power, displacement, etc. the best I can get is 15.5 knots.
    Sure your got the prop right???? 37" dia x 30" pitch makes more sense but I don't know the gear reduction.
    Bulb bow might help but the shallow installation could throw up some spray. Get some good windshield wipers
     
  6. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,050
    Likes: 635, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Is this a one-of-its-kind boat ? If not, it would be interesting to compare with sister vessels, as to weight, power, speed differences. The presence of those strakes running all the way along the bottom seems like an anomaly, they are doing nothing useful, I would say. Looking at the considerable vee at the stern, it is to be expected it would squat quite a bit at 15 knots, and those trim flaps would be somewhat ineffective in countering that, at that modest speed. Maybe drop 10 tons and it is a different story.
     
  7. whitepointer23

    whitepointer23 Previous Member

    this is a planing hull, I think a bulbous bow will be out of the water over 10 knots.
     
  8. TANSL
    Joined: Sep 2011
    Posts: 6,233
    Likes: 299, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    whitepointer23, sure you have very strong reasons to believe that but I do not see how a ship of 44 tons, 22.8 m in length, 15 knots, can reach the status of "planning".
    Of course, if you're right, what I said is nonsense.
     
  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,050
    Likes: 635, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I can't see how draft is just 0.8 metres, unless the propellors don't count !
     
  10. TANSL
    Joined: Sep 2011
    Posts: 6,233
    Likes: 299, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Taking as a reference the diameter of the propeller could deduce that the draft in the transom is 1.2 to 1.3 m. (area in red, without propellers)
     
  11. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,050
    Likes: 635, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    What is 610 kw in hp terms ? The boat probably needs more horses.
     
  12. whitepointer23

    whitepointer23 Previous Member

    I was looking more at the hull design in the pics, but you are right , 44 tons is a lot to get on the plane.
     
  13. TANSL
    Joined: Sep 2011
    Posts: 6,233
    Likes: 299, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

  14. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 247, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    With so big engine power, you should ideally be able to push that ship to around 25 kts. This number is based on the attached resistance curves, which can give you an approximate ballpark figure for a first estimate. The underlying assumptions are that the CoG of the boat is in the correct position and that L=22.8 m in your OP stands for LWL.

    At 15 kts, your ship should require approx. 400 kW with 65%-efficient props. So either your propellers are working at less than 30% efficiency (cavitation, barnacles or whatever), or your engines are badly underperforming, or the trim of the hull is so wrong that it creates too much drag, or the combination of these factors.
     

    Attached Files:

    Last edited: Feb 17, 2015

  15. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,050
    Likes: 635, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Must be plenty of bow lift to be fitting those trim flaps, isn't that amount of vee, aft, unusual in such a boat ?
     
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.