reducing hull friction

Discussion in 'Hydrodynamics and Aerodynamics' started by nimblemotors, May 12, 2011.

  1. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 155, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

  2. Tackwise
    Joined: Mar 2010
    Posts: 49
    Likes: 4, Points: 8, Legacy Rep: 59
    Location: Ashore

    Tackwise Member

    Some time ago I found some excellent video's on air lubrication by injection under a flat hull. It showed the difficulties of keeping the hull covered with an air film at various speeds.
    (The videos were contained in a zip file: smooth_wmv.zip. If anybody with better searching abilities than me can refind it, the project name I believe was PELS and/or smooth).


    Another air lubrication system which does seem to have more merit is from Damen (project ACES), which recently posted a video showing some model and full scale testing. (video is in dutch however the pictures tells how it works)
    http://www.youtube.com/watch?v=kDC11_kHxqE
     
    2 people like this.
  3. lobsterman
    Joined: Mar 2004
    Posts: 75
    Likes: 6, Points: 8, Legacy Rep: 24
    Location: Maine

    lobsterman Junior Member

    Thank you Tackwise, In the video you posted, i found a modern ship's underwater hull design that is somewhat similar in shape and design concept to a radical high speed, high stability, small commercial fishing boat hull configuration that i had come up with many years ago, It is great to see my concept finaly validated. (see the underwater air cavity shapes at 1:15 -1:40). Now if they would continue to think a bit more outside the box of conventional thinking they will come up with a hull configuration that is truly revolutionary, practicle, and extremely efficient. Thanks again.
     
  4. projetdared
    Joined: May 2007
    Posts: 18
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: FRANCE

    projetdared Junior Member

    Hello.

    Inspireted by cavitation reseach there is a new stuff for surfboard. www.spiiid.com
    It could be an other option for boat.
     
  5. messabout
    Joined: Jan 2006
    Posts: 3,367
    Likes: 510, Points: 113, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    Back to the OPs preference of running in another boats wake. Racing power boats avoid another boats wake because it slows them down. The racers term for that is running in "dirty water". My wild guess is that turbulence in the water affects the prop efficiency of the following boat. If there is any advantage with bubbly water it is more than offset by prop losses.
     
  6. nimblemotors
    Joined: Jun 2009
    Posts: 244
    Likes: 3, Points: 0, Legacy Rep: 4
    Location: Sacramento

    nimblemotors Senior Member

    that would make sense in that the reduction in viscosity of the bubbled water would reduce the ability of the propeller to propel. of course race boats want MAX forward motion regardless of fuel consumption, and are also on plane, so different than a hull speed boat.

     
  7. DCockey
    Joined: Oct 2009
    Posts: 5,229
    Likes: 634, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    It would be a decrease in the density, not viscosity, or water with entrained air which would affect propeller efficiency and thrust. Lower viscosity with the same density actually increases propeller efficiency and thrust.
     
  8. magny7
    Joined: Jan 2010
    Posts: 33
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Surabaya

    magny7 Junior Member

    i've heard somewhere that cavity induced by heat tend to corrode the surface, like what happened in propeller surface.
     
  9. daiquiri
    Joined: May 2004
    Posts: 5,371
    Likes: 258, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I agree with both of you, and plus you have to consider a simple physical fact: Newton's Third Law of Motion.

    Think about a boat which moves forward at some ground speed (a speed relative to a fixed observer) Vground under a thrust T. It will exert the same but opposite thrust T to the water, thus accelerating it backwards (by the means of propeller, waterjet or another propulsive device). It means that the water left in the wake of this boat has a negative mean velocity (relative to a fixed observer) - i.e. it is moving backwards at some mean speed Vwake.

    A second boat, which runs in the first boats' wake at the same ground speed Vground, will thus see a water velocity equal to Vground+Vwake, which means that it will be subject to a higher hydrodynamic drag, which will require a bigger propulsive power.

    So, for all the above reasons, it actually pays to stay out of other boats' wake.

    Cheers!
     
  10. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 155, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Unless, of course, the gain from reducing your wave drag is greater than the sum of all the other losses. :)
     
  11. daiquiri
    Joined: May 2004
    Posts: 5,371
    Likes: 258, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    That's an interesting observation Leo. I haven't thought about that possibility. :)

    Do you perhaps have some data about the drag of individual ships, when one of them is moving in the other one's wake? It should include the propeller-wake effect too, of course.

    I guess that the eventual gain for the aft ship could happen only when it is at some precise distance for a given speed?
     
  12. baeckmo
    Joined: Jun 2009
    Posts: 1,654
    Likes: 670, Points: 113, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    One example of this is surfing "down-hill" on the transverse wave following the forward craft. Where I live, we have a commuter traffic with ferries operating from the mainland. When boating down-hill after those, you can cut down engine power considerably if you find the right spot.
     
  13. daiquiri
    Joined: May 2004
    Posts: 5,371
    Likes: 258, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Hell, that's true Backmo! I have witnessed that situation several times. :)

    Now, another question arises: since the boat surfing the wave is getting the power necessary for it's movement from the wave, does it mean that the boat which is creating that wave is experiencing a correspondent increase in power demand?
     
  14. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 155, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    I don't have anything that includes the viscous debris due to, for example, props.
    There are some images showing what I mean at:
    http://www.cyberiad.net/waketandem.htm
    It's quite easy to calculate the reduction/increase due to wave cancellation/reinforcement using Michlet.

    Leo.
     

  15. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 155, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Not necessarily. The front vessel can be several wavelengths ahead of the other vessel so it isn't affected by the other ship's "near-field".
    The aft vessel gets a free ride, in a sense.
     
Loading...
Similar Threads
  1. lunatic
    Replies:
    15
    Views:
    2,508
  2. rwatson
    Replies:
    8
    Views:
    4,044
  3. dustman
    Replies:
    69
    Views:
    2,502
  4. Rounak Saha Niloy
    Replies:
    4
    Views:
    1,030
  5. Jhomer
    Replies:
    4
    Views:
    2,211
  6. ras
    Replies:
    9
    Views:
    1,896
  7. krawiec
    Replies:
    3
    Views:
    1,915
  8. dustman
    Replies:
    99
    Views:
    10,169
  9. Leo Ambtman
    Replies:
    24
    Views:
    4,254
  10. Bukmaster9
    Replies:
    32
    Views:
    4,419
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.