Best thru hull design to keep a gen set running at over 40kntsu Hulls

Discussion in 'Boat Design' started by ChrisN67, Jun 23, 2010.

  1. ChrisN67
    Joined: Jan 2008
    Posts: 130
    Likes: 6, Points: 18, Legacy Rep: 69
    Location: Kuwait

    ChrisN67 Senior Member

    I have had many opinions on this point. I have an intrepid 339with twin yanmar 6LY2 and surface drives. I am using transom scoops for engine raw water.

    For the Air Con and raw water system I have a scoop-type 1" pickup facing forwards;

    The book for the Paguro 4000 GENSET shows a scoop type pickup facing backwards...I would think this would create a vaccuum...

    Does anyone have a way to install a pickup so that the genset inlet receives neither pressure or vacuum at any speed?




    Thank you
     
  2. Landlubber
    Joined: Jun 2007
    Posts: 2,640
    Likes: 124, Points: 0, Legacy Rep: 1802
    Location: Brisbane

    Landlubber Senior Member

    Does anyone have a way to install a pickup so that the genset inlet receives neither pressure or vacuum at any speed?

    Good question, the displacement boats generally have then facing backwards and planing types facing forward, but neutral.....interesting to see what someone comes up with here...
     
  3. mark775

    mark775 Guest

    It can't face forward on a fast boat. On 25 knot boats they face aft with no problem but forty is another matter. I would simply put a sailboat thru-hull (flush). Let us know how you do - forty knots AND a running gen is new territory for me, at least!
     
  4. kenJ
    Joined: Jul 2005
    Posts: 349
    Likes: 5, Points: 0, Legacy Rep: 56
    Location: Williamsburg, VA

    kenJ Senior Member

    Perhaps use a pump that isn't effected by the high head pressure.
     
  5. Greybarn
    Joined: Apr 2006
    Posts: 60
    Likes: 1, Points: 0, Legacy Rep: 20
    Location: Maine

    Greybarn Junior Member

    We use a flush seacock, with a Groco slotted strainer, facing forward, on the outside surface of the hull.
     
  6. Typhoon
    Joined: Mar 2009
    Posts: 125
    Likes: 8, Points: 0, Legacy Rep: 150
    Location: Australia

    Typhoon Senior Member

    Why not use a forward facing scoop inlet, then just before the water pump, tee it off and run a return line overboard?
    This way, you are assured of a full intake line and excess pressure is dumped overboard, the water pump will only take what it needs.

    Regards, Andrew.
     
  7. jonr
    Joined: Sep 2008
    Posts: 721
    Likes: 11, Points: 0, Legacy Rep: 57
    Location: Great Lakes

    jonr Senior Member

    > the displacement boats generally have then facing backwards and planing types facing forward, but neutral.....

    Sideways?
     
  8. ChrisN67
    Joined: Jan 2008
    Posts: 130
    Likes: 6, Points: 18, Legacy Rep: 69
    Location: Kuwait

    ChrisN67 Senior Member

    If the scoop is facing backwards (for the genset) then would there not be a vacuum generated? A straight (not scoop) thru hull would also generate a vacuum?
     
  9. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 239, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Maybe you can try with a NACA duct (or scoop):

    http://www.recumbents.com/wisil/nacaduct/naca-duct.htm

    Don't know if it is correct to call it "the best", but it does meet your requirements (except for the simplicity of construction).
    It is being extensively used in automobile and aerospace industry, but I've never seen it on a submerged part of a boat. That's probably because it is not a simple geometric shape - not just a circular hole in the hull, but rather a modification of an area around the inlet (plus a lack of information and the fact that not many applications have a need for it).

    P.S. (edit):
    A typo - highlighted word "never" was missing above.
    Also, I forgot to say that these should be installed at the hull bottom... So now I'm not sure anymore they will meet the requirements - you decide. :rolleyes:

    Cheers!
     
    Last edited: Jun 29, 2010
  10. ChrisN67
    Joined: Jan 2008
    Posts: 130
    Likes: 6, Points: 18, Legacy Rep: 69
    Location: Kuwait

    ChrisN67 Senior Member

    Thank you for your input, as a pilot I can tell you that NACA airfoil are great when angle of attack is constant (ask an F16 pilot what happens to a Pratt and Whitney under high G and angle of attack) The angle of the boat will change in the water, additionally to determine the exact geometry and orientation of the inlet would be difficult without model analysis.

    On a side not, for my engine raw water; I am thinking about hardin marine dual rami pickups:

    http://www.keitheickert.com/detail.aspx?ID=8909

    But as with any transom pickup, you can develop 30+ psi in the raw water system. Disregarding issues that arise in the event of strainer or other plumbing failures; I am wondering if the additional water might constrict the exhaust system to a detriment.
     
    1 person likes this.
  11. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 239, Points: 73, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Good points. Thanks for the correction.
     
  12. singleprop
    Joined: Mar 2008
    Posts: 49
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Hong Kong

    singleprop Junior Member

    here is a simple solution (if you have a steel boat): how about running a small open metal tube trough the keel with a T-piece in the middle - facing up (the thru-keel pipe must obviously have mesh screens on both sides of the keel). This T-piece would then be attached to your genset/equipment and would most likely not add neither pressure nor vacum to your system. If any, it would be minimal.
     
  13. Landlubber
    Joined: Jun 2007
    Posts: 2,640
    Likes: 124, Points: 0, Legacy Rep: 1802
    Location: Brisbane

    Landlubber Senior Member

    "would most likely not add neither pressure nor vacum to your system"


    ...please explain why, or do i miss the point entirely...
     
  14. singleprop
    Joined: Mar 2008
    Posts: 49
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Hong Kong

    singleprop Junior Member

    It's a proven concept, I will try to explain the logic: Any aircraft that I know of have these static pressure sensors on the side of the body. They are placed perpendicular to the body and only sences the static pressure. They do this at any altitude (pressure) and at any normal speed range - say beween 0 kts and Mach 0.9)

    I am thinking that the water intake acts in the same way, it's like a small seachest with only the static water pressure in it.

    Since the "sea-chest/water intake" is perpendicular to the sea water stream (not exposed to 40 kts) then there would neither be created a vacum or a pressure to the intake water, just like the static air intake on the side of all aircrafts.

    The T-piece adds another 90 degree bend that would further enhance this effect (I think), anyway the T-piece is only there to guide the water in the right direction (towards the genset).....

    Does this make sence?
     

  15. Landlubber
    Joined: Jun 2007
    Posts: 2,640
    Likes: 124, Points: 0, Legacy Rep: 1802
    Location: Brisbane

    Landlubber Senior Member

    singleprop,

    ...so is what you are saying, the T piece removes somehow the actual pressure of the water(air), what about the flow past the opening...still lost, sorry mate.
     
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.