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Thru-hulls above props on Hatteras MY

Discussion in 'Hatteras Yacht' started by dan1000, Jun 16, 2011.

  1. dan1000

    dan1000 New Member

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    Wandering the yard yesterday, I noticed these holes above the props on a large Hatteras motor yacht. A similar Hatt next to it did not have these holes.

    photo.jpg

    Could someone let me know what these might be for? It seems strange to me to have thru hulls in the supposedly turbulent area right above the props. Perhaps they aren't thru-hulls, perhaps they are for some other purpose. Perhaps something to do with preventing cavitation or something like that.

    Enquiring minds want to know :) . Thanks for any light you can shed on it.

    Dan
  2. K1W1

    K1W1 Senior Member

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    Hi,

    Were the same holes and extra bit on the hull on both sides or just one side?

    That area will not see much turbulence when the boat is underway forwards as the turbulent areas will be aft of the prop with the boat moving forward.

    Two things I could think of for those holes would be inlets/outlets for some sort of bait tanks with the bolted on bit making a slight low pressure area for when the boat is underway at cruise or an attempt at getting an air cushion above the props in a futile attempt to reduce noise /increase slip.
  3. dan1000

    dan1000 New Member

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    I believe they were similar, if not identical, on both sides. Mmm. I was surprised to see so many of them all collected together. Perhaps there's some sort of sea chest above, plumbed to a bunch of small thru-hulls.

    Dan


  4. CatTech

    CatTech New Member

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    I have been on a vessel that has used exhaust injected into the prop during acceleration to aid it in achiving plane. this allowed them to use a bigger prop to get more speed out of the vessel at cruise. This might be the function of these thruhulls
  5. Loren Schweizer

    Loren Schweizer YF Associate Writer

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    Hatteras has been doing pockets/air induction on their sportfish boats for quite some time now, so it may not be a futile exercise.
  6. K1W1

    K1W1 Senior Member

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    Hi,

    Air pockets and Exhaust Ventilation of Props I can understand but not when they look like that.

    If there was an air injection system nearer the bow so as to provide bubbles under most of the boat I would be more inclined to believe it would make some difference to the drag but as far aft as those are I seriously doubt they would do much good.
  7. Capt J

    Capt J Senior Member

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    It could be used for ventilation of the props. But it looks like drains, for either the cockpit scuppers or bait tanks or generator waterflow etc etc. If you see the plate there foward of them, it's to divert waterflow on the hull below them, so they don't backflow when the boat is running at cruise and so they drain and don't fill from the water pressure while running.
  8. K1W1

    K1W1 Senior Member

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  9. old.one

    old.one New Member

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    Is it possible that these could be thru-hull lights, and maybe a hull mounted camera to observe the props at work? :confused:
    I have seen some underwater pictures of props 'in action', and the resulting cavitation that appeared.
  10. dan1000

    dan1000 New Member

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    They seemed to just be holes, no lights or glass. This was taken at a yard, so I suppose it is possible that something was in the process of being installed. But it didn't look like it to me. The boat was being bottom-painted, and as you can see, the fittings have been painted already (ie: not indicative of something in the process of being installed).

    Dan

  11. Beau

    Beau Senior Member

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    It all has an "after market' look to it. That "deflector" forward of the thru-hulls doesn't look well manufacturered at all, and probably something I wouldn't put on it I were concerned with hull dynamics. How big was this vessel?
  12. Loren Schweizer

    Loren Schweizer YF Associate Writer

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    K1W1, I grant you even the struts look different from that 77 pic you posted and, hard to tell from the angle if there is indeed a pocket. Maybe dan1000 could chime in as to what boat exactly we're looking at. He mentions a 'motoryacht'...and if you've been to the latest boat shows--which you have--you'd have noticed that the sportfish boats and their motoryachts look like they came out of different factories. So maybe this is, as you so aptly put it, a "Farmer Brown" version of the 77 underbody?
  13. YachtForums

    YachtForums Publisher/Admin

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    I don't know how I missed this thread. Maybe 'cause there's so much Cat talk in tech and I'm a dog with diesels. :rolleyes:

    All of you have the right answer. Like K1W1 original suggested and Loren confirmed, this is a ventilation system. While it could certainly be a vacuum actuated system to drain bait tanks, only one hole would be required with a deflector. Besides, this was a motoryacht according to Dan, not a fish boat.

    Like CatTech stated, venting the props allows slip, which can help swing a bigger wheel, which can help with acceleration and RPM's throughout the operational spectrum. But, it's not just a performance issue. While it may sound theoretical, venting creates an aerated boundary layer above the prop that helps insulate noise. The placement of holes, as well as the deflector to create a negative pressure zone over them looks just about right in my book, although it’s pretty crude.
  14. Marmot

    Marmot Senior Member

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    Nothing theoretical about it, I guess you could call them PRAIRIE dog holes.
  15. dan1000

    dan1000 New Member

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    I should have looked closer at exactly what model it was. My guess is: 80's vintage 70 foot Hatteras motor yacht. But beyond that, I'm not sure. Unfortunately, I'm now several thousand miles away from the yard, and cannot confirm. It's at Billfish Marina in Fort Lauderdale, in case any one is there (or at least, it was there a couple of days ago).

    Dan
  16. dennismc

    dennismc Senior Member

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    Holes

    They were std equipment on Some Hatts to help reduce prop rumble, they are connected to the transom also.
  17. Capt J

    Capt J Senior Member

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    That makes sense, and I've seen similar things from Hatteras. It's also possible the boat has had an extension put on and needed them for lift or something like that.......
  18. Capt Bill11

    Capt Bill11 Senior Member

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    What is the square partially filled opening on the right side of the picture all about? The original attempt to inject air?
  19. SHAZAM

    SHAZAM Senior Member

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    My old 65 SF had the same setup. I always thought it was to aerate the props.
  20. dan1000

    dan1000 New Member

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    Half way up the right hand side of the picture is the attachment point of the strut to the hull. I'm not quite sure what to call this strut, but it's the strut that holds the bearing inside which the prop shaft turns.

    In this picture, in case it isn't clear, the bow of the boat is off to the right, the stern to the left, starboard at the top, and port at the bottom. Between the blades of the prop, the port rudder post can be seen, but the port prop is not visible. The port strut (ahead of the port rudder post) is partially visible.

    The similar set of holes above the port prop is not visible, because the keel between the props blocks them from view, although this is not terribly obvious from the picture.

    Dan

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