Better than a Pocket or Tunnel?

Discussion in 'Propulsion' started by tom kane, Jan 10, 2016.

  1. tom kane
    Joined: Nov 2003
    Posts: 1,768
    Likes: 50, Points: 58, Legacy Rep: 389
    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Pockets and tunnels have some problems,perhaps this easier to build and simpler design could solve many of them.
     

    Attached Files:

  2. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 112, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    The Atkin reverse deadrise is also interesting as it may prevent the stern from sinking at under plainning speeds and with a box keel protects the prop when beaching .
     
  3. DCockey
    Joined: Oct 2009
    Posts: 5,268
    Likes: 650, Points: 113, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    What speed range is this intended for? Why are the edges rounded?
     
  4. tom kane
    Joined: Nov 2003
    Posts: 1,768
    Likes: 50, Points: 58, Legacy Rep: 389
    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Better than a pocket or tunnel

    There could be a lot of different versions, to give a better prop tip clearance or to allow a bigger prop or shallower shaft angle and even fit an I/O or shaft drive higher for S/P operation or just better shallow water operation.

    The application would be better for an inboard where the weight forward would help keep a shallow plane angle but not so good with a heavy outboard on the transom with out interference plates or trim tabs.
    There are many different options.
    With a retractable shaft drive any potential damage the the shaft or prop
    is eliminated with less drag from extra protection devices as the shaft would rise and fall with contact from any obstructions.
     
  5. tom kane
    Joined: Nov 2003
    Posts: 1,768
    Likes: 50, Points: 58, Legacy Rep: 389
    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Better than a pocket or tunnel

    Having curved edges helps water flow and reduces turbulence as different from
    sharper edges on some tunnels and pocket designs which interfere with prop
    efficiency (especially on turns) and can create aeration, also reduces the "running on rails" effect of some pockets and tunnels,easier and better steering.
    There is no reason why high speeds would be problematic and the water pressure released from front of the device would assist flow to the prop by rising to the prop.
     
  6. kapnD
    Joined: Jan 2003
    Posts: 1,381
    Likes: 464, Points: 83, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    It is a design that has worked well for me.
    I got frustrated with trying to design a perfect tunnel, and just bopped off a flat 8' long and 2' wide at the 14 deg. transom, gving the prop some 8" less draft.
    The prop runs very cleanly, no "tunnel noise" and no cavitation bubbles in its wash.
    The boat is somewhat underpowered, so I don't know really what would happen in high speed, but at wot 15 knots, it drags very little wake.
     

  7. tom kane
    Joined: Nov 2003
    Posts: 1,768
    Likes: 50, Points: 58, Legacy Rep: 389
    Location: Hamilton.New Zealand.

    tom kane Senior Member

    I am glad to see someone else has tried that design, and I tried several versions and think they were all better than any conventional tunnel designs which make a boat feel like it is running on rails.
    The mistake that could be made is making the image free flow plans to big.

    The amount of v or deadrise on a hull does dictate where the perimiter of the water flow will be.
    As with most S/P configurations it is the depth of the rudder needed to steer a boat well that prevents
    a boat from really shallow water operation. A deep rudder is needed about the same as a conventional subsurface drive at least.
     
Loading...
Similar Threads
  1. captdon65
    Replies:
    10
    Views:
    5,924
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.