Daggerboad well (sailing cat)

Discussion in 'Boatbuilding' started by Capt Ridder, Jul 27, 2020.

  1. Capt Ridder
    Joined: Jun 2020
    Posts: 5
    Likes: 0, Points: 1
    Location: Sooners

    Capt Ridder Junior Member

    Good morning (wherever that is!)

    I'm working on a cat design and looking at study plans for the build. I don't have much experience with cats yet at this level of detail. I know daggerboards are very common and I've never heard of the shaft being a concern.

    But in the vertical well (or trunk, shaft..) for daggerboards when they are up (and down). Is there much of an issue with the actual hole on the bottom of the hulls causing drag or water intake up inside of the well? Any unusual back pressure issues that would force water upwards?

    I know the space is sealed, so I'm not asking about water intake into the vessel. More just in the empty space where the daggerboards move up and down. As I plan this out and review design plans, I wanted to ping the community and ask if there's anything I should pay attention to that might not be blatantly obvious when figuring the build, engineering and design?

    Thank you for your time.
     

    Attached Files:

  2. Blueknarr
    Joined: Aug 2017
    Posts: 842
    Likes: 160, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Yes, water can climb up a board case.
    Two ways to minimize:
    1 A very tight fit between the board and opening. Just enough clearance to allow smooth operation of the board.
    2 rubber like flaps on each side of the opening which close when the board is retracted.
     
  3. Yobarnacle
    Joined: Nov 2011
    Posts: 1,730
    Likes: 121, Points: 63, Legacy Rep: 851
    Location: Mexico, Florida

    Yobarnacle Senior Member holding true course

    i have heard some use a short plug board, when the dagger board is totally removed, but why? Not a convenient task while racing, and why would the fractional resistance of the well be of concern other than for high tech racing.

    Here is another arrangement for catamaran boards. This eliminates wells.

    UNDER BRIDGE BOARDS catamarans.jpg
     
  4. Blueknarr
    Joined: Aug 2017
    Posts: 842
    Likes: 160, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Not all board cases are capped. Plug board's stop spray from exiting the open top. They also prevent marine life from taking up residents in the trunk.
     

  5. Capt Ridder
    Joined: Jun 2020
    Posts: 5
    Likes: 0, Points: 1
    Location: Sooners

    Capt Ridder Junior Member

    Ahh good stuff. On my list of homework is continue research on this. Makes sense though.

    Building a expedition cruising cat, I can see rubber flaps being added to the spare parts list. But sounds pretty legit.

    Thank you for the reply.
     
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.