Calculating bilge board/keel area

Discussion in 'Boat Design' started by hospadar, Jan 24, 2012.

  1. hospadar
    Joined: Apr 2011
    Posts: 60
    Likes: 3, Points: 8, Legacy Rep: 30
    Location: Michigan

    hospadar Junior Member

    I'm planning my new small boat after the untimely demise of my ill-fated first boat (http://www.boatdesign.net/forums/sailboats/hull-shape-simple-sailing-scow-37499-3.html#post490323)

    This time I'm thinking to build something like a PD Goose, which is basically a 12' long PD racer (a boxy 4' x 12' scow type boat).

    I'd really like to use bilge boards or some sort of fixed keel instead of a dagger/center/lee board. The reasons for this are:
    a) less separate parts/moving parts to haul around/maintain/mess with while sailing
    b) acceptable in shallow areas (most of my boating is inland lakes)
    c) I don't really care about sailing performance all that much, just needs to work
    d) no trunk in the middle of the boat

    The boards will probably look something a little like this: http://www.pdracer.com/keel/195.jpg (perhaps not full-length, but they will just be part of the sides extended below the bottom of the hull)

    My question pertains to calculating the area and placement of the boards, I assume the sail-area-to-underwater-foil area calculations I'd use for a daggerboard or leeboard still apply to bilgeboards, or will it be different since bilge boards are so low aspect? How will those calculations change because I have two boards (one on each chine) instead of a single board (should I just split the area between the boards?). Would the length of the boards matter all that much (the difference between full-length or 2/3 or 1/2 or 1/3)?

    I'm pretty sure I could just wing it and it would work OK for my little boat, but if there's a better way, I'd be interested to hear about it.

    Also, worst case scenario, the bilge boards suck and I hate them, I chop em off and use a leeboard, no real loss there.
     
  2. hospadar
    Joined: Apr 2011
    Posts: 60
    Likes: 3, Points: 8, Legacy Rep: 30
    Location: Michigan

    hospadar Junior Member

    I just had another thought, kick up centerboard style board where the trunk is built into one or both of the full length side airboxes. Little more work than the bilge boards but probably better performance.
     
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