Mast and fin position

Discussion in 'Boat Design' started by David Lees, Oct 23, 2021.

  1. David Lees
    Joined: Oct 2021
    Posts: 1
    Likes: 0, Points: 1
    Location: Spain

    David Lees New Member

    Help required. I am currently building a scale model of a Fire ball sailing dinghy, scaling the hull down to one metre. I want to use it with an International One Meter radio controled yacht (IOM)
    sail rig, as an exsperiment.

    My problems is do I keep the mast and and fin position as per the Fire Ball drawings, or do I change these position to copy the position on an IOM hull. I can build in a small degree of fore and aft movement for both the mast and the fin of 10 mm to help adjust the boats trim. The fin is located as a dagger board with a lead bulb. On a IOM the front of the fin is 500mm from the stern and the mast
    sits directly on top of the front edge of the fin. Will the centre of effort of the hull be down the centre
    of the fin which is 80mm wide and parallel. Any help will be appreciated.
  2. messabout
    Joined: Jan 2006
    Posts: 3,300
    Likes: 449, Points: 83, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    David; find the center of lateral area of the Fireball including the dagger board. Do so when the all up weight of the RC gear is in place. Find the center of effort of the IOM rig. Set the rig so that it's CE is about 5 or 8 percent of the waterline ahead of the hull center of lateral area. That is a conventional setup that would get you in the ballpark. You may have to fiddle with this later. Consider that the sail is never in perfect fore and aft position if it is to develop some drive. That is why you have the sail CE ahead of the Hull CLR.

    The whole deal gets a little bit uncertain because the boat is going to heel when under sail loading. You will need to account for the heeled center of lateral resistance and compromise the mast location with that in mind.

    In a full sized Fireball the crew is tasked with hiking like mad in order to keep the boat reasonably flat. The model does not have the benefit of an athletic crew.
    Ilan Voyager likes this.
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