Flat bottom skiff in parallel waves

Discussion in 'Boat Design' started by wollybugger, Jun 22, 2017.

  1. wollybugger
    Joined: Dec 2011
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    Location: MD

    wollybugger Junior Member

    Ran it a little yesterday. The boat is very sensational to rudder inputs, so it's almost like a quick yaw(right term?) with direction picking up after the yaw stops (if that makes sense). Kind of a slide then turn. That itself is a little uncomfortable.

    But it is designed to be maneuverable in shallows and pilings to grab soft shell crabs, and it does that perfect.

    So does the fact there is little resistance to yaw help set up the broach? Assume an unrealistic scenario of putting on a 10' deep skeg would it be yaw resistant? Broach resistant? With the detriment of heading reacting zero to steering input?
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Increasing lateral area will help a little, but not as much as you think. The same is true of lifting strakes, spray knockers and chine flats. The problem is the boat has very little grip on the water so lateral movement is normal, as the boat skids along in turns, until the chine bites and boat tries its best not to trip over it. Typical setups on this size/shape boat would be two or three 1x2's, laid on their flat, fore and aft on the bottom. This usually offers enough lateral resistance to help a bit in turns. On your boat, make the existing two rub strips, full length on the bottom and make another down the centerline. Leave the edges crisp (no heavy round over).
    philSweet likes this.
  3. wollybugger
    Joined: Dec 2011
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    wollybugger Junior Member

    Thanks. I am going to take your advise and it is very much appreciated.
  4. Dr. Oopy
    Joined: Sep 2016
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    Dr. Oopy Junior Member

    Good Day, I was away from the site for quite awhile and as it turns out you beat me to the water. What a beautiful boat. You really did a great job on that. I'll be lucky to get mine in the water at all this summer. Just wanted to compliment you on a job well done!
  5. coopscraft
    Joined: Dec 2013
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    Location: oregon

    coopscraft Junior Member

    In rolling waves water flows downhill on both sides of the crest and collects in the trough creating a crest in a new place. If your boat is in the trough but reaches up both sides of the wave for and aft, or plunged into the trough, it is encountering current in opposite directions which creates an unstable condition causing the boat to rotate around a vertical axis. There is no hull form immune to this in waves except a submerged one. When waves are steep and close together, adjust speed and the direction you travel to minimize the affects.

  6. Ike
    Joined: Apr 2006
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    Ike Senior Member

    Your skiff is essentially a big version of my 12 footer. I have always slowed down and turned toward (but not directly into) or away (lifts the stern where there is more buoyancy) Many people in large power boats haven't got a clue about their wakes and what havoc they can cause. When I built the boat I deliberately put a three inch skeg running down the center of the bottom for slightly more than half the length. This gives it better tracking and keeps it from sliding sideways., although I did consider using two small skegs on either side of the bottom. I don't plane the boat because it would require a much bigger o/b (I have a 2.5) and I don't want that extra weight on the stern. Skegs will help, but moving the CG aft to raise the bow would also help the bow rise to an oncoming wave. Of course it would also increase slamming on a plane but you have to make compromises.
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