Monday, January 30, 2017

A Good Start On An Off Center Board

I made the decision some time ago not to use conventional leeboards.  There are several reasons:  The windward board provides no function.  Also, since Autarkia will heel very little, an off center board  able to bear the load on either tack will be effective enough for us.  A single side mounted off center board is used by Jim Michalak in many of his designs.

I intend to mount the board flat against the hull with a single pivot bolt, bearing the flat surface of the board tight against the hull with a piece of sheet plastic sandwiched in between.

Today I started making up the board.  I cut 16 pieces of 2by4 8 feet long.  This is the good structural fir I had left over from the boat build.  Here I just laid them out on the bench and clamped them together to see how they fit and to do some marking.




I drew an arc here.  The area to the right of the arc will remain flat on both sides, since this is the area that will be in contact with the hull side.  It has to bear tight against the hull without any play, and be able to take torsional loads as well as side loads from port and starboard.  Below the arc is where the board will be shaped to a symmetrical foil.   Much of the material to shape the foil is removed on the table saw.  I stop ripping at the arc and use a handsaw to remove the piece.



Of course I need to know what to rip away, so I made up a template to give a rough idea.




I did not angle the saw blade to follow the exact contour.  The reason is I would only be able to do one side since the blade only angles in one direction.  To do both sides I would have to cut from eith end, and that was impossible since I am only removing material partway up the board.  No matter, since once it's all together there will be a lot of grinder and belt sander work anyway to do the final shaping.



Those transitions will get a nice radius and b blended in smooth.



Here they are going together with PL Premium and 3 inch  epoxy coated deck screws.



All together and curing.



So once cured in a couple of days I'll fair it up.  I may use some steel as a leading edge and for weight to sink it, and then it will all get glassed over with a couple of layers of 10 oz cloth set in epoxy.  I may also put in a sleeve for the pivot bolt.

2 comments:

  1. Woo! We happen to be working on OCBs ourselves, but ain't so purty as yourn!

    For shaping, consider a power planer... we can usually start with that and finish with a sander (no grinder).

    One thought about 'bearing plate' OCBs... if it isn't wung out from the hull, you only get to count area from the hull down. If you need to up the effective lateral resistance, consider angling it out a ways... lets you count area from the waterline down.

    Consider Layden chine runners (more info at http://www.piano-tuning.co.uk/microcruisers-and-the-chine-runner-concept/) to add lateral resistance at little cost.

    Looking good!

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    1. Thanks Dave! I do have a power planer and don't have a grinder so I guess I'm in luck! I did consider chine runners at one time. Too late now though with her in the water for the next couple of years or so. No doubt future tweakage will be in order. We are sure looking forward to seeing more of Wayward as she progresses. The best to you both.

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