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sternsailart3S.jpg (49905 bytes) Summer Breeze! - This is the story of an 11'8" long 50" beam 16" sides, 500 lb capacity skiff from two sheets of 1/4" 4x8 plywood. Award winning - She won the 2001 Duckworks design contest. 
   Leeboard and brace plate:
Introduction
Getting started
Sides 
  Skarfing
Frame
Transom 
Stem
Bending
Chines
Bottom
Gunwales
Breasthook
Quarter knees
Seat
Mast Partner
Keel&Skeg
Mast & Spars
Leeboard
Rudder
Sail 
Floatation 
Painting 
Resources 

The leeboard is made per the drawing. If you want to stay very basic you can get away with just rounding all the edges. If you want to make it a bit more efficient you can taper it towards the leading and aft edges. Generally the thickest point of a "foil," as they call them, is a third of the way back from the leading edge. Some say leaving the trailing edge squared off is more effective then rounded. That's a bit over my head, but if you want to research it Jim Michalak is the guy to go to. Here are a couple of his articles on leeboards:

http://homepages.apci.net/~michalak/1sep01.htm#LEEBOARD%20ISSUES

http://marina.fortunecity.com/breakwater/274/1998/0615/index.htm#Pivoting Leeboard Design

Here's a quote from one of his recent newsletters:

"THE LEEBOARD...

The leeboard - always best to laminate it from thinner plywood to avoid warpage. So if the leeboard is to finish at 3/4" thick you should make it from two layers of 3/8" plywood or three layers of 1/4" plywood. What I like to do is to make one lamination exactly the right size and the others a bit oversized. Then apply lots of glue between the layers, place the layers on top of each other on a flat surface and tap light nails through the stack so that the layers can't slide around on each other. Then place something like concrete blocks on the stack of layers to aply pressure. Then walk away until the glue has set hard.

Trim the glued up leeboard blank to final shape. Then streamline the front and aft edges that will flow through the water. Don't just round the edges with a router bit. It doesn't have to be carved to a full airfoil shape but I would suggest something like this:"

Read the whole thing here:   http://homepages.apci.net/~michalak/ and browse his boat plans. He has some great ones, and very reasonably priced.

He also has some great articles in his archives on leeboards and rudders. 

The pivot bolt on Summer Breeze  is placed the same distance from the aft edge and the top edge of the leeboard. That distance will be 8" for external chine logs, and 6 1/2" for internal or stitch and glue. The difference is because with external chine logs the leeboard will bear against the gunwale, the pivot bolt spacer, and the chine log when deployed. The other version is bolted flat against the side with a plastic spacer to reduce friction, and touches the underside of the gunwale when deployed. It sort of "bump" stops against the gunwale in the down position. 

   A 3/4" thick backing plate of 3 pieces of the 3" wide ply is fastened to the inside of the side, opposite the leeboard. This reinforces the pivot bolt mounting point and distributes the forces over a wider area.

board up.jpg (77540 bytes)  board down.jpg (79785 bytes) leeboardown.jpg (24859 bytes)

This leeboard idea I got from my friend Richard Frye. It will work with internal chine logs or stitch and glue. 
SBleebrd1.gif (11361 bytes) I find no perceivable difference in the tacks. My theory about why these simple leeboards work so well is that on the shallow tack they are more vertical, and on the deeper tack they are more slanted in the water. SBleebrd2.gif (11238 bytes)

   
   
 

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