Finished Leeboard Weight: 4 lbs. 7 oz. (~2.1 kilo), Travel 75º


Back side


Side cover removed

Locate the mounting holes

This might seem as if it should be the last thing to be done, but moving the board forwards toward the bow or backwards toward the stern will change all the angles, so we must do this first. Measuring from the bow along the rubrail (NOT straight back from the bow), mark and drill two 1/4" (6.5mm) holes perpendicular to the rubrail/gunwale centered between the top and bottom of the rubrail.   By perpendicular, I mean they will be angled somewhat due the the curve of the side. I.E., they will be angled downward on the outside of the boat, but will not be parallel to each other. You can make the holes larger later if you wish.

A long straightedge in laid between the bow plate and the transom. The green line is where you measure the distance from the center of the dinghy. Make sure this distance is the same for the transom. Now you have a reference that is parallel to the center line of the dinghy.  When fitting the bracket for the leeboard, simply measure the distance from the center reference (purple lines). That way you can be certain that the leeboard will be aligned to the direction of travel when sailing. A little piece of scrap is placed on the seat to help keep the straightedge from sagging.

Hold a piece of 2 x 6 (or similar) as shown below such that it is parallel to the centerline of the dinghy.  I could not hold it and photograph it at the same time, but the photos above should give you an idea how.  From the underside, mark the piece of 2 x 6 with a pencil following the curve of the rubrail.   The 2 x 6 was fir, but use what you like.

If you have a saber saw (jigsaw to some) set the blade angle to 20º and cut along the line from the end of the 2x 6 that will make the other side the widest. (because we marked it from the bottom and the bottom should be the widest).  Finish fitting it with a disc sander attached to a drill motor, or if you have one, a planer attachment for the little high-speed hand grinder.  You could make a cutout in the middle to make fitting easier and sort of artistic so that less wood would have to be removed.

Trim the ends of the 2 x 6 to 14 1/2" (36.8cm) if necessary. Notch the ends like this:



Drill a hole in the skinniest end and insert a bolt to hold it in place so the second hole can be drilled.  It should resemble the photo above.

This is the time to mount it with bolts on both ends and check it for parallel and level with the top of the boat.  Trim the width to 1 1/4" at the skinny end and about 2" at the wide end.
NOTE Don't try to make it too much less than these figures, because the board will hit the side of the boat when you try to raise it.

It should still be parallel to the centerline of the boat. (If it is not, the leeboard will pull the Flapdoodle to one side when sailing, wasting forward motion). Make corrections if necessary.


I used 3/8" (9mm) ply for the vertical bearing surface. Use what you have that is close to that as long as it is sound and strong. It measures 7 x 11.5 inches (17.8 x 29.2cm).

Cut one side at 15 degrees (see the red lines below).  The plywood was attached with glue and 4 screws to the notch and allowed to dry. The blue area below can be trimmed with a hand saw.  You can blend it in the the bracket with a Dremel tool, or sand with course sandpaper. But even this is not absolutely necessary.




Double checking for squareness and parallel. Note that the angle in front has not been cut yet on the vertical bearing surface in this photo, because it was still being developed.


The Board Itself


We begin with two pieces of ply with the dimensions shown above. Laminate them as you did with the rudder. 5mm, 5.2mm, 6mm, or 1/4" will all do nicely it it is fairly good wood.

When dry, two more pieces are laminated to it, but at a 15º angle to make the reinforcement for the upper part of the board. Bevel the edges first at the lower edge. When dry, drill the 1/4" (or fit for a similar metric size) for the pivot. A coffee can was used to trace out the circle. Feather the leading and trailing edges below the reinforcement pieces as well as the bottom and its radii as you did for the rudder.

DON'T radius the upper rounded part. We will cut a groove in part of its circumference for the lowering line later (unless you opted to save time by omitting it and the pulleys). But even that can probably be omitted.

Sand all surfaces smooth and varnish. Paint if you wish.


I used oak to make the spacing strips because I wanted the screws to hold well. Of course, other woods will do. 1/2 (12mm) x 16 inches (40cm) will work fine to make all the spacer strips.  But the thickness will have to be determined by you. Their width will be the thickness of the leeboard + the two polyethylene discs + a few thousandths for clearance (~.5 mm).  A little on the loose side is better than too tight. The nut on the pivot bolt can be used to remove any side play when finished.  Cut one piece a little over 7" to make the one shown above. it should hang over the edges a little so they can be trimmed flush. Glue and screw it in place flush with the angles edge.  When dry, you can trim the ends and front side along with the plywood so it is attractive.

This part is real easy...  Take an attractive piece of 5mm to 1/4" piece of ply that will cover the top part, glue and clamp till dry. It will measure 13 1/4" by 4" (34 x 10cm), but larger is okay. Your choice as the which way you want the grain to run. Trim the edge on the boat side flush with the bracket. A sanding disc on a drill motor does this quickly.
Leave a little extra on the outside for final trimming to match the cover plate (if you want one).

 The top will look like this after trimming.


Find the pivot point.

With the board flush against the spacing strip, (red line above) mark where the pivot hole is.

Check the up position.

The distance shown should be 3 3/4" (9.5cm). The circular top part of the board should be close to the spacer strip you just installed.

Note that the bracket has not been trimmed in front yet in the photo because it was taken during development. Make a mark through the pivot hole on the plywood vertical bearing surface. Draw a line through the mark parallel to the top of the leeboard bracket.

Make sure the marks will allow the board to be in both positions before drilling for 1/4" (6mm).
Put a bolt through, and check again! You should be able to pivot the board through the entire 75º.  If there was an error, glue a piece of wood dowel in the hole and start over.

Two more spacer strips are cut, one 5 1/2" long  (14cm) and one 1" long (2.4cm).
Glue them to both the top plate and the vertical bearing plate.
Clean up any glue that seeps out.

The version shown has a hole drilled through the rear of the brace that rests against the side of the dinghy, 5/8" in diameter. It requires a long bit, hard to drill and difficult to align with the hole on the other side. For these reasons, we will deviate from the photos and do it a simpler way.

I made the side cover plate from two layers of 5mm  luan. you can use almost any type of plywood 7 inches by 12 inches.  (17.8 x  30.5cm)  Place the bracket part on it, get it centered and drill through from the back so that the holes are aligned.

Put the board in place in the box, bolt through from the rear, apply the new side plate and fasten with a nut.  When it "feels" like it is properly aligned, drill the edge for one of the 6 screws. Countersink and put a screw in. They will be centered with the spacer strip if you put them 3/8" (9mm) from the edge.
 
Trace around the edges of the sideplate from the rear with a pencil. Remove the plate and trim to the pencil line.  Reinstall it without the board and do the other 6 screws. I did the curved cutout part on the left freehand by roughing it first with the saber saw. You can be artistic if you wish. The sideplate can be finished now.


I cut the side support from some scrap white oak I knew to be easy to work with, yet strong. We will place it just behind the head of the carriage bolt, so the bolt can be removed if necessary.  The side of your boat may not be exactly 20º.  

First, we want the angle the edge that contacts the side of the boat. The easy way is to use a hand plane and just try it until it seems to be in contact with most of the side. Perfection isn't necessary, because the side of the boat flexes some.

Trim the top end until it is in contact with the underside of the bracket, the back of the vertical bearing plywood, and the side of the boat all at the same time. Sounds tricky, but it really isn't.

The tongue at the bottom is two thicknesses of 1/8 x 3/4" aluminum stock 3 1/2 inches long (but can be longer if desired). It would have been 1 inch wide, and 1/4" thick, but that is what I had on hand. Use whatever is handy. Strength is what is important.   Cut a recess in the brace for it so that about 1 1/2" sticks out the bottom. Drill two holes and countersink for #8 x 1" stainless sheet metal screws.  I would not use brass here. Before attaching the aluminum, taper the end and round the edges.  This is important because we do not want it to gouge the side of the boat when it slides into the nylon loop that holds it.

When we are SURE everything fits properly, attach the brace to the vertical bearing plate with long screws and glue.  

The control lines
I used 1/8" nylon cord for the control lines. Not the best choice. Braided 3/16 would be better.


Placement of the holes for the knots are not critical, but your choice of line diameter will determine the diameter of the holes.  A groove was cut in the edge of the rounded upper part of the board to accept the line just as was done for the rudder.  

The placement of the pulleys is also not critical, and the pulley will determine the size and shape of the slots in the top plate. But DO try to make the slot as small as necessary to help keep the line from slipping between the pulley and the top plate.

Install the pulleys, lines and test before replacing the side cover. If all is well, put the side cover on. I used a wing nut on the pivot bolt to make sort of a tension adjustment.

 

A short length of 1" nylon salvaged from an animal harness completes the mounting for the leeboard. It is the same material I used for the rudder hinges. Two #8 stainless machine screws with finish washers attach it through the side of the Flapdoodle.

Stainless fender washers and SS nyloc nuts inside the boat complete the installation.


A friction cleat like the one I designed for the rudder provides positive control for raising and lowering.  I have decided that round wood balls might make it easier to untangle it when needed. The handles are color coded as we did for the rudder.

One final touch... little mark using an indelible Magic Maker on the line near the "down" pulley will let you know at a glance if the leeboard is all the way down or not.



NOTE Something occurred to me that I have never seen addressed before.  Some authorities estimate the side force on the leeboard to be about 50 pounds (22.7 kilo) for a boat the size of the Flapdoodle. That is far in excess of anything I expect to encounter personally, but ok, lets assume that is so.

The side bearing faces of my board are circular with ~6.25" (15.9cm) and the board is 36" (91cm). Lets assume the center of force is half way down the board, or 18".  This would give the force a 3:1 leverage. Or 150  pounds (~45 kilo) on the bearing surface.

In a worst-case-scenario we are sailing along nicely parallel to the shore and hit an obstruction. Leeboards are meant to swing upward when they hit an obstacle. If the side force is near the maximum, binding on a wood-to-wood side bearing would increase friction, possibly making it stick enough that the board gets broken. We did not have this problem with the rudder to this extent, but I will recommend a brass or stainless pivot bushing and the 2 polyethylene discs (coffee can lids are good) that I suggested for the rudder. Polyethylene on varnish is very slippery.

I know this adds even more to a fairly complex design, but in the interest of reliability and safety I think it wise.

NOTE   I am sure this could create a lot of discussion, but I don't recommend adding weight to the bottom of the board. The heavier it is, the more inertia it has when the inevitable object is hit, increasing the risk of damage.  The control lines work well keeping the board where you want it, and the friction cleat will allow the board to swing upward in a collision. 

This set of plans and all its contents are copyrighted 2006-2007, Bill Weller