The story and photos of my folding boat © 2007, 2008 by Man of the Cloth Productions.
Instead of building a dagger board with a trunk in the middle of the hull, I made a lee board. A leeboard is dropped over the lee side of a sailboat to provide lateral resistance to the sideways push of the sail. This allows the craft to sail closer into the wind. While not as popular in the USA as center boards, a leeboard can be effective in a small craft that is not designed for racing.
The simplest method of supplying a boat with the means of offering lateral resistance to the water, and so checking leeway, is to fit her with leeboards. Leeboards are not often to be seen in England save on Thames barges; but on the shallow Dutch waters, where small-boat sailing is as well understood as it is here, leeboards are to be found on nearly every yacht. Leeboards have several advantages over centerboards; they do not jam, break off, or strain the boat when one runs aground, but always come up at once on touching the bottom. Some shallow waters (the Danish fjords, for example, among which the author once cruised in a leeboard boat) are in summer overgrown with weeds, through which a centerboard craft could never force her way: the long water growth would wind round the plate and choke the trunk; on the other hand, a leeboard can always be pulled up without difficulty when it gets foul, and be quickly cleared of the weeds.
Barend Migcheksen wrote:
The Dutch did not invent leeboards. They saw them being used in the
Far Eastduring their discovery voyages in the early 1500s. Their merit is that they gave the boards the curved shape of a light aircraft wing with the thicker edge fore, becoming thinner toward aft. The convex side of the board is against the hull. The concave side is on the outside. The lift from the leeboard makes the boat point slightly higher on a tack. It is very easy to explain with what we know today about aerodynamics. However, they discovered that 300 years ago without knowing anything about these principles.
Barend offered this drawing of a "Dutch" style leeboard, which is what I used as the basis for my construction. Jim Michalak has informative articles (1, 2) about leeboards, too.
I cut out a blank form from some birch plywood left over from another project. I laid out the basic contour lines of the leeboard in pencil. This is not a precision underwater foil. The center of the foil will be 1/3 from the leading edge. The trailing 2/3 tapers to a fair edge. Something like this:
I trimmed away even more unnecessary wood after I settled on the basic shape. Then I glued additional plys onto the base to build up the profile of the foil. Only the part submerged in the water needs the foil shape. I cut the crook in the top of the board so the leeboard would trail in the water when it hangs down. This slight trailing angle reduces spray from the board and it prepares the boards to tip up if it contacts an underwater obstacle.
The foil shape provides lift on the hull side of the leeboard. It is this lift that helps the boat point into the wind. On old ships that used leeboards, the vessel often carried one leeboard made for the port side and another for the starboard side. Each lee board had a convex foil on the side toward the hull. The seaward side was flat or concave.
My leeboard will be used only on the starboard side of the Barquito. Based on the Dutch leeboards, I am experimenting by putting a greater foil on the side of the leeboard toward the hull. I hope that the addition of the foil gives me a higher angle of attack to windward on one tack and at least moderate performance into the wind on the other one. If it is a disaster, I will make another leeboard with a more typical foil. Experience will tell. Since I hope to use this board on both tacks, technically it is an off-center centerboard. I'll still call it a leeboard, since it looks like one.
Before I started filing down the profile of the foil, I marked the centerline on the leading and trailing edge of the board with a pencil. As I removed the wood to achieve the shape of the foil, I planned down to this line.
I began putting a uniform taper on the flat side of the leeboard. You can see I removed wood down to the line. In profile the shape of the wood above my finger curves away from the line to meet the flat surface.
Here is how I made the foil using the basic shape described above. I started by filling the steps between the various plys with epoxy wood filler. There was nothing precise about this. I just pressed it in and smoothed the epoxy as much as possible with a putty blade.
As you can tell in the photo below, I started with the leading edge of the board. When the epoxy was cured I used a micro plane to remove the high spots.
Working with the micro plane was a breeze. The wood and epoxy I exposed were lighter in color. The darker color indicated a few low spots.
I repeated these steps a few times to build up the low spots. Between each step I would remove the excess epoxy with the micro plane. What a great tool.
The process was the same for the trailing side of the foil. Notice that I didn't try to fill all the the area at once.
After repeating the steps two times, the trailing side of the foil looked like this. You can see that I began to remove more wood to give a greater taper to the foil as the line approached the trailing edge.
After another step of filling the low spots, it looked like this. You might notice how I painted the other side of the board already to save time.
This photo shows the foil near completion. The evenly rounded edge on the left is the leading edge. The long tapered side on the right is the trailing edge. The trailing edge tapers down to a nice 1/16".
I thinned some oil based paint and painted the leeboard with several thin coats of this penetrating oil paint. This photo give a nice overall view of the starboard side of the leeboard.
I applied several thin coats of oil based paint and hung the leeboard to dry.
Jim Michalak designs home-built boats that have a leeboard on only one side. These leeboards function like an offset centerboard. Using some of his ideas, I came up with the basic shape of a leeboard case. It was limited in part to the size of plywood scraps I had lying around. Below, the large piece will connect with the mast supports on the right and will hold the pivot for the leeboard on the left. The interior will also hold a line and pulleys to control the leeboard's angle of attack to the water. Adjusting this line will also move the center of lateral resistance fore or aft.
The size of the case was also limited by the dimensions determined by my sail plan. I knew I would rig a lugsail. When I did the math for this sail plan I found that the centerline of the leeboard (center of lateral resistance) needed to be 18" from the pivot of the mast step. I know that my leeboard can swing fore and aft. I also know that my mast can be raked toward the stern. These two factors will give me some room to adjust my rig, but my sail design calls for a distance of 18". If it turns out that I need to move the leeboard aft, I still have room to drill another pivot point and still use this case.
My next step was to temporarily mount the case to the hull. The leeboard case will need a support to help hold it in place when under lateral load. This support piece had several angles to it. But it wasn't that hard to make. The only tools I used beside my saws were a pencil and my angle gauge / marker. The first step in making this support was to scribe a line at 90 degrees from the case to the rub rail.
I used this line as my reference or ledger line. I found the angle of the hull at this line.
Then I transferred the angle to two blanks of 3/8" plywood.
Next I found the angle of the other axis at the ledger line.
I transferred this angle to the blade of my table saw. I cut the line scribed two pictures above using this saw blade setting. The next photo shows the two pieces of plywood as I checked the cuts against the gauge.
I glued the two pieces and let the glue bond the wood together under pressure.
When the piece was dry, I inverted the plywood stock at the ledger line and marked the distance from the rub rail to the case. Using the mark, with my saw set at 90 degrees, I cut the excess off the side that will mount against the case.
Now I have the correct blank. I traced the outline of the support onto the blank which already has the correct outside angles and edges.
Using the saber saw I cut out the blank to make the support for the case. I thought a nice curve would serve well. The photo below shows the angled cut on the lowest side of the support. This is the side that matches the angle of the boat hull.
The next photo shows the dry fitting when I tested the result of the cuts. Looks good!
The next picture shows the slight gap between the support and the hull below the rub rail. I filled this gap with cork to tighten the fit and to reduce rubbing on the hull.
I ran two long screws through the leeboard case into the head of the support. I also applied cork to the lower part of support using tube adhesive.
This photo shows the support in place. That is how I made a custom shape without needing any measurements except the angle gauge. See how the support is square to the leeboard case, tight to the rub rail and flush with the hull because of the cork filler. The support will help hold the case away from the hull, keeping the leeboard square with the centerline of the boat. I think this view reminds me of an outrigger.
After coming up with a graphic design for the starboard side of the case I painted all the pieces. After the paint was dry I applied paste wax to the inside of the case and to the top of the leeboard so the painted surfaces would not bind or scuff. Then I installed the bolts for the pulleys. The rope will be attached to the leading edge of the leeboard. Pulling up on this rope will hold the board in the water at the desired angle.
I realized that I wanted the bolt heads showing to starboard. This meat I had to figure out a way to drop the bolts with the pulleys and rope attached into the proper place in the case show at the top of the picture.
Holding the pulleys in place with masking tape was my solution. Once the bolt threads mated with their holes, I pulled the tape off. Everything dropped right into place.
When I had the side of the case in place, I screwed it together. Then I removed the pivot bolt, show on the left in the picture above, inserted the leeboard and reinserted the pivot. I secured all the nuts with a lock washer.
I tested the movement of the leeboard, pivoting in the case. I adjusted the nut on the pivot until the degree of friction seemed right.
Since the leeboard rope was already installed and run through the pulleys, my next step was to secure the rope to the leading edge of the leeboard. I drilled two holed. One through the flat side of the board, the other from the leading edge of the board to the first hole. I passed the rope through both holes. With the rope drawn up and out of the hole seen below, I heated the end of the rope until the end of the polypropylene melted into a ball. I shoved this ball back into the hole and filled the hole on both sides with epoxy.
This photo gives a sense of proportion between the leeboard and the case. The leeboard is about 5 % of the area of the sail. I looks large, perhaps it is. But I think it will work well because there is a lot of rocker in the hull of the Barquito and no lateral resistance.
The next photo shows the leeboard and case attached to the hull. So far so good.
Assemble the Barquito Gallery of Pictures
1 Basic Boating String Theory 2 Sewing the Hull 3 Keeping the Water Out
4 Center Thwart 5 Bow 6 Foredeck 7 Transom 8 Oarlocks / Oars 9 Skeg
10 Conversion to Sail 11 Leeboard 12 Rudder 13 Mast and Spars 14 Sail and Rig
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