a folding dinghy sailboat
barquito:
Spanish for little boat
The story and photos of my
folding boat ©
2007, 2008 by Man of the Cloth
Productions.
- Leeboard -
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 East
during 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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