To paraphrase Mark
Twain, I'm writing a long article here because I
don't have time to write a short one. But why am I
even writing this article? Good question.
Aside from a few
"adventurous" designers like Phil Bolger, nobody
seems to like leeboards very much. And I do
understand why. Leeboards, especially if poorly
done, can look like weird appendages or odd little
"wings" tacked onto the side of an otherwise nice
But properly done,
leeboards look great. Even better, they work great
-- especially in our skinny local waters here in
Florida's "Sunshine Coast" (the south central Gulf
[Please see the
photos of two of my leeboards
Now, I won't bore you
here with the reasons why I think leeboards are so
great, because I already did that in my previous
article :) So let's get to the point of this
article: How to build a leeboard that works great
and looks great.
We need to start with
an understanding of what a leeboard actually does.
And yes, I said "a" leeboard, because on a trimaran
you only need one. Trimarans heel so little that the
amount of the leeboard that's in the water varies
only about 7 percent from one tack to the other.
Of course, I should
note that my first "real" trimaran, No Commotion,
did have twin leeboards, and still does. But that
was because the highly curved and flared hull sides
made it challenging to install a single leeboard.
Twin leeboards also add weight -- not just the added
board, but the mechanism that connects them so they
are sturdy and work in tandem
The good news is that
twin leeboards are even more effective than single
ones, and have the added advantage of allowing you
to get the leeboard away from the hull. This cuts
down significantly on noise, turbulence, and
splashing -- three things that are potentially
annoying about leeboards.
But despite what I
just said about the advantages of twin leeboards,
single leeboards are all I now use. Why? Because
having built and sailed four boats with single
leeboards, I know that's all they need to be great
So what does a
leeboard actually do? Why do we need to have one in
the first place? The primary purpose of the leeboard
is to help the boat go upwind, by keeping it from
sliding sideways excessively when the quartering
wind is trying to make it to so by pushing the sail
The leeboard adds a
big chunk of lateral resistance (ideally, right
where it's most needed) while adding only a minimum
amount of resistance to forward movement. More
importantly, you can actually move this lateral
resistance fore and aft a couple of feet, which
allows you to fine-tune your helm balance in a way
that a leeboard's two main rivals -- centerboards
and daggerboards -- can only dream about.
And a single leeboard
mounted directly to the hull is going to weigh a lot
less than any centerboard or daggerboard plus their
attendant waterproof trunks and necessary structural
bracing. And of course, there's no need to "hole
your hull" when you build you boat with a leeboard.
Then there's the
simplicity factor. It's a complex and fussy
procedure to build a trunk for your centerboard or
daggerboard, hope that it's watertight, hope that it
stays that way, hope the leeboard or daggerboard
actually fits the trunk so that it's not too lose or
too tight, and hope the whole mess doesn't get
clogged or jammed with shells, gravel, sand, or any
other seaside junk.
Leeboards, on the
other hand, are entirely outside the boat. The only
hull penetration is a 3/8" hole about 6" above the
waterline. Now, you do need to reinforce the
interior of the hull for about 8" in all direction
around that hole. But all you'll need to do that is
a bit of plywood (details later).
Leeboards involve a
few critical design considerations, so let's talk
about them now. First, your leeboard needs to be
strong enough not to break under even the most sever
lateral strain it will ever experience. Fortunately,
this is easy to accomplish. I have found that the
best material to build your leeboard from is a
"select" grade of pine, available at most all box
As for the foil shape
(cross section), I like an extended "teardrop" shape
-- one where the forward half of the board is a bit
thicker than the aft half. The maximum thickness is
perhaps 1/3 of the way back. The leading edge is
more rounded than the trailing edge, but both are
pretty sharp. Is that the ideal shape" Who knows?
But it works fine for me, so I'm sticking with it.
I use a 1" x 12"
board, and if I want it a bit wider on the bottom
end, I edge-glue on a 1" x 3" board to extend the
trailing edge. The leeboard on my current favorite
boat (the16' okoume-hulled "folder") is 14" wide at
I do the rough
shaping with a hand-held electric plane (which is
BTW the most dangerous tool I know of. 30 years in
the construction biz and my only injury -- ever --
was from one of these buggers). Then I do the next
stage of shaping with a belt sander with 40-grit
paper. Final shaping is dome with sanding blocks and
60 then 100-grit paper.
I also cover all my
leeboards with 4 oz. fiberglass and 3 coats of
epoxy, which not only stiffens and strengthens them,
but also makes them much tougher-skinned while
allowing me to get a very sharp and durable leading
and trailing edge. And because of this covering, I
also don't have to have a super-perfect finish on
How Big Does Your
Leeboard Need To Be?
That can vary quite a
bit, depending on your situation. Here are some of
the important design variables:
- Number and type
of hulls your boat has: It's really important to
understand that multihulls and monohulls have
different leeboard requirements. That's not only
because of the difference in heeling, but also in
inherent lateral resistance.
A word about lateral
resistance: We need to understand that the lateral
resistance of a boat comes from many places other
than just the "board," and this is especially true
in multihulls. Depending on the shape of your main
hull(s) and amas (if any), your leeboard will play a
more or less significant role in helping you go
A perfect example is
my wife, Laura's, boat. The original set of amas I
built for her boat were "tortured plywood" and had a
very sharp V bottom. I didn't understand at the time
just how much these sharp V amas were contributing
to her boat's excellent upwind capabilities. But now
I have a better idea.
Laura's boat has what
I call a 5-piece hull, with vertical sides,
45-degree bilge panels, and a flat bottom with just
2" of overall rocker. A hull like that, while it
will turn on a dime, also is in desperate need of
something to make it go straight. And to have any
hope of going upwind well, it needs a serious dose
of lateral resistance added into the mix.
When I built her boat
about 2 ˝ years ago, I had originally assumed that
the leeboard would provide all that lateral
resistance, even though it was only 11 ˝ " wide. And
it did go upwind beautifully -- until I swapped out
her original deep V amas for some "better" one with
On her very first
trip out with those new amas (which happened to be
at Cedar Key, 2011) she started complaining her boat
wouldn't point upwind like it used to. Since the
only change had been the amas, I reinstalled the old
ones. Problem solved! We found that her boat not
only points better, but goes faster and rides
smoother with the deep V amas. But that's another
The point here is
that your own boat is going to have some built-in
lateral resistance that exists before you ever
factor in what you'll get from a leeboard. So your
leeboard will end up playing somewhere between a
medium role and a major role in determining your
boat's upwind performance.
The good news is that
your leeboard gives you a lot of flexibility in
fine-tuning where your boat's CLR (center of lateral
resistance) is -- much more so than any centerboard
or daggerboard ever could. But even so, you will
need to have it located in approximately the right
place to balance out your sail plan, or your boat
will want to turn upwind or downwind on it own, and
require a heavy rudder to keep it going straight.
square footage (or square meterage?) of your sails:
This is a pretty important factor. If your leeboard
doesn't have enough surface area (square footage),
your boat won't be able to effectively resist
slipping sideways as it tries to go upwind.
For reasons already
noted, a monohull will nee a proportionately bigger
leeboard -- the general guideline being at least 3
percent of the upwind sail area. But my trimarans
seem to do just great with 2 percent. So if you're
planning on 100 sq ft of sail (about 9 sq meters),
then a leeboard that has in the neighborhood of 2 sq
ft below the hull will do the job just fine.
For the sails I use
on my boats (typically a single sail of 85-105 sq
ft), I find that having as little as 1 1/2 sq ft of
leeboard in the water gives excellent upwind
leeboard length: You want
the top end of your leeboard to be just even with
your sheer, and the bottom end to be sticking as far
below the hull as is necessary to give you enough
lateral resistance (on both tacks) to do the job.
below the bottom of the hull:
How far does your leeboard need to stick down below
that hull? That, of course, determines how long it
will be. Conventional wisdom says that "long and
narrow" foils (boards and rudders) are best upwind.
Probably true, but maybe not all that big of a deal.
also says that long and narrow -- i.e. "high aspect"
sails are best upwind. Also probably true. But in
reality, that advantage disappears quickly as your
course moves off the wind. And high aspect sails are
easily outperformed by lower-aspect ones downwind.
So if the leeboard
that meets your needs turns out to be completely
square in its underwater section, no worries! My
best rudder is also virtually square in its
underwater section, and all of my sails are low- to
medium aspect. And you know what? They work great!
- Leeboard pivot
point: This is also important. I'll cover below the
importance of the fore-and-aft location of your
leeboard's location, but it's also important where
your leeboard pivots in the vertical dimension.
Your leeboard with
experience its greatest stress when you are
close-hauled and trying to go upwind in heavy air.
Ideally, your leeboard will be vertical or very
close to it in this situation. As such, you want
support both above and below your pivot point.
But you also want to
be able to get your leeboard entirely out of the
water when going downwind. (Not that it will always be
so, but in light air this can make a difference) So
the pivot point needs to be high enough on your hull
to get the leeboard completely out of the water when
it's in the horizontal position, but low enough to
give it great support when close hauled.
This is something
you'll have to determine for yourself, based on the
boat you have or build, and the leeboard you make
for it. This is why your leeboard should not be
"tacked on as an afterthought," but designed in from
the start as the rest of the boat is created.
A Huge Factor:
Aligning Your Leeboard
Parallel With The
Centerline Of The Boat
I can't overstress
the importance of making sure your leeboard's
fore-and-aft alignment is perfectly parallel to your
boat's keel line. If it's not, you have just added a
new "rudder" amidships, which is going to make its
handling weird, unpredictable, and sub-optimal.
The simplest solution
is to locate your leeboard at exactly the widest
point of your hull, which will guarantee parallel
alignment. This is great if that widest point
happens to be in the right location to balance out
your sail plan. (Yet another article…) But if it's
not, you'll have to shim out the exterior of your
hull just a bit to make sure this alignment end up
being correct. Fortunately, that's easy to do.
You also may want
your leeboard to be as vertical as possible, though
that's not as important as you might think. I have
gotten great results from leeboards that were as
much as 15 degrees off vertical, so don't worry too
much about this. It's the fore-and-aft alignment
that's much more critical.
Major Key To
Success: The All-Important "Friction Washer"
How do you install
your leeboard so that it pivots smoothly, yet stays
where you put it? The secret is in the "friction
washer." Now, I could see early on that just bolting
your leeboard directly to the side of your hull
wasn't going to work very well. I knew there would
be wear and tear and well as friction I couldn't
predict or control very well.
The solution came in
the form of a cheap but very tough translucent
plastic cutting board, available for $2 at my local
flea market, and probably at your local dollar store
or equivalent. Once I know exactly where the
leeboard's going to mount, I cut a "washer" from
this material that's rectangular with rounded edges,
just a bit smaller than the area covered by the
leeboard when it's vertical, and not extending down
as far as the waterline.
Then I drill a 3/8"
hole in it (because I use that size stainless steel
bolts to mount the board). Then I drill two holes
about 3/16" near the upper corners of the washer. I
countersink these holes and run two 3/16" SS bolts
through the hull and plywood interior backing board.
A couple of 3/16" flathead bolts keeps the friction
washer from pivoting along with the leeboard, and
the washer itself provides the perfect amount of
adjustable friction to keep the leeboard right where
you want it.
To help distribute
the bolt pressure over a wider area (so everything
works better and longer without adjustment), make
some 1/2" or 3/4" thick plywood "washers" either 2 ˝"
or 3" dia., or however big your biggest hole saw is.
Then get some stainless steel fender washers, as big
and as thick as you can find them.
All together, the
wood and metal washers will make for a much superior
finished product vs. not using them. They will also
allow you to use a longer pivot bolt, which is
inherently good because it makes for a more
torque-resistant setup. Use a locknut with a captive
nylon piece in it, and then add another locknut to
keep the whole thing from loosening up.
Once you have
everything drilled and installed exactly where you
want it, take it all apart. Then drill out the hole
in your plastic friction washer to at least 2 ˝".
Why" because now, instead of having all your pivot
bolt tension near the dead center of the hole, the
friction point moves out to the edge of the bigger
hole you just drilled.
How does that help?
The larger friction surface now permits you to have
a lot of friction with less locknut tension, and
also stays tight much longer without adjustment
because the pressure is no longer concentrated in
such a small area (which compresses / wears more
OK, I know I haven't
answered all of the questions you might have. So
please do feel free to contact me
with any additional questions you may have, and I'll
post my responses here in the article as an ongoing