A
bit of mystery, mast “rake” is
the angle a mast slopes aft from
vertical, as viewed from the side.
(If a mast is raked forward—rare but used
occasionally to correct or increase lead—
it has “forward rake”.) For reasons that
aren’t well understood most boats seem
to sail best with a bit of rake. They also
look better (to modern eyes anyway).
The majority of modern boats have mast
rake between ¾’s of a degree aft to 1-½
degree aft, with 2 to 2-½ degrees being
the conventional upper limit. Rake is
determined and set during in the design
and can help in getting the right lead for
proper helm balance. Adjusting mast rake
after launching can be used to correct lead
and thus helm balance, if helm balance
should be a problem for some reason.
Many traditional boats have considerable
rake (over 3 degrees) because it looks right.
In fact, old-time fast coasting schooners
and yachts often had a lot of rake which
was associated with speed. This is where
the term “rakish” comes from—fast
and stylish.
The drawing is of a 52-foot, aluminum
center-cockpit ketch (“Magic Moment”)
designed by my office (built by Kanter).
This boat has 6-½ degree rake on the
mainmast and 7-½ degrees rake on
the mizzen, which is extreme and is
about as much rake as practical for any
ordinary boat.
On multi-masted rigs the rake should
always be slightly greater on each mast as
you go aft. For example, on a ketch, if the
rake were, say, 2 degrees on the mainmast,
it should be 2-½ to 3 degrees on the
mizzen. If they masts have the same rake,
they appear to converge together at the
top, which looks wrong.
A dead vertical mast will work acceptably
as will a mast raked forward a bit, but this
usually looks askew. (Some traditional
boats around the world had masts with
tremendous forward rake. For instance,
the foremast on some Chinese junks is
raked forward as much as 15 degrees.)
In theory, slight rake combined with a
moderate roach on the mainsail, more
closely approximates the theoretically
optimum elliptical planform for a wing
(a lift generating surface). I’m not sure
this is really a noticeable effect in the real
world, however.
Rake also affects the swing of the boom. A
raked mast lifts the boom end as the boom
is eased out. This is good for offshore
work; it keeps the boom from dipping
in the water when the boat rolls deeply.
On the other hand, because the boom
has to lift as it swings out, the weight of
the boom (on a well-raked mast) tends to
keep the boom inboard and thus makes it
a bit harder to fill the sail in light air.
Rake has an important effect on staying.
A 2-degree rake means that swept-back
lowers and uppers and intermediates to
an aftish located chainplate, will have a
strong backstay effect. Combined with
double lowers and an inner forestay,
such a configuration means less need for
runners. At a 3-degree rake, or more,
such a boat could usually dispense with
runners, or employ runners only in very
heavy weather.
The forward component of mast-
compression load from rake is minor.
Even at an extreme 6-degree rake, the
resultant forward load is just 10% of the
mast compression. (The sine of the rake
angle gives the forward component of
force at the partners or mast step). On a
standard modern rig with around 1- to
2-degree rake, the forward component is
just 3.5% of mast compression.
Traditional coasting schooners and cargo
ketches, sometimes employed a trick to
avoid backstays at each mast. They would
By Dave Gerr, Director, Westlawn Institute of Marine Technology
What Mast Rake is All About
Rakish Rigs
20
American Boat & Yacht Council •
the
Reference Point
• Winter 2014
