Gemini 105Mc Owner’s Manual
28
Copyright © 2004 Performance Cruising Inc.
Performance and Use of the Centerboards
The centerboards are only needed when sailing to
windward with apparent winds closer than 70º. From
experience we have found that only the leeward
board is necessary. In fact the boat is ½ knot faster
with only the leeward board down. The rationale is
that the leeward hull is the hull doing all the work,
whereas the windward hull is parasitic drag. Having
the keel down on the windward hull will simply in-
crease the drag of that hull. Having discovered this
it was necessary to increase the size of the center-
boards so that only one had sufficient area to pre-
vent leeway.
For leisurely sailing use both boards 1¼ turns down.
However, if the boards are down, and they do not
need to be, then the lack of side pressure may cause
the boards to rattle in the slot. Simply raising them
eliminates any rattling. The boat will sail at any
angle with no boards. However tacking is more diffi-
cult and the boat will slip sideways when sailing
close to windward.
In light air, it is more difficult to sail without the
centerboards in the “Down” position. In heavy airs
the leeward hull makes a good keel as it is pushed
down into the water. In fact, in rough conditions it is
advisable to slightly raise the centerboard to take
some stress off it when punching to windward.
The technique to changing the boards for maximum
efficiency when beating is to lower the windward
centerboard before the tack when the hull is slightly
raised, and the leeward centerboard takes the side
pressure. After the tack when the sails are set then
raise the new windward centerboard.
Motoring and Docking with Centerboards
When motoring, the centerboards are not needed
and, in fact will cause drag. However, in preparation
for docking or maneuvering in tight harbors, the boat
is much more maneuverable at slower speeds with
the centerboards in the “down” position. When
docking, especially with strong crosswinds, it is ad-
visable to place both boards in the “Down” position
to stop the boat being blown.
Strong Winds and the Use of Centerboards
When reaching with winds above 25 knots the use of
the leeward centerboard ¾ turn down will steer the
boat straight, reducing the load on the rudders. With
strong winds there are big seas and it is these seas
that can cause a problem as the boat tries to broach
when the leeward bow digs in. Of course with the
boards up on a broad reach the boat will travel per-
haps 14 knots, which is also putting stress on the
rudders. Lowering the leeward centerboards part
way reduces the top speed perhaps to 12 knots but
Centerboards and Rudders
the reduction of stress on the helmsman is worth it
as the boat is much more responsive.
Offshore Use of the Centerboards
Offshore with larger waves the centerboards can be
used less. In fact, offshore it is possible to sail up to
50º without the use of the centerboards.
In survival conditions raising the centerboards will
allow the boat to slip sideways away from breaking
waves.
Rudders
Like the centerboards, the Gemini’s rudder system
has uniquely beneficial engineering. The rudders on
Gemini are a spade rudder glassed to a 1 ½" solid
rudderstock, with a permanently fixed 8" tiller that
faces aft. There are two split rudder-bearing molds
that are riveted around the rudderstock. These bear-
ings are filled and faired, then painted.
There is a ¾" hole in the
back top of the rudder
bearing and the rudder
recess also at the top
back. After the rudder
and bearing assembly is
inserted into the rudder
case recess, a ¾" stainless
tube is inserted in the ¾”
hole. This ¾" tube is part
of the Uflex steering sys-
tem.
The Uflex steering system has a double head with
two individual cables. The port steering cable is 19’
while the starboard steering cable is 14’.
The outer ends of the inner cable have a stainless
rod that passes through the 7/8" tube at the rudders.
The outer cable is secured to the 7/8” tube. The
7/8” tube is threaded with 1 5/16” nuts to lock it
either side of the rudder case. The stainless rods are
connected to the tiller by means of a link arm. In
this way, as the wheel is turned one rod pushes one
tiller while the other rod pulls the other tiller. This
is a totally balanced system, better than a single
cable going to one rudder that is not good in com-
pression but good in tension.
Rudder Usage
The rudders should always be all the way down even
in light airs. Part way up, the slot is opened and that
will cause drag. The sheet stoppers that hold the
rudders down only need the minimum of force just
to hold them down. Too much force will cause the
rudders to stick and not kick up quick enough if the
rudder touches bottom.
