Gemini 105Mc Owner’s Manual
32Copyright © 2004 Performance Cruising Inc.
Design Considerations
In comparison to any other cruising sailboat with
the same accommodation, the Gemini is faster,
lighter, has less sail area, draws less water, and
sails more upright. Performance Cruising has built
more than 800 Gemini’s and is constantly refining
the product and manufacturing techniques. As
such, Performance Cruising builds a 34' catamaran
more cost effectively than any other sailboat fac-
tory can build a sailboat of similar accommodation.
The conventional monohull has a fixed keel, fixed
rudders, and fixed inboard diesel. This simplicity
makes the boat easier to build and less expensive.
The cheap cast iron keel is the low cost solution to
turning an unstable single hull into a sailboat with a
mast and sails that are trying to tip it over. The
draw back to this keel is deep draft and weight. A
heavy boat needs more sail and a larger engine.
Most people think the keel is a weight hanging un-
der the boat trying to pull it upright. Unfortunately,
with the keel weighing, say 5,000 lbs., and the
loaded hull weighing 11,000 lb., the point at which
all this weight can be assumed to act to bring the
boat upright (the center of gravity), is near the
water line and not several feet under the boat. This
makes for a boat that will tip easily and is very un-
comfortable.
The modern fast monohull has a very deep keel
with a bulb, a high-tech light hull, and wide beam.
Interior Molds
The Gemini 105Mc advanced construction includes a
single interior mold encompassing the area from
stem to stern and port to starboard. This interior
mold is unique to the entire multihull industry and
provides a multitude of benefits including enormous
weight savings as well as incredible strength. The
interior mold is built with a wiring harness which
includes 110 volt wires, hoses, and conduit for elec-
tronics glassed in before it is structurally glassed in
to the hull. There are also several small accent
molds.
The roof mold is rather light and has 12 volt wire
glassed into position before it is glassed to the
deck. This mold has cutouts to facilitate bolting on
genoa tracks, winches and cabin lights. This mold
also has a glassed in flange to take the main bulk-
head.
The refrigerator mold is 7' wide and high and cov-
ers the main cockpit bulkhead. This mold has a box
to enclose the refrigerator and another box for stor-
age or an air conditioner. This mold is glassed into
position and ensures that the refrigerator vents to
the outside. This mold also has the grooves for the
Construction
Sails and Sailing
window slider.
The aft cabin walls are large molds that stand verti-
cal to separate the aft cabin. They are bolted into
place after the hull and deck have been bonded
.
Buoyancy Tanks
The Gemini has (4) four buoyancy tanks situated in
each corner of the boat. These buoyancy tanks are
not designed to float the whole boat but to stop a
holed hull from going down too far and allowing
water to flood across to the other hull and capsize
the boat.
These buoyancy tanks are air filled tanks, but are
not guaranteed as fully airtight. They should be in-
spected periodically to make sure they are dry.
Each tank has an opening inspection port. In the
head, the port is located directly behind the toilet
plumbing. In the aft cabins, the port is located on
the aft cabin stern wall. In the master cabin, the
port is located under the carpeting in the large for-
ward storage locker.
For offshore use, it is advisable to fill the tanks
with either airtight plastic bottles or Styrofoam
chips contained in netting (to make removal easier).
The inside of the tank should be accessible to test
for leaks. As such, it is not advisable to fill the
tanks with permanent foam or any material that
cannot be easily removed.
Leaks
If a leak is detected, first taste the water to see if it
is salty. If it is fresh, the leak is either water from
the water tanks or a topside leak from rain. If it is
salty then it is a hull leak.
The best way to find a hull leak is to completely dry
the bilge and look for telltale trickles of water. It
may be necessary to dry the bilge repeatedly be-
cause the first telltale trickle could be from water
trapped behind a bulkhead. The leaks are almost
certainly from a through-hull fitting, so be sure to
check
x Speedo
x Depth sounder
x Toilet through hulls
x Centerboard pivot
x Engine water inlet
x Air Conditioning inlet
A boat in rough seas could have a leak from up high
such, as the gunwale joint, sail locker, anchor
locker, or deck fittings.
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