Gemini 105Mc Owner’s Manual
42Copyright © 2004 Performance Cruising Inc.
Sea Anchors
A sea anchor is without doubt a good addition to a
cruising boat's inventory. When weather conditions
have deteriorated to the point where you just want
to stop, then a sea anchor will keep the boat where
it is. For survival there are certain types of boats
that must have them but for others, the need is
marginal. The boats that race around the world do
not use them. Sailing through a storm is still the
best defense. There are enormous forces in the
anchor line if a sea anchor is deployed in a storm.
Racing trimarans will use a sea anchor to keep the
bow of the windward hull down. The cruising trima-
ran will use the sea anchor off the bow or stern like
a monohull.
The monohull will use the sea anchor to turn the
boat so that the keel faces the on-coming waves, so
that the boat will not trip over the keel.
One of the biggest problems concerning the use of
a sea anchor is the effect on the boat’s rudders.
The enormous force of a breaking wave over the
bow will force the boat down onto the rudder. If
the rudder turns sideways it is likely to get dam-
aged or ripped off. Anchoring by the stern will pro-
tect the rudder. Unfortunately the stern is not de-
signed to take breaking waves and the hatches are
now exposed.
The sea anchor is normally set so that the anchor is
one wavelength away so that the anchor and boat
are in the same water particle movements.
Gemini, in survival conditions, is best just left
without a sea anchor. Pull the sails down, pull the
centerboards up, and turn the wheel so that the
boat will be turning into the waves. If you prefer, a
sea anchor is acceptable if you just want to stop
and do not want to be blown to leeward.
The effects of lightning on a boat can vary wildly. If
a boat is going to be completely grounded, every-
thing on the deck must be connected together and
connected to a 12" square steel plate, with 3/4"
bolts. All the equipment used must be capable of
handling 100 million volts, 100,000 amps of current,
and temperatures up to 10,000º centigrade.
Lightning does not travel in straight lines. If it
strikes the boat at the shroud, it will jump to the
next metal object before it will follow the shortest
path through wires to the ground plate. If there is
no grounding on the next metal part, the lightning
will go through the hull to the water. Grounded
Use of Sea Anchors
boats are struck more often than ungrounded boats.
The main purpose for grounding is to protect people.
The height of the mast gives a cone of protection
with the base the same diameter as the height of the
mast.
In over 800 Geminis, only a very few have been hit
by lightning. People inside one boat reported a loud
bang, all fuses being blown, everything magnetic
demagnetized, some electronics lost, and for the
next year reported strange problems – however there
was no evidence of the actual lightning strike. An-
other Gemini showed obvious signs of a strike coming
down the backstay and jumping to the rudders. An-
other had electronic problems and magnetic prob-
lems. None showed severe signs of a lightning strike.
In an ungrounded boat, if a Gemini is in the vicinity
of a lightning strike, there will still be a magnetic
pulse induced in metal conductors that will destroy
electronics and demagnetize magnets.
Lightning is normally cloud-to-cloud but occasion-
ally there is a discharge to the ground. When light-
ning starts from a cloud, instantaneously there are
feeders sent up from all high points on the ground.
The lightning will connect with one of the feeders
and that will be where the lightning strikes. These
feeders need to be a better conductor of electricity
than air. A lightning rod is normally metal, well
grounded to earth with metal strap.
The worst thing to do is to have a badly grounded
boat that will start the feeder lines, but will not be
capable of handling the huge return current. Hanging
starter cables off the backstay into the water is one
example of bad grounding.
If you suspect a storm is coming, turn the radio to an
AM station to listen for static associated with light-
ning strikes. Listen to the weather reports for the
latest forecast. Watch for distant lighting. Listen
for distant thunder. You may hear the thunder be-
fore you can see the lightning on a bright day. Sel-
dom will you hear thunder more than five miles from
its source. That thunder was caused by lightning 25
seconds earlier. The sound of thunder travels at one
mile per five seconds. The best advice when faced
with a lightning storm is to get to shore as soon as is
possible.
Care and Cleaning of Fiberglass
For general cleaning, we have found a cup of Tide
clothes detergent and hot water an effective
cleaner. On average, it takes two buckets of hot
water to clean the boat, each with a cup of Tide.
Spray Clorox is also a good cleaner. Acetone may be
necessary to remove resins, glue, or sealers used to
manufacture the boat. Keep acetone away from vi-
nyl, paint, and the windows. Older gelcoat may de-
Lightning
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