Navigation under sail
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BEWARE
A catamaran presents 6 times greater heel resistance than a single-
hull vessel. In terms of ship design we speak of righting moment
(multiplication of the vessel's weight by the transverse distance
between the centre of gravity and the centre of flotation (or
buoyancy).
See illustration on previous page.
This fact has real consequences for the handling and sail-trimming of
a catamaran.
The fact that the boat will not heel over could conceal an excessive
sail surface area in use, which could be dangerous for the crew and
the vessel. It is therefore essential to constantly monitor the real wind
speed and to trim the sail surface area as a priority in accordance
with this speed.
These latter adjustments are valid in calm seas. In rough seas one
should take the precaution of reducing 10% earlier in terms of real
wind speed. Generally speaking, it is essential to constantly look to
relieve the vessel rather than to put it under stress.
One should always look for the sail angle of attack to be headed to the
apparent wind and the sails to be not over-trimmed so that the
airflows leaving the sail are parallel to each other, that is to say they
do not create turbulence behind the sail.
Failure to follow the above recommendations can be dangerous for
the boat and the crew, and the manufacturer cannot be held
responsible in the event of an accident.
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CLOSE HAULED TRIMMING (between 75 and 50° to true wind)
GGiivveenn wwiinndd ffoorrccee iinn aappppaarreenntt wwiinndd
- FFrroomm 00 ttoo 1166 kknnoottss
: full sail; mainsail traveler 30 cm to windward of
center, mainsail trimmed with a slightly opened leech (boom
centered).
The Genoa jib is trimmed near the spreader, the Genoa traveler is
placed so that the angle of the Genoa sheet forms a straight line with
the clew and the luff, at 40% of its height.
- FFrroomm 1166 ttoo 2200 kknnoottss
: full sail; the mainsail traveler moves up to 60
cm to windward of center, mainsail trimmed with a slightly more open
leech (boom still in line: so the sheet will have to be slackened).
The Genoa traveler does not change position but adjust the sheet so
that the leech is 10 cm from the spreader.
- FFrroomm 2200 ttoo 2266 kknnoottss
: 1 reef, full Genoa; the mainsail traveler comes
back to 30 cm to windward of center.
The Genoa traveler does not change position but the sheet is
slackened slightly so that the leech is 20 cm from the spreader.
- FFrroomm 2266 ttoo 3300 kknnoottss
: 1 reef, 75% of the Genoa; the mainsail traveler
moves up to 60 cm to windward of center.
The Genoa traveler remains in place or moves slightly forward but it
is adjusted so that the leech forms a propeller, the upper part
dumping air out under strong gusts of wind.
- FFrroomm 3300 ttoo 3366 kknnoottss
: 2 reefs, 60% of the Genoa; the mainsail
traveler returns to the 30 cm to windward of center, the boom is
slackened to fly 50 cm leeward.
The Genoa traveler is moved slightly forward, the adjustment remains
the same.
NAVIGATION
11
NAVIGATION
1
LAGOON 44O
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