Section 1: Getting Started 9
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Figure 1-17. Sailboat pivot
point
Factors Influencing
Seaworthiness
Three important factors affect the seaworthiness
and safety of a boat: size, design, and
construction materials.
The length and beam of a boat affect
seaworthiness. Generally speaking, the longer
and wider the boat the safer it will be.
More freeboard increases safety.
However, higher sides on a boat expose a
larger surface to the wind, which can affect
maneuverability.
The shape and size of a hull affect
buoyancy, which can influence seaworthiness.
For maximum stability, the greatest
weight of the boat should be concentrated
low in the hull.
Today most recreational boats are
built of fiberglass. This mixture of plastic
resin and glass fibers makes strong and
relatively lightweight boats that are reasonable
in cost and require little maintenance.
The availability of fiberglass boats
is one reason for the popularity of boating
today.
Other materials used in boat construction
include wood, aluminum, steel,
neoprene-coated fabrics, and other forms
of plastic. The stronger the materials used
to construct a boat, the safer and more seaworthy
it will be.
How a Boat Steers
Most of us are familiar with how an automobile
steers. It has four wheels that make
reasonably firm contact with the ground.
The front two wheels are turned to one
side to steer the car. When this happens the
front moves into the turn and the rest of
the car follows.
Not so in a powerboat. The boat
floats in the water and does not make firm
contact, and the boat steers from the rear
(Figure 1-16). When the boat begins a turn
while moving forward, the stern swings out
in the opposite direction of the turn to the
direction of the boat and the boat begins to
move in the new direction. Thus in a turn
to port, the stern will swing to starboard,
Since the boat does not have firm footing, it
will tend to slide sideways a bit. The hull is
designed to track and help resist this sideslip.
If you look down on a powerboat
when it turns, you will discover that it turns
about a point called the pivot point. This
point is located along the keel on the centerline
of the boat, but it may move fore
or aft depending upon whether the boat
is going forward or in reverse. For most
powerboats, this pivot point lies about onethird
of the way from the bow to the stern
when going forward, and about two-thirds
of the way (nearer the stern) when going in
reverse.
The pivot point on sailboats and
trawlers with extensive keels may tend to
stay close to one location, determined by
the centerline of the keel. For example, the
point on a sailboat with a fin keel is likely to
be the keel mid-point (Figure 1-17).
Sailboat
Forward Reverse
Figure 1-16. Powerboats steer
from the back.
pivot point
Sailboat