the waves (Figure 1-11). Their bottoms tend
to ride parallel with the surface of the water,
so they resist tipping from shifting loads on
flat seas. However on rolling seas, the bottom
will track the surface of the undulating
seas and tip with the waves. In larger breaking
waves, they can even overturn. They do
not track or hold a course well. These boats
are usually inexpensive to build.
Boats with V-bottoms and deep V
bottoms are variations of planing hulls that
offer good stability and less pounding in
rough water (Figures 1-12 and 1-13). The
sloping bottom surfaces help the boat cut
through the waves and track very well. The
lengthwise breaks in the hulls shape are
called chines, and the angle of each side
from the horizontal at the transom is called
deadrise. A flat bottom boat has a deadrise
of 0°, a V-bottom boat might be as high as
25°. Chines can be easily spotted since they
form a sharp bend in the hull rather than
the gradual turn of the round bottom.
There are boat bottoms that are combinations
of two types: one type forward,
gradually changing to another type toward
the stern in an attempt to balance advantages
and drawbacks to provide hull performance
that buyers will like. A good example
is the modified V-hull. This hull has a sharp
entry forward with a deep vee shape that
gradually flattens toward the stern. The forward
part cuts through the waves while the
stern provides lift for planing.
The catamaran uses two hulls, each
usually having a deep-V shape (Figure
1-14). The hulls are connected by a deck
structure. They offer expansive deck space
and great initial resistance to capsizing or
tipping. If tipped too far, they can become
unstable and capsize quickly. Usually, this
point of capsize occurs at a very large angle
of heel (tipping).
The cathedral hull uses three hulls (Figure
1-15). This design is basically one hull
incorporating a large central section and keel
and a smaller keel on each side. These boats
resist tipping and are popular for fishing and
recreation. With their expansive hull surfaces,
they can lead to pounding in choppy seas and
are most popular in sheltered waters.
A variation on the cathedral hull is the
trimaran. The central hull is larger and two
small outrigger hulls lend stability. They,
too, have large decks and the larger central
hull provides more below decks space than
a catamaran.
8 Chapter One
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79
80
81
82
Figure 1-10. Round bottom
boat
Figure 1-11. Flat bottom boat
Figure 1-12. V-bottom boat
Figure 1-13. Deep V boat
Figure 1-14 Catamaran twin
hulled boat
Figure 1-15 Cathedral hull
boat with three mini-hulls
chine
deadrise angle