New York Safe Boating - 2020 - 7

Planing Hull

down) in choppy water. It also tends to "slide" when turning,
which makes it difficult to maneuver at high speed. Common
examples of this hull type may be found in small fishing
boats ( jon boats), rowboats, and houseboats.

At rest and slow speeds, the planing hull operates just as
a displacement hull does-it displaces a weight of water
equal to the weight of the boat and its load. But as power
increases, the shape of the planing hull provides lift that
enables the boat to ride upon the bow wave. This is called
being "on plane."

Round bottom hulls move easily through the water at slow
speeds, but they may roll or capsize in high seas. Sailboats
and trawlers often have round hulls.
The deep-V hull has a steep angle (>20 degrees) at the
bow that carries all the way to the stern of the boat. This
hull shape performs very well at high speed and in rough
water because its bow slices through the waves rather than
crashing into them. The deep-V requires more power than
the other shapes to get on plane but is faster and more
stable once there. The main disadvantages of this hull
shape are that it requires a deeper draft and it tends to roll
more at rest. The deep-V is best for ocean racing, sport
fishing, and any other application where high speed may be
required in rough water.

When the boat is on plane it escapes the wave system that
limits the speed of boats with displacement hulls. Less of the
hull is actually in contact with the water, so there is less water
resistance.
The amount of power available determines the top speed
of a planing hull, not the waterline length. While it takes a
considerable amount of power to get the boat on plane,
less power is needed to maintain plane or even to rapidly
increase speed once on plane. There are several shapes
used in planing hulls, including flat bottom, deep-V, and
semi-V hulls.

The semi-V hull has a wider angle at the bow than the
deep-V hull, and the hull flattens toward the stern. In
The flat-bottomed boat has a shallow draft and is relatively
comparison to the flat-bottom, the V shape of the bow
stable. It requires the least amount of power to get on plane
cuts the waves and provides a better ride in choppy water
because its flat surface provides excellent lift. This hull
and reduces the tendency for the hull to "slide" in a turn.
shape gives a rough ride and tends to pound (slap up and
Compared to the deep-V
hull, the flat stern section
of the semi-V hull provides
Types of Hulls
Advantages
Disadvantages
Comments
excellent lift allowing the
hull to get on plane quickly
using less power. It also
Flat Bottom Hull
The flat bottom offers
Flat bottoms tend to
Examples of flat
tends to roll less at rest. The
the best planing hull and
pound excessively at
bottom hulls are
has a shallow draft.
planing speeds or in
skiffs or jon boats.
key disadvantages become
choppy water.
evident as the seas increase.
At higher speeds, this hull
shape pounds almost as
Round Bottom
A round bottom hull
Round bottom hulls
Trawlers and many
badly as the flat-bottomed
Hull
offers the best
have a tendency to roll
sailboats have
hull. The flat stern also
displacement hull.
without a deep keel
round bottoms.
increases the possibility of
It will move easily through
or stabilizers. They are
broaching from a large wave
the water at slow speeds.
more prone to capsizing
astern.
than other hull types.
Vee Hulls

Deep Vee Hulls

Multi-Hulls

Vee bottom boats are
planing hulls. They offer a
smoother ride in choppy
water.

Vee hulls require more
power to move through
the water at the same
speeds than flat bottom
boats.

Some small utility
boats and some
runabouts have
vee hulls.

Deep vee bottom boats
have a sharper entry into
water and are smoother
riding than a vee hull.

The deep vee requires
more power than a vee
hull at the same speed

Most runabouts
have this hull
shape.

A catamaran, or multi-hull,
has two or more hulls
connected. It is a very
stable type of boat
because of the wide beam.

Narrow dock slips are
a problem.
Less popular than
conventional hulls.

Examples include
pontoon boats
and Hobie Cats.

7

Multi-hulls are seen on
catamarans and trimarans.
These are very stable boats
because their beams are
wide, giving a smooth,
stable ride. Twin hull design
produces less drag so it
requires less horsepower
and has better fuel efficiency.
The dual engines make the
boat much easier to handle.
New York Safe Boating - 2020

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