| hull speed |
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Some Basic Naval Architecture and Marine Engineering
The concept of hull speed, put another way, is "how fast can a tugboat go?" It’s
no secret that tugboats aren’t designed for speed. They have deep, full-
displacement hulls. They are wide. Their diesel engines and gearboxes are
designed for torque and power, not speed. There is an engineering concept
governing hull speed that every naval architect is familiar with.
Hull speed equals roughly 1.34 times the square root of the waterline length.
For a vessel with a waterline length of 144 feet, the square root is 12. We
multiply 12 times 1.34, which gives us 16.08, or rounded off two decimal places,
16 knots. Now remember that this is a general engineering relationship. There
are vessels that defy it, such as destroyers and other very slender warships.
However, a tug without a tow making speed carves out a deep trough of a wave
at hull speed. This is visible in the footage of the tug Dorothy Elizabeth in the
New York Harbor Tugboat race.
The concept of hull speed, put another way, is "how fast can a tugboat go?" It’s
no secret that tugboats aren’t designed for speed. They have deep, full-
displacement hulls. They are wide. Their diesel engines and gearboxes are
designed for torque and power, not speed. There is an engineering concept
governing hull speed that every naval architect is familiar with.
Hull speed equals roughly 1.34 times the square root of the waterline length.
For a vessel with a waterline length of 144 feet, the square root is 12. We
multiply 12 times 1.34, which gives us 16.08, or rounded off two decimal places,
16 knots. Now remember that this is a general engineering relationship. There
are vessels that defy it, such as destroyers and other very slender warships.
However, a tug without a tow making speed carves out a deep trough of a wave
at hull speed. This is visible in the footage of the tug Dorothy Elizabeth in the
New York Harbor Tugboat race.
A hullform vastly different than the
hard-working harbor tug is the U.S. Navy
Frigate U.S.S. Rentz, shown at left. The
ship exhibits a much finer form which is
evidenced by her clean wake, with a
very shallow trough, in contrast to the
deep wave carved out by the Dorothy
Elizabeth above.
Much of the engineering and design work
that goes into specifying engineering
parameters for a hull form often begins
far from the ocean, in a tank testing basin
like the one below, pictured in a
photograph from the early 1900s. This
brings us to the realization that these
engineering concepts were understood
for a long time.
hard-working harbor tug is the U.S. Navy
Frigate U.S.S. Rentz, shown at left. The
ship exhibits a much finer form which is
evidenced by her clean wake, with a
very shallow trough, in contrast to the
deep wave carved out by the Dorothy
Elizabeth above.
Much of the engineering and design work
that goes into specifying engineering
parameters for a hull form often begins
far from the ocean, in a tank testing basin
like the one below, pictured in a
photograph from the early 1900s. This
brings us to the realization that these
engineering concepts were understood
for a long time.