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Vessel Draft
What Is Vessel Draft?
Different
Drafts and Their Importance
By Paul Bruno
In the simplest terms, the
draft of a ship or boat is the distance between the surface of the water and
the lowest point of the vessel.
The measurement should be made
as close to vertical as possible.
Types of Boats
The lowest point on a boat is
found at different places in different designs and hull shapes.
Sailing vessels have some of
the deepest keels and large boats may need water as deep as some small ships.
For example, tugboats have
much of their mass below the waterline. This helps them push and tow ships
without making the ride uncomfortable for the crew.
Shallow draft vessels are
built for getting to favorite beaches and fishing areas.
Many militaries have developed
hovercraft or shallow draft ships to protect coastlines and deliver troops and
supplies directly to shore.
Taking on heavy loads of
passengers, equipment, or fuel can change your draft significantly.
Observing the normal waterline
can give you some idea of your change in draft. If you want to know how
much load you can carry safely, look for a certification placard for
passengers.
If you want to carry supplies
or equipment then you can use the concept of displacement to make a close
estimate of a loaded draft.
Why Is the Knowing the Draft Important?
When the majority of people
are wondering about the draft of their boat it’s usually because they want to know
if an area is too shallow.
Avoiding contact between
underwater objects is important so every person driving the boat needs to be
aware of the draft of the vessel.
How To Figure Out the Depth of Water
Depth markings usually don’t
appear on navigation buoys, but sometimes special areas like anchorages are
marked so scope ratio can be estimated before
anchoring.
Depth markings are more common
along wharves and seawalls especially if there is a fuel dock or crane
facility. A variety of vessels visit these kinds of facilities so knowing the
depth is important.
In general, it is a good idea
to carry and understand a chart or survey map even on an inland body of water.
Don’t ever assume that a
shallow area or sub-surface obstruction will be marked as a hazard.
In tidal areas and on rivers
knowing the depth is more difficult since the tides can be tens of feet in some
places.
Observing the high and low
water marks on nearby structures is the best way to know depths unless you have
a chart.
Depth sounders are good
secondary devices but they are limited since they need to be set up near the
bow to allow any warning.
Often these small sonar
devices are mounted just in front of the rudder or at the stern. The idea is to
protect the rudder which usually is lower than the keel.
A forward mounted depth
sounder can be added to allow some warning when the boat is moving into shallow
water.
Maritime Traffic Rules
It’s important to understand
the limitations of the different vessels operating in your traffic area since
all ships and large boats take a long time to stop.
Understanding maritime traffic lanes and observing traffic
is one of the first things any good pilot must learn.
Paul
Bruno
Maritime
Expert
Education
USCG
Master's License
B.A.,
Creative Nonfiction and Technical Writing, University of Wisconsin
Introduction
United
States Coast Guard licensed Ship Master with Passenger Certification.
A
marine contractor familiar with all ship systems who has worked in the industry
for more than 20 years.
Has
a USCG Master's License and a degree in Creative Nonfiction and Technical
Writing, from the University of Wisconsin.
Experience
Paul
Bruno is a former writer for ThoughtCo who contributed work for over five years
on the maritime industry. He has worked with a variety of vessels throughout
his maritime career, including various commercial ships as well as the Great
Lakes schooner reproduction "Dennis Sullivan." As a marine
contractor, Paul is familiar with all ship systems, and his lifelong passion
for electronics has led to a focus on marine hardware and software development.
When he is not working, Paul's favorite hobby is knot work, keeping busy with
the nearly 4,000 documented knots, splices, and eyes.
Education
USCG
Master's License, 1993
Creative
Nonfiction and Technical Writing, University of Wisconsin, Milwaukee and University
of Waikato, Hamilton NZ
A
Message from Paul Bruno
ThoughtCo
and Dotdash
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