Have you wondered how Naval Architects
calculate areas of uneven objects like the hulls of ships? How
how much power is needed to drive a ship? Or how much the ship
will tilt whenever cargo, fuel oil, or water are added or
removed from the ship. Also how much depth the ship will sink
down with each cargo loading.
Before a ship is even built, the
designers must know how it will behave.
For rectangular blocks, it is very
simple to calculate the volume. However ship hulls are pointed
at the bow, parallel at the middle portion, and slightly
pointed again at the stern.
For uneven or curved objects like ship
hulls, naval architects make use of measurement of different
lengths from fixed axis, do a summation of all the values to
get a very good estimation of the total areas, or volumes.
Simpson's 1st and 2nd rules are good examples of these types
Block coefficient, prismatic
coefficient, midship section area coefficient, waterplane area
coefficient are some of the well known multiplying factors
that compares the shape of a ship hull to the rectangular
Calculation of water pressure acting a
submerged body, center of gravity, center of buoyancy are
covered as hydrostatics.
Stability and Trim
This is a study of how shifting weights
will affect the center of gravity, center of buoyancy, the
righting lever that will tend to bring the ship to equilibrium
and how they will affect the transverse stability of the ship.
Also to determine at what angle of heel the
ship will turn over beyond recovery.
In the study of trim, naval architects,
marine engineers, or deck officers determine how the ship will
behave as dry cargo is loaded in the cargo holds or liquid
cargo in the cargo tanks, or when fuel oil or water is
consumed during long voyages. Also when the ship is damaged
and flooded, or ballast water is transferred into or out of
The naval architect must be able to determine how big the
rudder needs to be in order to turn a ship, and how big the
turning angle of the ship is and how large the forces on the rudder stock
From the study, a suitable rudder stock shaft could be
chosen to withstand the shearing forces on the shaft, and the
driving steering gear needed to hold the forces of the water
flowing past the rudder.
Power, Resistance, Speed, Fuel Consumption
How much power is needed to drive the ship?
The naval architect must choose the prime mover engine based
on calculations and referring to results of experiments
on scale models in controlled conditions.
The relationships between speeds, length
of ship, wetted surface areas, and displacements have already
been discovered and are very useful for the calculations.
In this study, frictional resistances
and residual resistances have to be determined.
Questions and Answers in
Now, we have compiled a reference e-book for people
interested in knowing how to apply the calculations to various
situations in Naval Architecture.
The e-book can be
I hope this information will serve you well if you ever
need to determine the behavior of ships.
Marine Engineer World
P.S. The professional seafarer, whether Navigation Officer
or Engineer, would find the e-book
Answers in Naval Architecture very useful.