general overview of the forces involved

during maneuvering and sailing of ships

increased velocity gives decreased

pressure water is a liquid it flows and

it is nearly incompressible when water

has to pass through a smaller space its

velocity will increase the increased

velocity will decrease the pressure an

example of this is squat when the water

has to pass between the hull and the

seabed its velocity will increase this

increase will result in a decrease

pressure which will make the vessel sink

deeper in the water accepting that ship

handling can be defined as using forces

under control to manage forces not under

control these forces can be divided into

the following three categories forces

under direct control forces under

indirect control forces not under

control click the pictures to learn more

about these forces these forces should

be under direct control during ship

handling ship's main engine ship's

propeller ships thruster ships rather

ship's anchor ships moorings

professional ship handlers should

familiarize themselves with the

performance and limitations of various

ships systems used during maneuvering

the most important forces said to be

under indirect control are the ship's

inertia other hydrodynamic factors such

as bank effects squat interaction etc

the ship inertia varies with different

loading conditions but the loading

conditions can normally not be changed

during a maneuver to a certain extent

changing the speed

either the vessel can control the

hydrodynamic moment of inertia other

hydrodynamic factors such as squat bank

effects etc can to a certain extent to

be avoided or minimized if the unknown

and understood in practice it is not

possible to calculate the influence from

all these forces continuously in real

life

these forces must be estimated based on

experience and up-to-date information

there is no substitute for experience in

ship handling the most important forces

not under control are tied wind waves

current fouling although we cannot

control these forces we can through

close observation and by using available

information sources obtain relevant

information which can be used to

minimize the effect of these forces the

pivot point is the point of the ship

turns around

click this text to continue when the

ship is dead in the water

the pivot point is generally in the

center of the ship when initially

ordering engines ahead the pivot point

shifts forward as the speed increases

once the ship is steady state steaming

the pivot point settles back at about

one third from the bow when ordering

engines are stern the opposite takes

place the pivot point shifts aft and

settles at about one third from the

stern

the distance from the pivot points to

the applied force gives you the turning

livre a long lever gives you more

turning moment than a short click this

text to continue when making headway you

get a long turning liver and

consequently you get a greater turning

moment when making stern way you get a

short turning liver and consequently you

have less moment to turn the ship with

as you can see from the animations the

rudder is much more effective when

making headway the same principles apply

when you use bow thrusters or tugs

the water flow from the propeller around

the rather creates forces that help you

turn the vessel if you do not have a

water flow around the rudder you will

have no turning effect when turning the

rudder the water flowing around it will

create a pressure zone on one side and a

suction zone on the other these two

zones together will create a force

called lift if you study the animation

to the right you will see that the water

flow is faster on one side of the rudder

by employing a Bernoulli's law you will

understand how the lift force is created

ship handling in practice can be said to

be a circular movement between observing

estimating assessing deciding and

executing a good advice to all ship

handless is to remember the old saying

full speed is full-speed the first step

on the way to becoming a professional

ship handler is observation of the whole

situation estimating and assessing

possible actions deciding what to do

executing the decisions

relevant and up-to-date information is

essential for the ship handler such

information can be obtained by visual

observation instrument observation

studying the ship's maneuvering

characteristics estimating the external

forces correctly obtaining detailed

local knowledge communicating with

relevant information sources ie other

ships vessel traffic services etc it's

not possible and relevant to calculate

all the forces and their influence on a

particular maneuver

however in order to undertake a correct

estimate of what to do in a particular

maneuver situation as many of these

forces as possible should be known and

taken into account a ship's ability to

maneuver depends on the ship's steering

ability

the ship's turning ability

the ship stopping ability

it's important that the ship handler is

aware that the majority of the ships in

service today are operated without any

proven documentation of the ships

maneuvering performance standards the

professional ship handler should

familiarize themselves with the

advantages and limitations of available

equipment in order to optimize its use

whenever needed another important

qualification necessary for the

professional ship handler is an ability

to think and plan ahead of the ship

thus being at all times prepared for the

next move