Sistemul de guvernare.pdf

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Sistemul de guvernare

07 Feb 2011



SISTEMUL DE GUVERNARE

Destinatie:

1. realizeazã menținerea direcției de navigație în

timpul marșului și manevra navei când se impun

schimbãri de direcție.

2. asigură for ța lateralã necesarã girației navei si

men ț ine valoarea acestei for ț e p â n ã la

urmãtoarea comandã.



SISTEMUL DE GUVERNARECerințe:

1. Valoarea for ței laterale trebuie sã fie obținutã

într-un timp impus.

2. Să asigure controlul elementului de execu ț ie

(este neap ã rat necesar ã asigurarea limit ã riifor ței laterale în transmisia de for țã si asigurarea

existenței unei acționãri de avarie).

3. Sa asigure for ța lateralã necesarã guvernãriinavei pe traiectoria doritã.









Clasificare:

-organe de guvernare pasivã,

-organe de guvernare activã,

respectiv

- cu comandã în circuit închis;

- cu comandã în circuit deschis.




Clasificare:

Instalația de guvernare pasivã funcționeazã în douã

regimuri:

-naviga ț ia pe drum drept: instala ț ia are rolul

de a corecta drumul navei perturbat de factori

externi, prin bandãri ale cârmei la unghiuri mici,

-manevre în zone înguste, intr ã ri î n porturi,

evit ã ri, schimb ã ri ale drumului cu unghiuri mari:

situații în care instalația este solicitatã la maximum.



CURBA PORTANȚEI

1

0

P O R T A N

Ț A

VITEZA NAVEI (nd)

A i c i î n c e p

e c a v

i t a ț i a

F ă r ă

c a v i t a

ț i e

Cu ca v i ta ț ie



SISTEMUL DE GUVERNARESchema bloc a instalației cu comanda in circuit deschis:

1 – timona; 2 – transmisia de comandã; 3 – mașina cârmei; 4 – transmisiade for țã; 5 – cârma; 6 – transmisia de control; 7 –axiometrul



TERMINOLOGY

A rudder is a device used to steer a ship that moves through

water.

A rudder operates by redirecting the fluid past the hull, thus

imparting a turning motion to the shift.

In basic form, a rudder is a flat plane or sheet of material

attached with hinges, being shaped so as to minimize

hydrodynamic drag.

In larger vessels, cables hydraulics may be used to linkrudders to steering wheels.



TERMINOLOGY

The wheel of a ship is the modern method of adjusting the

angle of a boat or ship’s rudder in order to cause the vessel to

change its course. Together with the rest of the steering

mechanism it forms part of the helm. It is typically connected to

a mechanical, electric servo, or hydraulic system. In some

modern ships the wheel is replaced with a simple toggle that

remotely controls an electro-mechanical or electro-hydraulic

drive for the rudder, with a rudder position indicator presenting

feedback to the helmsman.



SHIP’S (STEERING) WHEEL











STEERING GEAR PUMP

STARTER

RUDDER POSNINDICATOR

STEERINGMODE

SWITCH

TILLER AUTOPILOT

CONTROL 1 CONTROL 2

PUMPSTARTER

FEEDBACK UNIT

DUAL NON FOLLOW-UP SYSTEM

MIDSHIPINDICATOR

• SISTEM MULT MAISIMPLU, MAI SIGUR

• NU UTILIZEAZA AMPLIFICATOARE SIINFORMATII FEEDBACK

• UNGHIUL LA CARMA SEOBTINE ROTIND TIMONAIN BORDUL DORIT PANASE OBTINE UNGHIUL DECARMA DORIT











DF DF













COMMONLY USED COMMANDS

When a command is given to the helmsman, the first part of the

order indicates the direction (right or left) for the helmsman to turnthe wheel. The second part of the command states the amount of angle. The following are some commonly used steering commands.

“Right (or left) full rudder.” Full rudder designates a 30 rudder.

When the rudder is turned past 30 (usually designated hard right or

left), care must be exercised to avoid jamming it against the stops.“Right (or left) 5, 10, 15 and so on.” This indicates the angle, indegrees, that the rudder is to be offset.“Right (or left) easy.” Usually indicates 2 or 3 degrees of rudder angle in the direction indicated. Some Masters may prefer 5 degreesof rudder angle for this command. This should be understood in the

vessels SOP.



“Give her more rudder.” To increase the rudder angle already onwhen it is desired to turn the ship more rapidly in the direction inwhich she is already turning.“Ease the rudder.” To decrease the rudder angle which is on. The

order may also be: “Ease to (state number) degrees.”“Rudder amidships.” To place the rudder on the centerline.“ Steady ” or “ steady as you go. ” To steer the present coursewhile the ship is swinging. The course should be noted at the timethe order is given and the ship steadied on that course.

“ Shift the rudder. ” To change from right to left (or left to right)rudder. Usually given when a ship loses her headway and begins togather sternway and it is desired to keep her turning in the samedirection.“ Mind your rudder. ” To steer more carefully or stand by for anorder.

“ Keep her so. ” To steer the course just reported, following arequest for that course.



PROPELLER ACTION

A propeller draws its supply of water from every direction

forward and around the blades, forcing it in a powerful

stream toward the stern. This moving current which

provides the power for propulsion is called “ screw

current. ” The water flowing into the propeller is called

“ suction screw current, ” that being ejected is called

“discharge current.”



Figure shows the waterpressure effect of the suction current

vaporizing off the tips of the blades and spiraling back in ahelical pattern.



The factors that affect propeller action:

Pitch

The pitch of a propeller is the distance the propeller wouldadvance in one revolution if the water was a solid medium.

Slip

The difference between the speed of the ship and the speedof the propeller is known as the “slip”. Slip is caused by theyield of the water against the propeller thrust. In other words,

it is the percentage of distance lost because water is ayielding substance.



Cavitation

When the blade-tip speed is excessive for the size andshape of the propeller, there is an unequal pressure on the

lower and upper blade surfaces. This condition produces

cavities or bubbles around the propeller known as

“ cavitation. ” The result is an increase in revolutions per minute without an equivalent increase in thrust. This results

in loss of efficiency. When cavitation is fully developed, it

limits a vessel s speed regardless of the available engine

power.



Rudder Action

The rudder acts the same on a large vessel as on a small craft. The

rudder is placed directly behind the propeller to use the powerful

discharge current to turn the boat. Moving the rudder to the right deflects

the discharge current to the right, which forces the stern to the left. This

action is reversed when the left rudder is applied. At very slow propeller

speed and with very little way on, there may not be enough control over

a ship to maneuver it, especially if other forces are acting upon it at the

same time. When this condition prevails, the propeller may be speeded

up enough to give it a more powerful thrust against the rudder. Using

sudden thrusts of power to kick (move) the stern in this manner is one of

the fundamental principles of vessel handling. A vessel can often be

turned in twice its length by kicking the stern.



OTHER FACTORS AFFECTING SHIP’S CONTROL

Wind, tidal, ocean currents (waves or sea), and depth of

water must be considered when handling a vessel.

Shallow water particularly affects deep draft vessels

because of the cushion effect similar to that

encountered when navigating in narrow channels.



REPEATING COMMANDS

To assure the watch officer that his orders have been

correctly received, the helmsman must always repeat,

word for word, any command received. As soon as the

command has been executed, the helmsman must also

report it to the watch officer. The watch officer confirms

that the order is understood by replying, “Very well.”



Thank you !

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