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Navigational systems employed on gas carriers while approaching terminals

-    determination of the current position of the wa-terplane in the manoeuvring area and ship movement parameters:

-    determination of the projected position of ship’s waterplane in the manoeuvring area and the ship movement parameters;

-    establishing the parameters of the manoeuvre to be madę, accounting for the prevailing naviga-tional conditions (hydrometeorological and ba-thymetric conditions);

-    coming to a decision conceming the settings of the rudder, engines, thrusters and tugs.

Modem systems of manoeuvre prediction based

on the display of futurę ship movement trajectory or the ship dynamie domain on electronic charts may also assist the navigator in his decision making process leading to the determination of rudder, engine and thruster settings and the tugs involved.

Navigation of gas carriers on restricted waters

The size of world gas carriers fleet estimated for the year 2013 is presented at figurę 2 taking into account the size of ships [2],

Fig. 2. Size of gas carriers fleet with the division of the ships' size. predicted for 2013

Rys. 2. Wielkość floty LNG z podziałem na wielkości statków, przewidywana na 2013 r.

Basic parametres of standard and large gas carriers are shown in table 1 [2],

They are usually two-propeller vessels with conventional fixed propellers and a turbinę engine. Most of the modem gas carriers achieves the speed between 19 and 20 knots.

Regardless of employed loading systems basie parametres of modem standard and large gas carriers are in the following rangę:

-    length    270 + 340 m

-    width    42 54 m

-    maximum draught    11,0 -t-12,5 m

-    side surface of air blow 6000 7000 m²

-    speed    19,0 20,0 knots

-    propellers    2 or 1 conventional

proppeler.

Manoeuvring with a gas carrier with the parametres presented above on restricted waters is a com-plex undertaking which reąuires employment of special systems supporting the process of naviga-tion.

The navigational systems employed on gas carriers entering LNG terminals support the process of pilot navigation during the manoeuvres:

1.    Fairway passage’,

2.    Portentry’,

3.    Tuming’,

4.    Berthing and unberthing.

Navigation during the first three types of manoeuvring is supported by Pilot Navigation Systems (PNS), whereas Docking Systems are used to facilitate berthing and unberthing operations. Attempts are being madę to integrate the two systems by designing a navigational pilot-docking system.

Pilot navigation systems (PNS)

The idea behind the construction of a pilot navigation system is to enhance mental process of the pilot conducting the ship by providing him with information enabling safe performance of a planned manoeuvre in specific navigational conditions in a set time. This information has to be [3j:

-    sufficient for the manoeuvre to be performed safely;

Table 1. Parametres of typical gas carriers Tabela 1. Parametr}' typowych gazowców LNG

No.	Overall length	Length between the plumbs	Width	Maximum draught	Gross weight	Gasholder capacity	Exemplary
	Lc	Lpp [m]	B [ml	Hm]	GT [10^5t]	f/,l-10^3m^5]
1	270 - 275	260 - 265	42	11-12	90-111	132-135	Inigo Tapias Golar
2	315		50	12,0	136	216	Q-flex
3	340		54	12,0		270	Q-max

Zeszyty Naukowe 20(92)

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