Vertical Force instrument.
Graduated compass needle attached with sliding weight.
Rides on a sharp pivot point.
Housed in a brass case.
Graduated compass needle can align itself with Earth’s magnetic field.
Sliding weight can move in or move out from center.
By measuring the sliding weight distance, vertical force is found.
List and describe the main sources of errors in the determined position of GPS.
When radio waves radiated from satellite passes through different layers of the ionosphere and
troposphere the velocity of wave very which affects the time difference measurement and the fix will
not be accurate. For this a dual frequency receiver receives both of The frequencies and correction is calculated and
compensated with the receiver. For low elevation of satellite, radio waves is affected by refraction. So, receiver is designed to select
satellites whose elevation is more than 9.5 degrees.
If the users clock is not perfectly synchronized with the satellite clock the range measurements will not
be accurate. This error can be eliminated within the receiver by obtaining the pseudo range from 3
satellites automatically.
This error is caused due to error in the satellite clock with respect to GPS time. This is monitored from
ground based control segments and eliminated.
The geometry of the position of the satellites determine the angle of cut of the position lines. As the
angular separation between the satellites are higher, more accurate is the fix.
To indicate the satellite geometry, the DOP (dilution of precision ) values are used.In DOP calculations
the following different varients are used.
-GDOP(geometric dilution of precision)
-PDOP(positional dilution of precision)
-HDOP(horizontal dilution of precision)
-VDOP(vertical dilution of precision)
-TDOP (time dilution of precision)
GPS receiver is promulgated to select the best available satellites, considering their elevation and
geometry.
This error is caused by satellite signal arriving at the ships antenna both directly from the satellite and
having being reflected by some other object causing in accuracy in range measurement, sitting the
antenna at a suitable place can minimise this error.
Although satellites are very precisely placed in orbits, slight shifts are possible due to gravitation
forces.Sun & moon have waek influence over the satellite orbits.how ever this is monitored from the
ground control segment of the satelliye & corrections applied as necessary. The error resulting is never
more than 2 meters
SA if the international degradation of SPS(satellite positioning system)SA is controlled by the United
States department of Defence to limit accuracy for non us military and government users. The potential
accuracy of C/A code around 10M-30 M is reduced to 100M-150 M.Mean while it is permanently
deactivated due to broad distribution & worldwide use of GPS.
Pseudo random noise code: Each satellite have a unique code to identify the satellite called a
random noise code. The satellites are identified by the users through this PRN codes. These PRN codes are only pseudo random.
Transmission of signals: The satellite translate the signal into different codes. P- code: Precision code is only received by USA military and its allies. Only their GPS receiver has access and and can decode the P-code. In case of P- code, the chief frequency is 10.23 Mbits/sec. The entire sequence is a 266 days long but only 7 days piece of code is used. during this period there is no repetition of the code.
P code can be transmitted encrypted. During this anti spoofing mode the P code is encrypted into Y
code.
C/A code: It is known as course acquisition Code. All civil uses of GPS decode the CA code And it also
helps the military receivers to access more accurate P-code.
The CA code is weight of a sequence of keeps having a frequency of 1. 023 MHz. This codes are modulated by phase modulation techniques on to carrier frequencies.
L1= 1575.42 megahertz
L2= 1227.60 megahertz
The L1 signal consists of both P-code & C/A code and L2 signal consists only P-code.
L1= 1575.42 megahertz
L2= 1227.60 megahertz
The L1 signal consists of both P-code & C/A code and L2 signal consists only P-code.
L1 frequency is accessible by any civil user as well as the military services. But L2 frequency is only
accessible by the US military and its allies for their own security advantages. Therefore there are two
frequencies used in GPS.
Dual frequency receiver are also used for eliminating the error due to ionospheric and tropospheric
delay.
Chapter II-2 of SOLAS contains regulations on fire protection, fire detection and fire extinction. The regulations require that ships should be designed and constructed to minimize the risk of fire and to minimize the spread of fire. The regulations also require that ships should be provided with appropriate means of detecting and extinguishing fires.
GENERAL INSPECTION BY CLASSIFICATION SOCIETY
Yard attending manager, superintendent, Master, C/E, C/O, and 2/E will carry out this general inspection.
This Inspection to be carried out during daylight hours.
Check: Deep dents, dented shell plating, damages to stiffeners, shell plating that have wasted badly.
BOTTOM
Check the areas that requires grit blasting (Top side, boot side, bottom).
Coating thickness to be checked using a paint thickness gauge.
ANCHOR CABLES
Both anchor cables are lowered and ranged into the drydock bottom and to be calibrated.
Both anchor chains to be turn end to end at each dry docking.
Check the diameters of the links.
CHAIN LOCKER
Chain locker to be cleaned of mud and water and to be painted.
REPAIR THE HAWSE PIPE STEEL COLLARS
ECHO SOUNDER
Ensure the transducer plates are cleaned.
Check water tight terminal box.
SPEED LOG or DOPPLER SPEED LOG
Speed log to be serviced and calibrated.
SACRIFICIAL ZINC ANODES
All zinc anodes are to be checked and renewed.
Ensure sufficient anodes on the bilge keels, the stern part and on the rudder.
In case of impressed current system, it should be calibrated.
SEA CHESTS
Check sea chest of high sea suction, low sea suction and emergency fire pump sea suction.
Internal surface to be scraped and cleaned of marine growth.
Zinc anodes on the sea chests are to be checked.
SEA SUCTION VALVES AND DISCHARGE VALVES
To be overhauled.
Main intermediate valves and attached mud filters to be overhauled.
SANITARY STORM VALVES OVERHAUL.
DAMAGED BILGE KEELS TO BE RENEWED.
RUDDER
Check rudder bottom plug for any ingress of water.
Repair rudder plating that is cracked.
Check rudder top plug for tightness.
Check pintle bush clearance (top and bottom pintles). If clearances too much, then bushes are need to be renewed.
