Navigation Flashcards
What is nominal range, luminous range and geographic range?
Nominal range is the distance a light can be seen in meteorological visibility of 10nm (luminous range when vis is 10nm)
Luminous range is the maximum distance that a light can be seen taking in to account the lights luminosity and the current visibility
Geographical range is the distance it can be seen taking into account its height above the water and the curvature of the earth
What are the adjustable sextant errors.
Error of perpendicularity: index mirror is not perpendicular to the plane of the instrument
Side error: horizon mirror is not perpendicular to plane of instrument
Index error: index mirror and horizon mirror are not parallel with each other when the arm is reading 0*
Collimation error: telescope is not perpendicular to plane of instrument, light does not travel down Centre of telescope
What are the uncorrectable errors
Graduation error: engravings are inaccurately marked
Rack and worm: Play between teeth of rack and worm drive due to either poor manufacturing or wear and tear
Shade error: the glass shades not optically flat because they have not been machined correctly.
Centring error: pivot arm is not exactly in the Centre of the circle that forms the arc.
Collimation Error: Telescope not parallel with the plane of the instrument.
How to correct sextant errors
Perpendicularity: adjusted with screw behind the index mirror by lining reflected image of Arc with the Arc itself well holding sextant horizontal
Side error: Arm to 0deg, Look through telescope, with sextant horizontal, look at distant horizon, True and reflected horizons should line up. If not, adjust screw furthest from the frame at the back of the horizon mirror.
Index error: set index arm to 0*. Sextant vertical, look at horizon Observe horizon true and reflected horizon should line up. Correct with screw closest to handle. After adjustment check side error again, adjust, then recheck index error.
How often musty an emergency steering drill be conducted and what must be checked
Every 3 months
- Communications
- Control of the steering gear in the steering compartment through all different means of control. (Manual activation of solenoids, securing rudder via block and tackle, Manual hand crank)
- Operation with alternate power sources.
- Steering of vessel while under way
When must the steering gear be tested and what needs to be tested.
- Once every watch after prolonged use of autopilot.
- Check rudder response from all steering positions with individual and dual power units. - Before entering coastal waters
- Check Rudder response from all steering position
- Check communications between bridge and steering compartment - Prior to departure (no more than 12hours prior)
- Communications
- Operation of main steering gear
- Auxiliary steering gear
- Steering positions on the bridge
- Emergency power supply
- All rudder angle indicators
- steering gear Power unit failure alarms
- Automatic isolation arrangements
How quickly must it be possible to change from auto pilot to hand steering?
30Sec
What tests and checks should be included in the steering gear testing procedures?
- The full movement of the rudder according to the required capabilities of the steering gear
- A visual inspection for the steering gear and its connecting linkage
- The operation of the means of communication between the navigation bridge and steering gear compartment
Requirements of the steering gear. (Time and power)
SOLAS
- Full service speed, sufficient power to move rudder from 35 to 35 in no more than 28 sec
- Auxiliary steering, at navigable speed capable to steer the vessel, rudder from 15 to 15 in no more than 60 seconds at half maximum ahead speed or 7knts which ever greater.
Types of visual fixes
3 point fix Running fix Horizontal Sextant angle (with use of Station pointer) Horizontal angle with use of Vertical sextant angle and bearing Bearing and depth contour Celestial fix: Meridian passage, Sun run sun, Start sight, Luna sight Dipping teh light and bearing
Pre-Departure checks\
Captain, Bridge Team, Engineering
- Captain:
- Certificates
- Manning
- Crew and Guest lists
- Mister Lists
- Agents and port authority
- Customs clearance
- Accounts
- Tides, Weather
- Stability, Draught
- Crew and Passenger documents
2. Bridge team: Meeting: - Passage Plan - Standing Orders - Risk assessment and toolbox talk for mooring operations - Pilot and Tugs
Checks:
- Nav equipment
- Radar
- Compass
- Engine
- Steering
- Thrusters
- Garbage
- watertight integrity
- Stowaway search
- ALL ABOARD
- Engineering
- Status of all equipment
- Sufficient Bunkers of foil and oil
- Any concert s
- Ready for Sea?
Meridian passage
Lat
- Check time of Mer pas in Day table
- Sextant altitude at Mer pas and time UT
- To get LAT combine dec and alt
( L&D same & lat >dec then lat = dec+(90-alt))
Longitude
- Check time diff between local time and UT at merpas
- time difference to Arc to time tables
1deg = 15 minutes
