Nav and radar Notes Flashcards
list what actions you would take for correcting charts
- i would obtain my weekly Notices to mariners from an approved source.
- i would use section 1 to update my chart portfolio
- section 2 to high light the charts i need to correct
- i will insure i have a copy of MP5011, mp294, mp133a.
- check i have the equipment i need, magenta pen, cutter, glue, stencil and a hacksaw blade.
- i will check the bottom left hand corner to see if the previous correction has been applied.
- i will familiarise myself with the correction and plot it in magenta pen.
- put correction in bottom left and in the chart correction log.
What is Echo ranging principle?
A pulse of energy known as a constant speed (speed of light) is sent out into space. Range can be determined when the pulse hits a target and returns.
what are the three main factors that govern the radars detection range?
Radar pulse length
antenna hight
vertical beam width.
what vessels sizes are required to carry which type of radars?
vessels 300-499Gt required 1x Xband
Vessels 500-3000Gt require 1x Xband radar
Vessels 3000-9999Gt required either 2 Xband radar or 1 Xband and 1 Sband
Vessels over 10’000 require 1 Xband and 1 Sband
what are the sections in the weekly Notice to mariners in order?
I. explanatory notes. Publications list
II. ADMIRALTY Notice to Mariners. Updates to standard nautical charts
III. Reprints of NAVAREA1 navigational warnings
IV. Updates to ADMIRALTY Sailing directions
V. Updates to ADMIRALTY List of lights and fog signals.
VI. Updates to ADMIRALTY List of radio signals
VII. Update to Miscellaneous ADMIRALTY Nautical Publications.
VIII. Updates to ADMIRALTY Digital services
what is the best fit datum for the world?
WGS 84
Describe with a diagram how a doppler log may provide a mariner with a vessels speed.
A doppler log use the doppler effect to determine speed. If a know frequency is sent out and that pulse strikes an object. the frequency will be different when it returns. the difference between the omitted and received frequency, known as the beat, is used to calculate speed. doppler log uses acoustic energy travelling at 1500m/s for this purpose. A preferred angle of 60 degrees to the horizontal plain is used to provide the most accurate reading. Multiple transducers can be used at different angles to help eliminate the Pythagoras errors that are caused by pitch and roll this is knows as the Janas configuration.
State two advantages and disadvantages that an electromagnetic log has over a doppler log
Advantages;
no moving part.
Works better in shallow water
Much cheaper
disadvantages;
salinity and water temperature can affect the calibration.
Can only calculate STW
Not as accurate
State two advantages that Xband Radar has over Sband
Better range discrimination,
Better bearing accuracy,
picks up SART’s.
State two Advantages Sband has over Xband radar.
Has a longer range.
Can cut through rain and sea clutter better.
Describe the effects of radar interference and how one might account for this
Occurs when two radars operating on similar frequency’s are near one another. Can result in a spiral affect on the screen, often short lived. You can account for this by the interference rejection controls.
list 5 factor the may determine the strength of a returned echo.
Material
Aspect,
size,
Shape,
Hight.
Describe Range discrimination.
Range Discrimination is the radars ability to distinguish two targets on the same bearing in a similar range.
State the three main causes of deviation of the magnetic compass onboard.
Hard iron or permanent magnetism.
Induced Magnetism
electric magnetic
explain why radar ranges are more accurate the bearings when used to fix a ships position.
Radar ranges are required to meet performance standards to be accurate within 30m or 1% of the range scale in use, which ever is larger. Bearing taken from radar suffer an error due to horizontal beam width. this can cause a distortion of bearings in radar object by up to half the beam width of radars position.
