Welcome Aboard Mariners Alike - Malaysia Rule The Waves

its hard to describe how a man could left everything he had on land and went out to sea...
its even harder to describe how bright the stars at night and how fresh the cool morning air when you are in the middle of the ocean...
the hardest thing is to describe how close you are to death and how god could took your life at any time...
come to sea and see for yourself...

GOD SPEED AND FAIR WINDS


come to sea and see for yourself

this blog is dedicated to mariners,navigators and seafarers alike, merchant or naval for others to had a glimpse of what we do and what we faced in the vast blue oceans.

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Thank you.

Monday, March 22, 2010

nautical studies - camne navigator calculate position...


sextant..almanac..chart...parallel ruler..sungguh old school eh..


pada zaman dahulu kala...para pelaut melayari samudera dan menentukan kedudukan dgn berpandukan objek2 samawi..sextant, kompas magnetik dan almanak nautika...xde GPS...xde GLONASS...mahupun henpon Nokia yg leh tunjuk jalan gi Damansara Utama...apalagi jalan nak gi umah mak sedara korang kat Sungai Lembing nun...

ok2...serius....

posting lepas aku ade cakap yg navigator menggunakan method Intercept...Longitude by Chronometer dan Meridian Passage utk menentukan garis latitude dan longitude mrk di laut yg luas tu...

ok serius...ak x pandai nk ceritakan camne nak wat benda alah ni dlm site ni sbb benda ni praktikal dan diajar scr hands on...krg ak cite panjang2 krg ade yg muntah darah then lari dr site ni sbb x paham sepatah haram....

tp..fine..ak try gak...

mula2 kita cite psl Intercept....

Intercept atau nama x glamour die Marc St Hilaire method adalah salah satu cara menentukan kedudukan dilautan dgn celestial observation....ini melibatkan pengunaan sextant..yg mana...objek samawi tersebut di observe dgn mengenalpasti sextant altitude...selalunya matahari digunakan sbb senang nk tembak...Intercept akan memberikan satu line of position...

dua atau lebih observation akan memberikan line of position yg pd akhirnya akan bertindih antara satu sama lain...yg merupakan kedudukan pemerhati atau observer...lg byk observation..lg accurate kedudukan kapal..

nautical almanac..satu British Admiralty..satu lagi US nye...ak pkai yg biru tu...tiap2 tahun kuar edition baru..

time of observation diambil...dlm format GMT/UT (Greenwich Meridian Time/Universal Time) pd chronometer kapal...time ni penting sbb ia digunakan utk mengetahui GHA (Greenwich Hour Angle) pd Nautical Almanac....yg mana pd akhir pengiraan akan memberikan bearing objek yg di observe...

ok...format kiraan nya adalah...SIODATT...yg membawa maksud..

Sextant Altitude - S.A : altitude pd sextant
Index Error - I.E : ralat pd sextant..ala cam yg korang blaja kat tolok skru mikrometer tu...
Observer Altitude - O.A : altitude sebenar selepas ralat dimansuhkan
Dip - Dip : Height of Eye atau ketinggian mata pemerhati.ini pun error gak.ade dlm nautical almanac
Apparent Altitude - A.A : altitude selepas ralat Dip dah di apply
Total Correction - T.Corr : ini kne carik kt dlm nautical almanac.kalau Sun dia ade Upper/Lower Limb
True Altitude - T.A : altitude sebenar objek selepas semua ralat kat atas tadi dah dimansuhkan...

bila dah dpt True Altitude...kene lak tolak 90 degree utk dpt TZX (True Zenith Distance)...amende TZX tu korang kne blaja ape itu spherical trigonometry...

dr sini...korang dapat kedudukan korang...iaitu latitude korang...tp ini x tau btul ke x...jd korang kene compare dgn DR (dead reckoning) position...berapa ribu batu dia lari...based on CZX (Calculated Zenith Distance)...CZX ni dapat dgn menggunakan formula...ape formula die ak x igt...

bila dah dpt TZX ngan CZX..korang leh tentukan berapa jauh kedudukan korang dari DR...samada towards atau away dari objek...selalunya...navigator yg old timer akan dpt difference sebanyak 0.1 batu nautika...kalau kadet2 yg baru blaja...difference leh dapat dari 1.0 smpailah beribu2 batu...jadi navigator kenelah rajin yg amat buat celestial observation utk jadi amat terror...wahaha...

 ini lines of position yg bersilang memberi kedudukan pd pukul 0600h..pakai 3 bijik bintang...iaitu Antares..Deneb dan Altair..
method yg sama diguna berulang kali dlm satu hari...maknanya pagi satu kali observation...petang satu observation...dgn satu observation dgn method Meridian Passage/Latitude by Meridian Altitude atau time malam tiga bintang berlainan bearing digunakan...masing2 akan memberikan Line of Position...dimana garisan2 ni akan bertindih antara satu sama lain...yg akan memberikan kedudukan kapal....

dah laa...nnt ak sambung utk method2 lain lak...ok...


-come to sea and see for yourself-

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