Kaj pomeni vozel?

http://sl.wikipedia.org/wiki/Vozel_(enota)

Vôzel je fizikalna enota za hitrost, ki se uporablja predvsem v pomorstvu in letalskem prometu. En vozel ustreza hitrosti ene morske milje na uro oziroma približno 0,5144 m/s.

vozel

Prva metoda

V zgodnjih dobah pomorstva so merili hitrost ladje tako, da so vrgli v vodo za ladjo kos lesa, privezanega z vrvico. Ker ostane kos lesa praktično nepremično v vodi je dolžina odvite vrvice v določenem času (na začetku merjeno 30 sekund s peščeno uro) merilo za hitrost ladje. Za lažje merjenje dolžine so bili na vrvici vozli. Razdalja med dvema vozloma je ustrezala hitrosti 1 morske milje na uro.

[uredi]Druga metoda

Ta je bila uporabna predvsem pri nizkih hitrostih, ko je bilo merjenje z kosom lesa in vrvico premalo natančno. Na bok ladje so nanesli oznake v razdalji 0,514 metra (morska milja / 3600 =1 morska milja / sekunda). Pri prvi oznaki so vrgli v vodo kos lesa in merili čas, ki ga je potreboval, da je prišel do zadnje oznake (oziroma se je ladja premaknila za to razdaljo). Primer: 100 oznak v 20 sekundah pomeni 100 / 20 = 5 vozlov.

The knot (pronounced not) is a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph.[1] The abbreviation kt is preferred by every major seafaring nation. The knot is a non-SI unit accepted for use with the International System of Units (SI).[2] Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridiantravels one minute of geographic latitude in one hour. Etymologically, the term knot derives from counting the number of knots in the line that unspooled from the reel of a chip log in a specific time.

Definitions

1 international knot =
nautical mile per hour (by definition),
1.852 kilometres per hour (exactly),[2]
0.514 metres per second.
1.151 miles per hour (approximately).

 

 

Until the mid-19th century vessel speed at sea was measured using a chip log. This consisted of a wooden panel, weighted on one edge to float upright, and thus present substantial resistance to moving with respect to the water around it, attached by line to a reel. The chip log was “cast” over the stern of the moving vessel and the line allowed to pay out.[4] Knots placed at a distance of 47 feet 3 inches(14.4018 m) passed through a sailor’s fingers, while another sailor used a 30 second sand-glass (28 second sand-glass is the current accepted timing) to time the operation.[5] The knot count would be reported and used in the sailing master‘s dead reckoning and navigation. This method gives a value for the knot of 20.25 in/s, or 1.85166 km/h. The difference from the modern definition is less than 0.02%.

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