A container vessel is undertaking passage from Auckland to Yokohama using a great circle track in January.
a) On departure from Auckland and during the earlier part of the voyage, currents are of little consistency and are varying in direction. Once the vessel crosses approx 25°S, the tidal stream becomes more ordered and a westerly stream develops. The vessel will enter the South Equatorial Current and be set to the west by approx half a knot with a consistency of 75%. Once the vessel is north of the equator, the Equatorial Counter Current is met which has the effect of setting the vessel eastwards. From 10° to 20° North the North Equatorial Current is crossed, which again sets her to the west. From then on the chart indicates that currents are variable, until some 350 miles from Japan a SE setting current is encountered, which has a low consistency of 25-50% and may reduce the vessels headway by some half knot. In the region of 150 miles from
b) The main area likely to be affected by a TRS is the area east of Australia and from Auckland north to approx 10°S. There are on average 7 Hurricanes a year, with two being over force 12. As the vessel crosses into northern latitudes, the chances of encountering a TRS are remote.
c) As the limit of sea ice is well south of Auckland and north of Japan, Ice is unlikely to be encountered.
d) Predominant wind direction on departure should be SW, subsequently becoming SE in the early passage. Strong to gale force E or NE winds may be encountered in the region of New Caledonia. Consistency is in the region of 40%. From then on an area of light SE winds is encountered (trades) until at about 10°S the convergence zone is crossed. This zone produces light and variable winds, interspersed with heavy squalls. Once passed through the ITCZ, winds begin to freshen from the NE (trades) and are very consistent with a force of force 3-5. Further north an area of lighter more variable winds is encountered before the effects of the Asian continental high-pressure system being felt closer to the shores of Japan, although the wind will be more NW or Nly.
From Auckland to 30°S the swell is predominantly from the SW and moderate or heavy, then between 20°-30°S the swell being from the SW or SE is moderate or heavy. Moderate seas are encountered from 20°S to the equator and are either SE or NE. North of the equator to approx 20°N, there is a swell from the NE which is low or moderate, but 10% of the time it could be expected to be rough. When approaching Japan, the swell runs from the NW and is moderate.
Although the vessel is mainly running before the wind and swell, she may have to reduce speed in heavy seas depending on her performance, especially during the latter stages of the passage.
e) According to routeing charts there is a 2% or less chance of reduced visibility on passage. Heavy rain may reduce vis in ITCZ showers.
f) Much of the Pacific has not been thoroughly surveyed, and some areas are prone volcanic activity. Shoals can build up even in those areas, which have been well surveyed. These shoals, along with the numerous islands have the effect of altering and accelerating currents. Extra care is to be taken to avoid vessels being driven on to barriers or fringing reefs, with no warning from soundings, as reefs generally have deep water by.
dariusz.lipinski