Climate is the statistics of weather over long periods of time. It is measured by assessing the patterns of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over long periods of time. Climate differs from weather, in that weather only describes the short-term conditions of these variables in a given region.
A region’s climate is generated by the climate system, which has five components: atmosphere, hydrosphere, cryosphere, lithosphere and biosphere.
The climate of a location is affected by its latitude, terrain and altitude, as well as nearby water bodies and their currents. Climates can be classified according to the average and the typical ranges of different variables, most commonly temperature and precipitation.
Climate in a narrow sense is usually defined as the “average weather“. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.
Impact on ships: While visiting any port, ships need to plan various activities like procuring stores, fuel, provisions, crew welfare etc. For example when visiting a place of cold climate, ship will need extra fuel to heat ship, may need salt for preventing icing, Extra warm clothes for crew etc. Sometimes ships need to change hydraulic oil grade to counter extreme cold. Normally ships are designed keeping climate in mind, hence impact is low.
Tides: Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of Earth.
Tide tables can be used to find the predicted times and amplitude (or “tidal range”) of tides at any given locale. The predictions are influenced by many factors including the alignment of the Sun and Moon, the phase and amplitude of the tide (pattern of tides in the deep ocean), the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry. They are however only predictions, the actual time and height of the tide is affected by wind and atmospheric pressure.
While tides are usually the largest source of short-term sea-level fluctuations, sea levels are also subject to forces such as wind and barometric pressure changes, resulting in storm surges, especially in shallow seas and near coasts.
Tidal phenomena are not limited to the oceans, but can occur in other systems whenever a gravitational field that varies in time and space is present. For example, the shape of the solid part of the Earth is affected slightly by Earth tide, though this is not as easily seen as the water tidal movements.
Tide changes proceed via the following stages:
Sea level rises over several hours, covering the intertidal zone; flood tide.
The water rises to its highest level, reaching high tide.
Sea level falls over several hours, revealing the intertidal zone; ebb tide.
The water stops falling, reaching low tide.
Oscillating currents produced by tides are known as tidal streams. The moment that the tidal current ceases is called slack water or slack tide. The tide then reverses direction and is said to be turning. Slack water usually occurs near high water and low water. But there are locations where the moments of slack tide differ significantly from those of high and low water.
Tides are commonly semi-diurnal (two high waters and two low waters each day), or diurnal (one tidal cycle per day). The two high waters on a given day are typically not the same height (the daily inequality); these are the higher high water and the lower high water in tide tables. Similarly, the two low waters each day are the higher low water and the lower low water. The daily inequality is not consistent and is generally small when the Moon is over the equator.
The main patterns in the tides are
the twice-daily variation, the difference between the first and second tide of a day
the spring–neap cycle
the annual variation
IMPACT ON SHIPS: Tides have highest impact on ships as height of tide decides available depth of water with respect to draft. Most of the ports are affected as ships have become much larger than the past. Ports have made their berths deeper but passage to the berth may not be deep enough making ships wait for High Tide to pass over the BAR. Entry to the port or berth may be affected by strong tidal streams and berthing/un-berthing may be done only during slack water time only.
WIND: On the surface of the Earth, wind consists of the bulk movement of air. In meteorology, winds are often referred to according to their strength, and the direction from which the wind is blowing. Short bursts of high-speed wind are termed gusts. Strong winds of intermediate duration (around one minute) are termed squalls. Long-duration winds have various names associated with their average strength, such as breeze, gale, storm and hurricane. Wind occurs on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hours, to global winds resulting from the difference in absorption of solar energy between the climate zones on Earth. The two main causes of large-scale atmospheric circulation are the differential heating between the equator and the poles, and the rotation of the planet (Coriolis effect). Within the tropics, thermal low circulations over terrain and high plateaus can drive monsoon circulations. In coastal areas the sea breeze/land breeze cycle can define local winds; in areas that have variable terrain, mountain and valley breezes can dominate local winds.
IMPACT ON SHIPS: Since we are discussing “Power driven ships”, Impact is not that severe. Impact of wind is according to the WINDAGE area of the ship. Most of the ships Accommodation block stands out above deck and creates lot of wind resistance. This is common for all ships. However Container ships, RO-RO ships, CAR carriers, Livestock carriers etc have very high freeboard areas which acts as sails. These ships need to make course corrections when facing strong winds at sea. Strong wind also affects wave height creating additional resistance for the movement of the ship through the water. Over all strong winds affect speed of the ship badly.
CURRENTS:
An ocean current is a seasonal directed movement of sea water generated by forces acting upon this mean flow, such as wind, the Coriolis effect, breaking waves, cabbing, temperature and salinity differences, while tides are caused by the gravitational pull of the Sun and Moon. Depth contours, shoreline configurations, and interactions with other currents influence a current’s direction and strength. Ocean currents are primarily horizontal water movements.
Ocean currents flow for great distances and together, create the global conveyor belt which plays a dominant role in determining the climate of many of the Earth’s regions. More specifically, ocean currents influence the temperature of the regions through which they travel. For example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate than any other region at the same latitude. Another example is Lima, Peru, where the climate is cooler, being sub-tropical, than the tropical latitudes in which the area is located, due to the effect of the Humboldt Current.
Also remember FOR EVERY CURRENT, THERE IS A COUNTER CURRENT NEARBY AND IN OPPOSITE DIRECTION. Currents are detected by measuring seawater temperature.
IMPACT ON THE SHIP: Currents are double edged sword for the ship. Strong current can increase speed by up to 4 knots saving lot of fuel or if it is against the direction can reduce speed by 4 knots. Normally passage planning considers taking advantage of currents. When going in opposite direction, Whenever possible axis of the current is avoided and counter current is searched.
AREAS OF BAD WEATHER: Some areas of the world always have bad weather due to various factors. Some of them are
1. Bay of Biscay, North Sea (Europe)
2. Gulf of Alaska (North America)
3. Drake passage, Cape Horn (South America)
4. Cape of Good Hope (Africa)
5. Bass Strait (Australia)
IMPACT ON SHIPS: These areas can slow down ships quite badly. When possible ships avoid these areas but most of the time they have to face the music.
TIME ZONES: A time zone is a region of the globe that observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries of countries and their subdivisions because it is convenient for areas in close commercial or other communication to keep the same time.
Most of the time zones on land are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−12 to UTC+14), but a few zones are offset by 30 or 45 minutes (e.g. Newfoundland Standard Time is UTC−03:30, Nepal Standard Time is UTC+05:45, and Indian Standard Time is UTC+05:30).
Some higher latitude and temperate zone countries use daylight saving time for part of the year, typically by adjusting local clock time by an hour. Many land time zones are skewed toward the west of the corresponding nautical time zones. This also creates a permanent daylight saving time effect.
Today, all nations use standard time zones for secular purposes, but they do not all apply the concept as originally conceived. Newfoundland, India, Iran, Afghanistan, Burma, Sri Lanka, the Marquesas, as well as parts of Australia use half-hour deviations from standard time, and some nations, such as Nepal and some provinces, such as the Chatham Islands of New Zealand, use quarter-hour deviations. Some countries, such as China and India, use a single time zone even though the extent of their territory far exceeds 15° of longitude.
IMPACT ON SHIPS: Theoretically time zones do not affect performance of the ship. However they can create some confusion about arrival time in next port. There is also an issue of synchronizing clocks every day with local time increasing or decreasing length of the day. Normally clocks are adjusted at night during sleeping hours, so either you get more or less sleep. When traveling EAST especially in higher latitudes, biological clock of the body can make it tiring.
The International Date Line (IDL) is an imaginary line on Earth’s surface defining the boundary between one day and the next.
Time Zone map showing the International Date Line.
The International Date Line (IDL) on the map.
The International Date Line is located halfway around the world from the prime meridian (0° longitude) or about 180° east (or west) of Greenwich, London, UK, the reference point of time zones. It is also known as the line of demarcation.
The Dateline Is Not Straight
The dateline runs from the North Pole to the South Pole and marks the divide between the Western and Eastern Hemisphere. It is not straight but zigzags to avoid political and country borders and to not cut some countries in half.
What Happens When You Cross the Dateline?
When you cross the International Date Line from west to east, you subtract a day, and if you cross the line from east to west, you add a day.
Three Dates at the Same Time
Every day between 10:00 and 11:59 UTC, three different dates on the calendar are in use at the same time on Earth. For example, our Time Zone Converter shows:
At 10:30 UTC on May 2, it is
23:30 (11.30 pm) on May 1 in American Samoa (UTC−11),
06:30 (6:30 am) on May 2 in New York (UTC-5), and
00:30 (0:30 am) on May 3 in Kiritimati (UTC+14).
Some Confusions
Planes from Asia and Australia to the western US arrive before they depart. For example, United flight 870, Sydney to San Francisco, currently departs Sydney at 2:30 p.m. and arrives San Francisco at 9:15 a.m. on the same calendar day.
This happens because even though you fly 13 hours and 45 minutes (gate-to-gate), you cross the international date line. The time change is a -19 hour time change so you have a net gain in time of 5 hours and 15 minutes.
Local time adjustments will change as each city enters or leaves Daylight Saving Time, so the schedule in April will differ from the schedule in January though the flying time will be roughly the same.
IMPACT ON SHIPS: Normally there is no impact except estimated timing of arrival at next port. You do not get extra or less salary for extra or missed day.
DENSITY Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world’s oceans has a salinity of about 3.5% (35 g/L). Average density at the surface is 1.025 kg/L. Seawater is denser than both fresh water and pure water (density 1.0 kg/L at 4 °C (39 °F)) because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F).
Seawater density in Mediterranean region is 1035. Water density in Great lakes or Panama canal is less than 1000.
IMPACT ON SHIPS: Ships are impacted severely due to effect of change of density. Change density can increase draft and also change TRIM (Affecting maximum draft). Ships need to make careful CARGO calculations to avoid “over maximum draft” situations.
LOAD LINE ZONES: The world has been divided into various “load line zones” and seasonal areas. These are shown in a chart carried on board the vessel. These zones govern the depth to which a vessel may be loaded.
A vessel passing in the course of her voyage from one zone or area into another zone or area, in which another load line applies, must have been loaded in such a way that when she arrives in the zone or area in question, her midship draught will not be in excess of the maximum draught allowed in the second zone or area.
Where seagoing vessels navigate a river or inland water deeper loading is permitted corresponding to the weight of fuel, water, etc., required for consumption between the point of departure and the open sea. When loading in fresh water or in dock or river water of any density less than that of sea water a “Dock Water Allowance” is made for the difference in density.
IMPACT ON SHIPS: Impact is same as Density change but deals with legal requirements.
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