Joint accounting of drift and current in manual graphical dead reckoning. Tides and tidal currents in estuaries Tidal currents

Tidal fluctuations in ocean level are accompanied by horizontal movement of water masses, which is called the tidal current. Therefore, the navigator must take into account not only changes in depths, but also the tidal current, which can reach significant speeds. In areas where there are high tides, the boatmaster must always be aware of the height of the tide and the elements of the tidal current.

Tides allow deep-draft ships to enter some ports located in shallow bays and estuaries.

In some places, the tides are intensified by surge phenomena, which leads to a significant increase or decrease in the level, and this in turn can lead to accidents of ships under cargo operations at berths or in the roadstead.

The nature and magnitude of tides in the World Ocean are very diverse and complex. The magnitude of the tide in the ocean does not exceed 1 m. In coastal areas, due to the decrease in depth and the complexity of the bottom topography, the nature of the tides changes significantly compared to tides in the open ocean. Along straight shores and capes protruding into the ocean, the tide fluctuates within 2-3 m; in the coastal part of the bays and with a heavily indented coastline, it reaches 16 m or more.

For example, in Penzhinskaya Bay (Sea of ​​Okhotsk) the tide reaches 13 m. On the Soviet shores of the Sea of ​​Japan its height does not exceed 2.5 m.

In the seas, the height of the tide depends on what kind of connection a given sea has with the ocean. If the sea extends far into the land and has a narrow and shallow strait with the ocean, then the tides in it are usually small.

In the Baltic Sea, tides are so small that they are measured in centimeters. The tide height in Calais is 7 cm, in the Gulf of Finland and Bothnia about 14 cm, and in Leningrad about 5 cm.

In the Black and Caspian Seas, the tides are almost imperceptible.

In the Barents Sea, tides are semi-diurnal.

In the Kola Bay they reach 4 m, and near the Iokan Islands - up to 6 m.

In the White Sea the tides are semi-diurnal. The highest tide height is observed on the Tersky coast in the throat of the sea, where at the Oryol lighthouse it reaches 8.5 m, and in the Mezen Bay - up to 12 m. In other areas of this sea, the tides are much lower; Thus, in Arkhangelsk it is about 1 m, in Kemi - 1.5 m, and in Kandalaksha - 2.3 m.

A tidal wave, penetrating into the mouths of rivers, contributes to fluctuations in their levels, and also significantly affects the speed of water flow in the mouths. Thus, often the speed of the tidal current, dominating the speed of the river, changes the flow of the river to the opposite direction.

Winds have a significant influence on tidal phenomena.

A comprehensive study and accounting of tidal phenomena is of great importance for the safety of navigation.

The current that is directed in the direction of the movement of the tidal wave is called tidal, the opposite is called ebb.

The speed of tidal currents is directly proportional to the magnitude of the tide. Consequently, for a certain point, the speed of tidal currents at syzygy will be significantly greater than the speed at quadrature.

With increasing declination of the Moon, as well as as the Moon moves from apogee to perigee, the speed of tidal currents increases.

Tidal currents differ from all other currents in that they capture the entire thickness of water masses from the surface to the bottom, only slightly reducing their speed in the near-bottom layers.

In straits, narrow bays and near the coast, tidal currents have the opposite (reversible) character, that is, the tidal current is constantly directed in one direction, and the ebb current has a direction directly opposite to the tidal one.

In the open sea, far from the coast, and in the middle parts of fairly wide bays, there is no sharp change in the direction of the tidal current to the opposite direction, i.e., the so-called change of currents.

In these places, a continuous change in current directions is most often observed, and a 360° change in current occurs with a semi-diurnal tide in 12 hours and 25 minutes and with a diurnal tide in 24 hours and 50 minutes. Such flows are called rotating flows. Changes in the directions of rotating currents in the northern hemisphere, as a rule, occur clockwise, and in the southern hemisphere, counterclockwise.

The change from tidal current to ebb current and vice versa occurs both at the moment of high and low waters, and at the moment of average level standing. Often, a change in currents occurs in the period of time between high and low water. When the tidal current changes to ebb and flow, the current speed is zero.

The general pattern of tidal currents is often disrupted by local conditions. Taking into account the tidal current, as mentioned above, is of great importance for the safety of navigation.

Data on the elements of tidal currents are selected from the Atlas of Tidal Currents, and for some areas of the seas - from tables located on navigation charts. General instructions about currents are also given in sea directions.

Relatively constant currents are shown on maps with arrows. The direction of each arrow corresponds to the direction of the current operating at a given location, and the numbers above the arrow indicate the speed of the current in knots.

The direction and speed of tidal currents are variable quantities, and in order to reflect them on the map with sufficient completeness, you need not one arrow, but a system of arrows - a vector diagram.

Despite the clarity of vector diagrams, they overload the map and make it difficult to read. To avoid this, elements of tidal currents are usually shown on the map in the form of tables placed in free spaces on the map. A complete table is a table that contains the following data:

Watch relative high water at the nearest tidal point; the inscription “Full water”, corresponding to zero hours, is placed on

In the middle of the column, from it up, in ascending order, are the digits of the hours until full water, and downwards, also in ascending order, are the digits of the hours after full water;

Geographic coordinates of points, usually designated by the letters A; B; IN; G, etc. ; the same letters are placed in the corresponding places on the map;

Elements of currents: direction in degrees and speed in syzygy and quadrature in knots (with an accuracy of 0.1 knots).

The determination of the speed and direction of the current at a given moment in a given place according to the Atlas is found as follows.

First, the main port for a given place is determined using the Atlas, after which, using the Tide Table (Part I), the time of high water closest to the given one is found, and the time interval (in hours) before or after the moment of high water in the main port relative to the given moment is calculated. Then, for the calculated period of time before or after the moment of high water, the direction of the current (in degrees) and speed (in knots) are found in the Atlas.

When sailing, the elements of tidal currents must be determined in advance; It is recommended to compile a table of currents for pre-calculated moments (after 1 hour) corresponding to the ship’s countable positions.

Below is an example of a table of tidal currents (Table 7).

The difference between zero depth and the high water level is called the high water height hPV. The difference between zero depth and low water level is called low water height hMV. The difference between the heights of high water and the following low water is called the magnitude of the tide B = hPV hMV. The time between two adjacent moments of high or low water is called the high tide period.

If this work does not suit you, at the bottom of the page there is a list of similar works. You can also use the search button

rocks of classical navigation. Pilot.

18. Tidal phenomena

and their accounting in navigation.

The surface of the oceans is not at rest, but periodically changes its position and fluctuates. This occurs under the influence of various processes and forces, which can be combined into the following main groups:

Geodynamic and geothermal phenomena in the earth's crust - earthquakes and seaquakes, volcanic eruptions (tsunamis), rise and fall of land (tectonics), heat flow through the ocean floor.

Mechanical and physico-chemical effects on the ocean surface solar radiation, changes in atmospheric pressure, wind, which causes surge fluctuations, precipitation, coastal runoff, etc.

Cosmic (astronomical) tidal forces, which are the main ones in tidal phenomena.

The concept of tides and terminology

Tidal phenomena are complex wave movements of ocean water masses. The consequence of these movements is periodic changes in level and currents.

Tidal phenomena occur due to the action of tidal forces between the Earth, Moon and Sun. The tidal force of the Moon is 2.17 times greater than the tidal force of the Sun (due to its distance), therefore the main features of tidal phenomena are determined mainly by the relative positions of the Earth and the Moon.

Physiographic conditions have a significant influence on the magnitude and nature of tidal phenomena in each specific place: depths, coastline, the presence of islands, and others. Due to the influence of physical and geographical conditions, the nature of the tides can vary within very wide limits. Thus, in the Baltic Sea they are practically absent; in the Bay of Fundy, located at approximately the same latitude, level fluctuations reach 18 meters.

Tidal phenomena are characterized by two main factors:

Level changes;

Tidal currents.

Both sides of this process are interconnected, however, due to the lack of a unified theory, tidal level fluctuations and tidal currents are studied separately.

Tidal phenomena have a great impact on navigation and navigation safety, therefore information about them is regularly published in special manuals. In order to use them correctly to solve various navigation problems, navigators must have a good understanding of the nature of this phenomenon.

Tidal fluctuations can be represented graphically.

On the daily tide graph, the x-axis is time, t , and along the ordinate axis is the height of the tide, h , above the conventionally accepted level zero depth, 0 gl.

The process of sea level rise is called high tide, low tide low tide.

The highest level position at high tide is called full water PV, low tide low water MV.

The difference between zero depth and full water level is calledhigh water height h PV.

The difference between zero depth and low water level is calledlow water height h MV.

The difference between the heights of high water and the following low water is calledthe magnitude of the tide

B = h PV - h MV.

Beyond zero depths on Russian nautical charts on tidal seas, the lowest theoretical level (LTU) is adopted the lowest level possible under astronomical conditions, that is, according to the relative positions of the Earth, Moon and Sun.

The time between two adjacent moments of high or low water is calledhigh tide period.

Depending on the size of the period, tides are divided into daily, semidiurnal, mixed, irregular semidiurnal, irregular diurnal and anomalous.

Daily allowance tides (C) those whose average period is equal to the lunar day (24 hours 50 minutes). Diurnal tides occur most often in the Pacific Ocean.

Half daily allowance tides (T) are those whose period is equal to half a lunar day (12 hours 25 minutes). Semi-diurnal tides are observed along the Murmansk coast of the Barents Sea, throughout most of the White Sea and almost throughout the entire Atlantic Ocean.

At semidiurnal tides, high water occurs twice a day, high water, and low water, low water, twice a day. Since both PV and both MV have different heights, they are designated as follows:

ERW high full water;

NPV low full water;

WWII high low water;

NMV low low water.

The heights of PV and MV of semidiurnal tides above zero depth are designated as follows:

h ERW height of high full water;

h IVC height of low high water;

h WWII height of high low water;

h NMV height of low low water.

Mixed tides are those whose period changes from semidiurnal to daily during the lunar month. Mixed tides are divided into irregular diurnal (ID), in which the diurnal period predominates, and irregular semidiurnal (SI), in which the semidiurnal period predominates.

Abnormal tides those in which the nature of the rise and fall of water is complicated by shallow water, these are daily shallow tides (SM) and semidiurnal shallow tides (SM). Abnormal tides are observed in some ports of the English Channel and in the White Sea.

The magnitude of tide B varies throughout the month, and on some days it reaches its maximum value, and on others it reaches its minimum. The magnitude of the tide varies according to the phase of the Moon, that is, it depends on the relative positions of the Earth, Moon and Sun.

The highest high water and the lowest low water, that is, the maximum tide (B) is observed after full moons and new moons, that is, when the Earth, Moon and Sun are approximately in the same straight line, and the tidal forces of the Moon and Sun add up. Such periods are called syzygy (gr. sizigia connection).

The lowest high water and the highest low water, that is, the minimum tide, are observed after I and after IV quarters in the phases of the moon. At this time, the Moon and the Sun are located approximately at right angles to the Earth, and the tidal forces of the Sun weaken the tidal forces of the Moon. Such periods are called quadrature (lat. quadrature fourth part, quarter).

The tides are also influenced by the declination of the Moon. At high declinations of the Moon, tides are called tropical , and when the Moon passes through the equatorequatorial.

The time interval between the moment of the upper or lower climax of the Moon and the moment of the onset of full water on a given meridian is calledlunar interval Tl.

The average of the lunar intervals on syzygy days, calculated from a large number of observations, is calledport application hour IF.

The following terms are used to characterize tides over time:

t PV moment of full water;

t MV moment of low water;

T r time of level rise time from the moment of low water to the moment of high water:

T r = t PV t MV;

T p time of level drop time from the moment of high water to the moment of low water:

T p = t MV t PV;

T st level standing time time during which the level, having reached a certain height, remains unchanged.

Russian tide tables

Tidal phenomena in different areas of the world's oceans have been studied differently. Depending on the degree of study, all points are divided into three groups:

Main points (ports) for which detailed tide data is available.

Additional points linked to the main ones, for which the tides are calculated through the main point.

Points for which applied clocks are given, from which it is possible to calculate the moments of PT and MV and their heights, based on the moments of the culmination of the Moon.

The Oceanographic Institute annually publishes Tables from which it is possible to pre-calculate the moments and heights of tides. Tide tables are published in four volumes:

Volume I . Waters of the European part of Russia.

Volume II . Waters of the Asian part of Russia.

Volume III . Foreign waters. Atlantic, Indian and Arctic oceans.

Volume IV . Foreign waters. Pacific Ocean.

Volume I and Volume II each consist of three parts:

Part I - Tides at main points.

Part II - Amendments for additional points.

Part III - Tidal currents.

Volume III and Volume IV Each consists of two parts:

Part I - Main points.

Part II Additional items.

At the beginning of each volume general information about tides is given, and at the end there are auxiliary tables and an alphabetical index of points.

The General Information section provides the following information:

The influence of hydrometeorological conditions on tides;

Basic terms and designations;

Information about tidal inequality;

Criteria that determine the nature of the tides;

Examples of using tide tables.

Tide tables from different years of publication may have differences in general information, so it is necessary to familiarize yourself with them each time you use new tables.

B I Part “Tides at the main points” shows the moments and heights of high and low waters for every day of a given calendar year for the main points, a list of which is given in alphabetical order on the back cover of the table.

In II Part “Corrections for Additional Items” contains corrections for moments and heights, introducing which into selected ones from the part I information on tides in the main port; you can obtain data on the moments and heights of PV and MV at additional points.

The “Auxiliary Tables” show:

Interpolation table for calculating the level at moments intermediate between MV and PV;

Average heights of syzygy and quadrature PV and MV and mean sea level (MSL) for some points;

Tables of mean sea level corrections for seasonal changes and atmospheric pressure;

Tables for converting standard time to local time;

Feet to meters conversion tables;

Astronomical data (phases, declination, perigee and apogee of the Moon).

Problems solved using tables

Determination of the moment and height of high and low waters at the main point.

Determination of the height of the tide level at any intermediate moment between MF and SW at the main point.

Determination of the moment and height of high and low waters in an additional paragraph.

Determination of the height of the tide level at any intermediate moment between MF and MF at an additional point.

Teacher of the highest category Kisenkov Vladimir Ilyich

Some rivers flowing into the seas experience significant tides. Rivers can be thought of as natural channels through which tidal waves travel upstream. The propagating wave is greatly modified by shallow depths, currents, and changes in the contours of the river bed. In some rivers, tidal waves travel over considerable distances (up to several hundred kilometers).

Sea water arriving with a tidal wave, being heavier, first spreads along the bottom, under river water. The rise in water level at the mouth of the river at high tide creates a tidal current, which stops the river's own flow and even reverses it.

If a tidal wave enters the river over a long distance, then the rise in the water level in the river continues even when the tide has already set at the mouth. At low tide, the direction of the ebb current coincides with the direction of the river flow.

Tidal flow at river mouths, compared to ebb flow, takes less time. Thanks to this, high water lasts longer, which makes it possible for sea vessels to enter river mouths.

During periods of high water, tidal phenomena at river mouths decrease and sometimes disappear completely.

The speed of tidal currents at river mouths often exceeds the speed of tidal currents in the sea. This occurs due to the fact that due to the decrease in the living cross-section of the channel, the magnitude of the tide increases significantly. During the period when the tide is low, due to the slope of the water surface and the combined flow of sea and river water, the speed also increases significantly. At the mouths of the northern rivers of the USSR, these speeds reach 2 m/s or more.

When a tidal wave propagates up a river, its shape sometimes changes very sharply due to the fact that the speed of propagation of the crest is greater than that of the trough. The front slope of the wave reaches a height of more than l-2 m and becomes very steep, almost vertical. The wave quickly, sometimes at a speed of up to 15-20 km/h, spreads up the river, breaking in small places with loud noise. Often the first wave is followed by a second and third wave, but of lower height and at lower speed. As they move upward, the waves gradually become smaller. This phenomenon of the propagation of a tidal wave is called boron in England, and mascare in France.

At the mouth of the Northern Dvina, a slightly different phenomenon is observed - manikha. During maniha, after low water, the rise in level stops and remains almost unchanged for about two hours. After this, the level rises again until the water reaches full water. During the day there are four rises and four decreases in the level. Phenomena similar to Maniha are observed on some other rivers.

When navigating in sea estuaries, navigators are required to take into account changes in water levels and the uniqueness of currents in these areas. Tidal currents are periodic horizontal movements of water under the influence of tidal forces. These currents have strict periodicity and cover the entire thickness of water from the surface to the bottom, only slightly decreasing at depth.

Its own - speed due to friction at the bottom. The nature of tidal currents in the open sea and off the coast is different.

In the open sea there is no change in currents. Tidal currents do not stop here, but their direction and speed, for example in the northern hemisphere, constantly change clockwise (in the southern hemisphere, vice versa). Currents “bypass” the compass card during semi-diurnal tides in 12 hours 25 minutes, and during daily tides in 24 hours 50 minutes. Such flows are called rotational.

In the open sea with sufficiently large depths, where the tide is low, the speed of tidal currents is relatively low (0.2-1.0 km/h).

The highest speed of tidal currents is observed during high and low waters. During the syzygy period, the speed of tidal currents increases sharply, and during quadratures it decreases by two to three times. As the declination of the Moon increases and it moves from apogee to perigee, the speed of tidal currents increases.

Near the coast, in narrow bays, bays or straits, as well as at river mouths, tidal currents change direction and are called reverse currents.

With a semi-diurnal cycle of tidal currents, the movement of water masses occurs with an increase in speed for 3 hours, and then over the next 3 hours the speed decreases, after which the direction of the flow reverses. During the daily cycle, the movement of water occurs in one direction for 12 hours. In the first 6 hours of the period, the flow speed increases, and in the second 6 hours it decreases.

A change in the direction of reverse currents occurs around the moment of high or low water or at an average level. During the period of change in reverse currents, there are moments when there is no current at all and the water is at rest.

Tidal currents in narrow areas have significantly higher speeds compared to the open ocean. Near the coast of the Soviet Union, in narrows and straits, the speed of tidal currents reaches significant values ​​(5-13 km/h). For example, in the Kara Sea near the island. Belyi tidal current speed reaches 6.5 km/h, near the island. Begichev in the Laptev Sea area - 4.5 km/h, in the throat of the White Sea - 4.5 km/h, and in the La Perouse Strait - 9 km/h.

When leaving the straits or from behind capes, strong tidal currents, diverging like a fan, create peculiar whirlpools, countercurrents, and crushing water with foamy stripes called ripples. Suloi are steep waves with reverse surges and whirlpools that occur in some areas with strong tidal currents. Suloi are observed in almost all straits.

Small swells are observed in the Black Sea (in the Kerch Strait), stronger ones in the narrows off the Pacific coast. Suloi reach their largest sizes in shallow water areas with strong reverse currents, for example in the Kuril Straits. Particularly strong suloi are created by river currents flowing into the seas, for example in the Kara Sea near the Gulf of Ob and the Yenisei Bay.

Rice. 8

The formation of ripples is usually associated with the interaction of two counter flows of water (Fig. 9). In the frontal zone, vortices are formed, emerging to the surface in the form of random waves, the energy of which is greater, the higher the speed of the flows.

Suloi are also created as a result of the flow entering shallow water (Fig. b), when high speeds, vortices and waves arise on the surface of the water. The largest rips of this type are created on tidal currents, when the flow covers the entire thickness of the water from the surface to the bottom and carries great energy. The energy of such a flow, when entering shallow water, due to a decrease in cross-section, is concentrated in a smaller volume of water and creates random waves.

Suloi, created when two water flows meet, are observed near the bays of the northern coast of the Kola Peninsula. Here the tidal flow, entering the bays, creates a slope of the water surface. - The current caused by this slope meets the tidal current and ripples are created in the throat of these bays and bays.

Suloi are dangerous for swimming. Even large ships experience erratic rolling and yaw. High waves can cause great damage to deck machinery and equipment. Crossing the Suloi area by small vessels can cause the death of the latter. When approaching suloi areas, boaters must take into account the phases of the tide and choose the time of passage through the dangerous area.

In some cases, whirlpools are created in the coastal strip of the sea with a complex bottom topography, winding coastlines and a certain combination of tidal current directions. Whirlpools are strongest during syzygy periods and with corresponding wind directions. Just like riptides, strong whirlpools in narrows and among islands pose a danger to navigation (especially for small vessels). Whirlpools are observed in the White Sea, in the Matochkin Shar Strait, in the Yenisei Bay, in the Gulf of Ob, in the Khatanga Bay and other places.

We learned to read tide maps and calculate. But this is not enough for comfortable yachting. In yachting, you must be able to take into account the direction and speed of the tidal current when planning your trip. This is what we will do now. Let's imagine that the Earth is absolutely round and all covered with water. If so, then the two formed “humps” are on opposite sides of the Earth will smoothly increase and decrease under the influence of the attraction of the Moon and the Sun, and the Earth will make its full revolution under this blanket of water in one day. The speed of this movement at the equator will be: equator length/24 hours = 900 knots!

However, don't be alarmed, this is the speed of the wave, not the speed of the water. In the absence of continents, everything would be very calm - small changes in water levels and almost complete absence of tidal currents. The situation changes radically, as we noted earlier, when interacting with the coastline. All the enormous energy of the tides hits the shores of the continents and, depending on the shape of the coastline and the topography of the seabed, raises water to a height of up to 17 meters in Fundy Bay (USA and Canada). It is obvious that such rises of water are accompanied by very rapid movement of huge masses of water and, accordingly, a rapid and changing direction current. And when narrow passages between the islands stand in the way of the tide, the current reaches a speed of 20 knots.

Just as with tide levels, humanity has accumulated enough information to predict the direction and speed of tidal currents.

For us, besides, of course, computer programs, there are two more main sources of information about the flow. These are already well-known tide maps (almanacs), containing Atlases of tidal currents, and tidal rhombuses.

Tide charts. Tidal current atlases.

Tide maps and atlases of tidal currents give a very clear picture, or rather 12 pictures: like frames from a cartoon, they show a consistent change in the direction and strength of the current in the zone you have chosen. These “frames” appear to be taken at one-hour intervals, ensuring coverage of the entire high tide period. As an example, the figure shows a spread of the tide map from the REEDS almanac for the Channel Islands.
Please note that the time axis in this example is set relative to HW in Dover (the port relative to which the time is set is called the Reference Port).

The time axis is always set relative to HW in the Reference Port.
To determine the real time to which each picture belongs, you must first obtain from the tide charts (almanac) the HW value closest to the time you are interested in in the Reference Port, and then under each picture sign the value of the time to which it belongs. Do not forget about the possible adjustment of daylight saving time and, most importantly, that a port that is not only far from the place you are interested in, but even located in a different time zone, can be selected as a standard port.

Don't go wrong with your timing! The error may last several hours and therefore may be critical!
Now let's look at one square of the tide map in more detail. Obviously, the arrows in the figure indicate the direction of the flow. Intuitively, the longer and thicker the arrow, the stronger the tidal current, but the four-digit number separated by a comma next to the arrow requires some explanation. You and I know very well that at the same time, both in syzygy and quadrature, the direction of the current should coincide, but the speed of the tidal current will differ, since during the same time more water must pass through syzygy.

So, the mysterious inscription next to the arrow on the tide maps shows the values ​​of the tidal current velocity at syzygy and quadrature, separated by commas. For better readability of tide maps, cartographers try to save symbols, so speeds are indicated in tenths of a knot. Thus, the inscription 58.97 tells us that at this time in this place the speed of the current is 5.8 knots at quadrature, and 9.7 at syzygy. Agree that, for example, such a record is 5.8; 9.7 would be much more bulky.

Please note: these are real values; it is not for nothing that the tide maps in this place proudly display the inscription Race of Alderney and the warning Heavy Overfalls! Avoid appearing in such places when there is a strong tidal current and headwind. The collision of two elements generates large crashing waves. Be prepared for the fact that whirlpools can turn the boat around at any moment, and if you are sailing, beware of involuntary jibes.

An inquisitive reader should have a question: how to determine the speed of the tidal current if we are planning a transition not on syzygy or quadrature, but on another day? The answer is simple: you need to solve the interpolation problem. We will look at how this is done below.

Another designation you will see on tide maps is slack. As follows from the translation, the tidal current is absent or negligible.

As an example, let's determine when there will be a favorable current to leave Alderney Island from Vgaue Bay if we go to Cherbourg on September 20, 2012. The crossing range is about 30 miles. And if we assume our speed is 6 knots and do not take into account the speed of the tidal current, then we will need 5 hours. If you plan the crossing so that the current is favorable the whole way, you can save a lot of time and fuel if you have to go under a motor. And if we make a mistake and find ourselves there when the current is rushing towards the island of Jersey at a speed of 7 knots, then we simply cannot cope with the current, and we will be carried south, where we will be forced to wait for the tidal current to change.

Based on the above, it seems appropriate that the time of departure from Alderney corresponds to the picture of the tide charts, which says HW-5. At this time, the current is already becoming favorable in direction and will intensify, these are pictures HW-4, HW-3 and HW-2.

Now we need to solve the following problem: what time will it be on the clock in Alderney when I am in Dover (Reference Port) will it be HW-5?
To do this, open the tide maps (almanac) for Dover for the date we are interested in - let it be September 20. First of all, we make sure that Alderney is in the same time zone as Dover. HW on this day falls on 0101 and 1326. We are interested in the time five hours earlier, and we also need to add one hour of summer time, i.e. favorable time to leave:

0101-0500+0100=2101 of the previous date

1326-0500+0100=0926 today.

Decide when it’s better for you to go - last night or today morning!

These are not all methods for determining the direction and speed of tidal currents. Many yachtsmen prefer a simpler method. . But more on that in the next article.

TIDAL CURRENTS

TIDAL CURRENTS

Currents arising as a result of tidal phenomena, periodically changing direction and speed and reaching the highest speeds in coastal areas and in narrow areas.

Samoilov K. I. Marine Dictionary. - M.-L.: State Naval Publishing House of the NKVMF of the USSR, 1941

See what "TIDAL CURRENTS" are in other dictionaries:

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Collier's Encyclopedia

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