GB2329496A - Tidal calculator - Google Patents

Abstract

A tidal calculator comprises a base marked with horizontal lines corresponding with times and vertical lines corresponding with water depths, a clock 1 rotatable in the base so that the times of high and low water can be set against the uppermost and lowermost horizontal lines respectively, and an adjustable bar 2 whose ends can be located on the upper and lower lines to indicate the depths of water at high and low tide respectively. Positions along the bar thus indicate the depth of water at any particular time. Whether the water is rising or falling and the potential strength of current can also be ascertained from inspecting the device.

Description

BACKGROUND Successful cruising by boat on Tidal Waters is dependant upon, availability of Tidal Information, and a Skippers experience and ability to use tizat information.

A Skipper must at all times be able to ascertain, whether or not, there is sufficient depth of water for his vessel to float, without risk of collision with submerged objects, (including the possibility of running aground.) at any time and position ofhis passage, furthermore, he must be able to use Tidal FLOWS to his advantage, and avoid being trapped or disadvantaged by them, le. Strong foul tides.

Tidal Information may be obtained from Tide Tables and Nautical Almanacs, together with Tidal Atlases and Information shown on Charts. The Skipper may then take several gears of stud in order to use this information to advantage.

Publications required Tide Tables give Times and Heights of High and Low water Nautical Almanac gives Tidal Curves four vnrious Ports Tidal Atlases give Tidal Rate and Direction for any gien time Charts give Tidal depth relative to Chart Datum Armed with this knowledge, a Skipper who has successfully learned to use the information, will (may) draw up a graph to establish the Tidal Height and Range for a chosen Port or Area, and then another graph, on a Tidal Curve, to ascertain the height for that area af any given time.

The problem is that although an accurate prediction may be obtained, the graph has to be updated, as required, at all points on the passage, and the Skipper has to have the knowledge and ability to do this.

In many, if not most instances, these graphs are not drawn at all, either because the Skipper does not have the knowledge, or that he is so familiar with his local cruising area that the information is not required by him4ier.

But the information will become beneficial, if not crucial, if bad weather etc. makes the Skipper retreat to a Port of Shelter with which they are not familiar. These conditions are often accompanied by a troubled sea, when it is often impossible to go below to draw graphs.

Also, in some sailing areas renown for their strong tidal currents and/or rock strewn approaches, the information is of vital importance. Charts of these areas will show rocks etc. of importance to the cruising sailor, some will be uncovered at all states of the tide and are not a particular hazard, in fact are beneficial to use as navigational marks.

The danger lies with rocks that are awash between High and Low water, and to know which of these lies just below the surface at any given time, waiting to take a lump out of an unsuspecting hull the sailor must know the Tidal Height, for that time and be kept continually updated until they have sailed clear of the arez It is also important to know whether the height is increasing or decreasing, and whether the flow is strengthening or weakening, as well as the relative strength at the time.

A Skipper who crises foreign waters will be faced with a further problem, ie. that of a change in Chart Datum.

71ereas Great Britain uses Mean Low Water Springs (MEWS) as its datum, and Mean High Water Springs (MHWS) to refer to heights of bridges, towers, overhead cables erc. some foreign charts use 'Mean Level' (ML) for both Chart Datum and Heights. This is a calculation of the average of Mean High Water Springs (MHWS) Mean Low Water Springs (ML WS) Mean High Water Neaps (MH'?\) and Mean Low Water Neaps (ML wN) TIDAL CALCULATOR This invention relates to an instrument to calculate the heights of tides by mathematical percentages or fractions, and incorporates other tidal information.

The use of average percentages or fractions to predict the height of a tide at a given time is a well known formula.

However, this would normally require substantial mental arithmetic, a calculator or paperwork, and the drawing of a graph on paper for each time or depth of the tide that the information is required.

According to the present invention, a means is provided to ascertain the height of the tide for any given time, or for the time to be ascertained for any given height, without reference to any other means, mental arithmetic, paperwork or graphs.

This is adileved by mounting an adjustable scale to indicate the passage of hours (1) together with a graph using accepted proportions, and an adjustable device, 629 to represent a line to cross the graph relative to various reference points.

A specific design is now shown b way of example.., Figure 1. (Page 1/1) shows a rotatable circular dial, tl) marked out in equal proportions of 1 to 12, set on the side of the graph, the height of which is equal to the diameter of the dial, with horizontal lines spaced at the following proportions.

Ist line to 2nd line = 1/12th. of height of graph.

2nd line to 3rd line = 1/6th. of height of graph.

3rd line to 4th line = 1/4th. of height of graph.

4th line to 5th line = 1/4th. of height of graph.

5th line to 6th line = 1/6to. of height of graph.

6th line to 7th line = 1/12th. of height of graph.

and vertical lines set at equal spacings to incorporate numbers relevant to the heights of tides envisaged.

A bar set onto a pivot pin (2) is located in one of a number of holes incorporated in the middle line, which allows it to be set to correspond with numbers marked above and below the graph.

A clock mechanism is incorporated in the dial (1) together with an hour hand, by way of design, which allows updated information to be obtained without further adjustment.

Referring to Figure 1. Drawing 1/1. The TIME of High Water has been set at 11.30. kv rotating the dial on the left. The HEIGHT of high Water has been set at 9.5 and Low Water at 2. b locating and adjusting the bar on the right, (2) shown as a bold tine angled across the graph.

We will assume for the purpose of example that the numbers represent metres, which is now the most used measurement The internal clock maintains the time, Local or Greenwich Mean Time or other, as preferred, and the hour hand indicates the current time to be 1.30.

The pointer is 2 divisions past the High Water mark (HW) indicating 2 hours after High Water. As it is travelling from the HW mark to the L W mark indicates that the tide is going out.

As it is in the top section of the graph it indicates that the strength of the tidal flow is increasing, and as it enters the Ingest division, it indicates the strongest rate offlow per hour.

Following the horizontal line from the pointer to the graph bar, then vertically upwards, an indication of 7.6 metres of tide is given for the current time.

A further example, for instance to ascertain when a sand bar would uncover at say 3 metres, would be to follow a line vertically upwards from the 3 to the graph bar (2), then an assumed line horizontallp to the dial (I), which indicates that the sand bar would uncover at 4.15.

In order to obtain information from the instrument, the height and time of High and Low water must be ascertainedfor die required Port or Area, the dial (1) is then rotated so that, the High Water time corresponds with the HW mark shown above the dial. The bar and pivot (2) on the graph are set so that a line is established between the height of High Water and Low Water.

By assuming a line visually from the outer edge of the dial corresponding to the selected time, horizontally along the graph to the bar, then vertically to the upper or lower edge of the graph, the number marked will indicate the depth of water for that time, being in metres, feet or fathoms dependant upon the information used to set die instrument at the outset.

The time for any height can be obtained by taking an assumed line visually from any marked depth number, vertically to the line of the graph bar (2), then horizontally to the dial (1) wherebv the time will be indicated.

The inclusion of a clock mechanism indicates the current time by means of an hour kand, and if assumed lines are followed horizontally then vertically will show the CURRENT depth. The rotation of the hour hand dockwisefrnm L W to 11W indicates that the tide is coming in, or from HWto L us going out.

The vertical distance between the horizontal lines indicate the proportionate strength of the Tidal Flow, the greater the distance the greater the strength, the lesser the distance the lesser the strength.

The centre line indicates the Mean Water Level, and any calculations incorporated on the upper part of the graph indicate that the Tidal Flow is strengthening, or on the lower part of the graph weakening.

Claims (1)

1. l/An instrument which comprises an adjustable scale to indicate die passage of hours together with a graph using acceptable proportions, and an adjustable device, to represent a line to cross tlze graph relative to the various reference points.

   2/ An instrument as claimed in claim I whereby a clock mechanism is incorporated to keep solar time and approximate lunar time updated.

   3/An instrument ns claimed in claim I which does not require correction or adjustment during the currency of die tidal cydefor tlte chosen area, but can easily be adjusted to that of another area, or interpolated between two tidal areas.

   4/ An instrument as claimed in claim I to make use of previously known formula in an easy to read format relevant to the information required.