GB2414076A - Navigation plotter - Google Patents

Abstract

A rectangular base plate 28 is marked with a central scale 30 and parallel lines 31 a distance apart to be visually traced from one end to the other end. A cursor (20, fig 4) fitted to the commencement of the scale is fitted removably to a guide under a transparent rectangle on which are a central scale and a compass rose 13 fitted at zero of the scale. A tide scale 10 is fitted rotatably to the centra of the compass rose. A ground track course is plotted on the chart and corrected for variation, then the plotter is laid on a tidal atlas without moving the rose and the tide scale 10 is rotated in the direction of the tide. (this will be magnetic) The base plate 28 is clipped into the guide under the transparent plotter and the boat speed represented on the scale is indexed to the tidal rate on the tide scale. The correct water track course to counteract tide is indexed on the compass rose by the parallel line bisecting the rose or closest to. Every subsequent change of saillboat speed is indexed to the tidal rate and the fresh course read in seconds.

Description

24 1 4076 Navigation instrument providing vector triangles within the

parts of which the instrument is comprised.

This invention relates to a navigation instrument providing vector triangles within the parts of which the instrument is comprised.

Navigation proffers are available in a variety of designs and are commonly used applied to the surface of a map or sea chart on which is generally printed at least one compass rose as well as meridians of longitude indicating north to south alignment and parallels of latitude indicating east to west alignment.

A particular navigation proffer in common use consists of two main parts. One part is a flat oblong rectangle of transparent material with a line marked lengthways from one end to the other and positioned midway between the two longest edges. The second part is a flat transparent disc no larger in diameter than the width of the rectangle and graduated into 360 around the outer diameter thereby providing a compass rose.

This compass rose is marked with a grid fommed by north to south and east to west lines commensurate with those indications marked around the outer diameter. The compass rose is fixed at the centre rotatably to the centre of the upper surface of the rectangle previously described.

The method of determining the compass directions between two positions on a chart with this instrument is as follows: A long edge of the rectangle is placed in line with those positions and a line is drawn along the same edge. The rectangle is then moved along the drawn line until the grid on the compass rose can be aligned with a meridian of longitude or a parallel of latitude marked on the chart. The indication north on the compass rose is thereby correctly aligned with the direction north on the chart. The compass directions between the two relevant positions are indicated on the compass rose by the central line marked on the rectangle.

The method of plotting a given compass direction from a particular position on a chart is as follows: The compass rose is rotated until the given compass direction coincides with the central line on the rectangle. Then the instrument is laid on the chart with one long edge adjacent to the particular position while the indication north on the compass rose aligns with the direction north on the chart. North alignment is effected by referring the compass rose grid to a line of latitude or longitude. The plotting line is drawn on the chart from the particular position along the long edge of the instrument towards the given compass direction as indicated on the compass rose by the central line on the rectangle.

Two exercises for which a navigating proffer is used will now be described as for navigating a vessel allowing for tidal conditions, although the same description may apply as for navigating an aircraft allowing for wind conditions. Both exercises refer to plotting vector triangles on a sea chart.

One exercise is to establish the water track course to steer in consideration of tidal influence in order to maintain a desired ground track and provide an estimation of the nautical miles covered over the ground track in one hour.

The method of conducting this exercise is as follows: A line is drawn from the course commencement position directly towards the objective position (ground track). The tidal rate and direction in the area at the appropriate time is observed from the chart information or tidal atlas and a second line is drawn from the course commencement position in the direction the tide is expected to run. The distance the tide is expected to run in one hour (tidal rate) is measured on the chart scale and this distance is marked on the second line as measured from the course commencement position. The distance the vessel is expected to travel through the water during the same hour is measured on the chart scale and this distance is marked on the ground track line as measured from the mark indicating tidal rate on the second line. A third line is drawn between these two marks. The compass direction of the third line towards the ground track line is then established as the water track course the vessel must be steered in order to maintain the desired ground track, and the position where the water track line converges with the ground track line is the distance, as measured from the course commencement position, the vessel is expected to travel over the ground track is the following hour.

Another exercise is to estimate a vessel's position in consideration of tidal effects on the previous water track course.

A method of conducting this exercise is as follows: A line is drawn on the chart from the known course commencement position in the direction the vessel is steered through the water (water track). The distance travelled through the water by the vessel in one hour is measured from the chart scale and this distance is marked on the water track line as measured from the course commencement position. The tidal rate and direction for the area at the appropriate time is observed and a second line is drawn in the direction the tide runs from the mark indicating the distance travailed by the vessel in one hour on the water track line.

The distance the tide runs within the same hour is measured from the chart scale and this distance, as measured from the mark on the water track is marked on the line of the tidal direction. This mark on the line of the tidal direction identifies the estimated position of the vessel after one hour and a third line drawn from the course commencement position to the estimated position indicates the course and distance over the ground (ground track) the vessel has covered during this time.

Both exercises previously explained describe plotting vector triangles measured in nautical miles according to the scale of the chart. Some navigating plotters have a scale of units marked along an edge and a vector triangle may be measured and drawn more conveniently in these units without frequently referring to the chart scale.

The position of the vessel at a particular time may then be established by observing the number of units comprising the ground track and measuring the equivalent number of miles from the chart scale. This distance in miles is marked on the line of the ground track as measured from the course commencement position to establish the position of the vessel at that particular time.

Plotting a vector triangle on a chart most of the time is a simple procedure, such as when planning a voyage while in port or at sea in moderate conditions especially with more than one person on board to manage the boat while the navigator attends to the chart table in the cabin. There are circumstances however when it is difficult and sometimes impossible to plot a vector triangle on a chart. Such circumstances may include a single handed navigator steering a boat in rough weather conditions and having no opportunity to leave the helm. In another case it may be necessary to maintain a sailing boat's course along a particular ground track in constantly varying wind strengths resulting in the boat's speed changing more often than a fresh course correction vector can be drawn.

There have been a number of instruments in the past designed to provide vector triangles within the parts of which such instruments are comprised.

Most examples of such instruments involve manipulating locking devices attached to them so that they cannot easily be used with one hand by the navigator while steering the boat with the other hand. Other examples are not suitable for being used to produce vector triangles held in the hand as well as applied to the surface of a chart for conventional plotting.

According to the present invention there is provided a navigation instrument designed to produce navigating vector triangles within the parts of which the instrument is comprised without the need to manipulate locking devises and such vector triangles being produced by two optional methods. One method allows the instrument to be used with one hand while another method allows the instrument to be used more compactly on a small chart table. Additionally the instrument may be used as a navigating plotter applied to the surface of a chart as a conventional plotter.

A specific embodiment of the invention will now be described by way of example with reference to accompanying drawings.

The individual parts of which the instrument is comprised will first be described separately.

Figure 1 shows a part called a tide/wind gauge (10) this being a flat transparent item marked with a central line (12) on which there is a regular numerical scale (11) commencing from a point at which there is a hole through the item (10).

Figure 2 shows a part called a compass rose (13) this being a flat transparent disc marked around the outer diameter into 360 (14). A line bisects the compass rose (13) from north to south (15) and another line from east to west (16). A hole is provided through the centre of the compass rose (13).

Figure 3 shows a part called a compass rose cursor (17) which may be as described here a flat transparent rectangle with two parallel sides bevelled inwards towards the uppermost surface on which an index line (18) is marked perpendicular to the two bevelled sides and aligned through a central hole.

Figure 4 shows a part called a base plate cursor (20) which may be as described here a flat transparent rectangle with two parallel sides bevelled inwards- towards the underside. An index line (21) is marked on the upper surface perpendicular to the two bevelled sides and aligned through a central hole.

Both items in Figure 3 and Figure 4 have been drawn oversize relative to other parts for the purpose of clarity.

Figure 5 shows a part called a middle plate (23) this being a flat oblong rectangle of transparent material measuring at least as much in width as the diameter of the compass rose (13) in Figure 2. This middle plate (23) is marked with a central line (24) extending lengthways from one end to the other end. A regular numerical scale (25) is marked adjacent to the central line (24) and commencing a distance from one end of the middle plate (23) approximately equivalent to half the diameter of the compass rose (13) in Figure 2. This scale stops short of the far end of the middle,, plate (23) and the measurement between graduations is the same as the scale (11) on the bdelwnd gauge (10) in Figure 1. The colour in which the middle plate (23) is marked is distinctively different from the colour in which the tide/wind gauge (10) in figure 1 Is marked. The uppermost surface of the middle plate (23) is provided with a slot angled Inwards towards the upper surface thereby forming a cursor guide (26) commensurate with and to retain the compass rose cursor (17) described in Figure 3.

This cursor guide (26) commences from a position whereby the index on the compass rose cursor (17) when fitted indicates zero on the middle plate scale (25) and extends fully to the far end of the middle plate (23) in accord with the middle plate scale (25).

Where the central line (24) on the middle plate (23) encounters the cursor guide (26) it may extend along the bottom of the slot or divide and extend each side. The underside of the middle plate (23) is provided with another cursor guide which in this example is identical in dimensions and position as the compass rose cursor guide (26). While the width of the compass rose cursor guide (26) angles inwards towards the upper surface of the middle plate (23) the width of the lower cursor guide angles inwards towards the under surface of the middle plate (23). This lower cursor guide is therefore commensurate with and to retain the base place cursor (20) described in Figure 4. The numerical indication (26) in Figure 5 maybe taken to indicate the outline of both the compass rose and base plate cursor guides in the top and underside of the middle plate (23). The angled sides of the cursor guides have been omitted from the drawings for the purpose of avoiding clutter. Additional scales may be marked around the outer edges of the middle plate (23) as such scales are useful in general navigation. Such scales are not referred to for providing vector triangles within the parts of which the instrument is comprised.

Figure 6 shows a part called a base plate (28), this being a flat oblong rectangle which may be approximately of the same dimensions as the middle plate figure Abut In any event tneltem must measure twice the led Scale (11) on the tidehNind gauge (10) in Figure 1. This base plate (28) is marked with a central line (29) extending lengthwaqs from one end to the other end. A regular numerical scale (30) is' marked adjacent to the central line (29) commencing a distance from one end and extending fully to the far end. The measurement between graduations Is the same as the scale on the tide/wind gauge (10) in Figure 1.

Parallel lines (31) are marked on the base plate running parallel to the central line (29). These lines are spaced closely together but of a sufficient distance apart for an observer to visually identify and trace any individual line from one end of the base plate (28) to the other end. The colour in which the base plate (28) is marked is distinctively different from the colours in which the middle plate (23) in Figure 5 and the tideAvind gauge (10) in Figure 1 are marked. The base plate (28) itself is visually distinct from all markings on the instrument. A fixing point or hole is provided through the base plate (28) at the point where the scale (30) commences.

Figure 7 shows the instrument assembled for using held in the hand to Determine water track courses or used for normal chart plotting.

Figure 8 shows the instrument for using held in the hand to determine Future ground track courses or used for normal chart plotting.

Figure 9 shows the instrument for using compactly on a small chart table to Determine water track courses or used for normal chart plotting.

Figure 10 shows the instrument for using compactly on a small chart table to determine previous or fixture ground track courses or used on a chart for normal chart plotting.

Figure 11 shows a further example design of a middle plate as shown in Fig 6 Figure 12 shows a further example design of a base cursor commensurate With the cursor guide in the middle plate in Fig 11.

lone means by which the components are connected together to form the instrument are as follows: The tidehvind gauge (10) in Figure 1 is placed on top of the compass rose (13) in Figure 2. The compass rose (13) is placed on top of the compass rose cursor (17) in Figure 3.

These three items are fixed together rotatably via the hole through each one by a rivet type fastener or similar. The compass rose cursor (17) fitted under this compass rose (13) and tidewind gauge (10) assembly is entered into the compass rose cursor guide (26) on the middle plate (23) via the opening at one end. This then allows the compass rose (13) and the tidehNind gauge (10 to slide along the length of the scale (25) on the middle plate (23) and be independently rotated. A short plug of a similar shape in section as the compass rose cursor (17) may be fixed into the open end of the compass rose guide (26) thereby permanently retaining the compass rose cursor (17) within the guide (26). The base plate cursor (20) in Figure 4 is placed on top of the base plate (28) in Figure 6. These two items are fixed together rotatably via the hole in each one by a rivet type fastener or similar. This base plate cursor (20) is entered into the base plate cursor guide in the urerside of the middle plate (23) via the opening at one end. This then allows the base plate (28) to slide and rotate along the length of the scale (25) on the middle plate and be observed visibly through the transparent components of Figures 1, 2, 3, 4, and 5.

Two optional methods by which the instrument is used for producing navigating vector triangles will now be described. The method of using the instrument with one hand will be described first. Two exercises will be described using this hrst method with reference to Figure 7 and Figure 8. Both exercises require the index line (18) on the co'mpass rose (13) cursor (17) to remain at zero on the middle plate (23) scale (25) Assuming a vessel is required to maintain a ground track in the direction north at a speed of 12.4 knots through the water. Assuming also the tide in the area at the same time is running in the direction of 300 at a rate of 2.6 knots.

In this exercise the central line (24) on the muddle plate (23) in the direction the scale (25) increases represents the required ground track line and the distance the vessel travels over the ground track in one hour is indicated on the middle plate (23) scale (25) by the index line (21) on the base plate (28) cursor (20).

The index line (18) on the compass rose (13) cursor (17) represents the course commencement position and the compass rose (13) is rotated until the required ground track course coincides with the ground track line (24) on the middle plate (23) in the direction the scale (25) increases.

The central line (12) on the tide/wind gauge (10) Indexes the direction of the tide on the compass rose (13) and the rate of the tide is ' ndexed on the scale (11) on the tide/wind gauge (10) by the central line (29) on the base plate (28).

The centerline (29) on the base plate (28) towards the central line (24) on the middle plate (23) determines the water track course to steer while the speed of the vessel is indexed on the scale (30) on the base plate (28) by the central line (12) on the tide/wind gauge (10).

A summary of the procedure is as follows:

The compass rose (13) is rotated until the desired ground track (north) coincides with the ground track line (24) on the middle plate (23) in the direction the scale (25) increases.

The tidelwind gauge (10) is rotated until the central line (12) coincides with the tidal direction (300 ) on the compass rose (13).

The base plate (28) is manipulated slidably and pivotably until the vessel's speed (12.4 knots) on the water track scale (30) coincides with the tidal rate (2.6 knots) on the scale (11) on the tide/wind gauge (10).

The compass direction of the water track line (29) on the base plate (28) towards the ground track line (24) on the middle plate (23) detemmines the water track course the vessel must be steered in order to maintain the desired ground rack.

This water track course is identified on the compass rose as follows: Since all the lines (31) on the base plate (28) are parallel to the centre line (29) representing the water track course, the parallel line (31) bisecting the compass rose (13) is traced visually in the appropriate direction to the graduation on the compass rose (13) to identify the water track course.

In this case the water track course is seen to be 010 . (approximately) The distance the vessel is expected to travel over the ground track in the following hour is indicated on the middle plate {23) scale (25) by the index line (21) on the base plate (28) Cursor (21). In this case the distance is seen to be indicted as 13.4 nautical miles. (approximately) In the previous exercise, determining the water track course to steer to counteract the tide is very fast in practice, since there is no need to draw lines on the chart.

The middle plate with compass rose in situ is detached from the base plate and laid on the chart with one long edge adjacent the course commencement and objective positions, withthe central scale increasing in the direction of the objective position. The compass rose is aligned to north and corrected for variation. If variation is west, the rose is rotated anticlockwise. If variation is east, the rose is rotated clockwise.Without moving the rose, the middle plate is laid on a tidal atlas with north on the rose aligned with north on the atlas, and the tide/wind gauge is aligned with the direction of the tide. Then the base plate is connected to the middle plate and the boat speed on the scale indexed onto the tidal rate. The water track course M is read from the compass rose as indicated by the parallel line.

f rom then on every change of sailing boat speed is Indexed onto the tidal rate and the water track course M, read from the compass rose.

These corrections actually take two or three seconds and can be elected with one hand. The boat speed on the base plate scale can be made to slide and index the tidal rate on the tide gauge,with the fingers of one hand under the base plate and thumb on the middle plate.

The same applies to changes of tidal rate.

Changes of tidal direction may be read from the sea chart as True and indexed on to the compass rose by holding the rose and base plate firmly between the fingers and thumb of one hand, and rotating the tide/wind gauge to the relevant tidal direction on the compass rose. If Magnetic variation is west the tide/wind gauge is rotated clockwise. If Magnetic variation is east the tide/wind gauge is rotated anticlockwise. The boat speed is indexed onto the tidal rate, and the advised water track course is read as Magnetic. This is because the required ground track course is previously corrected to Magnetc.

If it is required to correct the course for leeway and deviation, while attention is focused on the parallel line indicating the water track course M, the middle plate and base plate are held firmly together win one hand, then the compass rose is rotated to counteract leeway and duplicate the effects of deviation.

The parallel line will then indicate the course as Compass.(totally corrected) Since leeway and deviation are liable to change with courses, the rose is rotated to redact these corrections and re-establish the required ground track as Magnetic, ready for the next change of boat speed and course.

In the event of any exercise producing a vector triangle whereby no parallel line bisects the compass rose the correct course can be estimated within about one degree by reference to the line nearest to the centre of the compass rose.

The second exercise will described with reference to Figure 8.

To estimate a vessels position in consideration of tidal effects on the previous water track course.

The method of conducting this exercise is as follows: Assuming a vessel has maintained a water track course of 180 for a distance of 13.4 nautical miles through the water for one hour from a known course commencement position.

Assumir!g also the tide in the area has been running in the direction of 300 at the rate of 2.6 knots.

In this exercise the central line (24) on the middle plate (23) adjacent to the scale (25) represents the previous water track line and the distance the vessel has travailed through the water in the previous hour is indicated on the middle plat(23) scale (25) by the index line (21) on the base plate (28) cursor (20).

The index line (18) on the compass rose (13) cursor (17) represents the culmination of the previous water track course and the compass rose (13) is rotated until the previous course coincides with the central line (24) on the middle plate (23) in the opposite direction to the scale (25).

The central line (12) on the tidelwind gauge (10) indexes the previous direction of the tide on the compass rose (13) and the previous rate of the tideirepresentedon the scale (1 1) The central line (29) on the base plate (28) towards the tidel rate' on the tide/ wind gauge (10) represents the previous ground track and the distance the vessel has travelled over the ground is indicated on the scale (30) on the base plate (28) by the central line (12) on the tide/wind gauge (10).

Asummary of the procedure is as follows:

The compass rose (13) is rotated until the previous water track course (180 ) coincides with the water track line (24) on the middle plate (23) in the opposite director to the scale (25). The tide/wind gauge (10) is rotated until the central line (12) coincides with the previous tidal direction 300 on the compass rose.

The base plate (28) is manipulated slideably until the index line (21) on the base plate (28) cursor (20) coincide with the distance me vessel has travailed through the water represented on the middle plate (23) scale (25) (13.4 nautical miles). Then the base plate (28) is manipulated pivotably until the central line (29) representing the ground track coincides with the tidal rate (2.6 knot) represented on the scale (11) on the tide/wind gauge (10).

The compass direction of the ground track line (29) on the base plate (28) towards the tidal rate on the tide/wind gauge is then established as the previous ground track course. The parallel line (31) on the base plate (28) bisecting or closest to bisecting the compass rose (13) is traced visually in the appropriate direction to the graduation on the compass rose (13) to identify that course.

In this case the previous ground track course is seen to be 190 . (approximately) The distance the vessel has covered over the ground track is indicated on the ground track scale (30) on the base plate (8) by the centre line (12) on the tidehNind gauge (10).

In this case the distance is seen to be 12.4 nautical miles. (approximately) This course and distance may be plotted on a chart from the course commencement position to establish the vessels current position.

It w''' be apparent by observing Figure 7 and Figure 8 that should a vector triangle be produced in consideration of a slower vessel speed the overall surface area of the instrument as a whole is elongated. When the index line (21) on the base plate (28) cursor (20) is positioned at the lower end of the middle plate (23) scale (25) the base plate (28) extends considerably beyond the area of the middle plate (23). This elongated surface area does not matter when the instrument is hem in the hand of the navigator.

In consideration of using the instrument more compactly on small chart tables or fitted and used removably to bulkheads the optional method will now be described.

This optional method tends to result in a broadening rather than an elongation of the instrument as a whole in the composition of vector triangles. Since the instrument measures less in width than in length this broadening rather then elongating is more suitable for chart tables or bulkheads of limited surface area.

Two exercises will be described using this optional method with reference to Figure 9 and Figure 10. 1 to

Both exercises require the index line (21) on the base plate (28) cursor (20) to remain at Zero on the middle plate (23) scale (25) throughout.

Additionally both exercises commence whereby the direction of the scale (30) on the rotatable base plate (28) corresponds to the direction of the scale (25) on the middle plate (23).

The first exercise using this optional method will now be described with reference to Figure 9.

To determine the water track course to steer in consideration of tidal influence in order to maintain a desired ground track and provide an estimation of the nautical miles covered over the ground track in one hour.

Assuming a vessel is required to maintain a ground track in the direction of north at a speed of 7 knots through the water.

Assuming also the tide in the area is running in the direction of 300 at the rate of 2.8 knots.

In this exercise the central line (24) on the middle plate (23) in the direction the scale (25) decreases represents the required ground track line and the distance the vessel travels over the ground track in one hour is indicated on the middle plate (23) scale (25) by the index line (18) on the compass rose (13) cursor (17).

The index line (18) on the compass rose (13) cursor (17) ultimately represents the course commencement position and the compass rose (13) is rotated until the required ground track course coincides with the ground track line (24) on the middle plate (23) in the direction the scale (25) decreases).

The central line (12) on the tidelwind gauge (10) indexes the direction ofthe tide on thecompass rose (13) and rate of the tide represented on the scale (11) The centre line (29) on the base plate (28) towards the centre line (24) on the middle plate (23) determines the water track course to steer while the speed of the vessel is indexed on the scale (30) on the base plate (28) by the centre line (12) on the tide/wind gauge (10).

A summary of the procedure is as folio ws:

The compass rose (13) is rotated until the desired ground track (north) coincides with the ground track line (24) on the middle plate (23) in the direction the scale (25) decreases.

The tide/wind gauge (10) is rotated until the centre line (12) coincides with the tidal direction (300 ) on the compass rose (13).

The base plate (28) is manipulated pivotably while the compass rose (13) is manipulated slidably until the vessel's speed (7 knots) on the water track scale (30) on the base plate (28) coincides with the tidal rate (2. 8 knots) on the scale (11) on the tide/wind gauge (10).

The compass direction of the water track line (29) on the base plate (28) towards the ground track line (24) on the middle plate (23) determines the water track course the vessel must be steered in order to maintain the desired ground track. The parallel line (31) on the base plate (28) bisecting or closest to bisecting the compass rose (13) is traced visually in the appropriate direction to the graduation on the compass rose (13) to identify the water track course.

In this case the water track course is seen to be 20 . (approximately) The distance the vessel is expected to travel over the ground track in the following hour is indicated on the middle plate (23) scale (25) by the index line (18) on the compass rose (13) cursor (17).

In this case the distance is seen to be 8 nautical miles. (approximately) The second exercise using this optional method will now be described with reference to Figure 10.

To estimate a vessel's position in consideration of tidal effects on the previous water track course.

The method of conducting this exercise is as follows: Assuming a vessel has maintained a water track course of 180 for a distance of 8 nautical miles through the water for one hour from a known course commencement position.

Assuming also the tide in the area has been running in the direction of 300 at a rate of 2.8 knots.

In this exercise the centre line (24) on the middle plate (23) from zero on the scale (25) to the index line (18) on the compass rose (13) cursor (17) represents the previous water track line.

The index line (18) on the compass rose (13) cursor (17) indexes the distance the vessel has travailed through the water on the middle plate (23) scale (25) and the compass rose (13) is rotated until the previous water track course coincides with the centre line (24) on the middle plate (23) in the opposite direction to the previous water track line.

The centre line (12) on the tide/wind gauge (10) indexes the previous direction of the tide on the compass rose (13) and the previous rate of the tide representedon the scale (11) The centre line (29) on the base plate (28) towards the centre line (12) on the tide/wind gauge (10) represents the previous ground track course and the distance the vessel has travailed over the ground is indicated on the scale (30) on the base plate (28) by the centre line (12) on the tide/wind gauge (10).

A summary of the procedure is as follows:

The compass rose is rotated until the previous water track curse (180 ) coincides with the water track line (24) on the middle plate (23) in the opposite direction to zero on the scale. Then the compass rose (13) is manipulated slidably until the index line (18) on the compass rose (13) cursor (17) coincides with the distance the vessel has travelled through the water (8nautical miles) represented on the middle plate (23) scale (25).

The tide/wind gauge (10) is rotated until the central line (12) coincides with the previous tidal direction (300 ) on the compass rose (13).

The base plate (28) is manipulated pivotably until the centre line (29) representing the ground track coincides with the tidal rate (2.8 knots) represented on the scale (11) on the tide/wind gauge (10).

The compass direction of the ground track line (29) on the base plate (28) towards the tidal rate on the tide wind gauge (10) is then established as the previous ground track course.

The parallel line (31) on the base (28) bisecting or closest to bisecting the compass rose (13) is traced visually in the appropriate direction to the graduation on the compass rose (13) to identify that course.

In this case the previous ground track course is seen to be 200 . (approximately) The distance the vessel has covered over the ground track is indicated on the ground track scale (30) on the base plate (28) by the centre line (12) on the tide/wind gauge (10).

In this case the distance is seen to be 7 nautical miles. (approximately) This course and distance may be plotted on a chart from the course commencement position to establish the vessels current position.

A navigating vector triangle produced by the three scales as previously described is easy to discern in a full size instrument especially since each scale may be marked in a deferent colour against a white background surface of the base plate (28).

All scales illustrated in the drawings are examples only and are not represented as definitive.

It may however sometimes be expedient to produce a navigating vector triangle representing a time duration of less than an hour. As an example the distance a fast vessel travels through the water may be greater than the highest numerical representation of vessel speed on the water track or ground track scale, or the tide rate may be greater than the highest numerical representation on the tide/wind gauge scale (11). In such cases perhaps half the distance a vessel travels in one hour and therefore half the tidal rate may be indexed on the respective scales. A vector triangle thus produced still provides the correct water track or ground track course while the distance the vessel travels is indexed on the ground track scale as for a half hour.

The means of using the instrument as a navigating plotter applied to the surface of a chart is as follows: An extended straight edge may be formed by positioning me base plate (28) cursor (20) at the higher end of the middle plate (23) scale (25) with the scale (30) on me base plate (28) in line with the scale (25) on the middle plate (23) and both scales increasing in the same direction. This extended straight edge Is useful for establishing a direct line between two distant positions on a chart. An indefinitely extended line may be affected by moving the middle plate (23) and base plate (28) alternatively in the required direction while keeping the centre lines on these two items in line.

Altematively the base plate (28) may be detached from the middle plate (23) by sliding the base plate (28) cursor (20) out of the cursor guide under the middle plate (23) and the middle plate (23) with compass rose (13) in situ used alone for conventional chart plotting.

The method of determining the compass directions between two positions on a chart is as follows: Along edge of the instrument is placed in line with those positions. The instrument is then moved in a linear direction until the centre of the compass rose (13) is positioned over a parallel of latitude or a meridian of longitude printed on the chart. Then the compass rose (13) is rotated until the north to south line (15) is aligned with a meridian of longitude or the east to west line (16) is aligned with a parallel of latitude. The Indication north on the compass rose (13) is thereby correctly aligned with the direction north on the chart.

The compass directions between the two relevant positions are indicated on the compass rose (13) by the centre line (24) on the middle plate (23).

The method of plotting a given compass direction from a particular position on a chart Is as follows: The compass rose (13) is rotated until the given compass direction coincides with the centre line (24) on the middle plate (23). Then the instrument is laid on the chart so that one long edge is adjacent to the particular position while the indication north on the compass rose (13) aligns with the direction north on the chart. North alignment of the compass rose (13) is affected by referring the north to south line (15) to a meridian of longitude or the east west line (16) to a parallel of latitude. The plotting line is drawn on the chart from the particular position along the long edge of the instrument towards the given compass direction as indicated on the compass rose (13) by the centre line (24) on the middle plate (23).

One alternative method of constructing the instrument to be used specifically in the manner illustrated in Fig 7and Fig 8 is as follows.

Referring to Fig l l,the middle plate (23) is provided with a hole (32) at the commencement of the middle plate scale (25).

The tide/wind gauge Fig (1) is positioned on the compass rose Fig 2.

The compass rose is positioned on the middle plate (23) illustrated in Fig 11.

These three items are fitted rotatably together via the hole in each by a rivet or similar fastener. A washer is fitted over the rivet type fastener between the upper surface of the middle plate and the under surface of the compass rose.

The cursor guide (26) in the middle plate (23) as illustrated in Fig 1 lmay be formed by a slot through the middle plate (23).

The slot commences a short distance from the hole (32) at the commencement of the middle plate scale (23) and extends to a distance from the far end of the middle plate (23).

A round metal cursor, tee shaped in cross section Fig 12, (shown oversize) is fixed to the upper surface of the base plate Fig 6 at the commencement of the base plate scale 30.

This tee shaped cursor, with the wider diameter uppermost is entered into the cursor guide (26) in the middle plate Fig 11, from the underside via an enlarged hole (33) at one end.

Since the narrowest diameter of the cursor Fig 12, is less than the width of the cursor guide (26), and the widest diameter is greater, the base plate is able to slide and pivot freely along the full length of the cursor guide without becoming detached, except at the point of entry.

The washer previously described as being fitted between the upper surface of the middle plate and the under surface of the compass rose serves to provide a gap, wider than the thickness of the cursor head, thereby allowing the cursor unrestricted movement to both ends of the cursor guide.

Alternately the upper surface of the middle plate in Fig 11 may be rebated each side of the cursor guide (26) commensurate with the diameter and thickness of the cursor, thereby allowing a shorter cursor to be fitted with the top of the head level with the upper surface of the middle plate.

The scale (25) on the middle plate in Fig 11 is marked both sides of the cursor guide and extends to a point adjacent to the centre of the enlarged hole (33) at the end of the guide.

Claims (1)

1. CLAIMS i/l A navigating plotter comprising a flat surface marked with a

   scale and a series of lines parallel to both sides of the scale,visible through a transparent rectangle having a central scale marked lengthways, and bisecting a transparent compass rose, having a point of rotation in common with a transparent indicator marked with a central tide/wind set and rate scale, commencing from the point of rotation and extending a distance equivalent to that from the outer parallel line to the scale marked on the flat surface, thereby,a navigating vector is formed and understood by, a tideind direction being indexed to the compass rose by the tidewind indicator, a course being indexed to the scale on the transparent rectangle by the compass rose, a distance/course being indeed to the commencement of the scale on the flat surface by the scale on the transparent rectangle, a distancekourse being indexed to the tidefwind/ speed on the tide{vind speed indicator by the scale on the flat surface, a course being indeed to the compass rose and understood by the parallel line on the flat surface bisecting or closest to bisecting the compass rose.