Navigation and Charting

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Which is concerned with Charting, and of the three necessary things contained in all good charts, along with their uses.

Over-decoration of Charts

On the making of charts, and the science of Hydrographia, I mean to say little, for that is sufficiently covered in other works. Having said this, I would wish that the makers of charts did not paint their compasses with so many colours, nor the Land with so many flags, for that does more harm than good. Although it may be said they are only painted in otherwise vacant places, I would wish them to furnish those vacancies with two other matters, in this order.

Marking of Full Tides

First in some vacant place with a compass, to place against every point of the bottom half of the compass, letters or other figures or characters, then in like manner to place that letter or character at each haven, port or place according to when the moon makes a full sea at that place. And where it runs quarter or half-tide under the other, a further mark should be made.

For example, I place A at the East point, B at East and by South, C at East Southeast, D at Southeast and by East, and so on consequently to all the point unto the West. Then, where a tide runs high under an East moon, I mark that place with an A, and where it does so under an East and by South moon, I mark that place with a B, and so forth.

Marking of Headlands

It is also very necessary to furnish the remaining places on the chart by drawing the shape or silhouette of every headland or high point along every coast that is needed to be recognised, at what point of the compass the land is of that form, and at how far off that land rises in that fashion; and to so draw the land as often as the land alters its form and fashion, for being on one side, the land rises in one manner, and on another, it is of another form, and being near the land it will be in one fashion, and far off, in another again. And the reason for these drawings is that there is nothing more needful and necessary for a Mariner than to know the land when it is before them, and these is no better way to recall it that to have notes and drawings on how the land rises upon every side. And what greater inconvenience may there be than occurs by mistaking a place? For it is twenty times better to be thoroughly persuaded that you don't know where you are, than to think you know it, but are mistaken. For whereas the first thinks to prevent unknown dangers, the other may willingly run upon the dangers, believing they are not present.

The Use of Charts

The use of charts is most necessary for Navigation for long voyages, first for that it shows you how one places bears from another, second that it shows the distance between any places, third that it shows in what Latitude any place is. And these are shown by the lines of the compass, by the scale or measure, and by the line of degrees, if the chart be made true.

Taking a Bearing

Now, to direct your course through the Sea by the chart to any place assigned, you must first look on which point of the compass it bears from you, from the place you mean to set off from, to the place you would first seek landfall. And some say you shall know this by laying a straight edge rule between these two points, and then while keeping the edge at a constant angle, move the rule to the nearest compass rose. From here, you can read off the bearing, taking care that it is from the place you would depart from and to the landfall, and not the reverse. But others say that you should use your compasses instead, and they recommend that you open your compass to measure between your departure point and the nearest part of a line from a compass rose, and then run along that line until you reach your destination. And if the distance from the line to the destination is the same, then this line is your true bearing, and if the compasses fall short, then take the next line from the compass rose to test for your bearing. And this method is most accurate, if your course lies on one of the 32 points, but when it lies between, the laying of an edge is a better measure, so both methods should be taken, and the better bearing used to decide the point of the compass to lay your course.

Measuring Distances

If you would know how far any place is from you, set one foot of your compasses upon your current location, and stretch out the other foot unto the place assigned, then set the compasses against the scale of the chart, and that shall show you exactly how many miles or leagues it is from one to the other. If the distance between the two places is more than the compasses will reach in a single span, then first set your compasses against the scale, opening them to a convenient amount such as 100 miles, as your scale and compasses give you leave; after that, set one foot at your location, and the other foot towards the destination as best you estimate, and step your compasses as often as the distance between then requires, and from this you may conclude it to be just as many hundreds of miles (or other convenient amount) as the compasses did step. But if there is any odd measure left and the end, then reduce the span of your compasses to this distance, and set them against the scale, and it will show you the amount of extra distance to add on to the amount just concluded.

Determining Latitude

And touching upon the third commodity, being the Latitude of any place, set one foot of the compass against the place assigned, and open the compasses to the nearest place of the next East-West line, then carry than span to the line of degrees, keeping one foot on the same East-West line, and it will show exactly the number of degrees that the Pole is above the Horizon, being your Latitude.

Using Contrary Charts and Tables

Many sets of Navigational Tables also list common ports and havens with their Latitude and Longitude, and this is also good to use if the table is drawn by the same people who have drawn the chart, but if the two values be different, then the chart is to be preferred even if it be wrong, for if your courses are laid by a chart, and your position recorded on that chart, then that chart is a true record of where you are, wherever the Sun and Stars may put your actual Latitude.

Tracking a Course on a Chart

Now with all these values you may think you know how to attain the port or place assigned with the utmost ease. Yet there is to be considered, whenever directing the course of a ship, what impediments may be along the way, such as tides, currents, the force of the winds which may blow a ship to leeward of the course, as may the surging of the seas. And all this must be considered by the Master or Navigator. Likewise also in long voyages, the wind may often shift, and sometime the wind may be such that the vessel cannot lay her course, wherefore the Navigator must keep a perfect account of the ship's way, and consider on what point the ship has truly made her way, and not just where she points or what course was laid. And every time that the wind shifts so the ship can no longer lay her course, to note on the chart in what place the ship may be, having a special regard for the swiftness of the ship and so what progress has been made on the last course. And if the weather is clear either by night or day, to take the true Altitude of the Pole, and thus the Latitude of the ship, for by that, they may correct the ship's way, and give a very near guess as to how the destination bears from them, and how far it is from the ship, saving if you have set an East or West course, and then there is no other help but only the way as accounted in the Ship's Log.

Correcting Dead Reckoning of a Course

And to correct their dead reckoning by the Latitude, they must do the following (especially if the ship has often veered from her course due to contrary winds): first set your compasses against the line of degrees, with one foot on the observed Latitude, and the other on the nearest East-West line, and then carry them to the place where you suppose your ship to be, leaving the second foot on the same East-West line. Then bring forward with the other set of compasses or the straight edge rule what point of the compass the ship has sailed by, and at the meeting of the two measures make a mark for the ships location and record the date and time. Now from this place you may use your compasses to see how your destination bears, and how far off you still lie. And if you have plotted several points since your last true reading of the Latitude, you must pull back or extend your overall course from that last true mark, and not from your most recent mark from dead reckoning, for you don't know which of the later marks may be wrong, and it is most likely that it is all of them.

Other Uses of a Chart

As I have explained in an earlier chapter, you may know how far land is from you if you know the distance between any two landmarks. Now, by setting the landmarks with your compasses, you may do the same with your chart, by measuring the distance between the landmarks on the scale, or more accurately the distance between them as lies parallel to your position, so you know that they are so many miles or leagues asunder, then take bearing to each of the landmarks by the points of the compass, and mark these bearings on your chart. Then where these bearing cross, so lies your ship. And setting the compasses on this location and the nearest part of land, then adjourning them to the scale, shall reveal the distance to shore. But as there are always inaccuracies, then the distance between the landmarks and the number of points between the bearings should be applied as explained in an earlier chapter, which also gives a distance from shore. And if these are similar, then your position is known, but if they differ by much, then your distance from shore is uncertain, and you must carefully re-measure and re-plot, or use dead reckoning of the distance to shore.