The safe navigation of ships in every corner of the Seven Seas depends mainly on the accurate and painstaking work of a handful of surveying vessels which collect information for the making of charts
ON THE BRIDGE of H.M.S. ENDEAVOUR, engaged in survey work. The seaman is looking at the magnetic compass, which is the ship’s standard. On top of it is the azimuth-
OF those who use the sea probably few ever spend much time in thinking of the enormous amount of labour which goes and has gone, for more than a century past, to the production of the charts which they use daily They would be lost without them. Yet they expect, as a matter of course, in whatever part of the Seven Seas they may find themselves, that they will always be able to obtain, at a moderate cost, an Admiralty chart which is strictly accurate and up to date. The chart must show the coast, with all its outlying dangers, such as reefs and shoals, the lights, buoys, and beacons, the principal channels and, above all, the exact depth of water to be found in any position. They have been able to obtain this information for such a long time past that, they see nothing wonderful in it — for them it is a daily commonplace.
Wherever the navigator goes he can never (unless he manages to cross the magic line marked “farthest South reached hitherto” on some of the Admiralty charts of the Antarctic) come to a shore which has not already been visited and charted by a surveying ship, or, at least, by one sailing “on discovery”. The work has been done, the coasts of the world have been charted, and he is reaping the benefit.
The magnitude of that work can be appreciated only by consulting the catalogue, and some specimens, of such a modern collection of published charts as the 4,000 issued by the British Admiralty. France, Germany and the United States also publish sets of charts embracing the-
This enormous body of information, accurate to a degree which is almost incredible, results from the work of a handful of little ships. They work far from the limelight, devoting their days to obscure drudgery whose nature few understand or are competent to appreciate. Their only reward is the production of a new chart now and then, and the knowledge that, because they spend their time thus, the seamen of all nations can go safely and prosperously about the world’s seas. By the nature of things — and by the workings of Nature — their labours are never-
The beginnings of accurate marine surveying coincide with the rise to fame of Captain James Cook, R.N., F.R.S., probably the greatest-
It is in the St. Lawrence and Newfoundland charts produced by Cook in the ten years preceding 1769, when he sailed with the famous Endeavour (a name still borne by a British surveying ship), on the first of his three great Voyages round the World, that we see the results of the first really accurate marine surveys. Cook’s earliest chart, for example, that of the St. Lawrence River,was based on a triangulated survey of the principal points. It has always been a mystery where and how, in the limited amount of spare time at his disposal, Cook had acquired the necessary knowledge of geometry and trigonometry to undertake such a piece of work. In his Newfoundland and Labrador surveys, too, he is known to have used a theodolite, an instrument of which, in his day, few seamen had even heard.
The difference between Cook’s surveys and the general run of those made by his predecessors and contemporaries was this: that if Cook had been sent to survey a place the authorities could rest assured that the job would not need to be done again, and that that part of the world would not require re-
The utmost faith could be placed in his charts, but navigators were better off without most of the others. And as this fact gradually came home to the various Admiralties, the old rule-
This, however, did not occur immediately and not, at first, in home waters. Cook’s chart of New Zealand, for instance, executed under heavy difficulties in 1769-
The lion’s share of the work of surveying the unexplored or imperfectly-
Charting the World
There were also Fitzroy’s surveys, of similar extent and duration, in Patagonia, the enormous amount of exploration done in the Arctic during the protracted and fruitless searches for Franklin and his men, and in the Antarctic by Ross during his great voyage of 1840-
Those days will never come again. There is little left to discover and, except in the Polar regions, surveying ships are no longer free to go where they wish. A British survey of the Argentine and Chilean coasts, for example, such as that performed in the Beagle by Fitzroy a century ago, would be impossible to-
SURVEY SHIPS OF THE WORLD’S NAVIES, 1936
British Empire 12
Germany. . 1
CONVERTED FROM A MINESWEEPER into a surveying vessel, H.M.S. Kellett was built in 1919 at Renfrew, Scotland. A twin-
At the present day, therefore, fewer than seventy small ships carry out the work of surveying all the coasts of the world. Their work includes the making of new surveys, the amplification of former ones, and the detection and charting of previously undiscovered dangers and of the periodical changes which are brought about, almost daily, by the action of the sea or by the hand of man.
The great surveys of the past were mainly executed with what Herbert Spencer once described as “implements singularly ill-
In almost every instance, a modern marine survey is an extension of or an amendment to one previously made. The survey may be of a coast whose topography has already been thoroughly laid down by land surveys. In such instances the marine surveyor is saved a good deal of work, since he can connect the salient positions used in his survey with other points whose exact sites are already known and mapped.
Even on land, it would be a ruinously expensive and unbearably tedious business to make an accurate survey of an area more, say, than a square mile or so in extent by direct measurement from point to point. Instead, recourse is had to triangulation. All over the area, marks are erected in well-
These angles once obtained, the whole system of marks may be plotted on paper of any convenient size, each mark appearing at its correct distance and bearing from the others. Starting, say, from an initial base-
How accurate this process, when well executed, can be is well shown in the records of the Ordnance Survey. For the original triangulated survey of the British Isles, a base-
about two inches. The surveyor s first job, therefore, once he is anchored off the surveying ground, is to erect his primary marks, or “main stations”, and measure his base-
BUILT AT RENFREW IN 1919, H.M.S. Flinders, with the Kellett (illustrated above), the Beaufort and the Fitzroy, was originally designed as a minesweeper. The dimensions of these vessels are identical. Driven by vertical triple-
Sometimes when working off-
Two of the main stations will have been carefully selected to serve as the end-
The next step is to erect a “tidepole” and to take continuous observations of the height of the tide hourly or even oftener, day and night. This is of vital importance. The whole of the sea-
If the effects of tide were to be neglected, for instance, a sounding-
Importance of Soundings
Meanwhile another party or parties will have taken in hand what is probably the most important part of any marine survey — the soundings. The spectacle of a detached party leaving a surveying ship in the early morning for a day’s sounding or coast-
SPECIALLY BUILT FOR SURVEY WORK at Glasgow in 1912, H.M.S. Endeavour is a vessel of 1,280 tons. She has an overall length of 241 ft. 3 in., a beam of 34 ft. 2 in. and a draught of 11 ft. 8 in. Her complement is 140 and her speed 13 knots.
The soundings shown on any chart are its most essential feature and are also the most striking point of difference between a chart and a map. Laying down the coast-
A careful watch, however, is kept on the soundings when they are first plotted. They are usually taken from boats to the nearest foot, along spaced lines, the boat’s position being frequently checked by angles. Any unusual shallowing in an area whose depths are generally uniform is the signal for an even closer examination of its vicinity. As a final precaution a wire-
How difficult, and how expensive, the discovery of pinnacle rocks, even in well-
It also came to light that many years earlier the coastguard warship Hoche had hit a third rock of the kind, not far away. In this instance a special survey of the vicinity had been put in hand, but it had been discontinued, “for reasons of expense”, when it was a few yards from the rock which later sank the France. The saving of a few thousand francs had cost the French nation a new super-
On March 4, 1887, the steamer Avocet, laden with iron rails, was steaming southward down the Red Sea when she experienced a slight shock and promptly began to fill with water. Her crew, luckily, were all rescued by another steamer, the St. Oswald, which had been in company with her for some hours and was not far off. An official inquiry held at Aden endorsed the Avocet’s story —that she had been lost through striking on an unknown rock in about 14° 21' N., 42° 38' E.
AN INSULATED WATER BOTTLE being adjusted in H.M. surveying ship Challenger. Important information relating to such matters as currents is gathered from samples of water or solid matter lifted from the sea-
As, however, this position lay close to the deep-
The Court sat, but not for long. At its first meeting, on June 10, 1887, a telegram was handed to its President, stating that the Teddington had foundered, “after striking an unknown rock”, not more than 5 miles north-
The positive evidence for the rock’s existence, however, was too heavy to be outweighed by the negative result of two searches, and in October H.M. surveying ship Sylvia was detailed to make an exhaustive examination of the region near the Teddington’s position. The Sylvia prosecuted her search for six weeks, but no trace of any submerged danger approaching the surface more
closely than 28 fathoms (168 feet) could be discovered in the vicinity. Undeterred by the complete failure of three successive searches, the Admiralty directed H.M. surveying ship Stork to re-
The Hydrographic Department
With the completion of the soundings, the end of the survey — so far as concerns the work done in the field — is in sight. Meanwhile, astronomical observations have been taken, either with the sextant or with the prismatic astrolabe to determine the absolute latitude and longitude of one or more of the main stations. By this means the corresponding latitude and longitude of any point within the limits of the triangulation can, if necessary, be calculated. Observations have also been taken to determine the “variation” of the compass, of its deflection from true North, and the position of true North relative to the baseline.
Finally, when the surveying season is over, the ship returns to civilization. Her officers settle down to “drawing the fair charts”, preparing their work for publication in the form of a chart or charts, with the accompanying commentary of “sailing directions”.
The connecting link between the work of the surveying ships and the sea-
Such is the manner in which the modern Admiralty charts, and those of other nations, come into being. They embody, in condensed and handy form, a mass of accurate information, slowly accumulated over many years.
MEASURING STRENGTH OF CURRENT in H.M.S. Endeavour. The seaman is holding a float, with a light line attached, which he is about to “stream” — that is, to throw overboard. The ship is anchored in the current, and as the float drifts away it will take the line out — this being allowed to run freely. The officer will note the exact time of streaming the float; when a stated period has elapsed he will order the line to be held. The amount run out, combined with the time, gives the necessary data for working out the speed of the current. The method is that of the old-