Britain is often thought of as a maritime nation. The history books certainly support this thesis with their chronicles of explorations for trade routes, of the development of overseas commerce, which became rather absentmindedly an empire, of the growth of a navy to defend these interests. As an island race which aspired to global enterprise, maritime affairs have never been far from central policy considerations as our livelihood began to depend increasingly on overseas trade routes for food, raw materials and export markets. And along the way we developed merchant and fighting marines that were supreme in their day. From this global perspective we have been and will, probably, always be a maritime nation.

Following traditional naval tactics when outgunned, Captain Wylie laid a smoke screen in the January issue of the Journal and discussed what ‘imply’, ‘seem to think’ and ‘suggest’. Before my actual assertion becomes entirely lost to view may I repeat that a prediction of C.P.A., based only on radar data acquired in less than about three minutes, may be seriously in error. Precisely displayed, with no indication of the magnitude of the possible error, it can mislead. To say as he does that this danger is 'supposed' is certainly to beg the question, and supports my belief that the possible size of the error in C.P.A. is still not fully appreciated.

In principle there is of course no difference between the navigation of small and any other kind of craft at sea. In practice, though, the differences seem more apparent than the similarities—differences due to the conditions in which the navigator works and the greater vulnerability of small craft to the elements. I propose to offer some thoughts on three types of small craft navigation which reflect these differences. In terms of sail I concentrate on ocean racing because clearly whatever is effective in that demanding game will also satisfy less urgent requirements. I then refer to single-handed navigation which brings its own problems, and end up with some thoughts on high-speed navigation as exemplified in offshore powerboat racing.

In Captain F. J. Wylie's article, ‘Maritime radar automatic plotter display philosophy’ in the July 1974 issue of the Journal, he states that the IBM Maritime Application Bridge System (MABS) tracks only six targets for collision assessment purposes. This statement is incomplete and I would like to clarify the impression left with your readers.

The IBM MABS tracks up to 21 targets continuously while performing either automatic or manual acquisition. However, since the MABS also prioritizes targets according to threat potential (based on C.P.A. and T.C.P.A.), only the six most threatening are displayed continuously on the alpha-numeric data display and on the PPI. Should the operator wish to obtain data on the fifteen targets of lower priority he can request them in groups of six, in descending order.

The size and construction of powerboats are governed by the international U.I.M. which has established classes related to engine size and length. Class I boats, where most of my experience lies, can have a maximum length of 4.5 feet and power is limited to petrol engines of up to 16 litres. The speeds of the fastest boats are in the region of 85 m.p.h. with full fuel on board, increasing to around 90 m.p.h. at the end of the race. Over a ton of aviation spirit is carried as fuel. This speed can only be fully utilized in fairly calm conditions. Trim tabs on the transom and a jack for the stern drive units help the driver to keep the boat on the water.

If an analysis is made of the speed of a ship using data recorded in log-books the results are extremely disappointing, and do not reflect the accuracies of the instrumentation in use. Even data from a satellite navigator, where the speeds should have an accuracy of better than I per cent, give a I-knot band in recorded speed; in a 20-knot ship this is 5. per cent. Such inaccuracies require explanation.

To begin with one must ask what is meant by ship's speed, and different interpretations come from different people. The navigator is concerned with speed over the ground, while the naval architect or marine engineer is mainly interested in the forward speed of the ship through the water. On the other hand a compiler of ocean current data will require both the speed over the ground and the speed made good through the water, but the latter must take leeway into account. Finally, a weather routing consultant is looking for the actual forward speed the ship can achieve through the water in the prevailing weather conditions. All users of speed data may require other related information, such as the ocean currents and the leeway characteristics of the ship, which can in fact only be compiled from ship speed data. At the present time all these different requirements have to be satisfied by the speeds measured at sea and recorded in the logbooks and their abstracts. Ships' officers compile these records, but by the nature of their work they are biased towards the navigational concept of speed.

Captain R. K. Emden in his paper in the April 1975 issue of this Journal notes on page 135 that ‘the chief problem’ is ‘to identify by name and port of registry the radar “blip” deemed to be a contravening ship’, and that ‘the problem will be exacerbated as the Service expands’. In the discussion which followed Commander R. B. Richardson mentioned the m.f./d.f. receivers being used to assist ships to keep in lanes, and Captain Lusted mentioned investigations into the use of shore based v.h.f./d.f. for identifying ships.

Having read Professor Hugon's informative paper on ‘Navigation in the French merchant navy’ and in particular his remarks regarding the cluttering of the 182 kHz band, I would hazard a guess that he has not listened to the v.h.f. channel 16 band in recent years, when clear of the U.K. and continental areas.

In the open sea well away from land this channel is not often abused, but off the West African coast between about 13° N. and 22° N. the air at night is, more often than not, cluttered with noises like animal and bird calls for long periods on channel 16, and during the day with lengthy chitchat, possibly between foreign fishermen, on this and other channels.

The basis of wheelhouse design is comprehended in that wonderful Anglo-Saxon word—sea-man-ship. For the design of a wheelhouse should be such that the three elements in a mariner's work—the sea, the man and the ship are linked together in the most efficient manner. At all times and in all positions in a wheelhouse the mariner should have a clear view of the scene outside and also have as many clues as possible to the direction of the ship's head—so that he may relate the ship's head and the outside situation as easily as possible.

As one of the perhaps ‘younger personnel’ mentioned by P. R. J. Rawlinson in his note (this Journal, 28, 243) I would like to make a few points. First and foremost, in agreeing with him, I can best quote the Preliminary to the Steering and Sailing Rules of the Rules and Regulations for Preventing Collision at Sea, 1965: ‘In obeying and construing these rules, any action taken should be positive, in ample time, and with due regard to the observance of good seamanship …’

The method here described for finding the position of an observer from horizontal angles to fixed marks, without the use of a station pointer and without the necessity of drawing position circles, was devised by the author and although it may not be original it may be of interest to other navigators.

I would take issue with Spooner on his article in the April 1974 issue of the Journal. On a clear night, with no navigational hazards, a ship is reported at green 30, three miles! An assessment is made and decision to alter course to starboard is ordered. In this time the approaching vessel has made her own decision and altered course to port. Why therefore is the approaching vessel criticized for a port alteration? in my opinion she, the ‘stand on vessel’, has taken such action as to avoid collision without bringing on a close-quarters situation. On such a clear night the approaching vessel must have been visible for at least ten miles and at that range would have been showing all her lights, a clear case for an alteration to starboard on the part of Spooner's vessel to pass clear of the other vessel port to port. Was a lookout being kept at all?

It is generally assumed that the ideal distribution for the lateral or vertical distribution of aircraft on neighbouring tracks is as in Fig. 1, where A and B are the centre lines of the routes or altitudes. Navaids and altimeters seem to be designed with this distribution as the ideal. Where air traffic control is imperfect and there is an appreciable risk that two aircraft without longitudinal separation will be at the same nominal altitude on the same route, then I suggest that neither the distribution of Fig. 1 nor that of Fig. 2 is ideal but that Fig. 3 represents the ideal because it minimizes the risk of collision due to air traffic control failure. This hypothesis has implications for the design of navaids and altimeters and for the specification of vertical and lateral separation procedures.

As a result of the recent marketing of small pocket computers I have found much interest among navigators who would like to use them for working out celestial sights. One computer calculator (the Hewlett-Packard HP-35) in particular appears to be of considerable interest due to its ability to compute trigonometric functions with algebraic logic as well as to store and recall derived intermediate values. Not having been able to find any published work on the use of this type of equipment for the rapid and precise working of sights I have given some thought to the matter and as a result believe the following notes may well be of interest to others.

Investigation into the design and accuracy of old-time instruments is always of interest. The Nocturnal probably used from the sixteenth century onwards for estimating the approximate local time at night is well known; with this primitive instrument the Pole Star was viewed through a central hole in a pair of wooden or brass discs. A pivoted arm turned to coincide with the ‘Guards’ of the Lesser Bear, the local time being deduced from an engraved scale. A seventeenthcentury improvement included an extra scale for determining the time by aligning the pointer with the Great Bear ‘Pointers’.

Some navigators may prefer other methods and other tools, but the Hewlett Packard HP-45 has some fascinating abilities. It might be called the poor man's INS computer, though it does not of course find position. Its only disadvantages are the need for a hood in sunlight and the need for concentration and freedom from distraction. It can be used on the knee for no table is required, and it replaces conversion tables and several other mathematical tables. To a large extent it can replace plotting charts, flight planning charts, Dalton computers, protractors and dividers.