The Channel Bridge. I am happy to report that Commandant Poll's admirable scheme for traffic in the Strait of Dover (p. 75) has provoked, at least on paper, a most interesting reaction. Commandant Poll brought out his plan in February 1960. In March the Compagnie Française d'Entreprises consulted me about a scheme for a Channel Bridge which they had drawn up in conjunction with the English firm of Dorman Long and the American Merrit-Chapman and Scott Company.

As seamen we hold no brief either for a bridge or for a tunnel; our personal interest can be no more than an expression of our attitude as citizens of our respective countries. But as soon as the matter was brought to my attention I realized that there can be no two opinions about our professional attitude: we must first make sure that the bridge will neither endanger nor delay shipping, and when we are satisfied on that point, we must do nothing to hinder the realization of a project which cannot fail to improve international relations in our ageing West.

How are we to make sure of our necessary condition? The first and most important step is to establish the one-way routes detailed by Commandant Poll, and to see to it that the arches which cross them are as wide as possible. The normal span, 200 metres from pier to pier, with a clearance of 53 metres, is suitable only for small ships.

Following the publication of E. S. Calvert's Manœuvres to Ensure the Avoidance of Collision (Journal, 13, 127) a number of people closely concerned with the problem of collision at sea were invited to comment on Mr. Calvert's ideas. This comment was published in Vol. 13, Nos. 3 and 4 (pp. 350–352 and 455–464). Mr. Calvert here replies to some of the criticisms. The paper he refers to as his latest will be published in the October number of the Journal.

to Captain H. D. Harries

Without a more precise definition of ‘open sea’ and ‘crowded waters', I doubt if any figure for the proportion of collisions in each has much meaning. (The same kind of difficulty arises in defining a ‘near miss’.) More precise figures might possibly be obtained by giving the proportion of collisions which occur within so many miles of the mouth of a channel, a channel being defined as an area where local or ‘edge’ rules are in force, or where the traffic is controlled. However, I doubt whether the use which could be made of such statistics would justify the trouble of collecting them. In my latest paper, i.e. the one to be published in the next issue of the Journal, I have given what I believe to be the only possible solution to the crowded-water situation, in so far as rules can provide a solution.

As every schoolboy learns, a point has position but no size, and a line has length but no breadth. Nevertheless, to a navigator concerned with fixing his ship, points and lines are represented on his chart as fine pencil marks.

The manner of representing the results of observations as pencil ‘points’ or ‘lines’, has undoubtedly led to the belief that a ship's position must be represented as lying at a point on a position line which is drawn on a chart. Nothing short of perfection in position lines is ever expected by most practical navigators, and two position lines crossing at a point are usually regarded by seamen as yielding a perfect position: and if three position lines meet at a point! … there is seldom even the slightest doubt in the mariner's mind about the reliability of such a fix. On the other hand, three position lines which do not meet at a point are usually regarded as being something not quite respectable.

The problem of errors in radar plotting were considered by Capt. H. Topley (11, 167) and Capt. F. J. Wylie (12, 198), and it was shown that the error in the estimated distance of the C.P.A. depends upon mean range and range change in plotting interval. I want to introduce the term rate of error in the estimated distance of C.P.A., in the same way that Topley shows the percentage error in the estimated speed.

The Working Party on Fuel Reserves for aircraft recommends that a major statistical attack should be made by a qualified body with the aid of an electronic computer on the problem of how to rationalize fuel reserves. I C.A.O's Standing Committee on Performance did much to standardize the risk of an aircraft hitting the ground on take-off and on landing, hence increasing profitability without prejudicing safety. Might not I.C.A.O. set up a committee to tackle fuel reserves on similar lines?

I think that even now, in advance of such a major undertaking, fuel reserves might be rationalized a little if certain information were available to flight planners and crews. For instance, Durst has given the accuracy of forecast mean equivalent head winds for a few routes (this Journal, 13, 288); if it were given for a wider selection of routes, perhaps the fuel reserve carried for ‘navigational error’ could be roughly specified as the extra fuel needed to cope with 95 per cent (say) of the errors expected in forecast M.E.H.W. The use of extra fuel enroute for other causes is much less frequent (on piston-engined aircraft anyway) and could generally be covered by change of destination or by use of fuel nominally carried for diversion.