Some time ago while the writer was serving aboard the Dorsey, in Adriatic waters, he had the opportunity of using a tide graph similar to the one attached.
The Italian Hydrographic Office prints these graphs monthly for their principal ports.
In ordinary navigation it matters less to the captain or navigator to know that high water will occur at exactly 9.53 a. m. to a height of exactly 6.2 feet than to know that it occurs shortly before 10 a. m., and that the height is about 6 feet.
There are times, of course, when the exact data are absolutely necessary, such as when a gunboat has to go across some Mexican harbor bar with little or no water to spare. However, such cases are out of the general run.
The graph will prove its value to vessels which frequently make the same port.
After a long weary vigil making port in fog or bad weather, the navigator is just as likely to pick September as November out of the tables, or the 13th as the 18th, and so on, by the dozen. Right there is where the graph "comes in strong." No thumbing through pages with numbed fingers, no wild efforts to find the intersection of the proper arguments, no reading fine print—simply look at the diagram, it shows at a glance.
The necessary data were taken from the "General Tide Tables, 1919." Any assistant navigator with the aid of a sharp pencil and a ruler can plot a month's curve on cross-section paper in 15 or 20 minutes.
No originality is claimed for the idea, but it is considered of sufficient value to "pass down the line."