In 1805, in the days of topgallants and royals, Admiral Sir F. Beaufort devised a numerical scale according to which wind velocity or force at sea might be estimated non-instrumentally.1 According to his scale, the force of the wind was ascertained from the speed imparted to an early nineteenth century man-of-war, the object being to eliminate much of the “seaman’s-eye” method then universally employed in recording wind force data. At that time, and for many years thereafter, it succeeded so well in fulfilling its purpose of standardizing this type of meteorological record that it was officially adopted by Great Britain and the United States, as well as other maritime nations. There can be no question of the importance of Admiral Beaufort’s contribution to seamanship and meteorology, for his scale clarified the observations and rendered them capable of more universal interpretation.
Beaufort’s scale, as every seaman knows, ranges wind force from zero, calm, to force twelve, hurricane. The specifications for determination of various wind speeds are set forth in the lower grades of the scale in terms of speed imparted to early ships of the line sailing full and by, and expressed in the upper grades by the amount of canvas carried when sailing close-hauled. Although this scale is given in practically every recent book on navigation or meteorology, and is used on the most modern steam vessels, logically it should be relegated to historical texts on these subjects along with discussions of the sails upon which the system is based, since the only canvas on a modern ship is in the form of awnings, boat covers, weather screens, and occasionally a wind sail. Hence, any consideration of the Beaufort scale must force one to the conclusion that present-day ships, bare of canvas, lack the essentials for the determination of wind velocity as laid down in even the modified Beaufort scale which refers to a modern steel full-rigged ship or to a sailing trawler of average size.
This being the case, two possible alternatives remain for consideration: (a) further modification of the Beaufort scale for adaption to present-day craft, and (b) an instrument for precision measurement to replace the scale entirely.
In order to adapt the scale to present, day craft, the observer at sea must find a substitute for such indications as "wind, fills sails," or "good working breeze." Obviously, this scale cannot be replaced by a table based upon the "effect of wind on awnings" or "sound of wind in rigging" as any true basis for wind determination. Moreover, any mariner is faced with the perplexing problem of relative velocity is judging wind force when a ship is under way, a fact which is rarely given due consideration. The average quartermaster will invariably overestimate wind velocity if the ship is heading into the wind, the relative velocity thereby being increased, and he will as frequently underestimate it when the wind is astern. Thus on a 15-knot ship a true wind of Beaufort force 4 usually is logged as a force 6 or more when ahead, but becomes a wind of force 2 when astern.
A substitute for the antiquated action-of-wind-on-canvas scale has frequently been suggested in a scale built upon the state of the surface of the sea. The ides has been advanced that, after careful observation, the effect of the various wind Speeds upon the surface of the sea could be used as a basis in drawing up a fairly accurate wind force scale. Perhaps some such system could be devised which would be useful on modern ships and particularly helpful to yachtsmen and other small craft handlers; and, moreover, it could scarcely avoid being an improvement over the present inadequate system.
On the other hand, such a sea-surface scale would be open to many of the just criticisms directed against the Beaufort system. Determination of wind force would still be a matter of individual judgment, varying with the mariner, his experience, and his discernment. The initial determination of a scale based upon the condition of the surface of the sea would offer serious difficulty to the modern Beaufort, as the writer has found through his own experience. After observing almost every type of storm at sea in the northern hemisphere, including several hurricanes and typhoons, the following observations are the only ones which the writer has observed with any degree of regularity:
Beaufort scale Sea surface (open sea)
Force 0 Smooth sea—glassy sea.
Force 1 Slight ripples—cat's-paw observed.
Force 2 Small waves but without whitecaps.
Force 3 Occasional whitecaps.
Force 4 Many whitecaps.
Force 5 ?
Force 6 (or greater) Many whitecaps and white streaks on the water.
Force 7 (or greater) In addition to conditions under Force 6—tops blown off waves.
Force 8 (or greater) Mountainous waves.
Forces 9-12 ?
There are, no doubt, other sea-surface conditions which would indicate winds of from force 8 to force 12, but inasmuch as the writer has never observed anything but mountainous waves under these conditions, he is at a loss in attempting to make accurate differentiations, and any such scale would have to be drawn from observations of more experienced mariners.
Moreover, it must be kept in mind that any system devised to estimate wind force from the condition of the sea’s surface would be complicated by a number of modifying factors. Unfortunately, the appearances of sea surfaces differ when acted upon by the same wind velocity due to varying depths of the water. Comparatively small shallow bodies, like a small gulf or bay, the China Sea, or the North Sea, are set in motion much more rapidly and vigorously by a given surface wind than larger and deeper bodies. Consequently, the magnitude of the waves will vary with the depth and size of the body of water upon which a surface wind of a given velocity blows, and thus this factor must be taken into account in making an estimate.
Furthermore, observations of wind force based upon sea-surface conditions are likely to be influenced by the course of a ship. A following sea never appears so mountainous to the eye as a head sea, and is thus more difficult to classify according to any scale. A sea surface in which there is a current, either tidal or ocean (especially the Gulf or Japan current), is disproportionately affected by a wind blowing from the opposite direction, since a greater number of whitecaps is observed than the same wind would produce when blowing over a sea surface free from currents. Ground swells when running from the same direction that the wind is blowing tend to give the observer a false impression of the wind’s force and hence erroneous estimates.
One of the most serious defects in Beaufort’s scale, and in any modified or similar scale which depends upon individual estimates made by the human eye, is its dependence upon reasonably good visibility conditions. Consequently, there would be no method of applying such a scale at night or when the sea’s surface was not visible.
From the foregoing discussion it may be seen that a sea-surface wind scale, even if it could be devised successfully, would be of but limited assistance in obtaining correct knowledge of wind velocity, and open to at least some of the chances for errors or inaccuracies inherent in Beaufort’s method. The question, therefore, logically arises: Why cling to the use of such a scale, based upon far from infallible human judgments, and devised long before instruments which record wind velocity had been invented or perfected?
The average seaman thinks of wind speed as of ship’s speed in terms of knots, and, therefore, he makes his observations in that familiar system of units. Since the deck-log instructions require that wind data be recorded according to the Beaufort scale, it thus becomes necessary to refer to a Beaufort table,2 usually conveniently placed in the front of the deck log, in order to make conversion of knots into Beaufort numbers, and thus the proper entry. This procedure necessitates a re-conversion of the recorded Beaufort number if the observation is to be used later in the knot scale as is customary. Of what value is the extra and unnecessary step?
It has been argued that the Beaufort wind scale is internationally understood and is therefore useful. The writer doubts the truth of such a statement. Last September, while waiting in the signal tower on the Bund of Shanghai for information concerning a typhoon headed toward the Yangtze, he was given the opportunity to observe the puzzled expressions and to hear the babel of questions from a dozen merchant officers of different nationalities when the director announced, “Gutzlaff reports force 8.”
It has been suggested that the abolition of the Beaufort scale would render the pilot charts less serviceable since the number of barbs on the arrows showing wind direction indicate the wind force Beau fort scale. It is probable that 16 K or simply the numeral 16 along the shaft of the wind direction arrow would be more significant to most mariners than four barbs, and offers no typographical difficulty. It is true that the Weather Bureau uses Beaufort terms in making forecasts, but again it is probable that winds "Ten to twenty northwest" would be more intelligible and serviceable, as well as a more accurate prognostication than "moderate to fresh northwest."
Since the value of the Beaufort wind force scale is so open to question, what, other than tradition, keeps it still in general use? There will always be some mariners who maintain that since it is impossible to measure wind force with absolute accuracy at sea,3 the Beaufort scale, covering wide and rather loosely defined ranges, is perfectly acceptable. On the other hand, when there are simple, rugged, relatively inexpensive instruments on the market today, which require little attention and upkeep and which give a continuous record of wind velocity comparatively accurate and dependable, why not make full use of the practical mechanical device and eliminate the scale based upon individual estimates? The 3- or 4-cup anemometer gives a continuous automatic record within acceptable limits of accuracy of apparent wind velocity at sea. Unlike the present system it is not dependent upon an observer and registers wind force for every minute of the 24-hour period, regardless of fog, mist, heavy rain, sleet or snow. With such standard equipment, the wind force could be entered directly in the deck log in knots, and the "seaman's eye," could be confirmed or discredited.
1 This scale was later adapted for use on land by specifying certain effects of different wind velocities ashore. It is still in use although the descriptive terms employed by the Weather Bureau are more commonly used and understood than their corresponding number.
2 There are probably very few mariners who can use the Beaufort scale accurately from memory, since it is not a decimal system, nor is one force any even or truly precise multiple of another, but based simply upon descriptive phrases.
3 Absolute accuracy depends upon correct determination of ship's speed for use in converting apparent wind velocity to true wind velocity.