Photo by] [M. Bar
THE “GYMNOTE.”
Another system of “dip” rudder, proposed in 1891, executed in 1893, and tested towards the end of 1894, consists in the employment of two horizontal floatboards, placed on each side of the boat at the height of the midship frame. Their use, combined with that of the stern rudder, has given better results. The boat is inclined less for the “dive,” dips more regularly, and lurches or “yaws” less.
When navigating on the surface or when her hull is immersed to the water-line the Gymnote carries a cupola, or movable shell with sidelights.
This apparatus is composed essentially of a metal shell provided with sidelights all round its circumference. A cylinder of strong tarred canvas fixed on steel springs, which ensure rigidity, bind the shell itself to the upper part of the hull. Horizontal folds in front permit this canvas to double up regularly upon itself after the style of a Venetian lantern, and in such a way that when the doubling up is complete the height of the shell (or “casque”) comes exactly on a level with the upper platform of the boat. During navigation at the surface or on the water-line the whole structure can be raised or lowered by means of a vertical screw moved by a horizontal hand-wheel of which the movable nut constitutes the lower part of a vertical frame formed of metallic uprights, which go to rejoin the hull. When the system is at the end of an upward course the canvas is completely stretched and the observatory is at its maximum height; when, on the contrary, it is at the end of a downward run, the canvas is completely contracted and the “kiosk” has externally disappeared.
Such a system (as a French writer has pointed out) is very faulty and dangerous, as may be easily conceived. In the first place, considering the feeble resistance which a canvas can oppose even when mounted on steel springs, it was indispensable to protect it against the pressure of the water during the “dive.” This was believed to have been accomplished by providing the shell with an indiarubber crown, forming a sort of beak, which, when the system was completely folded up and closed, came to rest on another washer of indiarubber placed at the bottom of a groove, where it formed a watertight joint. This would have been very good if there had been certitude that the beak or cap fixed on the shell rested exactly at the bottom of the groove. To make sure of that there had been arranged a small opening, which ought to give water when the closure was not sufficient, but this only gave an almost illusory means of control, the opening being found almost always obstructed by some detritus, débris of sea-wrack, and other foreign bodies encountered by the vessel. It will be seen what permanent danger was created by this apparatus—danger which on two occasions just missed causing the loss of the craft, an unlooked-for chance alone preventing it from foundering.
It would further be easy to show that in spite of its danger the movable shell, with canvas folded in accordion pleats, was almost unusable—that it could not serve when there was a slight sea on; that it caused, even during progress on the water-line, infiltrations capable of sinking the boat; and finally that, even in a calm sea and under the best conditions, the length of the manœuvre of raising and lowering made the operations of the “dive” slow and wanting in precision—operations which demand so much rapidity and delicacy, and to which alone it is allowable to sacrifice something on a submarine boat. This movable shell was 0·35 metre (about 13½ to 14 inches) in diameter; it was abandoned after all the Commandants had successively condemned it, and to-day it is never used.
For use below the surface the Gymnote carries an optical tube with two inclined mirrors and a periscope, but these have so far given but poor results.
The Gymnote was first tried on September 24, 1888, in Toulon harbour. The French Press was enthusiastic about the qualities of the new boat. According to Le Temps she was a complete success: “She steers like a fish both as regards direction and depth; she masters the desired depth with ease and exactness; at full power she attains to anticipated speed of from nine to ten knots; the lighting is excellent, there is no difficulty about heating. It was a strange sight to see the vessel skimming along the top of the water, suddenly give a downward plunge with its snout and disappear with a shark-like wriggle of its stern, only to come up again at a distance out and in an unlooked-for direction. A few small matters connected with the accumulators have to be seen to; but they will not take a month.”
At the trials which took place before the Maritime Prefect of Toulon in 1888, the Gymnote behaved very well, as far as speed and stability were concerned, but it was found difficult to keep her at a constant level when submerged.