"When blows the breeze we spread our sail ON SAIL AS AN AUXILIARY One day, while standing talking to a builder, we were joined by the owner of a naphtha launch who was desirous of having his vessel rigged as a yawl, and had come to get the builder's opinion as to what the change would accomplish and cost. In response to an inquiry as to what speed he might expect to get out of the craft under canvas, the builder answered, "four miles." "Then," replied the owner in jubilant tones, "she will go eleven miles, as I get seven out of her now without any sail." He was greatly surprised, and rather suspicious of our knowledge, when we informed him that if sail increased the speed of his craft over her maximum to the extent of half-a-mile an hour, he might consider himself fortunate. Now, this man is by no means a lone bird in his belief; he shares the misconception with many launch-owners and others. Like some of our popular authors who write sea stories that are not Now, to the question of what use is sail as an auxiliary power. In vessels of a speed exceeding ten knots, it is of little or no use, except when due to the form of the hull, or for other reasons the slip of the screw is excessive. As, for instance, in a vessel towing others, such as sea-going tugs, where the actual speed is one-half of the screw speed, sail is an aid. Again, in a vessel of bad form, when, frequently owing to the weight on the engine it is unable to run at its highest working speed, sail is an aid, as it lifts some of the weight off the engine, and allows an increase of revolutions without an in A vessel whose screw speed is eight knots and whose actual speed is six knots has a slip of twenty-five per cent. Supposing that her sail power is sufficient to drive her five knots or three knots in excess of the slip. Now, if her speed be increased to eleven knots by using canvas, it must not only take up the slip, but induce an acceleration of the engine, so as to give an additional screw speed of three knots—an increase of 37½ per cent. over the working speed of the engine. This is practically impossible. No engine is built to run at a speed of 37½ per cent. over its working speed, yet unless the screw travels as fast as the hull, it is useless. It is exactly the same thing as when trying to row a boat running under sail; unless you move the oars faster through the water than the boat is moving you do not assist in the propulsion. Reasoning from this, we may lay it down as an When mechanical propulsion is the auxiliary power, we have a different problem. Take a vessel capable of being driven by sail at a speed of eight knots, and by her engines alone at four knots. Now, if she be sailing at a speed of eight knots, and we start her engine to make the number of revolutions necessary to induce a speed of four knots, the screw, not traveling as fast as the hull, will be dragged to the amount of the difference between its speed and the speed of the boat—four knots. In that the screw shall have a propulsive force it must be driven at a speed to exceed eight knots, an increase of over 100 per cent. Reasoning from this, we may lay it down as an axiom, that: A vessel whose maximum speed under sail exceeds her maximum speed under power will not increase her speed by employing sail and screw conjointly. While auxiliary sail is of little or no value, auxiliary mechanical propulsion is. But its chief value lies in it as a substitute, and not as an auxiliary. The wind—the
Let us suppose that a similar craft is fitted with a motor to drive her at a speed of five miles an hour. She voyages 100 miles, the first sixty in ten hours. During the doldrums she uses her power for six hours, and makes thirty miles, and in sixteen hours has covered ninety miles against the sail yacht's seventy. Having Last summer I ran thirty-eight miles in fourteen hours in a small sloop. Thirty-two miles of this distance was made in eight hours, the remaining six miles taking six hours to cover, and if you analyze a set of cruising runs you will see that mine was an exceptionally good performance. I usually, in cruising, figure on making an average of three miles, thirty miles being a fair day's work and forty a good one, while a fifty-mile run is possible only once or twice during the season. This is in a boat whose maximum speed is seven knots. I have not the slightest doubt but what a man with a yacht fitted with a motor capable of driving her at a speed of five miles, and using the engine only as a substitute for sail when the wind is dead or fickle, could cruise twice as far and see twice as much as one who depended solely upon canvas. This is a deal to promise, but no doubt those who have had a long experience in cruising in our Eastern waters will underwrite the opinion. But while auxiliary power has its advantages, it also has its disadvantages. It increases the expense; it takes |