Ship speed

“ At high speeds the resistance of the ship, of which we have already said something, increases far more rapidly than it does when the speed through the water is slow or even moderately fast. When a ship reaches the speed of 20 knots the influential factor of wave-making comes in prominently. Furthermore, in order to coax an extra knot or two out of the ship, you must needs increase her weight and usurp a very serious amount of space by larger engines and boilers. ”

“ War-ships, on the contrary, ordinarily cruise at very low speeds, and yet must be capable of reaching very high speeds when required in action or chasing. A war-ship, for instance, that attained about sixteen knots on the measured mile, and could steam continuously at sea, as long as her coal lasted, at a speed of about fifteen knots, would ordinarily have to cruise at from nine to ten knots. ”

“ It is only her bottom that is getting foul. A very little affects the speed of an iron ship which is not driven on by a merciless propeller. Often it is impossible to tell what inconsiderate trifle puts her off her stride. A certain mysteriousness hangs around the quality of speed as it was displayed by the old sailing-ships commanded by a competent seaman. In those days the speed depended upon the seaman; therefore, apart from the laws, rules, and regulations for the good preservation of his cargo, he was careful of his loading, or what is technically called the trim of his ship. ”

“ The steamer was to starboard and was heading at a good speed across our bows. To judge from the foaming waves which were cut off from the bow, I calculated that her speed must be about sixteen knots.
The hunter knows how important it is to have a knowledge of the speed at which his prey is moving. He can calculate [51] the speed a little closer when it is a wounded hare than when it is one which in flight rushes past at high speed.
It was only necessary for me, therefore, to calculate the speed of the ship for which a sailor has an experienced eye. ”

“ The speed of the ship can be roughly estimated from the speed of the engines; it is more accurately obtained by one or other of the various forms of log, or it may be measured by paying out continuously a steel wire over a measuring wheel. The average speed is obtained very accurately from solar and stellar observations for the position of the ship. ”

“ Whether it is the maximum rate possible to ocean steamships, or whether it is destined to be surpassed by a still higher degree of speed, remains to be seen. Many persons are of opinion that the increased facilities of speed which are now within reach of travellers on long voyages will gradually lead to the total disuse of sailing ships for passenger traffic. It may be so, but there are still not a few who would prefer a sailing to a steam ship for a long sea voyage, notwithstanding its so greatly inferior rate of speed. But nowadays everything must be sacrificed to time. ”

“ This moderate rate is far below the popular mark; but, in considering this important question, it should not be forgotten, that, unlike the paddle, the screw will always coöperate with sail,—and that, if a ship would go far under steam, she must be content to go gently. The natural law regulating the speed of a ship is, that the power requisite to propel her varies as the cube of the velocity. ”

“ A ship must therefore be of a length that depends largely upon the length of wave which at a high speed she will tend to produce in order that she may be driven at such a speed without an expenditure of power disproportionate to the effect produced. This length, if very high speeds are desired, is best wholly taken up in fining the entrance and run, leaving no parallelism of middle body, and broadening48 and deepening the ship to keep the necessary displacement. ”

“ Every ship, whether a sailing ship or a steamship, shall in a fog, mist, or falling snow go at a moderate speed.'
'Art. 18. Every steamship, when approaching another ship so as to involve risk of collision, shall slacken her speed, or stop and reverse, if necessary.'
The former of these articles deals with the general speed of ships in a fog; the latter, with the special precautions to be observed after the proximity of another vessel has been ascertained by her signals. ”

“ The theory that with an increase in speed the tendency of a ship is to rise, so that when travelling at a fast rate she will draw less water than when going slowly, and consequently will have less resistance and less skin friction, has attracted the attention of naval architects for many years. So far as theory is concerned, there is nothing to prevent a vessel being built on this principle, but when it comes to considering stability, it is another question altogether. ”

“ Fresh from the troubling time limit of the Deutsch prize competition I amused myself frankly with my air-ship, making observations of great value to myself, but not seeking to prove anything to anyone.
The speed problem is, doubtless, the first of all air-ship problems. Speed must always be the final test between rival air-ships, and until high speed shall be arrived at certain other problems of aerial navigation must remain in part unsolved. ”

“ The best form of hull, model of propeller, and plan of engine are already so well established, that it is not easy to fall into error; that which is most to be guarded against is the popular demand, the prevailing mania for high speed,—for which single advantage there is such a proneness to sacrifice every other warlike quality. That measure of speed or power which will enable a ship to stem the currents of rivers, to enter or leave a port in the face of a moderate gale, or to meet the dangers of a lee-shore, should, it is conceived by many, be sufficient ”

“ Large tonnage not essential for high speed. Assuming, however, that extreme speed is required, it by no means follows that large tonnage is a necessity, The fastest vessel in the navy, the yacht 'Osborne,' is a comparatively small ship. The fastest ships in the merchant service are the steamers carrying the mails between Holyhead and Kingstown, and the blockade-runners which, during the war of the secession, escaped the United States cruisers by their superior speed. ”

“ The usual practice, therefore, of going ahead as fast as the engines will take the ship must be entirely abandoned. Careful observations, systematically pursued, will show the speed which, under different states of immersion, can be attained without a disproportionate expenditure of power, and to this speed the engines must be limited. A little experience will probably show that, under certain circumstances of immersion of the ship, or of the state of the sea, it may be economical to force the screw or the paddle engine, the one more than the other. ”

“ In battle practice the only movement of the target is that which the towing ship can give to it. Its speed and manœuvring power are strictly limited, whereas a 30-knot battle-cruiser can change speed and direction at will. The smallest change of course must alter the range, and the smallest miscalculation of speed or course must make accurate forecast of range impossible. But the movements of the target are only a part of the difficulty. Those that arise from the manœuvres of the firing ship may be still greater and more confusing. ”

“ In naval affairs nothing is improvised, and a satisfactory conclusion upon these points can be arrived at only through long experiment, and perhaps frequent disappointment. Yet it is not doubted that the same ship may exhibit a handy and efficient rig, develop a high velocity canvas, and, without great power, a sufficient speed under steam. ”

“ It will be seen that when a ship is going at a relatively slow speed, the greater portion of the whole resistance is due to skin friction, but when going at a high speed, the greater portion of the resistance is due to wave-making. Hence the moral is that ships and boats intended to move [93] at a high speed must be so fashioned as to reduce to a minimum the wave-making power. In general, the naval architect has to consider many other matters besides speed. ”

“ If he navigates against the current he accomplishes 10 miles an hour with respect to the shore, though he has been travelling at the rate of 20 miles an hour through the water. If he goes with the current he accomplishes 30 miles an hour with respect to the shore, though he has not been going any faster through the water. This is one of the reasons why it is so difficult to estimate the speed of an air-ship. ”

“ As already stated, in the ship whose coefficient is 0.78 any increase of power produces very little gain in speed, and if such a ship were fitted with engines and boilers of the same size and developing the same power as those of a 20-knot Atlantic greyhound, the increase in speed would be very insignificant, but the disturbance in its immediate neighborhood would be very great ”

“ It seems extremely improbable that she could have maintained uniform speed of 17 2/3 knots throughout the twenty-four hours, but at times her speed probably slackened to 15 or 16 knots. If this supposition is correct, it follows that her speed must at times have exceeded 17 2/3 knots in order to account for this average. ”

“ Contrary to their expectations, there was scarcely any perceptible shock, but the ship’s speed was rapidly checked much as is the speed of an express train when the brakes are suddenly and powerfully applied, and in some six seconds, though the engines were still going ahead at their utmost speed, the progress of the Flying Fish over the ground was as effectually checked as though she had been lying at anchor. ”

“ Speed is costly, and as you increase it it is generally necessary to also increase the tonnage. Thus if the problem before you is to beat the record of a seven-thousand-ton ship, which has developed eighteen knots with engines of twelve thousand five hundred horse-power, you must (principally for economic reasons) have a larger hull as well as more powerful engines for your competing vessel. This forces upon your consideration tides, channels, harbor-bars, and dock accommodations, all of which impose limitations upon you. ”

“ Major McCarthy answered, “It all depends. A light ship can take off in about a hundred yards or less. A big ship heavily loaded may take a quarter or half a mile or even more to take off. In landing, the ground speed depends a lot upon the velocity of the wind. The stronger the wind, the less space required in which to land.”
They were walking towards the sheds. Pointing, Paul asked, “What’s that?” ”

“ So many inducements are now afforded to merchants to transact their dealings rapidly, [pg 115] that the ship-builders are beset on all sides with demands for more speed—more speed; and it is significant to observe that, in almost every recent newspaper account of a ship-launch, we are told how many knots an hour she is expected to attain when fitted. Every ship seems to beat every other ship, in the glowing language employed; but after making a little allowance for local vanity, there is a substratum of correctness which shews strongly how we are advancing in rate of speed. ”

“ Speed trials were carried out under various conditions of running, when it was found that the ship possessed a speed of 54 1/4 miles per hour with the engines running full out.
To summarize the performances of these ships as we did in the case of No. 9, we find:
Speed: Full 54 miles per hour Normal =2/3 48 " " " Cruising =1/3 33 " " " Endurance: Full 18 hours = 1,000 miles Normal 26 " = 1,250 " Cruising 50 " = 1,900 "
The production of the rigid airship during the war was always surrounded with a cloak of impenetrable mystery. ”

“ It is, however, true that sailing ships did then, and can now, sail, under favorable circumstances, at very much higher rates than we have just mentioned, and even as much as 15 knots can be obtained with one of fine lines with a favoring wind; but a sailing ship is not always free to traverse the shortest distance from port to port, and even when wind and weather permit of this, the average speed falls far below 15 knots with the best-designed vessels; hence if a steamer could do 9 knots she would make shorter passages than any sailer ”

“ Before this occurs the ship’s bottom must be cleaned, for a foul underwater skin will deaden the speed, and give altogether erroneous data. The weather should be favourable also, the sea calm, and the water not too shallow to cause resistance to ships of high speed, while a good steersman must be at the helm so as to keep the ship on a perfectly straight course. ”

“ He determined to measure the period of time occupied by the regular waves in overtaking the ship, their width from crest to crest, and the rate of their traveling. The first point to be known was the speed of the ship; this he ascertained to be nine knots. His next object was to note her course in reference to the direction of the waves. He found that the true course of the vessel was east, and that the waves came from the west-northwest, so that they passed under the vessel at a considerable angle. ”

“ And the speed has not been obtained at sacrifice of comfort. On the contrary, an ocean passenger steamer belonging to any of the great passenger lines is something like a floating palace.
After the Britannic and Germanic appeared, line after line put forth fine vessels; and in 1889 was launched the White Star steamer Teutonic, which for some time held the proud position of the fastest ship on the Atlantic. She had crossed in 5 days, 16 hours, 31 minutes. The average of several trips, both for [86] herself and her sister Majestic, was 5 days, 18 hours, 6 minutes. ”