Log (navigation)

“ The speed of vessels can be tolerably well calculated from the number of revolutions of the screw.
"Now," said the Captain, turning to the third officer, who was also on the bridge, "what was the last record of the chip log?"
"Twenty knots, sir."
"Common log is not much good at high speeds," commented the Captain.
The common log consists of a triangular wooden float, a line marked with knots at equal distances apart, and a reel. The float is thrown overboard, and the line allowed to run off the reel for a certain number of seconds. ”

“ The log-line was one hundred and fifty fathoms in length, and was wound on a reel, which turned very easily, so that the resistance of the chip to the water would unwind it. The log-line is divided into certain spaces called knots, the length of each of which is the same fractional part of a mile that a half minute is of an hour. If there be sixty-one hundred and twenty feet in a nautical mile, or the sixtieth part of a degree of a great circle, which is not far from accurate, and the ship be going ten knots an hour, she will run sixty-one thousand two hundred feet in an hour. ”

“ It is in reality the ship's diary, but it is called a log-book, because its chief object is to record the speed of the vessel.
This speed is found by using an instrument called a log, which is attached to a line, divided into equal spaces by knots. These are placed certain distances apart, so many to a mile. The log is made in such a way that it will remain almost stationary in the water when thrown overboard. The line, wound upon a reel, is allowed to run out for a few seconds ”

“ Along either bank, among the bushes, on sandbars, and in trees, hundreds and hundreds of logs had been stranded when the main drive passed. These logs the rear crew were engaged in restoring to the current.
And as a man had to be able to ride any kind of a log in any water; to propel that log by jumping on it, by rolling it squirrel fashion with the feet, by punting it as one would a canoe; to be skillful in pushing, prying, and poling other logs from the quarter deck of the same cranky craft ”

“ I was endeavouring to discover what particular nautical technicality might justify this application of ship in the sense of raft or float, when I recollected that sailors call the little float by which the log-line is held stationary in the water, by the term log-ship; and, by a rather singular coincidence, the origin of this very word log-ship is made the subject of comment in a recent number of "NOTES AND QUERIES" (p. 254.) , by a West Indian correspondent, A. L., who thinks the term log-chip. ”

“ Then, whatever mark you can distinguish on the line nearest to your hand at the expiration of the allotted twenty-eight or fourteen seconds, when the man holding the glass sings out “Stop!” as the last grain of sand empties itself out of the bulb, that will be the speed of the ship.
The division of knots on the log-line bear the same proportion to a mile, as the twenty-eight or fourteen seconds of the glass does to an hour of time; so, if the four-knot mark be to hand, and the “long” glass be used, she is going four knots, or nautical miles, per hour. ”

“ I am told by a gentleman familiar with the scenes and incidents connected with log driving, that he has frequently seen the drivers cross rivers which were comparatively free of logs, by standing upon a log and with their feet making it revolve quite swiftly, and thus gradually propelling it across the stream. ”

“ When the time comes for performing the operation of heaving the log, as they call it, the men appointed for the purpose bring the log and the reel to the stern of the ship. One man holds the log, and another man the reel. There are two handles, one at each end of the reel, by which the man who serves it can hold it up over his head, and let the line run off from it. Besides the two men who hold the log and the reel, there is a third, who has a minute glass in his hand. The minute glass is like an hour glass, only there is but just sand enough in it to run a minute. ”

“ As my air-ship ploughed ahead the wind struck my face and fluttered my coat, as on the deck of a transatlantic liner, though in other respects it will be more accurate to liken aerial to river navigation with a steamboat. It is not like sail navigation, and all talk about "tacking " is meaningless. If there is any wind at all it is in a given direction, so that the analogy with a river current is complete. When there is no wind at all we may liken it to the navigation of a smooth lake or pond. ”

“ The major was scanning the expanse of water by aid of his pilot glass, and the quartermaster who had been steering went to the line of the patent log to haul it in—his first duty at any time on the stopping of the vessel, to prevent the line—the strain being taken off it—fouling with the propeller.
When the steamer is under weigh it is the work of two sailors to take in the eighty fathoms of log-line, otherwise, however, the line is of course quite slack ”

“ All the passengers, from the upper deck, are watching the Kruboy lying across a log that heaves and rolls while he passes the chain beneath it, and at that moment another log is driven towards it with its full ton weight, the two colliding broadside. The passengers shout; if there is a lady aboard she screams. ”

“ It found them New Holland and the Indies, and both Americas. It was their longitude and often their latitude. It was their chronometer and sextant. We use it still, and cannot better it. A simple and noble old contrivance is the log. May the mariner never lose faith in it! Crutched by the log on one side, and the lead on the other, he may hobble round the globe in safety, defiant of shoals, regardless of fogs.
I hove the log, and made the speed seven knots.
“A good start!” exclaimed Greaves, rising and coming slowly to the rail, and looking over. ”

“ As the logs are floated down from the stationary "drive" above, which, perhaps, fills the river from bank to bank, and extends up the stream as far as the eye can reach, the men whose duty it is to separate the logs catch them as fast as they are floated down to them, hastily glance at the log-mark, mount the log, and, with the aid of the rope stretched from bank to bank, pull themselves and the log to a point directly above the boom of the owner of the log, and then release it, and permit it to be carried by the current into the proper boom. ”

“ When tacking out of sight of land, the direction and length of each successive board can be pricked out on the chart by using the dividers and parallel rule in the manner already described, and the position of the vessel at any time will thus be known. [124]
Before land is lost sight of, what is termed a departure is taken from the last well-known object on the shore. Its bearing is taken by compass, its distance by log is estimated, and the time is noted. A departure can also be taken by cross bearings. ”

“ But in Kelly and Woodes Rogers' days the log chip, reel, line, and half minute glass were the mariner's sole means of finding his longitude, or distance, sailed east or west.
Steam and patent logs have much simplified such calculations, which required many corrections not only for leeway but for errors in the log line and glass; "Shortness of the knots in a line," says Kelly, "being on the safer side, that a ship be not ahead of her reckoning; it being better to look for land before we come at it than to be ashoar before we expect it." ”

“ The Baker navigating machine, with the chart, was on my knees. Not knowing what kind of weather was before us, I knelt on my seat and made haste to take observations on the sea, the horizon, and the sun, through intervals in the covering of clouds.
The navigation of aircraft, in its present [Pg 43] stage, is distinctly more difficult than the navigation of seacraft. The speed at which they travel and the influence of the wind introduce problems which are not easily solved. ”

“ After toilets had been made with salty sea water, we squatted in the cockpit for breakfast of coffee and hardtack. Navigation was difficult in so small a boat. It was impossible to spread the charts out properly, and with the slightest carelessness the wind might take our priceless navigation papers overboard. We had to use the sextant and other navigation instruments in a boat that often pitched so much we could scarcely stand. The papers, charts, tables, logarithms, and so on, got sopping wet, and when we dried them in the sun they grew swollen and difficult to handle. ”

“ This operation is repeated as often as is necessary to cover the three or four miles between ship and shore, until at last the long line of tumbling logs are brought alongside their destined vessel, and secured to the big spar on the forecastle. At whatever time they arrive all hands must turn out to receive them, and on board the American ships the uproar used to be fearful ”

“ It is best used during daylight hours and for short distances. (2) Navigator-observer methods. This is the most accurate means of river navigation and can be used effectively in all light conditions. Equipment needed to do this is a compass, photo map (first choice) , topography map (second choice) , poncho (for night use) , and pencil and flashlight (for night use) . (a) The navigator is positioned in the front of the boat and does not paddle. The navigator keeps his map and compass oriented at all times. To check the map during darkness, he uses his flashlight under a poncho. ”

“ He then compares that position with his voyage plan, his operational commitments, and his predetermined “dead reckoning” position. A good navigator anticipates dangerous situations well before they arise, and always stays “ahead of the vessel.” He is ready for navigational emergencies at any time. He is increasingly a manager of a variety of resources--electronic, mechanical, and human. Navigation methods and techniques vary with the type of vessel, the conditions, and the navigator’s experience. ”

“ The Lead Line
SINCE the coming of the mariners’ compass many centuries ago, navigation has made steady headway. It is now an exact science, and vessels properly equipped with needed instruments and with men able to use them, can, no matter what the winds or seas, or how extended the voyage, be brought safely to their destination.
The instruments used in navigation are, the compass, by which ship’s courses are steered; the sextant by which observations of the sun, moon and stars are taken, and through which the latitude is ascertained ”

“ In practical navigation a vessel commences her voyage and attempts to sail in a certain direction, but the well-known elements of compass error, variation and deviation, current, wind, seas and poor steering all divert the vessel from the projected course. In dead reckoning a navigator strives to keep track of his position by keeping a record of actual courses steered and distances run. ”

“ Our final discovery was that this arrangement enabled us to use still smaller logs and thereby gain greater speed. And there our discoveries ended. We had invented the most primitive catamaran, and we did not have sense enough to know it. It never entered our heads to lash the logs together with tough vines or stringy roots. We were content to hold the logs together with our hands and feet.
It was not until we got over our first enthusiasm for navigation and had begun to return to our tree-shelter to sleep at night, that we found the Swift One. ”

“ It required the nicest steering to pick one's way through this rushing raft, even in the day-time, when crossing from point to point; and at night the difficulty was mightily increased; every now and then a huge log, lying deep in the water, would suddenly appear right under our bows, coming head-on; no use to try to avoid it then; we could only stop the engines, and one wheel would walk over that log from one end to the other, keeping up a thundering racket and careening the boat in a way that was very uncomfortable to passengers. ”

“ I've heard of navigators, you must know, whose reckoning by account has landed them by four degrees of longitude inland—same thing may happen with some folks' sextants. My course is your course, and you'll please to stick to it."
"There's not even yet southing enough," said Mr. Wilson.
"Yes, there is," cried Captain Punch. "you don't want to teach me navigation, do 'ee?"
Captain Parfitt rushed into the cabin and returned with a chart, which he laid open on the deck at Captain Punch's feet. ”

“ The difficulty of navigation is due to the fact that unless there is absolutely no wind, the compass, after the corrections for variation and [Pg 35] deviation are made, only shows the direction in which the head of the flying-boat is pointing and not the direction in which it is travelling, and the air-speed indicator only gives the speed of the machine in relation to the air. ”

“ Six feet by twelve is a fair size. The smaller the logs the larger the raft must be in order to carry any weight, for it must cover a wider surface of water than is [217] necessary for one made of large logs. One good-sized log will carry your weight easily, but a small one will sink beneath you.
If you have two long, strong ropes you can use them for binding the logs together; if not you must make the ropes from fibre of some kind. Daniel C. Beard in his book, "Boat-Building and Boating," tells of making a very strong rope of the inner bark of a chestnut-tree which had been killed by fire. ”