I. LEEWAY.

The angle included between the direction of the fore-and-aft line or keel of a ship, and that in which she moves through the water, as indicated by her wake, is called the leeway.

When the ship is not going before the wind, she will not only be forced forward in the direction of her head, but, in consequence of the wind pressing against her sideways, her actual course will be to leeward of the apparent course she is lying. When the wind is on the right hand side of a person looking forward, the vessel is said to be on the starboard tack; when on the left hand, on the port tack. The amount of leeway differs in different ships; depending on their construction, on the sails set, the velocity forward, and other circumstances. Experience and observation are required to judge what amount of leeway to allow in each case. The correction for leeway is necessary to deduce the course made good from the course steered, and it is one of the corrections to be applied in reducing the compass course to the true course in the day's work; the correction being allowed according to

RULE XXXVI.

When the ship is on the port tack, allow the leeway to the right of the course steered; but when on the starboard tack, allow it to the left, the observer looking from the centre of the compass towards the point the ship is sailing upon.

EXAMPLES.

Ex. 1. The course steered is N.W. by W., the wind N. by E., leeway 1 points.

The ship has the starboard tacks on board; therefore, the leeway (11 points) allowed to the left of N.W. by W., gives corrected Course W. by N. & N.

Ex. 3. Course N.E. by N., the wind N.W. by N., the leeway I point.

The ship being on the port tack, I point to the right, of N.E. by N. is N.E., the corrected Course.

Ex. 2. Course by Compass S. by E., wind E. by S., leeway 2 points.

The ship is on the port tack, then 2 points allowed to the right of S. by E., is S. by W. W., the Course corrected for leeway.

Ex. 4. Course steered W. by S., the wind N.W. by N., leeway 3 points.

The ship is on the starboard tack, 31 points to the left of W. by S. is S.W. S., the Compass Course made good.

The points of the compass are frequently treated with reference to their position to the right or left of the cardinal point towards which the spectator is looking, thus, N.N.E. is said to be "two points to the right of North;" W.N.W. "six points to the left of North." Adopting this notation the work in the above Examples will stand thus::

(a) When the ship is hove-to, take the middle point between that to which she comes up and that to which she falls off for the compass course, and correct this for leeway.

EXAMPLES.

2. THE VARIATION OF THE COMPASS.

The needle points to the magnetic north, which in few parts of the world agrees with the true north, the difference between them is called the Variation of the Compass. It is said to be easterly when the north end of the needle is drawn to the eastward, and westerly when drawn to the westward of the true north: thus, when the north end of the

needle points to that part of the horizon, which is true N.N.W. W., the variation is said to be 2 points west; but when it points to the N. by E. part of the horizon, the variation is said to be 1 point east. The variation is different in different places,* and it is also subject to a slow change in the same place, and becomes alternately east and west.f It also changes slightly at different times of the day.

Variation is one of the "corrections" in deducing the true course and bearing from the course and bearing observed with the compass. It is given on the charts used in navigation.

The method of correcting Compass Courses or Bearings for Variation will be readily understood by means of an example.

Suppose the variation of the compass is found to be two points east, that is, the needle is directed two points to the right of the north point of the heavens, that is,, points N.N.E. instead of N.; then the N.N.W. point of the compass-card will evidently point to the true north, and every other point on the card will be shifted round two points. If, therefore, a ship is sailing by compass N.N.W., or, as it is usually expressed, her compass course is N.N.W., her true course will be north; that is, two points to the right of the compass course. In a similar manner it may be shown that when the variation is two points westerly, the true course will be two points to the left of the compass course.

To find the true course, the compass course being given.

RULE XXXVII.

Allow easterly variation to the right of the compass course.

looking from the centre of the card over the point to be corrected.‡

At London the variation is 23 W., or the North end of the magnetic needle does not point exactly North, but 23 W. of North. In the West Indies the variation is nil; at Cape Farewell, 53° W.; at Cape Horn, 23° E.; at Hobart Town, 10' E.; at Canton, 1' E.; and Cape of Good Hope, 29° W.

+ In London, in 1580, the variation was one point E.; 1634, 4° 5' E.; subsequently to 1660 it was found to have diverged to the westward, attaining its maximum of 24° 30' W. about 1818, and then gradually returning towards the meridian again. At present it is about 22° W.

The learner must be careful to remember when correcting his courses that he is to suppose himself looking from the centre of the card over the point to be corrected. When he places the compass-card before him, mistakes very frequently occur in the application of the variation between the east and west points round by south; thus-taking the compass with the north point placed before or from the observer, while an error could scarcely arise when correcting courses in the N.E. and N.W. quadrants, it would be different with the S.E. and S.W. quadrants, unless he bore in mind, that in the latter instances the compass-card should be placed before him, as if he were facing the south. From what has been said it will be seen that in correcting courses, the significance of RIGHT, on the face of the compass-card, is as the hands of a watch move over the dial, and LEFT the contrary direction.