In our average ship, we may take it about one-quarter the length of the ship from the stem.' An analysis of the curve brings out the following points: Ist. The first effect of putting the helm over is to throw the whole mass of the ship off to leeward, so to speak; that is to say, to the side opposite that toward which it is desired to gain ground. The stern goes off most; but the whole ship, except the extreme bow, is thrown more or less to this side, and some experiments have seemed to show that even the bow goes off at first. This throw of the stern to leeward is technically the "kick." 2nd. The ship ranges ahead nearly along the line of her original course, but slightly to leeward of it, for a distance which may be roughly stated as from two to three ship's lengths, before she commences to gain ground in the desired direction. The momentum of the ship along her original course persists for a time and drives her on along this line in spite of the forces which are turning her head away from it. 3rd. The stern does not finally clear the line of the original course until it has covered from two to three lengths measured along that line. In the meantime, the ship's head has changed by more than three points. 4th. If this manoeuvre were resorted to for the purpose of avoiding a danger suddenly discovered dead ahead and distant from two to three ships' lengths, it would probably be ineffectual. 5th. The distance covered parallel to the original course from the time of putting the helm down until the ship has turned through eight points, is in this case approximately four lengths. This is called the "Advance" and in the figure is represented by the distance CK (Fig. 2, Plate 93). All of the above points are brought out in a very striking way in the curve of the Yashima-a ship of altogether exceptional manoeuvring power and of high speed (Fig. 1, Plate 94). 'It is doubtless true, as pointed out by Admiral Colomb and others, that the pivoting point changes its position in the early part of the turn and does not settle down as a fixed point until the ship's path has become a true circle. The variation, however, is not important for our present purpose The characteristics which have been noted in the other curves are all present here in an exaggerated form. It will be seen that if two Yashimas, sighting each other dead ahead, should put their helms hard aport1 while separated by a distance of 650 yards (5 ships' lengths) their sterns would collide (Fig. 2, Plate 94). The remarkable manoeuvring power of the Yashima is due to the fact that her after deadwood is cut away to a very unusual extent. This reduces the resistance of her afterbody to lateral motion, and as a result the stern is thrown off much more rapidly and to a greater distance than would ordinarily be the case. This illustrates very strikingly the fact that it is the stern and not the bow of the ship that moves in turning. With regard to the speed involved in these curves, this begins to fall off, as might be expected, the moment,the helm is put down, the reduction being due to the resistance of the rudder and the sidewise motion of the ship. It continues to fall off until the point is reached where the turning curve becomes uniform and circular, at which point it has fallen off to something like 60 per cent of its original value. From this time on, it remains constant as long as the turn continues with the same helm angle. It is found that the speed at which a ship is moving when her helm is put over does not greatly affect the space in which she will turn. A ship running at eight knots speed, putting her helm down suddenly, follows very nearly the same track as if she were running at twelve knots. This is a result which would perhaps hardly have been anticipated, but it has been demonstrated by too many experiments to be called in question. As regards the time of turning, there is, of course, a great difference in favor of high speed. It follows that if a ship is attempting to clear a stationary object by putting her helm hard over, it makes little difference with regard to her success whether she slows or continues at full speed, though it will make much difference in the force with which she strikes, if strike she must. If the object to be avoided is another ship under way, there will be an advantage in gaining time by slowing, as this will give an opportunity for both ships to recognize the situation clearly and to act accordingly. It is important to remember, moreover, that during the time actually occupied in putting the helm over, a steamer running at high speed will cover a greater distance than if she were running slow. 1. rudders full right. We do not here deal with the question of reversing the engines. This will be considered in a later section. We have thus far confined our attention to the effects of a helm put suddenly hard over. This is an exceptional case, but it brings out very clearly the points that are involved in the more common case in which a small angle of helm is used-generally for a short time only--and a small change of course effected. In this case, also, the stern is thrown off, and for some time the body of the ship moves along a line to leeward of the original course. This should always be taken into account. It becomes of great importance when manoeuvring in crowded waters, and in all cases where the danger to be avoided is close aboard. The realization that the stern moves and not the bow, will often make all the difference between a close shave and an inevitable disaster. We have seen that the effect of speed upon the space in which a ship will turn with a given angle of helm is not great. It should, however, be remarked, that a fair speed is essential for the proper handling of any ship. Not only is a ship when moving very slowly through the water at the mercy of the wind and sea and tide, which under such circumstances have an undue effect upon her, but all the varying and conflicting elements that have been described in § I are liable to manifest themselves in unexpected and seemingly erratic ways. It is therefore important always to keep up a reasonable speed; and while this term is hardly susceptible of exact definition, it will probably be agreed that such a ship as we are at present considering of average size and manœuvring powers-will not handle with certainty at speeds much below four knots. We shall discuss in another chapter the theory held by many seamen, that it is safer to run at maximum speed through a fog than to slow down. Although it is found, as has been explained, that when a ship is going ahead, the rudder so far outweighs all other elements involved in the steering that these other elements may in general be neglected, it is nevertheless true that hardly any ship turns with exactly the same readiness to port and to starboard; and it appears from experiments to determine the tactical diameter of men-of-war that the circle made with port helm2 may differ from that with starboard helm,1 by as much as ten per cent. Although we are dealing at present with the turning of ships, it may be well to add a word with regard to the power of stopping. It is found that a ship steaming ahead with the helm amidships, and suddenly reversing her engines without moving the helm, will stop in from three to five times her own length; and that this distance is practically independent of the size and speed of the ship. This supposes the same power used in backing as in going ahead. If there is a reserve of power available for backing, a ship should be stopped in twice her length. The space in which a ship can be stopped, as compared with that in which she can be turned, becomes important when danger is suddenly discovered ahead and on both bows; as, for example, when a ship finds herself heading for a coast or a line of reefs, and dangerously close. We have seen that she may, by putting her helm hard over, turn through eight points with an advance in the direction of the original course, of about four lengths. This would seem to show that it is at least as safe to try to clear such a danger by means of the helm, as by stopping the ship. This was the conclusion of the Committee of the British Association (see Report British Association 1878, page 422). It will be shown later that probably the safest course of all is to combine both methods, putting the helm hard over (preferably to port), and when the head has begun to swing decidedly, reversing full speed and immediately afterward shifting the helm. The time and space in which a ship may be brought to rest when moving at a given speed are matters of great practical importance. The time may be determined by the very simple experiment of reversing the engines and noting the number of seconds required to come to rest. Observations upon the space are not so easily made, but experience shows that the space may be determined with considerable accuracy from the observed time, by the simple formula: D= 7/10 ST. Where D Distance in feet required to stop. S = Speed in knots and tenths. Time in seconds (observed). See "General Information Series No. IX," issued by Office of Naval Intelligence, U. S. Navy Department. III. SHIP AND SCREW GOING ASTERN. (Plate 95.) This case is more complicated than the pieceding one, for the reason that the effects of the screw, which in going ahead are so |