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simply that your. compass does not head as it should. It deviates either to the one side or the other, You could not make a tperfect course from one place to another with an imper- fect compass unless you knew the amount of its error and allowed it. We will -suppose that our ship is lying at a dock or a pier where we know that she heads exactly north. Out on thé: dock away trom any disturbing influence, such as iron or steel, -we have a _ perfect compass. This compass. points in the same direction as the pier--exactly north. We now bring this compass aboard our boat and put it in, the binnacle box, but instead of showing north, as it should) we sow fund that it heads north by east, disturbing influ- ences aboard the boat having caused it to deviate from its proper bearing. It shows one point of westerly devia- tion, Its north point is one poimt to the westward of where it should be. When you wished to go north with your ship with this compass you ' 1 N 1 Ww Ss ( ' | ] THE WAY OUR COMPASS HEADS. FIG. TAE Manarint KEVIEW would have to steer north by east as shown in the foregoing cut, Fig. 1. But we cannot always correct our compasses at a dock or pier because we may have no way of finding just how this dock or pier may head. of course. we can correct them on the river ranges. The true bearing of all river ranges is given in the light- house. books or on charts. . ihese have only to be corrected for varia- tion (see variation of the compass) and you will then get the "correct magnetic bearing of any range. In several different lake pilot books the bearings ate 'all corrected dor" you and you have only to refer to them to get the correct magnetic bearing. Suppose we headed our ship ona river range and found that our com- pass refer to the book and find that she should head due north. pass therefore shows a half point of easterly deviation. Its north point is a half point to the east of where it should be. Thus: Zz THE WAY OUR COMPASS SHOULD HEAD. showed north half west. We- Our com--- 31 When you wished 'to go north with your ship with. this compass you would have to. steer north half west, as shown in Fig. 2. For compasses that deviate to the east simply allow the same amount to the west and you will' make just as. good courses as if your compass wals correct. But don't make a mistake when naming this error or deviation on courses in other directions. Suppose oun ship was on a range and our compass shows south by west. But we find the correct bearing should be: due south. (See Fig. 3.) The south point of our compass is heading one point to the westward of where it should. It might seem to us that this would be westerly devia- tion but it is easterly deviation. De- viation is always figured from the north point. While our compass is heading south by west look at the north side of the compass--it shows north by east. The north point of our compass is one point east of where it should be, therefore easterly devia- tion. If our compass shows to: the right of where it should we say east- erly deviation and if to the left we say westerly deviation. Therefore if we have found out that our com- pass deviates to the right of the cor- rect bearing we simply allow that amount to the left, or if we find that our compass deviates to the left then allow that much to the right. Another good way of allowing for deviation is as follows: Port your boat for westerly deviation and star- board for easterly deviation. means that if you find that your com- pass has a certain amount of westerly deviation then port your boat just that much. Or if you find that your com- pass has a certain amount of easterly deviation starboard your boat just that much. You simply pull your boat back where she belongs. , If your com- pass has/westerly deviation it is tak- ing your boat just that much to the left or port of where it should, Then to correct your boat's course you just port your boat back again. (See Fig. 4.) We wish to shape a course from the point A to the point B. These . places lie exactly north from each other. We put our ship at north by our compass. But we have previously found that our compass has one point westerly deviation when on north courses. If we continued on our course as shown by our compass we would go considerably to the left of where we should: go. Therefore we port our boat one point and this puts us on the correct course from A to B. This |