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HEELING DEVIATION. Editor Question and Answer Depart- ment, MARINE REVIEW :--I would like to have you explain the principal features of the changes in the deviation due to the heeling of a boat, and how to ascer- tain the amount for various degrees of heel and for all courses; what is the basis for computation? Is it true that the heeling deviation changes 2 degrees for every degree of heel? Can the heel- ing deviation be accurately adjusted and is it necessary to heel the boat in order to make the adjustment; can it be done without listing the ship by means of the dipping needle? Why is it that the heel- ing deviation is greatest on north and south and the needle is always drawn toward: the high side of the boat? I understand that the local inspector ques- tions candidates for licenses very thor- oughly on this subject. Don't you think this rather unnecessary and too compli- cated for lake men to understand? [I will thank you very much for your answer. a "ONE IN THE HARNESS." Cleveland. The magnetic field of a ship's mag- netism and its action on the compass! needle is altogether different between the positions of even beam and when listed. _ This is easily seen, but to make it all the more so, imagine a horizontal plane passing through the compass with the ship on an even beam. Imagine this horizontal plane to be the magnetic field of the ship's magnetism. When the ship is on an even beam this horizontal mag- netic field is parallel with the horizontal face of the ship's compass, and if the ship were on an even keel at the same time, this field would also be parallel with the ship's deck, or the whole of the ship's deck might be taken to represent the ship's field of mag- netism. Now, when the ship heels this. horizontal plane or magnetic field, heels with it, but the compass re- tains its balance owing to its gimbal ac- tion; hence, the same magnetism that acted on the compass in the first posi- tion does not act now, and the force might be either a stronger or a weaker one. ' As the ship heels over the earth's in- ductive force changes the magnetism in all iron that can only hold its magnetism; temporarily, as soft iron, for instance, and all vertical iron, whether it has per- manent or temporary magnetism, changes its field of operation in respect to the compass needle, so that the effects due to heel are not only a combination of causes, but a complication of causes as well, and the force that acted horizon- tally in the one case has now changed. toward a vertical force and the vertical toward a horizontal. TAE MarRINE REVIEW When a ship is on an even beam the various forces that produce deviation are considered as being horizontal, notwith- standing that there is a vertical force acting at the same time, and because this vertical force is a downward pull on one or the other of the poles of the compass needle, it is neglected, but when the ship heels this vertical force comes out on either one side or the other of the compass and produces a disturbing force and consequent change of devia- tion of the compass. Since the heeling deviation is always the greatest with the ship's head north or south correct magnetic, and nothing with ship's head east and west correct magnetic, the first thing to determine then is what is known as the heeling co-effi- cient. This is the deviation on north er south, caused by 1 degree of heel, and is found by dividing the difference between the deviation with the ship on an even beam and ship heeling, by the number of degrees of heel. Example: Dev. on N, ship on an even beam, 0°, when heeling 8° to starboard, Dev.. is 12° Wly.; therefore, 12 divided by 8 gives 1.5° Wly., as the heeling co-effi- cient, for each degree of heel to star-. board. From this it will be seen that the heeling error is directly proportional to the amount of the heel. Now, when the heeling deviation is re- quired to be known for any other course besides north and south, it can easily be found by knowing the co-efficient. on N ors. To get the heeling deviation for any other course and heel and knowing the heeling co-efficient: Rule--Multiply the number of degrees of heel by the heel- ing co-efficient. Enter the traverse tables under the angle equal to the course of ship's head correct magnetic ;' seek in the distance column for the prod- uct found in multiplying the degrees of heel by the heeling co-efficient and op- posite it in the column "Diff. Lat." will be found the heeling deviation on that' course. Steering NNE correct magnetic, heel- ing 14° to starboard, how much is the: heeling deviation, the heeling co-efficient being as above, 15°? Explanation: 14 mL = 210": turn to NNE in tables and find 21 in Dist. column and opposite} in the Lat. column will be the amount of the heeling deviation for that direction and the heel of the boat, the answer is 19.4°. Here is another and probably easier way of doing it: Take the parallel rul- ers and lay off a course of NNE and, draw it to a pencil line. Take the divid-} 'ers and measure off 19.4 from the mile scale and lay this off on the line drawn to represent the course of NNE; maki a dot to represent the points of the divid- ers. Next lay the parallel rulers over N and S on the chart compass and runy this over to the pencil line so that it ist directly over the lower of the two dots; draw this to a pencil line and draw it longer. than it need be. Next lay the parallel ruler over E and W of the chart, compass and transfer this line up to and directly over the upper dot and draw a pencil line that will reach from the sec- ond line (N and S) drawn to and through the first line (NNE) drawn. You have now constructed a right angle triangle, the same as given in the traverse tables. Measure the length of the N and §S line drawn using the mile scale of the chart and each mile will be a degree, and that is all there is to it. The NNE line rep- resents the hypotenuse of a right angle triangle and the N and §S line the per- pendicular. The length of this perpen- dicular will always be equal to the heel- ing deviation. Any chart may be used and the lines can be drawn at any place on: the chart. Any scale can be used, the larger the scale the larger the tri- -- angle. It will be seen from this that the ' heeling deviation changes in the same proportion as the sides of a right angle triangle. Now, to get the heeling co-efficient when the ship is heading other than N or S. Simply invert the above operation. Take the same example: Heading NNE, heeling 14°, Dev. between upright and heeled 19.4°. Draw a N and §S line 19.4 units long; draw a NNE line to inter- sect with the beginning of the first line, then draw an E and W line to intersect with the end of the first line drawn. You have drawn the same triangle as before, measure the length of the NNE line, which will be 21 units long and divide this by the amount of your heel and you get the heeling co-efficient as before. In some cases the heeling deviation amounts to as much as 2 degrees for every degree of heel. This is not a fixed rule and far from it. The adjustment for heeling deviation is no more perfect than the adjustment made with the ship upright. In some cases it can be done accurately, but in most cases it can not. The conditions must be very favorable. The adjustment can be made without heeling the ship by use of the dipping needle, but this is not as satisfactory a way as listing the ship. The heeling deviation is greatest on N and S for this reason: When the ship heels much of her magnetism changes owing to the earth's inductive force, that is, the low side becomes magnetic through the. earth's vertical force and the low side becomes an opposite pole to the earth's magnetism, which north of the equator is south in polarity. This makes a north pole of the low side of the ship' and a south pole of the high side, and