| The most useful technique anybody making a coastal | | | | Transferring simply means drawing a line parallel to the |
| passage should learn is how to double the angle on | | | | observed bearing through the dead reckoning position. |
| the bow. If your response to my statement is: "Why | | | | If, during the time between the first and second |
| should I do that? I've got a GPS." Think again! Not only | | | | observation, some observation has been made to |
| is there sense in knowing the basic techniques of | | | | establish whether the boat is being affected by |
| navigation - you might well need them in an | | | | current, that should be taken into account in plotting the |
| emergency - but there's great satisfaction. | | | | dead reckoning position. So if a current of say one |
| Doubling the angle on the bow will show you a position | | | | knot from dead ahead is established, then the amount |
| when you have only one object such as a headland, a | | | | of foul current suffered during the time between the |
| tree on a headland, or something of that kind to use. | | | | two bearings must be calculated. |
| The system is to take a bearing on the desired object | | | | For example, if the time was 45 minutes and you're |
| when it reads a whole angle, say 40º or | | | | travelling at four knots, then the boat will have travelled |
| 30º or 20º. You will be somewhere along | | | | three nautical miles between the two positions, but it |
| that position line. As you take the bearing, note the | | | | will also have been hindered by the current, which in 45 |
| boat's speed and course and the log reading. | | | | minutes at a rate of one knot will have held the boat |
| When the angle doubles to 80º or 60º or | | | | up by three-quarters of a nautical mile. So the actual |
| 40º, take another bearing to the same object | | | | position will be three-quarters of a nautical mile further |
| and plot it on the chart. At the same time or very | | | | back along the direction of travel. This is where the |
| quickly afterwards, read the log again. | | | | transferred position line must cut and this will be the |
| You now know how far the boat has travelled and in | | | | boat's position at the time of the second bearing. |
| what direction. That can be plotted off from any point | | | | If you show your crew how to do it, it will help them |
| along the first position line. The line should be drawn | | | | pass the time and give them a sense of achievement. |
| only as long as the distance travelled, and the second | | | | It may also stop them from asking the otherwise |
| position line then transferred to the end of the line | | | | inevitable questions: "Where are we?" and "Are we |
| marking the vessel's position by dead reckoning. | | | | nearly there? |