Fig. 6.
The position of a vessel may be ascertained simply and accurately by cross-bearings. Suppose you are in a ship at A in Fig. 6. The point with the lighthouse on it bears correct magnetic N. by W., and the point with the tree on it E. by N. You lay the parallel rules over the compass on your chart at N. by W., and work them to the lighthouse, preserving the direction. You then draw the line from the lighthouse to a. You then lay the parallel rules over the compass on your chart at E. by N., and work them in a similar way to the tree. Then draw the line from the tree to a. The spot where the two lines cut was the vessel's position on the chart when the bearings were first taken. The distance of the ship from both lighthouse and tree can be measured by taking in the dividers the distance between either and the ship, and referring to the scale on the chart.
It should be remembered that when sailing along the land cross-bearings will always determine your position, always allowing the proper corrections on the compass. In taking cross-bearings, try to have a difference between the two objects of as nearly ninety degrees as possible.
The old-fashioned log-ship and log-line for determining the distance run by a vessel need have no place in the equipment of a small yacht. There are several patent self-registering logs which record the distance run, either on the taffrail or on dials on the log itself. Their performance is fairly satisfactory, but they should be kept well oiled, and should be often examined and tested—for instance, in a run between two objects whose distance apart is well known.
By careful attention to the Lead, the Log and the Look-out, a boat may be navigated, by dead reckoning, with a certain amount of accuracy.
A nautical mile, or knot, is the same as a geographical mile. Its length is six thousand and eighty feet. A statute mile in the United States measures five thousand two hundred and eighty feet.
XVII.
MARLINESPIKE SEAMANSHIP.
WITH INSTRUCTIONS FOR MAKING SPLICES
KNOTS AND BENDS.
MARLINESPIKE.