Sailing Cruise

The one important tool for cruising around the ocean is a compass. It is a navigational tool for determining direction relative to the Earth’s magnetic poles. The compass consists of a magnetized pointer which marked on the North end, free to align itself with Earth’s magnetic field. A compass can be used to calculate heading, used with a sextant to calculate latitude, and with a marine chronometer to calculate longitude. It greatly improved the safety and efficiency of travel, especially ocean travel. The top of the traditional compass generally highlights the cardinal points of north, south, east and west. Often, compasses are built as a stand alone sealed instrument with a magnetized bar or needle turning freely upon a pivot or moving in a fluid. The traditional compass was invented in ancient China sometime before the 2nd century.

Magnetic Transmitting Compass
They make steering easier than with conventional compasses because they display steadier headings and do not suffer from the “lag” that occurs when making a turn. They can interface with chart plotters, autopilots and radar. Fluxgate Compasses consist of two pieces of readily saturated magnetic material with coils wound round them in opposing directions. AC current is passed through the coils and the material is saturated in one direction and then the other. The earth’s magnetic field affects slightly the time at which saturation occurs, earlier in one coil and later in the other. The difference is then calculated giving an output proportional to the earth’s magnetic field. They are accurate to 0.1 of a degree. Their output can be displayed digitally to the helmsman or they can interface with autopilots, chart plotters and radar.

Liquid compass
The liquid compass is a design in which the magnetized needle or card is damped by fluid to protect against excessive swing or wobble, improving readability while reducing wear. The first liquid mariner’s compass believed practicable for limited use was patented by the Englishman Francis Crow in 1813. Liquid-damped marine compasses for ships and small boats were occasionally used by the British Royal Navy from the 1830s through 1860, but the standard Admiralty compass remained a dry-mount type. In the latter year, the American physicist and inventor Edward Samuel Ritchie patented a greatly improved liquid marine compass that was adopted in revised form for general use by the U.S. Navy.

Mariner’s compass
They can have two or more magnetic needles permanently attached to a compass card. These move freely on a pivot. A lubber line, which can be a marking on the compass bowl or a small fixed needle indicates the ship’s heading on the compass card. Traditionally the card is divided into thirty-two points, although modern compasses are marked in degrees rather than cardinal points. The glass-covered box contains a suspended gimbal within a binnacle. This preserves the horizontal position. Mariners are concerned about very accurate measurements; however, casual users need not be concerned with differences between magnetic and true North. Except in areas of extreme magnetic declination variance, about 20 degrees or more, this is enough to protect from walking in a substantially different direction than expected over short distances, provided the terrain is fairly flat and visibility is not impaired. By carefully recording distances time or paces and magnetic bearings traveled, one can plot a course and return to one’s starting point using the compass alone.

Brunton 85R Dash/Surface Mount Marine Compass

The compass designed specifically for marine use, the Brunton 85R compass mounts to any dash or surface in the boat, where it provides intuitive, convenient navigation. The 85R includes such features as a direct reading disk and 5-degree graduations, making it easy to determine your bearing. And at 4.8 by 4.8 by 2.8 inches, it takes up a minimum of space. The 85R, which also weighs 12 ounces, is backed by a lifetime warranty.

Sources: soling-model-yacht.com, wikipedia.org