A Simplified Guide to Small Marine Craft Navigation.

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Chapter 10 (v.1) - Special Steering Compasses.

Submitted: December 14, 2016

Reads: 117

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Submitted: December 14, 2016

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Special Steering Compasses.

 

Grid Steering Compass.

If a craft has sails and steered by a tiller the helmsman will have to move from side to side, and may not be able to see clearly the card of a compass placed centrally over the crafts keel. Viewed from one side or the other, parallax will be introduced and he will not be able to see the correct card graduation against the lubber line. In these circumstances, a Grid Steering Compass is often more convenient and easier to steer by.

A grid compass has a top glass cover plate engraved or painted with a grid, a pair of parallel lines. This glass can be rotated and its outer edge is graduated 0° - 59° so that the grid parallels lie on either. side of the 0° - 180° direction. A lubber-line runs across the diameter of the underside of the compass bowl glass, not the underside of the grid plate. The compass card itself may or may not have degree markings on it, but will certainly have a line, usually in red, marked on its North–South  axis.

To use the grid, suppose the sailboat is heading 090°, East, but that it is required to alter course to 135°, South East, first rotate the grid glass until the 135° gradation on the glass is in line with the forward end of the lubber line and clamp the ring into position. Then steer until the grid wires lie parallel to and on each side of the red North-South wire on the card with the mark on the grid glass immediately over the end of the red wire. The sailboat will then be heading 135° and can easily be kept on that heading by keeping the grid wires parallel to the red wire on the card, even when the compass is viewed from one side.

 

Transmitting Steering Compass.

In these, a master compass drives or controls electronically one or more repeater or slave compasses. The advantage of this system is that the master compass can be sited anywhere in the craft providing it is clear of local magnetic influences, and the repeaters can be located wherever required for either steering or bearings. The disadvantage of the system is that it depends on a constant and voltage reliable electric power supply.

There are other steering compasses designed specifically for high-speed power driven craft. These compasses have been specially dampened to withstand the motion of this type of vessel and are available with or without grid facilities.


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