Choosing a Compass
Four Steps in Choosing a Compass
- What kind of boat will the compass be used on?
The main differences between sailboat compasses and powerboat compasses are the damping characteristics and the heeling angle limit. Powerboat compasses usually have fixed lubber lines in order to maintain best dynamic operation. Sailboat compasses will have gimballed lubber lines and a greater heeling angle limit.
- What size is the boat?
The further the compass will be from the helmsman, the larger the compass you should have. If your boat is greater than 8 meters (approximately 26 feet), consider a 100 Series or larger capsule. ComNav compass models are named for the apparent size of the compass card. For example, the compass card on a 70 Series compass has an apparent size of 70mm (2 3/4 ") while the 125 Series has an apparent size of 125mm (4.9"). We say "apparent" size since the dome and fluid inside the compass magnify the actual card size.
- Where will the compass be mounted?
There is a Comnav compass for every mounting need. Many series are available in different mounting styles: Bulkhead, Flush-mount, Overhead, On the Mast, or Bracket-mount. All compass models are designed to eliminate unnecessary drilling during installation. Regardless of mounting type, your compass should be positioned where it can easily be read from the helm, even in darkness when illuminated. Position the compass as far away as possible from iron objects or other magnetic sources such as loud speakers, windshield wiper motors, etc.
- What kind of compensators do you need?
Deviation or soft iron compensators are a must on steel-hulled vessels. However, magnetic disturbances will be found on almost every boat regardless of construction material. For this reason ComNav recommends the use of compensators for all compass applications where the compass will be used for navigation. Most of the various compass models are available with built-in compensators. Remember that the distance to the source of interference is more critical than the strength of it.
Features to look for in a compass
Look for these important features found on ComNav compasses:
The earth's magnetic field changes in intensity depending on geographic location. This varying field causes a compass card to tilt away from the horizontal. To offset this, counterweights are placed on the compass card so that it balances horizontally. This allows the compass card to swing smoothly rather than dragging on the top or bottom of the compass capsule. ComNav compasses are balanced to operate in one of three magnetic regions; MN, ME, and MS. Use of a compass outside its region can effect its ability to give an accurate heading; in extreme cases the compass may stick.
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