For, “coastal,” category navigation (no more than 2 miles from the coast,) the magnetic compass is obligatory by regulation. Prudence should demand it however, whatever the category.
Attention, certains compas dans ce catalogue ne sont pas homologués. Ils ne doivent pas servir pour la navigation mais peuvent être placés dans une cabine ou le carré pour surveiller le cap.

The right choice

One selects a compass according to function and rose diameter. It is the latter that determines ease of reading. A small rose must be close to the helmsman, the larger rose may be further away. The diameter should be chosen according to vessel size and helmsman’s position. In general a diameter of 75mm is reserved for boats of 9m and less, one of 90mm for those between 9 to 12m and one of 135mm for those larger than 12m. Of course these sizes must be related to reading distances. For good visibility one finds three types of rose: plate, conical and cylindrical. On a plate the reading is taken at the back of the rose. The rose plate read when the compass is below the line of sight of the helmsman. The conical or cylindrical rose (read vertically) is of more universal use with two reading options, on the side or above. In this case the compass may be read sitting or standing. The choice of model (encased, bracket, column) must be based on its location on the boat. On a motor boat, it must correspond to precise fabrication criteria (stability, sensitivity to vibration.) All manufacturers have models tailored to different types of boat (sail or motor.) Models for specific purposes are also available. These include reinforced and less sensitive models for motor boats as well as models with coloured roses for racing (tactical compass.)


The bearing compass

Portable, the bearing compass allows for an increase of marks. It is of great aid whatever the type of sailing. Note, the Plastimo Iris model, may be used as a bulkhead compass in its base or as a bearing compass with a practical handle.


How does it work?

A compass is a precision instrument which may use more than 12 elements. The vital part is the rose, equipped with magnets, which rest on a pivot without moving. To cushion the movement of the boat the rose rests in a solution more viscous than water (petrol based.) A membrane permits the dilation of the liquid without forming air bubbles.
Quand on est amené à changer son compas, on n'a pas souvent d'autre choix que de s'orienter vers un modèle du même diamètre que celui à changer.


Pour les bateaux à moteur, plus soumis aux chocs que les voiliers, il existe des modèles spécifiques pour supporter ce mauvais traitement. Les modèles "voiliers" ne tiendront pas longtemps ce comportement chaotique.

The Electronic compass

The electronic compass is reserved for the central instrumentation (pilot, radar.) They require a power supply (12 or 24 volts.) They consist of two parts: a sensor which must be placed at the boat’s centre of gravity and a display. They indicate the course followed, the route charted with deviation alarms…Of less sensitivity to magnetic masses and offering the possibility of installing more distant magnetic masses, they are recommended on steel vessels.

Deviation curve

A compass does not have the same precision over the entire rose. It can be accurate to the North and yet display a few degrees difference to the South. One notes these deviations on a curve; the deviation curve. It then serves to correct the course in order to follow the exact route, even if the differences are so small they are often overlooked. To meet the deviation curve, one may use a bearing compass free from any magnetic field (while standing on the bridge for example.) The difference (positive and negative,) is then modified to the curve. If the  deviation is significant, it is necessary to offset the compass.
Replacement; when it is necessary to change a compass we often have little choice other than to orient toward a model of the same diameter.
Vibration; for motor boats, more subject to shocks than sailing vessels, there are specific models. The sailing models will not hold up to this chaotic activity.
Bearing; the bearing compass is indispensable on board even if it used less and less. It is a delicate instrument that must be kept in an appropriate case.
Homologation; Beware, some compasses in the catalogue are not certified. They should not be used for navigation but can be placed in a cabin or other area, to watch the course.

The Earth’s magnetic field

A compass must be balanced according to the navigation zone. The magnetic field acting on the earth’s surface is the result of two forces: one horizontal, which acts on the directivity of the compass rose and the other vertical, which tends to tilt toward the south or the north. The intensity of the result depends on the geographic location. There are four zones which each affect the compass differently:
-Zone A: Northern hemisphere.
-Zone B: South Atlantic, Indian Ocean, Central Pacific.
-Zone BC: New Caledonia, Tahiti, Reunion.
-Zone C: South Pacific, Australia, New Zealand.