A New Direction in Compass Design
A compass mariners can look up to.
Viewing: This compass can be viewed from below with the same view as from above. This provides the user many mounting options; flush, bracket, bulkhead or binnacle housed with either a top view or a bottom view.
Compasses shouldn’t be looked down upon, they are directional instruments and should be looked across, either to observe, at a glance, the direction of the vessel’s heading or the direction of an object.
With an oblique view of the card, optimum optical benefit is achieved from the spherical bowl.
The clarity of the graduation markings is further enhanced by being perpendicular to the plane of the card and the observer’s line of vision.
Lubber line: The compass card rotates outside the lubber line marking which is from a shipshape in the middle of the compass.
This arrangement mimics the egocentric view of the vessel and her surrounding directions allowing for intuitive ease of reading and comprehending.
This is significantly different from traditional compasses where the compass card rotates inside the lubber line marking. Confusion can arise resulting in the helmsman trying to steer the card, a common error called “chasing the compass”.
Furthermore, on compasses read from an aft lubber line (“direct reading dial”, “front reading”) the display is counter-intuitive. The card’s graduations show starboard directions to port of the lubber line and when turning, the part of the card being read will move in the opposite direction of the external environment.
The style of the lubber line utilizing a bowsprit from a ship shape minimises parallax error when reading the heading from a position not directly behind the compass. This is further enhanced by the marking behind the card.
Compass bearings can be taken using the sighting peg on the card (when deck mounted) and the sighting peg from the ship shape (when deck head mounted).
Compass card: The card achieves greater stability by the moment of inertia derived from the circumference ring. The directive magnets are neodymium to provide;
¨ a powerful torque
¨ small sweep
¨ The closer positions of the directive magnets’ poles generate a weaker field outside the compass bowl. (Having the least power required to give the card directive force minimises deviations arising from soft iron induced by the compass card’s directive magnets.)
The gimbal assembly, pivot, lubber line and directive magnets all lie in the same plane. This maintains the relative position of the directive magnets to surrounding structures and importantly, any magnets or soft iron engaged to correct for deviation.
The card is kept level by engaging buoyancy. By placing the buoyant chamber at the top of the compass card’s sighting peg, a maximum righting force is developed. This righting force will keep the card near level in all navigable latitudes. The buoyant chamber also provides a platform on which to display a logo.
To achieve similar roll periods of the gimbaled mounting base (supporting the ship shape) and the compass card mounted on it, a weight is placed on the bottom of the lower sighting peg. The weight having of a mass and position to harmonise the roll period of the components. This weight also provides a platform on which to display a logo.
Materials: The use of clear plastics with a refractive index similar to the compass fluid gives a clear uncluttered view of only the;
¨ shipshape and lubber line
¨ card’s graduated rim,
¨ pivot and directional magnet assembly.
Lighting: The clear spherical bowl allows for many lighting options including illumination from within the binnacle or the other side of the observer with flush mountings. As the lighting arrangements are not on the side the card is viewed from, more elaborate lighting arrangements can be accommodated such as “heading only” for steering and “all around” if bearing are being taken.
The bowl: The spherical bowl is kept full of fluid by having an adjacent chamber that can accommodate the expansion and contraction of the fluid by the elasticity of air. By this method, there is no diaphragm. The failure of diaphragms is a common cause of compass break down.
¨ Top viewing mounting; the air is trapped in the chamber below the bowl by the joining orifice being at the bottom of the chamber (via a tube). This also allows for easy removal of bubbles (should they occur) by temporarily inverting the compass.
¨ Bulkhead mounting; as for top viewing but the tube is bent to have the opening at the bottom of the chamber when the compass is mounted
¨ Bottom viewing mounting; The air naturally will be at the top of the chamber.
This innovative design delivers a versatile reliable compass with many features attractive to boat owners, operators and skippers.
Deckhead mounting: There are many benefits in mounting a compass from the deckhead (ceiling).
¨ The area in front of the helm can be clear for,
o instruments and equipment
o chart space
o general useful space for coffee cup etc
¨ Being mounted on the deckhead, the compass is well clear from instruments and equipment, such as tachometers, steering mechanisms, flexible lamps and radio microphones that may have a variable effect on the compass.
¨ Radio sets and microphones (or other equipment that require manual attention) can be placed in front of the helm, removing the need to reach up, which can be dangerous in a seaway.
¨ There is little chance of objects being placed near the compass, inadvertently affecting the deviation. Tools (especially screwdrivers) and small portable appliances have a history of causing unexpected deviations.
¨ The compass will not be exposed to direct sunlight and the subsequent deteriorating effect of UV rays and excessive heat.
¨ It is unlikely that a bubble will form between the observer and the card.
¨ The simplicity and reliability of the expansion chamber being above the compass bowl is fully utilized.
¨ The compass heading is easily read at a glance up.
This new compass design has patents pending.