A while back, the question came up: what constitutes a compass? Is a fluxgate compass with no display considered a compass?
Here’s the definition from the glossary in Bowditch:
compass, n. An instrument for indicating a horizontal reference direction relative to the earth. Compasses used for navigation are equipped with a graduated compass card for direct indication of any horizontal direction.
Without an indication of direction it’s not a compass, at least not according to Bowditch and it can’t be used for navigation.
For less formal methods of navigation, especially in a familiar area, no compass is required. Instead of relying on a fixed framework of cardinal directions (North, South, East, West), one uses relative directions, such as left, right, ahead, or behind. This is how most people navigate in everyday life, whether it’s moving around the house, walking to the mailbox, or driving while following a GPS set to a head-up display.
Mariners navigating this way, with no compass and the radar on head up, using relative directions, are generally aware of the cardinal directions as well. It’s a simple matter to orient oneself using cardinal directions by referring to the chart, which is oriented north-up.
Looking at Polynesian navigation where there was no reference and each voyage was planned on individual vectors: wave swell patterns, migrating birds, limits of operations by birds such as frigate birds etc. Other references were the selected stars such as Altair.
Advancing to the 20th century in high latitude navigation the Alma Brown Gyro losing off North seeking ability and slaving it to a circumpolar star like ( can’t remember how to spell it, it started with Zub)
“Reference” is a good term in this context. The sun and stars, wind, swell direction, geography of familiar areas all provide a reference. I think '“indication” implies more precision.
The "graduated compass card implies the ability or possibility for quantification of directional information so that it could be plotted on a chart etc.
While I’m here - the Oxford Companion entry is a couple pages, here’s the crux of it:
COMPASS, the instrument by which a ship may be steered on a pre-selected course and by which bearings of visible objects may be taken to fix a ship’s position on a chart.
Pretty well covered everything. I like the mention of a directional gyro such as that fitted to the Mk.8 torpedo. The wheel used a burst of compressed air to spin to 30,000 rpm, sufficient to provide direction for the duration of the torpedo run time.
The directional gyro sounds similar in function as a swing meter. Had an interesting thread on them here. Swing meters wtf?
Both the swing meter and the directional gyro sense a change in direction.
A directional gyro sends a signal to be used in some automated process. A swing meter provides an indication on a display for a human to read.
Neither the swing meter or the directional gyro meet the definition of a compass as neither one is “an instrument for indicating a horizontal reference direction…”
