The compass is arguably one of the more important navigational tools on your boat and, as such, you should show due diligence in making a selection. Your basic concerns include quality, size, mounting, card design and the type of boat you have.

Price is certainly one indicator to consider. A compass with a bargain–basement price is probably not the one you want to rely on for your safety. That said, price is not the sole indicator of quality. Before buying a compass, read everything you can, then examine several models from reputable manufacturers. Are the graduations and headings easily read? Is there a rubber or metal expansion chamber to protect against significant temperature changes? Are there built–in compensating magnets? Are there provisions for night lighting? Are the lubber's line and card fully gimbaled?

Tip and turn each compass to simulate the motion of a boat in various conditions. Is the card inclined to stick anywhere? Does it remain level as you turn it? When it stops on the lubber's line, does it stop completely–as it should–or is there discernable oscillation? Are there any bubbles under the glass? You don't want them. You don't want parallax errors when viewing the compass from the side or the back, either.

You also need to consider mount types, not all of which may be suitable for your boat due to layout and/or space limitations. Binnacle mounts have an outer casing and, usually, some sort of hood to block the light. Bracket mounts are for dash or deck. Bulkhead mounts are frequently mounted on sailboats. These space savers tend to reduce interference with lines. Dash mounts need a vertical mounting space, and may work well on smaller power boats where space is an issue. Flushed mounts are recessed into the dash itself. Surface mounts are similar to flushed mounts in appearance and in their placement, but don't require a hole in the dash.

Size is another factor. Small is easier to stow, but that doesn't mean it's the best choice, even if you have a small boat. In fact, because small boats are more easily tossed around on the water than larger boats, a stable compass is especially important–and larger compasses are generally more stable.

Then there's the design of the compass card, in many ways a matter of personal preference. Skippers of larger boats often prefer compasses with a greater number of graduations than smaller boats–1 or 2 degrees versus 5. The reason is that bigger boats can hold a more precise course. On the other hand, the more graduations you have, the harder your eyes have to work and the more illumination you need.

Card design is particularly important to the sailboaters since spray and rain may well impede compass readings. Bigger graduation markings with more differentiation in size and larger numbers make it easier on the helmsman at night or in inclement weather. Cardinal points, too, must be easily distinguishable in reduced visibility circumstances.

A general rule of thumb when selecting a compass is that it should be as large as the mounting space permits, and the cost should be as much as you can reasonably afford.

– Linda Hoff