DAVIS Hand Bearing Compass User Manual

INSTRUCTIONS

Davis Hand Bearing Compasses are excellent for yachtsmen, racers, and fishermen as

an aid to position finding and steering. The instruments let you easily obtain quick mag-

netic bearings on shore or floating objects. Simply align front and rear sights on an object

and read off bearing. Use to take a quick bearing or position set, determine angular gain

or loss on the competition while racing, check distance offshore, establish lee-bow set

while cruising or racing in currents, determine drift vector, and plot a line of position.

All Hand Bearing Compasses feature stable, liquid-damped compass card graduated in

5° segments. Bold graduations every 15° for easy reading. Lightweight design for easier

bearing. High impact plastic housing. Lanyard included.

The Illuminated model has solid-state LED ( Light Emitting Diode) illumination system

which floods the compass capsule and sight vane with soft light. The LED will last for the

lifetime of the compass. Batteries, which are included, will last up to 10 times longer than

with regular bulbs. Average LED “half-life” is approximately 10 years if operated continu-

ously. The compass has a positive “push-on” switching action, with vinyl boot water pro-

tection. Battery housing has high watertight integrity.

Compasses are designed for Northern Hemisphere only.

Sighting Objects. Hold the compass in a relaxed position at

arms length, with the yellow cursor line facing you. With the com­pass slightly tipped so both pointers are visible, rotate your arm and
upper body until both pointers are in-line with the object being sight­ed (figure 1). Read the magnetic bearing as it appears at the yellow
cursor line.
Note: Standing near large metal objects will affect the accuracy of
your magnetic bearing.

Navigating Using Your Sightings. A line of position (LOP)

is simple to obtain (figure 2). Find an object that is easy to identify
on a chart and take a sighting to determine its magnetic bearing.
Draw a line from the object using its magnetic bearing and you know
that you are somewhere along that line of position. Take a sighting of
another object and plot its line of position. Your position is where the
two lines cross (figure 3). Tip: Three sightings plotted on the chart
(three LOP's) is even more accurate and these sighting form a trian­gle when plotted; you are somewhere inside that triangle.

Plotting Distance Offshore. This is easiest and most accu-

rate when your compass course is roughly parallel to the shoreline.
You must also know your speed over ground. Note the exact time
that you are abeam of (perpendicular to) or 45° off a prominent
object on shore like a lighthouse, smoke stack or radio tower. Take
the exact time again when you are perpendicular to or 45° off the
object. Plot these sightings on the chart and, with your distance run
as one leg, you have a right triangle (figure 4). Your speed multiplied

#211 Standard
#215 Illuminated

3465 Diablo Ave., Hayward, CA 94545 U.S.A.

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211_Engl.pdf October 2005

by the time equals both your distance offshore (A) and the distance
run (B). Tip: Another method to determine distance offshore is to
take two sightings off the same object exactly 60 minutes apart and
plot the two lines of position. Open a pair of dividers to match your
distance traveled in 60 minutes. Draw your actual travel line of posi­tion (A) parallel to the compass course you are steering at the point
where the angle is the same width as your distance traveled (figure

5).

Predicting Collision Course. Take a sighting on any mov-

ing or stationary object that you suspect might be on a collision
course and note its bearing. If repeated sightings yield the same
bearing, you are on a collision course (figure 6). Note that a collision
course with a stationary object means that your are being "set" by
drift or tide and you must alter course to avoid a collision. Tip: These
types of sightings are extremely useful in sailboat racing when two
boats are converging on different tacks.

Checking Drift While at Anchor. Take sightings on any two

or more objects on shore and write them down. Radical changes in
their magnetic bearings could indicate that your anchor is dragging.
Tip: The closer you are anchored to the objects on shore, the
greater the chances that simple swinging on the anchor will cause
these bearing to change.

Caring for Your Compass. The Davis Hand Bearing

Compass is a precision instrument. It is designed for rugged use and
built to last a lifetime, but must not be dropped or exposed to severe
shock trauma. It can be cleaned with fresh water or alcohol; do not
use any other solvents. Continuous vibration or exposure to magnet­ic influences can damage the pivot bearing or magnetism of the
compass and lessen its accuracy.

Factory Overhaul. Contact Davis Instruments if you would like

to have your Hand Bearing Compass overhauled.