This is my own personal list of favorites for plotting positions on paper charts
and coastal piloting. If you have GPS connected to a
chart plotter connected to an autopilot while you lie in bed keeping watch using
a video camera, just remember that all electronics break. A manual backup system
is always useful.
- Straight leg dividers measure distances on a chart and store easily. Buy
a good pair as you will have them forever.
- A rolling plotter is far easier to use than parallel rulers if you have
to transfer a bearing to a compass rose on a small chart table when things
start to pitch and roll.
- A magnifying glass is useful if your eyesight is not 20/20 to see those
tiny symbols that might be ROCKS. Buy one of those amazing plastic magnifying
"sheets" with the fresnel lens that magnifies everything under it. The nature
store also had tiny clear plastic "cubes" magnifiers that are very handy.
For some reason, it's difficult to find "drugstore" bifocal sunglasses in
Canada for the over-40 boaters who are beginning to need reading glasses
just to check a chart.
- On deck, a small spiral notebook with a pen clipped to is handy for making
notations of time, distance, direction, and any navigational aids to be added
periodically to your log for estimating position.
- A plastic chart cover protects your chart in the cockpit not only from rain,
but from dirt and folding. Buy some clear plastic from the hardware store
- measure your typical chart and double the shorter dimension (add several
inches for extra space and "hem". Fold it and sew along the two short sides
leaving the long side open. You can put two charts in it and fold them easily.
- A piece of masking tape cut in the shape of an arrow with the point coloured
red makes a very nice chart marker on your new plastic chart cover. Use it
to keep track of your progress as your move along courses with visual aids
to navigation like buoys and lighthouses. They can also safely be used on
- Good binoculars will get used often. Try 7x50 with coated optics for 7 magnification
(higher is bad on a moving platform) with a 50 mm lens (a nice wide lens give
a wide field of view). Waterproof is nice but adds a lot to the price (a dry
location by the companionway makes them easy to use). Price is $100 to $700.
You can get a build-in compass for about $300 up.
- A hand-bearing compass is nice to have for taking bearings on shore objects
($40 - $150). I prefer the kind that fits in a pocket and you sight through
at your eye. It should have a light that does not require batteries.
Create a Compass Deviation Table
A deviation table is important if you need to know the course to steer on open
water. It will enable you to calculate the compass course if you know either
the true course or the magnetic course from the course. Compass direction usually
needs to be adjusted for magnetic interference on your particular boat.
Everything from metal, radios, speakers, engine, to beer cans can affect the
compass needle as it tried to point to the North magnetic pole! Note that it
may be necessary for sailboats to make a separate deviation table for when the
motor is not running. A hand compass is very useful for making a deviation table
for your ship compass as you can usually find a place for it without any interference.
- Find a place on your boat where you can sight straight ahead, free of all
magnetic interference (electric wires, magnets, metal) for taking hand-bearing
- Turn on all instruments you normally use when underway.
- Be sure to work in calm, open water.
- Turn the boat slowly onto all compass points in turn. As the boat settles
on the points (0, 15, 30...) the helmsman calls "mark zero degrees".
The person with the hand compass takes a comparison reading and writes it
- Enter these courses as 3 digit numbers (e.g. 090) in a chart with the hand-bearing
compass measurement in the Magnetic column and Compass direction in the third
column. The Deviation is the difference between your Magnetic
measurement and your Compass measurement. It and is entered into the
middle column. Write W (west) after the difference if the compass course is
greater; E (east) if it is smaller.
Converting Chart directions to Compass courses
The movement of the earth's magnetic north has accelerated since 1980 and is now moving at about 50 km (30 miles) a year. It's moved from the coast of northern Canada a century ago to the middle of the Arctic Ocean, moving towards Russia.
TVMDC is the magic formula for comverting True chart directions
to compass directions. "Tough Virile Men Don't Cry" or "Tired Virgins
Make Dull Company" may help you remember the order. Navigators used to
For example 90 True (due east) on a chart is not the direction you steer using
your compass since a compass points to the earth's "magnetic pole" not the north
pole marked on a globe. Varation is the difference between these poles
and is marked on every chart printed. If the chart has a stated variation of
15W then a True direction of 90 degrees is actually 105 degress Magnetic.
In other words, you would have to head on a course of 105 degress to get where
you are going.
If your chart Variation is west you add it, if it is east you subtract. "East
is least and west is best" is a phrase to help you remember which to add
or subtract when moving from True to Compass (left to right).
If the chart states that the Variation is increasing or decreasing every year,
then you must calculate the Variation for the current year.. Multiply the number
of years since that chart was printed by the yearly change and add or subtract
it from the stated Variation. The Magnetic circle on the compass rose is only
accurate for the year the chart was printed in this case.
Now you know which Magnetic direction but you still cannot use your compass
to steer that course because all boats have some error in their compass. Everything
from electric wiring, metals, radios, speakers, gear, engine, to beer cans can
throw the compass needle off. This error is called compass Deviation
and is different for every boat. You should check the chart after you install
any new equipment that could affect your compass.
You must estimate values that are between others on your chart. For example,
105 degrees is not on your chart, but you will notice it lies between 094 and
120. Use the value between 4E and 5E that is the same distance between the values
-- 5E. Now add or subtract using the rule to get your Compass course. This is
the course you will steer to get where you want to go.
Deviation chart example from 0 to 115 degrees:
Magnetic Deviation Compass
355 5W 000
008 7W 015
028 2W 030
044 1W 045
060 0 060
076 1E 075
094 4E 090
120 5E 115
Convertion of chart direction (True) to a
compass course (ignoring currents/wind):
True Var Mag Dev Compass
090 15W 105 5E 100