A nautical chart is a "road map" to waterways where you take your boat.
It has a compass rose to give you a true bearing in which to steer your boat.
We plot or read our charts in true north.
However, our compass on board will always point to magnetic north.
This is the magnetic pull of the earth.
The difference between true north and magnetic north is called variation.
Variation alternates depending on your geographic location.
To determine the variation, look at the rose on your chart.
It will show the degree of variation and indicate if it is east or west.
The formula for converting magnetic north to true north is T-V-M-D-C.
T is for true course, V for variation, M for magnetic course, D is for deviation (this is the effect of the magnetic pull of your vessel) and C for compass course.
Deviation can be affected by something as simple as a screwdriver or a set of keys laying alongside your compass.
The compass course is the course you steer.
For example:
- True: 75 degrees
- Variation: 15 degrees west
- Magnetic: +15 degrees equals 90 degrees
- Deviation: -3 degrees east
- Course: 87 degrees. This is the course you will steer.
An easy way to remember this: east is least, or minus; west is best, or plus.
Most of us cruising on the Caloosahatchee, Pine Island Sound, Matlacha Pass or the Gulf of Mexico use landmarks, bridges, markers or buoys to come and go to our destination.
However, you could get caught in fog, rain or darkness, resulting in limited visibility.
Then, you will have to depend on your charts and compass to navigate.
If you steer a compass course without correcting true north from magnetic north in our example, you would have been 13 degrees off course.
This would put you in trouble anywhere in this area, except way out in the Gulf.
Learning to navigate can be challenging.
It can seem like there is a lot to learn, but with practice, mastering the art of navigation is very rewarding.
Learn the ins and outs of seamanship by taking the courses given by the Cape Coral Power Squadron, located at 917 SE 47th Terrace. For more information, call 549-9754.
Links : Sailing & Boating Lessons (videos) from NauticaLive
- Application of variations : 2 / 3 / 4
- Applying distance : 1
- Cardinal marks : 2 / 3
- Doubling angle : 1
- Chart symbols : 1
- Measuring distance : 1
- Natural features : 1
- Navigation terms : 1
- Reviewing the marks : 1
- Running fix : introduction / plotting
- Safer water marks : 1
- Sound signals : 1 / 2
- Special marks : 1
- Vessel fishing : 1
- Vessel mine clearing : 1
- Anchoring one anchor : 1
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