Question:

What do I need to know about sail charts when offshore sailing?

Plotting a Course When Sea Sailing

Maybe you've mastered the art and science of plotting the course of your boat along a coastline. This takes a great amount of skill as you have to maneuver your boat according to rocky areas, the ebb and flow of the tide, and other navigational hazards. But, plotting an offshore boat when sea sailing also requires its own set of skill development. Many people new to ocean sailing want to rely heavily on their GPS Navigation Systems (GPS). But, remember that GPS systems have potential faults that can contribute to you getting lost at sea: they can fail and they do not give you the same road map of the sea that a sailing chart can. Here are some tips and terms you should master when sailing an ocean yacht or other sailboat:

*If the distance between two points is longer than the spread of your dividers, spread them along the edge of the chart in a workable number of miles (or minutes of latitude). If you use five miles to the tip, lay one tip on your starting point while the other rests along a spot five miles down the course. Then 'walk' the dividers along the course at five mile intervals and take the last measurement (which will not be exactly five miles). If you need only a rough estimation, you can use your hands after you have determined the spread between two fingers. Be careful using this technique; when ocean sailing, it is always better to be more than less exact if you can.

*While GPS systems will give you a location where satellites think you are, radar will pinpoint your accuracy completely, including if you are close to other vessels and any misjudged shorelines. These devices are much more expensive than most GPS systems but, if you plan to do sea sailing, you should spend the money. A radar antenna utilizes microwave energy. For each degree of rotation, the antenna sends and receives as much as 30 bits of information about the area. Radar has the ability to measure the relative angle of objects from the boat's head and the distance away.

*Even when you are offshore sailing, it's likely you'll want to come ashore at some point to explore and take a rest. Using a depth sounder or echo sounder can help you approach a lighthouse, marking the way to a harbor. You can use chart depths to intersect a bearing line and give yourself a fix. If you approach a coastline from offshore sailing, set up a bearing on a fixed object--such as the lighthouse--at the same time monitoring your depth. Notice the point at which it crosses a given depth--called a fathom curve. Then use proper depth monitoring techniques to get a bearing and plot the line, get the fix and label it with time.