Tides and currents

Back to course

As discussed in several lessons previously, currents and tides are major factors which must be accounted for. Currents impact the movement of the boat with the water, relative to land. Tides impact the depth of the water thus the boat ability to sail certain areas and locations without hitting bottom.

Everywhere there are currents caused by the tide coming in (flooding) and going out (ebbing). Tides and currents are measured by monitoring stations (also called reference stations). Each monitoring station will have “subordinate stations” in its area. The difference is in the way data is presented for these different types of stations in the tides and currents publication. Monitoring stations will have detailed data for each day of the month showing when high and low tide will occur and what will be the water levels at those times. This means that each station will have a few pages of data to cover the entire year. The subordinate stations will have a single line showing how to adjust the information provided by its reference station to make it accurate for that specific subordinate station. Continue reading

Effects of current – Set/Drift

Back to course

All boats are sailing through a body of water. If that body of water moves the boat moves with it as well.

This means that currents impact the location and direction of the vessel. Currents are the most dominant forces applied to the boat outside the control of the captain.

All the forces applied on the boat affect the leeway of that boat through the water. Leeway refers to the diagonal movement of the boat, rather then it going straight by its steered course.

There are actual significant currents in the world oceans. Currents such as the Gulf stream for example. Additionally significant currents occur daily by the flood and ebb of the tide waters into bays and inlet waters. Continue reading

Deck log & Navigators notebook

Back to course

There are two documents supplementing the chart, taking part in the navigation of the boat and its safe passage.

Deck log

The deck log is in the cockpit, it is also known as the boat log and it’s used by the helmsperson or anyone else on duty to document meaningful events that occur during the trip. This document will have the following structure and information: Continue reading

Distance off & Danger bearings

Back to course

Estimating distance off

It’s important to know how to estimate distances to observed objects. The following techniques can give an estimation of the distance off observed objects.

  1. If individual trees can be counted the distance off is about 1 NM
  2. If windows on a house can be counted the distance off is about 2 NM
  3. If the junction line between land and water is identifiable the distance off is about 3 NM
  4. Distance to horizon =
    Based on above formula a 50 ft. tower observed by an eye which is 6 ft. above water level is about 13 NM away.
    1.76 * sqrt(50 + 6) 13.17 NM

Continue reading

Advanced tips and tricks

Back to course

Once you master and understand the navigation techniques for DR track. Here are a few tips and tricks required by every expert navigator. These are based on geometry and utilize multiple bearings to a single object to deduce additional information about your location. First understand the concept of relative bearing. When a bearing to an object is given, it’s a simple math to calculate the relative bearing.

In the example below the relative bearing is 45°. Use simple math of “Course” – “Bearing” to find the relative bearing. So 023° – 338° = -315° + 360° (as explained in Bearing and compass math) = 45° Continue reading

Deduced Reconnoiter a.k.a Dead Reckoning (DR)

Back to course

Before departing from the dock a course must be plotted between the points of origin and destination. A DR plot is the advancement of vessel position on the DR track based on time distance and speed. Remember the formula 60D = ST. This can be memorized by visualizing a street address for the house at “60d st”.

  • D = Distance (in nautical miles) [NM]
  • S = Speed (in knots) [Kt]
  • T = Time (in minutes) [min]

Continue reading

The north

Back to course

There is an absolute location to the north; this is called the true-north. Charts are in true north, so when we plot a line to take a bearing; it’s in true-north. True-north bearings are marked with a T.

The magnetic flux of the earth is shifting at a given rate every year. A compass will always align with the magnetic force present around it. As such, compass readings will always be in magnetic-north. Meaning that whenever we take a compass bearing (e.g. hand held compass, ships compass, or binocular compass) we are actually reading magnetic north bearing. Magnetic-north bearing are marked with M. Continue reading

Measuring distance on chart

Back to course

Once two locations on the chart have been identified open dividers for the distance between the two points. Then use the space measured by the dividers and see how many minutes it covers on the latitude scale. These parallel minutes can be found on the left or right sides (e.g. east or west) of the chart. Each parallel minute represents 1 nautical mile. Continue reading

Locating lat/lon position on the chart

Back to course

The most basic navigation skill is to accurately plot a position on the chart. In this lesson of our coastal navigation course, we will show how to do that correctly and ensure a sound foundation for the advanced navigational skills taught in later lessons of this course.

In order to locate a position on the map we need to use your dividers and rolling plotter. Now follow these steps: Continue reading