Tides and Current

We have discussed how tides are important in anchoring.

	At low tide one should let out the rode to a scope calculated at water depth at high tide.
	At high tide one must be sure to have enough water depth (along the entire swinging radius at anchor) at low tide to not be grounded.

Tides are important not only for water depth considerations but for the currents they create. The day and time you choose to sail may be determined by the magnitude and direction of tidal currents. Currents can also be found on rivers and in the ocean. The Gulf Stream can have a speed of over four knots, necessitating a course correction. (Note: Non-tidal currents are often called streams.)

If one is steering the boat directly towards the destination, use line-of-sight of two stationary objects on land (see right-hand figure) to determine if the sailboat is on the proper heading. This is called a range. Official ranges consist of two navigational aids with flashing lights. To the right is a photograph of the official range which defines the safe course into San Diego Bay. If two objects are not available, line the mast up with the boat's bow and fix on a single point on land. Keep on the same heading and repeat this process over time to determine if your boat is drifting sideways with the current. If it is, you must adjust the boat's steering to compensate. Using a GPS, line-of-sight technique utilizing two objects on shore, or repeated bearings on a single-fixed object can check the sailboat's direction of travel (heading). If currents are present, you will have to steer a different heading (course to steer), than the heading or track the sailboat is actually traveling (course to make good).

Tide charts, current charts and calculations are useful as a starting point in navigation, but actual currents and tide levels are hard to predict and are constantly changing. To maintain the proper heading, frequent changes in the direction the boat is steered is to be expected. Go To Tidal Height Page

	A GPS can be used to check your heading.
	Visually, line up two stationary objects on shore which you are trying to head to. Changes in their relationship indicate you are going off course.
	If two objects are not available, take a bearing on a single fixed object on shore. If the bearing to this object changes over time you will need to change your course to maintain your heading.

Go To Tidal Height Page

Go To Course to Steer
Hand Calculation Page

Go To Course to Steer
Calculator

Go To Current Deviation
Calculator

Bearing: The angle of a sailboat to a fixed point or object, usually given in degrees magnetic.

Fix: A position determined by two or more cross bearings - Lines of Position (LOP).

Heading: The course of a sailboat. (Where the boat is headed)

Track: The desired heading or Course to Make Good.

Use a calculator to determine the angle of course deviation created by a current.

NAOO Tides Online (You can view tide tables and graphs from various locations around the USA): http://tidesonline.nos.noaa.gov/monitor.html

Free Tide Prediction PDA Software for Palm OS : http://www.toolworks.com/bilofsky/tidetool.htm