Skipper's Cockpit Navigation Guide

Rene Westerhuis

• Publisher: Adlard Coles
• Year: 2022
• eBook ISBN: 9781472990655
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Aviation
• Index: Technology & Engineering

Whether planning a day sail or a longer passage, at home, at the wheel or at the chart table, the Skipper's Cockpit Navigation Guide is the perfect at-a-glance handbook for all skippers and crew. It covers all the essential navigation skills and techniques with a user friendly, easy to follow and succinct approach. Spiral bound to lie flat, and with laminated splash-proof pages, it is the hands-free ready reckoner to help you get where you want to go. Written in clear, practical language, with clear photos, step-by-step diagrams and actual chart extracts, the book covers:
- Using nautical charts
- Understanding buoys, marks and lights
- Using the compass, log and depth gauge
- Plotting positions (including by dead reckoning), courses and bearings
- Understanding tides (heights, streams, including using tide tables) and currents
- Factoring in the weather
- Making a passage plan, keeping a logbook, and more An essential title to have on board, this accessible book is aimed at skippers and crews of all levels, whether as a primer for those new to navigating or the perfect aide-memoire for those with prior experience.

RECKONING

Position fixing

Nowadays, the position of a ship can be continuously read on a device such as a GPS receiver, plotter or tablet. Should these electronics fail due to battery or power problems, the navigator must be able to fall back on two traditional methods of determining position: estimation and position fixing. By the way, the easiest way to determine a position is simply to sail close to a mark and read the identifying marks! Regardless of how a position is obtained, it must be entered on the chart at regular intervals (at least once an hour) in accordance with a fixed notation, including the time of observation.

Dead reckoning

In the absence of visible marks, the position is calculated from the last known position based on course and speed, corrected for leeway caused by the wind and tidal current. The method requires considerable calculation. The speed through the water is read from the log (see here). The angle of leeway can be estimated by plotting a line behind the ship and taking a bearing in relation to the keel line. The influence of the current on the course and speed is deduced from the data in the tidal atlas or on the nautical chart by means of vector calculations.

Visual fixes

By using a hand-bearing compass to determine the direction of marks and objects on the nautical chart, it is easy to plot the position on the chart. Depending on the situation, there are several possibilities. For all bearings, the compass bearing has to be converted to the magnetic bearing (deviation) and then to the true or chart bearing (variation) before drawing it on the chart. A cross fix is a bearing on two or more objects. The best results are obtained where the angle between the selected objects is approximately 90° from the boat’s position.

Position according to dead reckoning

Position by estimation

Position by bearing or GPS

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Three-point fix

Running fix

Double line bearing

Bearing with depth measurements

A running fix involves plotting two bearings of an object, with a time interval and notation of the log position at both bearings. The second bearing is taken when the angle of view is about 60° to the first bearing. By shifting the first bearing on the chart over the covered distance, a cross fix is created. The accuracy depends largely on the accuracy of the steered course and a correct estimation of leeway and current.

A useful variation on this is the double line bearing (for areas without current) with two measurements on a single object. The first bearing is at a small angle between the course and the object, for example 35°. The second is at (exactly) twice that, 70°. The difference in the log positions is adjusted on the second bearing and results directly in the position.

A fix can be achieved by combining a bearing of one object with a depth measurement (see here). Only in areas with a sufficiently distinctive bottom profile is this bearing reasonably reliable and tidal height calculations are necessary.

Electronic sight reading

Many professional binoculars are equipped with an (electronic) bearing compass, sometimes in combination with a range finder, which greatly simplifies the observation and measurement of both fixed and moving objects. The iPad’s camera can also be used to take cross bearings; the Compass Eye app remembers three bearings and, if necessary, plots them on Google Earth.

DEPTH

The current water depth (see here) determines whether a planned route can actually be used. With the help of an electronic depth gauge, it is possible to monitor the water depth continuously. Having adjusted for the vessel’s draught (keel offset) an alarm can be set to sound at a selected safety level.

Depth sounder

Depth sounders for yachts use ultrasonic sound waves. The instrument measures the time between the emission of a sound pulse and the reception of th...

Table of contents

• Cover
• Contents
• Charts
• Buoys, Marks & Lights
• Using a Compass
• Tides & Currents
• Log & Depth Gauge
• Passage Planning
• eCopyright