Nexus Marine is a leading manufacturer of navigation marine instrumentation for racing and cruising yachts. Manufacturing arm of Silva Group, Nexus brings with it seventy years of experience in the design and manufacture of precision navigation instruments, and continues to uphold that heritage with a product range that combines the very latest in technology and styling.
Instruments and Boat Parts
Optimal function, readability and qualityThe word Nexus is Latin for connection, summing up exactly what Nexus Instrument Systems are all about. The network has been designed to connect three groups...
Nexus handheld and fixed VHF radios can be found on a wide range of craft; from RIBs to large cruising and racing boats, and are particularly recommended for navigation stations where space for...
- Silva Compasses
Nexus Marine was the former marine arm of the Silva Group that specialised in developement and design of the marine products for Silva. In 2006 Silva became part of Gerber and Nexus Marine became an...
A medley of contemporary tools, instruments and devices handy for all yachtsmen.Nexus Marine was the former marine arm of the Silva Group that specialised in development and design.
Using a Hand Bearing Compass
In these days of GPS navigation and chartplotters, many older techniques for finding a boat’s location have fallen into disuse or have been relegated to backup status. While there is nothing inherently wrong with using the latest technology to make navigating easier, faster or more precise, prudent mariners should have a basic knowledge of plotting and navigating with traditional methods. When your newer electronic devices fail, if you're comfortable with DR (Dead Reckoning) techniques you won't be be left feeling lost.
It goes without saying that all electronic charting systems should be replicated with paper charts. A loss of electrical power or failure of the electronic device should result in a smooth transition of the boat’s position onto the paper charts. With a few dollars worth of plotting tools such as dividers and parallel rules, the boat can continue on its way by plotting on paper the old fashioned way.
Of all the simple and inexpensive tools you should add to the basics, very few items are of more value than a hand bearing compass. Many binoculars are fitted with a compass for this exact purpose, but an independent handheld compass can serve in many more capacities than the one on binoculars. A well designed unit can even be used to substitute for the main ship’s compass should it fail.
Course to Steer
The simplest task a handbearing compass can perform is to provide a course to steer. When a buoy or other mark first comes into view, a quick reading with the compass provides a course for the helmsperson to find it. Sighting down a channel with a hand bearing compass before a fog bank rolls in can give you the next leg before it's obscured.
Have you ever wondered whether you were going to pass ahead of or behind an approaching ship or perhaps collide with it? A series of readings with the handbearing compass will provide the answer. If the readings are always the same over time, you are on a collision course. If the readings change, you will not collide and the direction of change indicates which boat will cross in front of the other.
Lines of Position
In navigation, lines of position are abbreviated as LOPs. A course to steer as used above is simply an LOP taking you to a mark such as the first buoy of a channel. But other LOPs are useful too. By taking a bearing on a known object whose position is shown on the chart, you can pencil in the LOP and be assured that your boat lies somewhere on this line. A single LOP does not tell you where your boat is completely as you know only that you are at a certain bearing from the lighthouse, tower, steeple or other landmark that you chose. This pencil line does not tell you how far away you are from the landmark. Remember to plot in magnetic degrees on the chart, or convert to true, the local variation can make large errors of position if you use the wrong compass rose.
A fix is nothing more than two or more LOPs taken at the same time. If you have taken a handbearing compass reading on a lighthouse and a conspicuous building on the shore in quick succession, the spot where the two lines cross when you plot them on the chart is the boat’s location. Three or more LOPs will provide even more certainty, if they form a small triangle or square, you will most probably be inside the pattern.
Three notes with hand bearing fixes:
The closer the two objects are to the boat’s position, the less the error will be in plotting the actual position. A slight error in reading the compass when sighting on a headland or lighthouse at a great distance increases the probability that the boat’s position will be misplotted.
Using two objects as close to 90° apart as possible increases the accuracy of the fix. As the angle becomes more acute than 45° or more oblique than 135°, the fix approaches a straight line of a single LOP and its accuracy falls off dramatically.
The time between the two sightings must be minimal, especially if the boat is traveling at a high rate of speed. Since a fix represents position at a single moment in time, if the boat moves a long way between the two sightings, the bearings must be treated as a running fix.
A running fix is the same as a fix but with a time interval between the two bearings. To create a running fix you must add the elements of the boat’s course and speed, and the time between bearings. The first bearing is plotted on the chart and then "advanced" by creating a parallel line on the chart that is equal in distance and direction to the boat’s speed and heading until the time of subsequent bearings. The later bearing can then be plotted on the chart in the normal fashion and where it crosses the advanced first LOP is the boat’s estimated running position. When you take bearings, don’t forget to note the boat’s heading, speed and the time so that you can use the information later to advance an LOP.
There are a variety of options for mounting including flush, bracket and binnacle/surface, and within these standard mountings are other variations. The mounting of a Compass is dependent on the type of boating you do, your boat size and whether you have a sailboat or power boat. Another consideration is visibility as you may want to read the compass both from the helm and from other angles.
A flush mount compass can be installed into a horizontal or vertical surface where half of the unit is above the surface plane and half is below on a horizontal surface or on the backside of a vertical surface. A compass that mounts on a vertical surface may have the ability of double reading that is it can be viewed both from inside the cabin as well as the cockpit. These compasses can also be purchased for mounting on inclined vertical surfaces as well.
Bracket mount compasses are versatile in their mounting possibilities. They can be set on angled surfaces and then tilted to accommodate your viewing angle or can be mast mounted on small sailboats. When leaving the boat, you can remove the compass from the bracket for storage.
A binnacle/surface mount compass installs on a flat surface or on top of a steering pedestal. These compasses can be used on a sailboat with wheel steering or on a power boat that has no space below the mounting surface for a flush mount unit. You can also remove some of these compasses for storage if necessary.
To buy a compass
Boat needs at least one magnetic card compass on board even if the vessel is equipped with multiple fluxgate models. In the event of total failure of the ship's electrical system, you'll be able to find your way to your next destination. There are compasses available for specific types of boating such as racing, offshore cruising, small boat racing and for fast motor cruisers.
Select a magnetic compass with the largest card your space and budget allows as the increased volume required to accommodate a larger card also increases the amount of fluid, which in turn dampens the motion of the card. You'll be able to steer your course more accurately because the larger card is easier to read and more stable.
Some magnetic card compasses have internal compensation magnets and others do not. Never use a steel screwdriver to attempt to compensate a compass with internal magnets.
No matter where you live on earth, you can purchase a compass that is prebalanced
for your geographical location. Do buy a magnetic card compass balanced for
the southern hemisphere if you do most of your boating there.
Some compasses have multiple lubber lines so that the compass can be easily read from different positions. These are especially useful on sailboats for calculating tacking angles.
If at all possible, position your compass so that it can be used to read bearings of other objects. This makes the main ships compass useful for other navigation purposes.
Locate a new compass where there is the least amount of magnetic influence.
Be especially careful of mounting speakers, drink holders for canned beverages,
large electrical cables or other compasses near the location.
Unless you own a small boat in which you're never out after dark such as a small sailboat or fishing smack, be sure to buy a compass with night lighting. This will entail electrical power and connections to the compass.