Navigation

Understanding your boat’s compass

By on Apr 21, 2016 in Navigation, Practical | 0 comments

Article submitted by Mike Rossiter, Certificated Compass Adjuster. Since the magnetic compass was first used by the Chinese for navigation sometime around 1044, it has become an essential instrument on every boat, yacht & ship. There are a wide range of compass types, including Magnetic, Gyro, GPS, Astrocompass, Base plate & Card. For our purposes, the most commonly used are: Magnetic compass The magnetic compass is the most familiar compass type. It functions as a pointer to “magnetic north” because the magnetized needle at its heart aligns itself with the horizontal component of the Earth’s magnetic field. Most hand bearing compass’s are of this type. A hand bearing compass allows you to take bearings of distant objects, which you can then transfer to a paper chart to create plot lines. Taking bearings of at least two objects that are 45 or more degrees apart results in intersecting lines on the chart, giving a position fix. To improve accuracy, we recommend taking bearings of three different objects and several sightings of each one and taking an average of the readings. If you find that another vessel stays on the same bearing over a period of time then watch out as you are on a collision course. Fluxgate compass The fluxgate compass is used in boats mainly for the purpose of steering. Fluxgate compasses are typically made with coils of wire that employ electricity to amplify the directional signal. Unlike the traditional magnetic compass which relies on a moving needle that is placed atop the magnet, the fluxgate has no moving parts. These are typically found in Autopilots and Tiller Pilots like this from Raymarine: The inbuilt compass is housed in the dome underneath:   GPS compass These use satellites in a geo synchronous orbit over the Earth to show the exact location and direction of movement your vessel, as well as your speed over the ground. They determine true North, as opposed to magnetic North, and they are unaffected by variations in the Earth’s magnetic field. Additionally, compared with gyrocompasses, they are much cheaper. Best of all, you probably have one with you, built in to your smart ‘phone, as well as on your boat’s chart plotter. Mike Rossiter, Certificated Compass Adjuster, has contributed the following...

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A simple guide to understanding tides when passage planning

By on Feb 4, 2016 in Navigation, Practical, Preparation | 0 comments

Understanding tides when passage planning When planning a trip in tidal waters, check the tides before going afloat. Use almanacs, charts, tide tables and tidal stream atlases to gather all the data you need. It is advisable to have a written note of tidal data for your trip including: Your boat’s draft. The predicted times (in Universal Time) of high and low water. The heights of the tide. The tidal ranges. The direction and speeds of the tidal streams en route. Check when and how the state of the tide will affect local areas including shallows, harbour entrances, sand bars, headlands and estuaries. Check predictions and forecasts to determine if and when rough seas caused by wind against tide will occur. Be prepared to change your plan to avoid being caught in adverse conditions. Use all the data you gather to: Plan your departure time(s). Take advantage of tidal flow to shorten journey time. Estimate your journey time. Plan your arrival time(s). Avoid potential hazards caused by tidal conditions. Ensure there will be safe clearance under your keel at all times.   Tips: Double check all calculations. Remember to allow for Summer Time, if applicable. Avoid shallow water on a falling tide.  ...

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Sailing & Motoring in Fog

By on Jan 5, 2016 in Boat Handling, Navigation, Preparation | 1 comment

Sailing & Motoring in Fog You can only measure the visibility accurately if sailing & motoring in fog when you have another object in sight so assume that it is less than you think. It can take time to ‘see’ another vessel as you may not be looking directly at it when it first appears. Speed in fog You should be able to stop in half the distance of the visibility because a conflicting vessel will need a similar distance to stop. Slow speed is demanded. Keeping a lookout in fog at sea Post a crew member to keep a visual lookout, preferably stationed outside as you will be monitoring the radar and the chart plotter as well as trying to keep a lookout. Using radar at sea Radar is an important aid in fog but don’t expect it to pick up all the vessels around you particularly when the sea may be lively and wave clutter obstructs the centre of the display, obscuring small vessels. Using the autopilot The autopilot can be vital in fog as it avoids you having to concentrate on the steering and allows you to focus on the navigation. Make sure you know where the disconnect button is in case you need manual steering in a hurry. Navigation in fog You will not get many visual clues in fog so you will be heavily reliant on the chart plotter and/or the radar. Use both to check each other as well as the depth sounder. Types of fog Radiation fog is the one you get in the early morning mainly in harbours and it should clear when the sun warms things up. Advection fog is found at sea when warm moist air flows over a cold sea and needs a change of wind or sea temperature before clearing. Sailing in fog Ideally you should not be under sail in fog. You may not be able to manoeuvre quickly, the sail can obstruct visibility and white sails do not show up in fog. Safety margins Allow larger safety margins in fog particularly for making a landfall. Moderate your speed so you can stop or take avoiding action in good time. Make your boat more visible Have...

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Learn ColRegs: Traffic Separation Schemes

By on Dec 12, 2015 in Navigation | 0 comments

Learn ColRegs Rule 10: Traffic Separation Schemes. (c) A vessel shall, so far as practicable, avoid crossing traffic lanes but if obliged to do so shall cross on a heading as nearly as practicable at right angles to the general direction of traffic flow. (d) (i) A vessel shall not use an inshore traffic zone when she can safely use the appropriate traffic lane within the adjacent traffic separation scheme. However, vessels of less than 20 metres in length, sailing vessels and vessels engaged in fishing may use the inshore traffic zone. (From Nautical Rules of the Road – ColRegs for power boating and sailing – a Safe-Skipper...

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An explanation of the IALA maritime buoyage systems – IALA A and IALA B

By on Nov 24, 2015 in Navigation, Preparation | 0 comments

What are the differences between the two IALA buoyage systems, IALA Region A and IALA Region B, and where are they used?   As recently as the 1970s there were more than 30 buoyage systems in use around the world. This caused confusion and accidents and it was after two fatal incidents in the Dover Straits in 1971 that the IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) was established.  There followed a worldwide effort to develop a safe, unified maritime buoyage system that could be followed by all vessels at sea. This resulted in the IALA Maritime Buoyage System and by 1980 there were just 2 systems in use, IALA A and IALA B. Although there is not as yet one unified system for the whole world, this was a major achievement nonetheless and the differences between IALA A and IALA B are only minor. The IALA chose the two systems in order to keep the number of changes to existing systems to a minimum and to avoid major conflict. IALA REGION A IALA A is used by countries in Africa, most of Asia, Australia, Europe and India. IALA REGION B IALA B is used by countries in North, Central and South America, Japan, Korea and the Philippines. The differences – lateral marks The difference between the two systems is the colour and light characteristics used for lateral marks, as follows: •  IALA REGION A port lateral marks and lights are coloured red.  IALA  A starboard lateral marks and lights are coloured green. •  IALA REGION B port lateral marks and lights are coloured green.  IALA B starboard lateral marks and lights are coloured red. Lateral marks indicate the port and starboard sides of navigable channels. These are used in accordance with the direction of buoyage for the region or specific location, as indicated on marine charts. Where a channel divides a modified or “preferred” channel mark may be used to indicate the preferred route to take.  In IALA Region A the lateral marks on the starboard side of the channel are coloured green and should be passed on the starboard side of the vessel. Those on the port side of the channel should be passed...

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Passage Planning Advice & Safety for skippers

By on Nov 16, 2015 in Navigation, Preparation | 1 comment

Passage planning helps you to: • Decide where to go • Calculate how long it will take to get there • Avoid bad weather • Take advantage of favourable tides • Be aware of possible hazards, eg shipping lanes, tidal overfalls • Decide a watch system • Decide if the crew is experienced enough for the trip • Be prepared to react in case of emergency   A well prepared passage plan can make the difference between a safe, trouble-free trip, or an experience that could prove unenjoyable and possibly hazardous. When planning a passage, small scale charts are used to create an overall strategy. This helps the skipper and crew consider such factors as the most efficient route, alternate routes and possible ports of refuge in case of emergency. Large scale charts are needed for destinations and hazardous areas of the route. If going outside your country’s territorial waters, make sure you have original documents on board including ship’s log, registration certificate, insurance, radio licence, International Certificate of Competence and courtesy flags for your destination. Tips • Carry large and small scale paper charts in addition to electronic navigation aids • Carry pilot books that provide harbour information and passage notes for your cruising area • Study the tidal heights and streams and make notes to cover the whole trip. • Check on customs regulations if applicable • Check you have all necessary documents Contingency Plan Before going to sea, make a contingency plan in case conditions deteriorate unexpectedly or there is a problem with your vessel or a crew member is injured. Ensure you could navigate safely to places of refuge without the need for electronic aids, in case of power failure. Make a note of the tidal predictions at the emergency destination, to be sure of accessibility. Information Ashore Make sure someone ashore knows of your plans and how to raise the alarm if they become concerned for your well being. (taken from the Safe Skipper app for iPhone, iPad &...

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