9 NAVIGATION


For a flooding 6m tide, this would mean the water would rise by: ■ Hour 1: 0.5m ■ Hour 2: 1.0m ■ Hour 3: 1.5m ■ Hour 4: 1.5m ■ Hour 5: 1.0m ■ Hour 6: 0.5m


Naturally, the tidal stream will be at its strongest during hours 3 and 4. This rule only works for areas that have regular tides. In places where the tide is irregular – like the central southern coast of the UK – it isn’t really helpful.


Passage planning


All skippers have a duty to plan their trip in advance though this doesn’t have to be too elaborate. The Marine and Coastguard Agency’s (MCA) guidelines say that for “small craft and pleasure vessels, the degree of voyage planning will be dependent on the size of the vessel, its crew and the length of the voyage”.


This simply means that a skipper shouldn’t just whiz out of a harbour without a thought, but should take a little time first to plan his passage with regard to the tides, weather conditions and any hazards he might meet en route. This could be nothing more than jotting down the time of HW and LW, and perhaps noting a few details on the chart. Just common sense, really.


ELECTRONIC INSTRUMENTS


This is a huge and fast moving subject that deserves more space than can be allotted in this book. Technological developments have driven down costs to the point where small craft can now carry the sort of electronic gear that would been considered a navigational luxury even on merchant ships just a few decades ago. And there will be more marvels to come, for sure.


Global Positioning System (GPS)


GPS is by no means the first electronic navigational system the world has seen. Ground based Loran and Decca both emerged during World War II and the first satellite system became operational in the 1960s.


All have disappeared in favour of GPS which was originally intended for the US military. It relies on a minimum of at least twenty-four operational satellites orbiting about 20,000 metres above the Earth’s surface. Each satellite transmits a signal giving its position and the exact time. The receiver on your boat measures the time delays between transmission and reception and uses the information to compute your position. When you think that the radio signals travel at nearly 300 million metres per second, it’s easy to appreciate how incredibly small these delays are, and how astonishing are the devices that process the data.


68


RYA Seamanship for Sea Anglers


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