Mobile Crossing WayPoint Map Loader Manual do Operador descarregar pdf (Página 77)

SeaMarks manual VI. Menu Reference •

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• 77

While selecting Loran A pairs, you check two station sets rather than two master/slave sets. While the Loran A chains

have been out of service for many years, you will still find some fishermen hanging on to their old books of numbers.

Loran A chains only gave 1000 ft. or so of accuracy and converting them does not improve on that accuracy.

Nonetheless, these waypoints are a potentially useful source of information on reef and wreck locations. Selecting the

right Loran A stations can be a challenge in many locations if you have no clue as to what are the right ones. You can

set up what might be the right stations based on the station locations and then check the typical numbers on the User

Preferences spreadsheet. This shows what the Loran A waypoints will be at the center Lat/Lon. If this comes close to

any of the displayed choices, then that station pair is probably right. Alternatively, once the chains and stations are

chosen, you can plot a file with Loran C waypoints in the right area and select Loran lines in one of the Loran A chains.

This will show how those lines run and may give you a better idea. The graphic below shows the Loran A station

coverage areas.

Loran A used two station pairs to get a fix. For example, for Clearwater on the west coast of Florida, the typical pick

was 3H0 and 3H1.

Set conversion method

The conversion process from Loran to GPS uses complex mathematical formulas that require correction factors called

Additional Secondary Factors (ASFs) to achieve acceptable accuracy. These may be applied in the conversion process

by one of three methods:

Use ASF values out of user calibrated government tables

Use uncalibrated ASF values out of the government tables

Use single set of ASF values per file rather than a table. You would use this when there is no table coverage for that

area. An example is in the Caribbean.

See chapter V sections 1 and 2 for more information on what these mean.

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Mobile Crossing WayPoint Map Loader Manual do Operador Página 77