03-30-2023, 12:20 PM
Carlos
The confusion is the mislabeling of Assumed Position in the app.
That should have been labeled either " Dead Reckoning Position" or "Estimated Position."
Since it is an electronic calculation it does not require a whole degree of Local Hour Angle as do the printed tables.
You are correct that for a TABLES solution you would used AP lon of 60 12.3' because when you subtract the 47.7' of the Greenwich Hour Angle from 60.0' that is the result. Appending this to the whole degree value of the DR longitude gives you AP lon 60 12.3' E
And that added to the GHA results in a LHA of 74 00.0' which is listed in the tables.
But the app doesn't require a whole degree LHA so when they add the 60 30.0' E to the GHA of 13 47.7 they get a LHA of 74 17.7' That is not a whole degree and so would not be listed in the tables -- but the MATH doesn't require a whole degree LHA to work.
When using that app you can put any lat and lon you choose in under their field for "Assumed Position" so most of the time I suppose you would just put in your DR position.
A fun and free app to use for practice and checking your work is Sight Calc. Again for this one you don't NEED to use a whole degree of LHA but of course you CAN for checking your tables work.
Let me know if this doesn't clear things up.
Peter
The confusion is the mislabeling of Assumed Position in the app.
That should have been labeled either " Dead Reckoning Position" or "Estimated Position."
Since it is an electronic calculation it does not require a whole degree of Local Hour Angle as do the printed tables.
You are correct that for a TABLES solution you would used AP lon of 60 12.3' because when you subtract the 47.7' of the Greenwich Hour Angle from 60.0' that is the result. Appending this to the whole degree value of the DR longitude gives you AP lon 60 12.3' E
And that added to the GHA results in a LHA of 74 00.0' which is listed in the tables.
But the app doesn't require a whole degree LHA so when they add the 60 30.0' E to the GHA of 13 47.7 they get a LHA of 74 17.7' That is not a whole degree and so would not be listed in the tables -- but the MATH doesn't require a whole degree LHA to work.
When using that app you can put any lat and lon you choose in under their field for "Assumed Position" so most of the time I suppose you would just put in your DR position.
A fun and free app to use for practice and checking your work is Sight Calc. Again for this one you don't NEED to use a whole degree of LHA but of course you CAN for checking your tables work.
Let me know if this doesn't clear things up.
Peter