Video instructions and help with filling out and completing Which Form 2220 Navigation

Instructions and Help about Which Form 2220 Navigation

Hi i'm chris from sailing vessel navigator in the Eastern Caribbean Sea so far in this series we've learned how to use the Sun to navigate by at any time of the day in this episode we're on passage from Grenada to the Virgin Islands and will carry out the navigators routine for a day with the Sun for the morning site we'll shoot a little after 10 a.m. from the top of the Koecher which is a height of the eye of about 12 feet the measurement was 39 degrees eleven decimal six and this episode could be considered either a final exam or review depending on your perspective we won't be taking any shortcuts and we'll work each example completely first we need to convert to Greenwich Mean Time and then we need to correct the sextant reading for index error height of eye and main correction the last two of which are obtained from the 2014 nautical Almanac now that we have a corrected sextant reading we obtain our declination and Greenwich our angle from the Almanac correcting each for the ten minutes and 10 seconds of increments using the back pages of the nautical Almanac with the geographic position of the Sun calculated we determine our assumed position and local our angle which will enable us to use ho2 29 effectively from ho2 29 we pull the azimuth angle and the computed height making sure to correct each as required remember there are two options to correct the computed height either the interpolation tables or the direct math solution either way the next step is to compare the computed and observed values to determine the intercept now we can plot we need to set up the universal plotting sheet first graphically for a scale that we can use all day since we're going north at six knots we'll set it up with these values now we can plot the morning's online using our azmuth and intercept values it doesn't tell us much the most probable position is at the closest point to RDR but I haven't plotted anything since last night so it could be off by quite a bit either way it definitely tells us we're north or save a bank which is good it's not dangerous for our boat but it's nice to know so the Sun is getting a little higher in the sky now it's approaching my meridian or my line of longitude which means it's almost time to take the new insight I've also done an excellent job of keeping track of my courses and speeds over the last few hours and I feel really confident that I can combine this morning's line a position with this noon site to form a running fix but I need to determine the time of local apparent noon before I measure it so let's take a look at how to do that to determine the approximate time of local noon check the daily pages in the nautical Almanac for the time of Meridian passage these are calculated for standard meridians every 15 degrees since we're at about 64 degrees west we need to account for the extra four degrees west of the standard 60 using the conversion of art to time pages we see that each degree is worth four minutes so we're sixteen minutes late on the standard reading local noon should be about twelve twenty-six for us so we head out on deck a little earlier than that and wait for the Sun to reach its zenith for the day then it's time for the math again we correct the sextant reading for index error height of AI this time I was on the fantail and then the main correction of the Sun with a clean sextant reading we can calculate Zenith distance then we pull declination from the Almanac and figure out what situation we're in using our diagrams latitude in this case is Zenith distance - declination so we can quickly determine our latitude and plot it out now we have two lines of positions so we grab a running fix by advancing our morning site by a couple of hours so it's coming up on three o'clock in the afternoon and we've kept our same course in speed for the past few hours since the news site so we should be able to get a nice running fix out of this site what I've done this time is I've set my watch for exactly 3 o'clock since that conditions are so favorable and I can do the site sitting down I'm just going to keep the Sun on the horizon and wait for my watch alarm to go off and three that'll tell me the precise moment when I want to measure the angle of the Sun above the horizon it'll save us a little bit of work or trying to calculate bitchy news they're able to do that it's a nice little trick but meantime I'll wait till then and I'll measure the Sun okay that should do it we'll call this 1500s reduce this night in our next running face I wrote down an incorrect value for index error my mistake I covered it up with a title but it should be negative 1.2 so we correct our sextant reading for all standard corrections and then we head into the almanac for declination and GHA which are easy in this case because I shot at exactly 1900 GMT now you can see why we then march forward in our calculations to get ourselves into ho2 29 and retrieve the azimuth and computed height values after correcting them of course after comparing our computed height and our calculated height we can take the azimuth and intercept back to our plotting sheet and lay down our line of position then we can advance our noon site for second running fix both running fixes today we're a little east