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Sight Reduction Table HO249

URLs to print out the HO249 tables for your latitude at: www.lewishb.biz

as well as universal time clock and nautical almanac

Height Sight ___

Dip/Height Eye -___

Altitude Corr + ___

Eaquals  Height Observed ___

Time Watch ____________________

Watch Slow/fast ___________

Time Corrected _________________ 4__________


GHA Hours __________________ _________

GHA Min and Sec from Increments and Corrections Min___________Sec _____________

(((Time converted to Degrees minutes and seconds of arc.)))

GHA (longitude of the Sun) ______

Our Assumed Latitude ____________

Our assumed Longitude ____________


T or LHA ______________ (difference between the Suns and Your longitude)

If Declination is South / Contrary use higher Latitude...........In other words:

IF Your latitude is about 32D 40N Suns Declination is 06D 36m South.

You enter the tables with Latitude 33 degrees, your Assumed Latitude is 32D 24M

(((60 minus 36 is 24)) If Declination is North / Same use lower latitude...

If Declination is 06D 36M North,You enter the tables with Latitude 32 degrees, your Assumed Latitude is 32D 36M North

Assumed Latitude same Minutes seconds as Suns Declination

Assumed Longitude same Minutes seconds as Suns Longitude


Enter the LHA (difference between your longitude and the Suns longitude) in HO249

tables in Whole degrees in the pages corresponding to the Suns Declination --Same or Contrary Name. From San Diego “Same Name ” means the Sun is North of the Equator

Contrary Name”means the Sun is South of the Equator.

LHA ________________ Declination ________________


Height Computed___________ Azimuth _______________


Height Observed _____________ Subtract Greater from lesser. If your HC is

greater than HO you are that distance away from the Sun from your Assumed Position.

If your HO is greater than your HC, you are that distance closer to the Sun from your

assumed position. _____________ Towards // Away

The Azmuth is computed for the Morning. In the Afternoon, Subtract the Azmuth from 180 degrees then add the answer to 180 degrees to get your afternoon azmuth.

If you are confused email me quohog3@gmail.com A quohog is a cherry clam :)


Simple latitude and longitude at noon

Really, yes, you can determine both your latitude and longitude with your centuries old noon

time sextant sight ! All you need is accurate time ! For celestial navigation, I have an easy to read quartz movement pocket watch set at Greenwich England “Universal Time”.


Quite simply, you can easily find out from your Nautical Almanac about what time local noon is going to be.

To find Longitude, A few minutes before local noon, you take two (or three) altitude observations of the Sun, marking down both altitudes (54d 30' and 54d 51')and the Exact times.

For Latitude,

At local noon, the Sun will hang in the sky a couple minutes. You take several UN-timed observations and write them down. The highest and best observation is the correct one.


You then correct your sextant reading ((55 degrees)) by adding your Dip (height of eye above the water) and altitude corrections to get your “Height Observed.”


For the Bill, your height of eye of about 15 feet is Minus 4 minutes

Altitude semi diameter of the Sun is Plus 14 minutes


So you ADD 10 minutes of Arc to your sextant to get your height observed.

55 degrees and 10 minutes of arc.

You then Subtract the Height Observed from 90 degrees.

89d 60'

-55d 10' is

34d 10'

You then add your Suns declination if the Sun is north of the equator or subtract if the Sun is South of the equator

On that particular day The Sun's declination was 2 degrees South of the Equator

34 10

minus 2 degrees

Your latitude is 32 degrees and Ten minutes...... about 30 miles South of Point Loma

For my Longitude

The time of my watch gives me the exact longitude of the Sun every second of the day!

For your Longitude, you remember you took two sites before Noon? 54d 51' and 54d 30' ?

You set your sextant for the 54d 51' and when the sun kisses the horizon you mark the time.

There was 16 minutes between the first and second time the Sun was at 54d 51'

You calculate the time spreads between each set of those matching Sun sites and figure out the mid point of each spread. These times I average together to get the exact time of local noon and with it my longitude. :)

Parallel Sailing Centuries ago before accurate time, navigators would sail north

to the latitude of San Diego well off shore to avoid running into rocks in the middle of the night.

Then they would sail East along San Diego's latitude to Point Loma. This is “Parallel Sailing”



Latitude from The North Star Polaris

Polaris orbits True North by about one degree.

Polaris is exactly true north when the Constellation Cassiopeia --THE BIG W-- (( its trailing star Cassiopeia E)) is east or west or Polaris and is one degree north of true north when Cassiopeia is vertically above Polaris and one degree South of true North when Cassiopeia is vertically south of Polaris. One degree is 60 miles.

The trailing star of the Big Dipper (Alkaid) is the other indicator of Polaris location.


You subtract the correction when Cassiopeia E is above Polaris and add the correction if Cassiopeia E is below Polaris... The correct varies as Cassiopeia travels around the North star.

If Cassiopeia E is 45 degrees above Polaris, , you subtract about 33 minutes from your sextant observation to get your latitude. South is added. Your Nautical Almanac tells you the correction for the time of your observation.


Otherwise, Your sextant observation, corrected with your Dip / height of eye -4' is your latitude.

THE ONLY ACCURATE TIME to observe stars is at dusk; “Star Time” when you can still see the true horizon.... There is a table in Bowditch giving you correction values for closer horizons.


0

____1.0 for52 degrees use .6 and 56 degrees.... 56 x .6= 33.6 minutes correction

18

____.9 since Cassiopeia E is higher than Polaris, subtract the correction

31

____.8 for my latitude ….

41

____.7

49 Cass E >>>>*

____ .6 *

56 * l<<< 52 D >>l

____.5 *

63 *

____ .4

69 Polaris >> *

____.3 True North >>>>>>O

75

____.2 *

81 *

____.1 >>>Traverse table use lower value <<<

87 * *

____.0 *

90 Big Dipper Alkaid >>*


Longitude by the Polaris method

Whaaat ? Yes Indeed !!!

The basic point about Polaris sights is that what your sextant says is your latitude,

After your Dip correction.. about Minus 4 minutes/miles for the Bill of Rights.

Also it means that subtracting your sextant reading from 90 degrees gives you how far you are away from Polaris... The same thing can be done with a star due East or West of you. Lets say A star's longitude is about 10 degrees West of your longitude.

In this case, our Sextant reads 79 degrees 11 minutes ... Subtracting your sextant reading from 90 degrees tells you you are 10 degrees and 49 minutes East of the stars longitude at the moment you take the site.


(If your latitude is 40 North, you want a star whose latitude is about 40 North)

Next, you ask, what if the star is not exactly East or West of you? Simple, you subtract a correction from your sextant altitude.

If your star is, say, 5 degrees north or south of due East or West, you subtract about 3 miles from your sextant altitude for each 10 degrees of distance to the star.

If the star is 10 degrees north or south of due East or West, you subtract about 13 miles from your sextant altitude for each 10 degrees of distance to the star.

If the star is 15 degrees north or south of due East or West, you subtract about 24 miles from your sextant altitude for each 10 degrees of distance to the star.

Beyond that, of course, the corrections get more extreme... Due to the large number of stars in the constellations, we can find a suitable star within a few degrees East or West of us most of the time.

So, how do you find your star's longitude at the time of your observation?

Every star has its position in the constellations, and has a Declination (latitude) and longitude west of a place in the constellations we call Aries. This position Never changes !!!. What does change is that the Longitude of Aries changes as the heavens wheel past in the course of the night., moving West, at the same speed as the Sun. So You add the longitude of Aries at the moment of your sight to the longitude in Aries of Your star (subtracting from 360 if necessary, ) to get the longitude of the star the moment of your sight.

In the nautical Almanac, the hour angle (longitude) for Aries is given for every hour of the day and night … You go to the page “ Aries Increments and corrections” for the hour angle in minutes and seconds. Simple, Huh ??? !!! :0 :) :) . Takes some practice of course.



Navigation by Lights, Bells and Whistles

You are sailing South down the coast at night on a course of 180 degrees. You can see the street lights of the communities as you pass them. Occasionally, you see over the horizon on the Port bow a bright light flashing every 15 seconds. You know from your Dead Reckoning plot on your Chart that you are approaching San Diego. You see on your chart that the Point Loma Lighthouse flashes every 15 seconds, is at 88 feet above sea level and can be seen for 14 miles. You pick up your Hand Bearing Compass, and note that on this heading, your hand bearing compass is a few degrees different from your vessels compass. You take a bearing on Point Loma light. After correcting the compass bearing for Deviation, you see Point Loma lighthouse has a bearing of 160 degrees. This bearing is

20 degrees off your Port bow. You occasionally take other bearings. When the lighthouse

bears 140 degrees, or 40 degrees off your Port Bow, you know that since you traveled 7 miles between these two bearings, that when Port Loma Lighthouse is on a bearing of 090 degrees, broad on the Port Beam, your position will be 7 miles due West (270 degrees) from Point Loma Lighthouse. This is called “doubling the angle on the bow”.


You can also use a “Running Fix” in a similar situation. Your first bearing of the lighthouse at 8pm is 33 degrees. 60 minutes later, you take another bearing of 67 degrees.

You use your dead reckoning position at 8pm, and mark along your course the 7 miles you sailed in that hour in a new Assumed Position and draw a bearing line of 33 degrees through that assumed position. You then plot on your chart your new bearing from the lighthouse at 9pm. Where the two bearings cross in your real position. You begin your new Dead Reckoning plot from there.

You then know what course to take for the channel marker buoys. In San Diego, For example, you have a Green buoy number 5 flashing green every 2.5 seconds on the left side of the channel with a Red buoy number 6 flashing Red every 4 seconds on the Right side of the channel. Depth of 60 ft. The course up the channel is 339 degrees magnetic.

The lighthouses also have Horns and the buoys often have bells or whistles.

Chip log table For a 50 foot chip log line...

30sec 1 3.7 8

15sec 2 3.3 9

10sec 3 3 10

7.5 4 2.6 11

6 5 2.5 12

5sec 6 2.3 13

4 .3 7 2.2 14






AM/FM Radio

and Kelp Bed Navigation . Using Parallel Sailing :)

Yes, you can make a safe landfall at San Diego-or Timboutou :)

for that matter--using your AM/FM radio and the Kelp Beds... and the Horn of the Point Loma lighthouse...

Parallel sailing, as you remember (if you read the First Nav sheet) is the Art of sailing far enough offshore so you don't run aground at 3AM... You approach the latitude of San Diego, then head east... When you can hear the San Diego FM stations you know you are only maybe 20-30 miles offshore...

You switch to the AM band and find 760 KFMB AM radio tower which is at the 5 and 15 interchange, East of Point Loma...You can use it to help find the harbor entrance . AM radios are Directional!!! You can get a relative bearing of the station antenna within a few degrees... By heading East, you find the kelp beds and / or the 100 foot bottom contour line on the chart. You can follow the 100 foot line south getting close enough to hear the Point Loma lighthouse Fog Horn... If you are in such a Pea Soup Fog that you cant see Anything, Putting the Horn appropriately on the Port Bow helps you find your way in... Using your depth sounder you can feel your way in to the Bouys in the Channel following a bottom contour line as I stated in the . 2nd Nav Sheet “Bottom Profile-- Bowditch”...

That is AM/FM “Kelp Bed” Navigation........ :)


Speed Times Time


Bottom Profile (Bowditch c 1962 ) or

Bottom Speed / Time / Distance >>“Sounding Strip”<<

It has been in use for Centuries :) :) :)

How to:

Mark latitude miles on edge of paper as to your chart...

Take soundings every few minutes, mark on paper as to

your time / speed / distance...

From Bowditch table 19 (c1962) Time / Speed / Distance Table


Speed 1 2 3 4 5 6 7 8 9 10 11 12 13 14

5 .1 .2 .2 .3 .4 .5 .6 .7 .8 .8 .9 1 1.1 1.2

M 7.5 .1 .2 .4 .5 .65 .75 .85 1.0 1.1 1.25 1.4 1.5 1.6 1.75

I 10 .2 .3 .5 .7 .8 1 1.2 1.3 1.5 1.7 1.8 2.0 2.2 2.3

N 15 .2 .5 .8 1.0 1.2 1.5 1.8 2.0 2.2 2.5 2.8 3.0 3.2 3.5

U 22 .4 .7 1.1 1.5 1.8 2.2 2.6 2.9 3.3 3.7 4.0 4.4 4.8 5.1

T 30 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

E 37 .6 1.2 1.8 2.5 3.1 3.7 4.3 4.9 5.6 6.2 6.8 7.4 8.0 8.6

S 45 .8 1.5 2.2 3.0 3.8 4.5 5.2 6.0 6.8 7.5 8.2 9.0 9.8 11.5

52 .9 1.7 2.6 3.5 4.3 5.2 6.1 6.9 7.8 8.7 9.5 10.4 11.3 12.1


If you do not have a table, for LESS than an hour =

formula : 60/speed, for minutes and a decimal.(4.27 minutes for example) then the decimal (.27)times 60 for how many seconds...

So at 14 knots its 4min and 17 seconds to travel a mile.

1 knot=60 min 2=30min 3=20min 4=15min 5=12 min

6=10 min 7=8:34 (8min 34 sec) 8=7:30 9=6:40

10=6min 11=5:27 12= 5 min 13=4:36 14=4:17

After a while, match up your “Sounding Strip” with the bottom contours on your chart to see “exactly” :) where you are !!!




Can Dead Men Vote Twice?

or do

True Virgins Make Dull Company ?


A way of remembering “Compass Deviation Magnetic Variation True”

Converting Compass to True you Add easterly error and Subtract westerly error.

Converting True to Compass you Add West, Subtract East.


Anyway,The Earths magnetic pole is about 800 miles South of the true north pole on a Canadian Island due north of our MidWest. For this reason from San Diego, compasses pointing to the Magnetic North Pole will have a 14 degree Easterly error from true North. This is called “Variation”. The Iron in your ship effects your compass as well. This error is called “Deviation”. So if your compass heading says 035 degrees, if you have a 3 degree West deviation, you are on a Magnetic course of 32 degrees. If you have a variation of 14 degrees East you add 14 degrees to your Magnetic course of 32 Degrees to get your True course of 46 degrees.


Add East Subtract West

Compass +- Deviation= Magnetic +-Variation = True

35 -3W = 32 +14E = 46


If you see on a chart that the magnetic course you want is 32 degrees you add your 3 degrees East Deviation to get your compass course of 35 degrees


True to compass remember “True Virgins Make Dull Company”

True +- Variation = Magnetic +- Deviation = Compass

46 - 14E = 32 + 3W = 35

Round Deviation table

When you are cold wet tired its really easy to make a math mistake with your Deviation table

Magnetic to Compass ADD West SUBTRACT East

Compass to Magnetic ADD East SUBTRACT West

See www.lewishb.biz fot “Lewis Navigation tutorials AND my books :)


000 Magnetic

3E

345 357 Compass 015

6E 1E

339 104

330 030

7E 1W

323 031

315 045

8E 2W

307 047

300 060

8E 3W

292 063

285 075

9E 4W

276 079

270 090

9E 5W

261 095

255 105

8E 4W

247 109

240 120

7E 4W

233 124

225 135

6E 4W

219 139

210 150

5E 3W

205 153

195 165

3E 2W

192 167

180

1W

181

The intuitive Helmsman

The point is that a good helmsman knows what a ship is going to do before she does it and the helmsman moves the rudder to compensate as it is happening...


For example, when the swell is coming from the starboard quarter, you know each swell is going to push the stern to port. As the ship is going through the trough of the wave, you start putting the rudder left to Port turning the stern INTO the coming wave... When you do it the right way, the left rudder keeps the bow of the vessel from yawing to starboard, keeping her on course... As the stern passes over the wave you bring the rudder back to amidships keeping the vessel on course...


You can steer the vessel by only using varying degrees of left rudder...













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