Monday, December 12, 2011

New Life for Old Pub 249 Vol. 1

An out of date Pub 249 vol. #1 Air Navigation (selected stars) is still extremely useful for general star finding, selecting optimal stars for twilight observations, and determining star azimuths to the nearest degree. Combine Pub 249 (to tabulate selected star azimuths) with a scientific calculator (to calculate altitude from a DR assumed position) and save a great deal of calculator button pushing with no loss of precision. A must try on your next round of stars.

Sunday, October 16, 2011

Celestial Navigation by TI-36X Pro

The TI-36X Pro is an excellent value calculator for celestial navigation sight reduction. Enter the formula for calculating altitude into the NUM-SOLVE function then follow the prompts for variable entries.

Calculated altitude formula:
a=ArcSin(Cos(x)Cos(d)Cos(t) ± Sin(x)Sin(d))

x= Latitude
d= Declination
t= Meridian Angle
a=Calculated Altitude

Use the OP function to solve for azimuth Z.

Key the SET OP function and enter the formula:

Once (a) is solved in NUM-SOLVE then azimuth Z can quickly be solved in the OP function with one key push.

Convert calculated altitude (a) into degrees minutes and seconds using the MATH menu DMS6 or multiply degree fraction by 60 to get minutes and tenths.

Thursday, September 15, 2011

New Deck Shoe Break-in

Shorten the break-in time for a new pair of leather deck shoes using liquid lanolin rubbed onto the bare foot before inserting into the shoe naked and worn for a day. This will soften the leather inner sole so that it will mold to the bottom of the foot. A comfortable deck shoe equals a happy sailor :-)

Tuesday, September 13, 2011

The Elegant Amplitude

The amplitude is perhaps the most elegant way to determine compass deviation and gyro error*. Use Bowditch table #27 (4 pages ) or a pocket calculator and the formula:

INV SIN [ SIN (Declination) / COS (Latitude)]

Apply the result to due East (90) or West (270) in the direction of the elevated pole when Latitude and Declination are of the same name (away if contrary). Take observations when the Sun's lower limb is 2/3 of a diameter above the visible horizon.

Tip- Keep a photo copy of Bowditch table #27 with the current years Nautical Almanac.

*Checking the compass/gyro at sea requires a celestial solution. Until the GPS compass becomes commercially affordable navigators will need to keep their celestial compass checking skills sharp.

Friday, September 2, 2011

Companionway Step Brace

Older companionway steps are prone to splitting and loosening over time. A preemptive plywood stiffener and support bracket will aid in preventing step collapse and possible injury. Be sure to drill the appropriate sized pilot holes to accommodate the stainless wood screws.

Monday, July 25, 2011

Hybrid Ex-Meridian Method

Bowditch table 29 value (a) combined with a slide rule or calculator using the formula (a)(t^2)/60 generates a correction in minutes of arc to be added to the altitude (Ho) of an observation made within 30 minutes time of meridional passage. The sum is then solved as a standard meridional passage observation to get the Latitude [Lat.=90°- (Ho+ corr).~Dec.]. This hybrid method saves page turning, interpolation, and button pushing while adding precision.

Wednesday, June 22, 2011

HandiTak Chart Corners

A pea sized ball of HandiTak is just right for securing chart corners down on the chart table. This will put an end to the sliding of charts onto the deck. HandiTak generally will not rip a chart when removed but just in case tape the corners with clear packing tape.

Wednesday, June 8, 2011

Sextant Arc Maintenance

Clean old lubricant and grime from a sextant arc with GoJo hand cream. GoJo makes several types of cleaning solutions so it is important to use the one which is GRIT FREE and contains LANOLIN. Apply liberally then run the worm gear through the arc a few times. Wipe dry with a clean rag and follow up with a light oil applied a few drops at a time onto the worm gear as the micrometer drum is turned through the arc. Try Hoppe's #9 light oil for a gum free final touch.{2DCDC7EB-6048-4686-8021-95D684DA8ACF}&Cpn={BB2D686E-1BA0-408B-9D72-0E2C0CA21A7F}

Wednesday, May 11, 2011

The Lithium CR2032 Battery For Watch and Calculator

All of the pictured portable electronic devices are powered by the same common affordable lithium CR2032 battery. The CR2032 battery is about the size of a nickle and provides five years of power for watches and calculators. Batteries can be swapped between devices in the event of battery failure. The CR2032 has a longer than average shelf life so spares will have plenty of voltage when needed. Device battery type is as important as function for making the grade at the chart table.

Monday, April 18, 2011

Shaft Zinc Installation Tip # 27

Apply a pinch of handitack on the zinc hardware nut to secure and prevent loss during the underwater installation. Keep available extra hardware in the event nuts or bolts are dropped to the bottom.

Friday, April 15, 2011

Dutchman's Log

When the knot log fouls and the GPS goes on the blink then there is always the Dutchman's Log for estimating the speed through the water. Just count the number of seconds a bit of floating material takes to travel from bow to stern to get knots.

Use the formula:
Boat Length in nautical miles / drift seconds from bow to stern = Knots / 3600 seconds in an hour

Example for 33 ft. boat given 6076 ft. in a nautical mile and 3600 seconds in an hour:

Formula: .00543 NM boat length / drift seconds = knots / 3600 sec.

Knots = .00543 x 3600 / drift sec.

Knots = 19.6 / drift sec.

Table of Speed Though the Water for 33ft. Boat

9s = 2.2 kts.
8s = 2.5 kts.
7s = 2.8 kts.
6s = 3.3 kts.
5s = 3.9 kts.
4s = 4.9 kts.
3s = 6.5 kts.

Saturday, April 2, 2011

Sextant Scope Filter

Index error (I.E.) can be determined more precisely during the day by using a custom fitted solar mylar film filter (the type used to observe a solar eclipse) over the objective lens on the sextant scope. The result will be a pair of sharp uniform orange Sun images. Overlap the Sun images for direct index error readings or take half of the difference between the two limb to limb readings.

-When off the arc the reading is 60' minus the micrometer value.

-Shading the sextant scope directly allows the horizon mirror shades to be pulled aside which opens up better access for the adjustment tool.

Thousand Oaks Optical (928)692-8903

Friday, January 7, 2011

Ex-Meridian by Formula

The Ex-Meridian can be done by formula for improved precision over Bowditch vol.2 tables #29 and #30. (current edition table #24)

Formula :

(a) = 1.9635 x COS Latitude x COS Declination / SIN (Lat. ± Dec.*)
*RULES (+) if Lat. & Dec. are contrary in name. (-) if Lat. & Dec. are the same name.

Ex-Meridian Correction in minutes of arc to be added to Sun (Ho) near LAN (upper transit) :

Ex.Correction' = (a)( Time from LAN in minutes and tenths)^2 / 60


Ex.Correction' = (.267)(a)( Meridian Angle in degrees and tenths)^2


Lat.34°N Dec.20°S (Sun observed 20 minutes 30 seconds before LAN)

(a) = 1.9635(Cos 34)(Cos 20)/Sin (54) = 1.89
Ex.Corr.' = (1.89)(20.5)(20.5)/60 = 13.24' added to (Ho)


Ex.Corr.' = (.267)(1.89)(5.125)(5.125) = 13.24' added to (Ho) *

The corrected (Ho) is then reduced as a normal LAN to get the Latitude at the time of observation.

*Try a formula variant that uses meridian angle vs. time
.267 (a)(Meridian Angle)^2 = Ex.Correction' file:///Users/greg/Desktop/factors.html