Navigation NAU 102 Lesson 12

Time, Speed, Distance Calculation of Time, Speed and Distance A daily task for a navigator. Calculation requires accuracy and speed. When will I get there? How fast should I go?

Speed Unit is the Knot (kt. or kn. or knt.) From the knotted speed log.

Speed Unit is the Knot (kt. or kn. or knt.) 1 knot = 1 nm/hour Speed = Distance/Time

Calculation Several Methods Mental Calculation “6 Minute Rule” Logarithmic Scale Nomogram Mathematical Formula

Mental Calculation Solve using simple ratios of time units. e.g. ½, ⅓, ¼ Your speed is 20 kts. How far will you travel in 30 minutes? You travel 6 nm in 20 minutes. What is your speed? 10 nm 18 kts

“6 Minute Rule” 6 minutes is 1/10 th of an hour. Every 6 minutes, you travel a distance equal to 1/10 th of your speed. Move the decimal point 1 place to the left or right.

“6 Minute Rule” E.g. If your speed is 15 kts., how far will you travel in 6 minutes? nm

“6 Minute Rule” E.g. What is your speed if you travel 2.7 nm in 6 minutes? kts.

“6 Minute Rule” You can use multiples of 6 minutes as well. 6 minutes = 0.1 hour 12 minutes = 0.2 hour 18 minutes = 0.3 hour Etc.

“6 Minute Rule” E.g. If your speed is 15 kts., how far will you travel in 18 minutes? nm x 3 = 4.5 nm

Logarithmic Scale On some charts and radar plotting sheets.

Nomogram On some charts and maneuvering boards.

Nomogram E.g. How far will you travel in 16 minutes at 13 kts?

Nomogram E.g. How long will it take to travel 2.5 nm at 16 kts?

Math Formula Distance = Speed x Time D = S x T S = D/T T = D/S

ETA Estimated Time of Arrival What time will I get there? For short voyages: Transit Time = Distance/Speed Transit Time + Departure Time = ETA

ETA Example You depart Point A at 0800 and steam for 60 nm to Point B at 13 knots. What is your ETA at Point B? Transit Time = 60 nm/13 kts = hrs = 4 hrs hrs* 60 min/hr = 4 hrs 37 min = 1237

ETA For longer voyages, we need to know about Time Zones.

Time Zones Earth is divided into 24 time zones. Time differs by an hour from neighboring zones. Everyone in the zone keeps the same time.

Time Zones

Each time zone is 15° of longitude wide. 360° / 24 = 15° Zones are numbered (“zone descriptions”) 0 through -12 in east longitude 0 through +12 in west longitude

Time Zones First, calculate the central meridian of a zone E.g. ZD +4 Zones extends 7.5° east & west of the center. Zone Boundaries 15° x zone description 4 x 15° = 60° W

Time Zones

To find the zone of a particular location: Divide by 15 Round to the nearest whole number Convert longitude to degrees & tenths

Time Zones ZD = °/15 = ° 30’ = 141.5° E.g. What is the ZD of 141° 30’ E (- E/+W) ZD = °/15 = ° 40’ = ° E.g. What is the ZD of 142° 40’ E?

Time Zones And, sometimes, Zulu Time Also, Coordinated Universal Time (UTC) Known as Greenwich Mean Time (GMT) ZD 0 – The starting point for world’s time system We must be able to convert between Time Zones

Time Zones E.g. When it is 0815 in Vallejo (ZD +8), what time is it GMT? add the ZD to local time. To convert from local time to GMT (+8) = 1615 GMT

Time Zones E.g. When it is 2230 in ZD +4, what time is it GMT? (+4) = 2630 GMT 2630 = 0230 the next day

Time Zones E.g. When it is 2230 in ZD -4, what time is it GMT? (-4) = 1830 GMT

Time Zones E.g. When it is 0230 on 07 Oct in ZD -4, what time is it GMT? (-4) = ? 0230 = 2630 on 06 Oct (-4)= 2230 on 06 Oct

Time Zones E.g. When it is 0815 GMT, what time is it in Vallejo (ZD +8)? subtract the ZD from GMT To convert from GMT to local time (+8) = 0015 Local Time

Time Zones E.g. When it is 0815 GMT, what time is it in ZD -8? subtract the ZD from GMT To convert from GMT to local time (-8) = 1615 Local Time

Time Zones E.g. DST in Vallejo (ZD +7) Zones keep the time of the next zone to the east. Daylight Saving Time Usually 1 st Sunday in April to last Sunday in October.

Time Zones Daylight Saving Time 2007: 2 nd Sunday in March to first Sunday in November. Note: some locations don’t keep daylight saving time. Look in the Sailing Directions

Introduction to Navigation Questions?