Endorsed by Jack Lagan, author of The Barefoot Navigator ... · Barefoot Navigation: Better ways of measuring distances 25 The quadrant on the right is a recent edition. On the left

Endorsed by Jack Lagan, author of The Barefoot Navigator exclusive to the

St Vincent and the Grenadines

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“Our objective is this. After the course you’ll be a much better navigator than you were when you first stepped onto the boat. You’ll boast new practical

skills inherited from the seafarers of ancient times. With practice, you will become confident enough to stand on deck, look at the sky, look at the sea

around you and just kind of know where you are. You will be a Barefoot Navigator.”

Jack Lagan

In 2006 The Barefoot Navigator was nominated for the

Mountbatten Maritime Prize, awarded annually “to the author of a distinguished

publication that has made a significant contribution to

maritime history”.

This is your textbook.

Barefoot Navigation: The Course

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The text book… Enhanced graphics specific to the Grenadines… eLearning materials…

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… and seven days at sea in the Grenadines!

Designed and endorsed by Jack Lagan

author, seafarer and raconteur

Seen right, on a beach in Afghanistan…

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Saint Vincent and the Grenadines

There are 32 islands in The Grenadines

Barefoot Navigation: The Three Key Questions

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Where are we?

How do we get to the next place?

Why has the whole ocean

become a zone of uncertainty?

Passage to Barbados

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The Perfect Plan? Leave Blue Lagoon and head due East Speed x Time = Distance travelled

You’ll always know where you are!

But dead reckoning is never as simple as that…

Example: 6 hrs x 5 knots = 30 nm

Graphic by Jack Lagan

You are here

Passage to Barbados

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Perils and Problems

Example: 6 hrs x 5 knots = 30 nm


Are you really making 5 knots?

Is your departure-

point accurate?

Happy about your

heading?

The wind is blowing you off-course!

And the damned water’s moving!

NE Trades

North Equatorial Current

Your “zone of uncertainty” now reaches Senegal…

Holding a heading

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WIND SWELL Desired heading

Winds are variable

Swell is much more

consistent

Check your wake: Is it a straight line, straight astern?

Consistency!

The Dutchman’s Log Used to measure the speed of the boat through the water

The equation: How long does it take an object to travel

25ft (7.62m) alongside the boat?

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The instrument:

Time Speed

1s 15 knots

2s 7.5 knots

3s 5 knots

4s 3.75 knots

5s 3 knots

6s 2.5 knots

7s 2.14 knots

8s 1.88 knots A banana skin: high-visibility, biodegradable, nutritious content, user-friendly and multi-

functional. Save the ocean. Support Saint Vincent’s economy

Annual variation of sunrise (2016)

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On latitude 13° N the sun rises at an

angle of 77°


E

Annual variations

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Image courtesy of Starry Night: astronomy.starrynight.com

E

Annual variation of sunset (2016)

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W On latitude 13° N the sun sets at an

angle of 77°

The Grenadines after dark: Finding East

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Graphic by Jack Lagan Finding East at night No need to apply Declination!

The Grenadines after dark: Finding North

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Finding North: first find Polaris But there’s a problem at 13° North Latitude…

N

Polaris

Cassiopeia

Ursa Minor

Ursa Major

NB: Polaris wobbles a bit, about 1° off North.

The barefoot navigator needn’t worry about this

Arrow shows direction of circumpolar rotation

The Grenadines after dark: Finding North

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From the Grenadines the circumpolar stars are low on the horizon. As they rotate

this can cause a problem…

N

Polaris

Cassiopeia

Ursa Minor

Ursa Major

Horizon

The Grenadines after dark: Finding Ursa Major

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Ursa Major has rotated below the horizon Cassiopeia is about 25° (2.5 fists!) from Polaris

And Ursa Minor is faint: it’s often easier to find Polaris first

N

Polaris Cassiopeia

Ursa Minor

What’s happened to Ursa Major?

Horizon

The Great Barrier Reef after dark: Finding South

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This is the view of the Southern circumpolar stars from the Great Barrier Reef, 65nm east of Townsville, Australia

Be careful not to confuse the False Cross with the Southern Cross! There is no South Polar Star!

S

Crux

Where’s the South Pole Star?

The Southern Triangle

The Southern Pointers

The False Cross

The Great Barrier Reef after dark: Finding South

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The intersection of the pointers from Crux, the Southern Pointers and the Southern Triangle gives a good-enough South

for the barefoot navigator

S

Crux

You have to do some

approximation!

The Southern Triangle


The False Cross

Yes, but we’re in the Grenadines, not Australia!

The Grenadines after dark: Finding South

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The Southern Triangle is not visible yet and the False Cross is no help at all.

But the Southern Cross can help us in a limited way…

Crux

This is a nightmare!


The False Cross

?

The Grenadines after dark: Finding South

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When the Southern Cross is near-vertical it will give us a barefoot navigator’s South.

Crux will be invisible when it’s upside down!

Crux

Now it’s like a stopped clock – it’s right twice a day!


The False Cross

S

Seeing part of the circumpolar stars gives the barefoot navigator lots of horizon events. These happen when a star rises or sets (and shouldn’t be confused with “event horizons” which, as you

know, are boundaries in spacetime beyond which events can’t affect an outside observer).

The Grenadines after dark: Not all bad news…

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Merak, Megrez, Alioth and Mizar pass through 32-35°, each taking over from the other. This is a star path.

Horizon events can be used to create star compasses. See next slide for a conceptual star compass

Crux


The False Cross

Image by User: Alain r - Own work. Licensed under CC BY-SA 2.5

A horizon event: Mizar rises An event horizon: An imagined black hole

Merak Dubhe

Megrez Phad 64

Mizar

Alioth

Polaris in this direction

Ursa Major working hard

Barefoot Navigation: The Universal Star Compass

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Original compass rose CC 3.0

Pola

ris

Mintaka (Orion) Mintaka (Orion)

Verti

cal

S. C

ross

RISING SETTING

RISING SETTING

Barefoot Navigation: The Hand of Koha’s Apprentice

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Barefoot Navigation: Calibrate your hand

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Barefoot Navigation: Better ways of measuring distances

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The quadrant on the right is a recent edition. On the left is Jack Lagan’s original, soon the be auctioned by Sotheby's…

An Arab-style kamal improvised from a 30cm ruler. If the blue bead is held

between the teeth 57cm from the ruler, each centimetre on the scale represents

one degree.

The Ultimate Task: Can we get a LAT and LONG from Noon Sun Sight?

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To get a latitude (LAT) you need to measure the altitude of the sun at its highest point above the horizon (ALT). You also need the latitude of the sun on that day; the declination (DEC). You find the DEC in our one-page almanac. Zenith is a point vertically above your head; sometimes known as ‘up’. First step is always calculation of Zenith Difference: ZD = 90° - ALT. Then:

LAT = DEC + ZD

Look up DEC for the day of the sight and see example on the left.

Zenith

ZD = 90° - 30° = 60°

ALT = 30°

EXAMPLE: The navigator gets a noon altitude of 30° on November 21st Interpolating, DEC = -19.9 + ( 20.7 – 19.9) /4 = - 20.1°

ZD = 90° - 30° = 60° So, her LAT = -20.1 + 60° = 39.9°N

So, our little boat is somewhere off New Jersey. Or Northern California. A longitude would help…


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Getting a good latitude in the Grenadines is a challenge. In this example the navigator is getting a Noon ALT of 60° on February 1st. In the Northern Hemisphere’s winter! That’s six fists on top of each other… A kamal might not be long enough so you’ll probably need to use a quadrant and a flat sea. Or a beach. No-one said Barefoot Navigation was going to be easy…

Zenith

ZD = 30°

ALT = 60°

EXAMPLE: The navigator gets a noon altitude of 60° on February 1st Interpolating, DEC = -16.8 + (18.0 – 16.8) /4 = - 17.1°

ZD = 90° - 60° = 30° This time her LAT = -17.1 + 30° = 12.9°N

So, our little boat is somewhere off the island of Bequia… Make a course change for the Frangipani

Beach Bar! Can we radio ahead our orders for lobster and steak?


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If you thought a 60° altitude (ALT) was challenging, how about this? We’re still in the Grenadines but now it’s Summer and we’re south of the sun’s latitude. Remember that the declination (DEC) varies from 23.5°S to 23.5°N and back again and St Vincent and the Grenadines lie between 12° and 14°N. We’ve been mugged by the Equator.

All right, now we’ll get a longitude. Compared with latitude, this is easy.

Old salts with sextants find it hard to deal with an overhead sun. “Actually, such a sight is virtually impossible to get because the sun is whizzing by from east to west and, as you swing the arc, you have to spin around in a complete circle.” Hewitt Schlereth

Zenith

The sun’s geographical position (GP) has moved

north of our Zenith


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Longitude is all about time. The Earth rotates at 15° per hour. So, if you compare the time the sun reaches noon at your location and compare it with time it passed the fixed point of the Greenwich Meridian, you get a time difference that can be converted to a number of degrees East or West of that meridian. That’s why you need is one of these set to the time at Greenwich.

This is a Harrison H4, the first accurate navigator’s timepiece, 1761

Direction of rotation

See next slide


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As you track the altitude (ALT) of the noon sun with your quadrant, looking for its highest point in the South, note the time of each reading. As soon as the ALT decreases, the previous value should be local Noon, near-enough. Use the third column of the table to get Noon at Greenwich (adjusted by the Equation of Time) for the day of the sight: March 13.

35° 34.5° 33°

34.5°

ALT and Time about every 20 secs

Stop when ALT starts to decrease

EXAMPLE: Local noon from the sight (hh:mm:ss): 16:21:30 Noon at Greenwich (from table): 12:13:43

Difference in time: 04:07:47 Longitude (in Degrees and Minutes): 62° WEST

That’s 40nm west of the Frangipani Bar.

Landfall! Cumulus clouds

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We think there’s a small island around here somewhere… Ah! See the little cumulus cloud? Clouds like that don’t form spontaneously. The rising sun will heat land more quickly than water and the resulting ‘thermal’ current of air will cause the formation of a cumulus cloud like this one. Worth a course change?

There are other ways of detecting land below the horizon: see next slide. Maybe the Frangipani Bar isn’t too far away.

Photo: NOAA (Public domain)

Landfall! Ways to reduce your zone of uncertainty

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Have you tried our Grenadine Seabird App? Learn how to identify the birds, their feeding ranges and

nest sites

Main photo: NOAA (Public domain)

Local seabirds can show you the direction and likely distance of land

Wheels down, flaps extended, this light

aircraft is about to land at one of the six airfields in

the Grenadines

The top of a 30m (100ft) radio mast will be the first landmark you see. It’s in the same colours as a safe water mark

Sea traffic can help. But if this foreign-flag schooner

is not ‘coast-hugging’ it may just be passing

through

Like buses, ferries have routes and

schedules. Did you pick up a brochure

at the airport?

Has the colour of the sea changed?

Barefoot Navigation All our yachts carry GPS receivers, charts, sailing

directions, depth-finders and VHF radios

and

we’re confident yours does too…

SAIL SAFE!

Documents

Endorsed by Jack Lagan, author of The Barefoot Navigator ... · Barefoot Navigation: Better ways of measuring distances 25 The quadrant on the right is a recent edition. On the left