View Full Version : Seaman's Eye - Article Thought

Ian McColgin
01-15-2012, 12:32 PM
I’m not good enough to tell folk how to do this, but an article on aspects of the “seaman’s eye” that can be taught.

For sure, how to judge relative angles both for eyeballing position or distance - small angle use of the knuckles as a range finder for example or bearing change and collision avoidance.

But also some of the ocular “tricks” like:

Since the eye’s cones are near the center and the rods are more out, periferal vision is more effective for night use; or

Controlled focus not only makes airplanes visible in a clear sky, but also objects on the ocean or horizon; or

When sighting on anything - microscope or gun sights or sextant or monocular - how to use the off eye to see the macro environment.

I’m sure there are many more.

George Ray
01-15-2012, 01:04 PM
Pretty interesting stuff, are you going to elaborate on this topic?

David Burch in his book 'Emergency Navigation' discusses methods of determining angles using many methods including as you mention knuckles.


Judging distance/angles is a skill I have long been interested in.
************************************************** ****

Less 100 yds
whites of the eyes : 30yds
clearly see mouth and eyes : 50 yd

eyes are dots : 100 yards
all parts body seen distinctly and slight movements seen : 100 yd eyes and mouth can be seen clearly : 110yd
brass buttons : 150 yards
brass buttons become stripes : 200 yd
buttons and details of clothing : 200 yd
buttons and details of clothing are recognizable : 220 yd
faces discernible but not recognizable : 250-300 yd
buttons not visible: 300 yd
face can be seen : 300 yd
movement of legs/arms : 400 yd
Movement of persons arms/legs : 400 yd
face is a dot but can see legs/arms move : 400 yd

1/4 mile-1/2mile
color of uniform : 500 yards
shoulders appear bottle shaped : 550 yd
files of a squad of men counted in good light : 600 yd
head is visible as a dot : 660 yd
head is not yet visible : 770 yd
cannot count men or see their movements : 800 yd man looks a post : 1/2mile (880 yd)

line of men resembles a broad belt : 1000 yd
infantry can be plainly distinguished from cavalry 1200 yd mounted man looks like a speck: 2,000 yd
Individual trees : less than mile
person is a black dot : 1 mile
color of buoy discernible : 1 mile
shape of small buoy discernible : 1 mile
small buoy visible but no shape/color : 1 1/2 miles
windows on house : less two miles
large buoy visible 2 miles
individual windows discernible day or night : 2 miles
canʼt see line between land and water : greater than 3 miles
light colored beach distinguishable from 8ʼ HOE : 4 miles
low coast at 10 miles appears as narrow dark line w/ occasional tank or large building

Body Parts:
At arms length:
..02 deg: Finger width
..15 deg: Outstretched thumb tip to index finger tip
..20 deg: Outstretched thumb tip to little finger tip

Short calibrated stick on a string which is held in the teeth to keep the distance from the eye, and square to the line of sight orientation, constant so angles can be measured.
( At 57” from the eye, one centimeter is one degree. Good up to about 15 degrees)

Angle - Distance:
Object with 6 deg vert angle (three fingers) is 10 times as far away as it is high (e.g. light house 60 yds high is 600 yards away when 3 fingers tall)

Sources of Info:
Emergency Navigation, (David Burch)
Boat Navigation for the Rest of Us, (Captain Bill Brogdon) Sailing for dummies, (J.J. Isler)
The Practical Mariners Book of Knowledge, (John Vigor) Scouting for Boys, (Robert Baden-Powell)
Scout Masters Handbook,
“The Eyes are Telltales” (NYT article 1895)

A friend that recently completed the NW passage and is wintering in Sitka, AK sent me a scan of a distance/angle judging table from a guide to the pacific 'Inside Passage', and the distance judging is 90% based on characteristics/texture/color of deciduous trees, evergreen trees and the forest overall, made me laugh. I have yet to go through the table and incorporate it into the text above.

01-15-2012, 01:08 PM
I'm all for it. Periferal vision is definitely better for night use, though it can be annoying, trying to pick out a light on the horizon that you can only see out of the corner of your eye.

George Ray
01-15-2012, 01:41 PM
Wonder how to best make practical use of this info on the way the eye works?
This is truly an important and under discussed topic.

For night work the hopeful slowdown in middle east hostilities will free up scads of night vision apparatus. When we went into Afghanistan and Iraq the makers of night vision shifted all output to military and the latest technology (Generation-3) has only been available as used or a trickle of new at grossly inflated prices. It's nice to be able to see the loom of a ships lights over the horizon long before the eye can spot it or make out navigation lights at a distance in rainy squally hazy Wx.

Ian McColgin
01-15-2012, 02:12 PM
Yeah, well wearing all that gear is a pain if you're sailing or rowing. Knowing how to see out the corner of your eye (side to side periferal is much more accute - that's my Dad's PhD and first used practically in the cockpit design of the DC-8) is the way to go at night.

I am personally, by the way, not good at shifting my focus against a blank. I can do it a little moving my eyes up the water to the horizon but that's not very reliable - as anyone who has searched and searched for a buoy only to have it pop out of the ocean suddenly visible has experienced even if not knowing the reason why.

In the early days of arial combat they did not know how to teach this, especially against a blank sky, and the guys who had it naturally - or like my Dad somewhere between super- and praternaturally - couldn't explain it. I am sure someone must have figured out eye exercises for this by now but I have no idea what they might be.

01-15-2012, 05:20 PM
As a note there are eye exercises that improve vision and detail, particulary peripheral.

01-16-2012, 07:02 PM
Any decent pair of marine binoculars (7x50s or 6x35s, etc) will let you see a surprising amount of detail in low light conditions. That's why they used to be called "night glasses" in the WWII era, before the active light amplification Night Vision technologies were invented.

You need a large objective lens combined with a relatively low magnification, which result in a relatively large "exit pupil", the diameter of the focused light beam coming out of the eyepiece lenses. The pupil in a dark adapted eye (in a young person) is about 7mm, and as you age it gets smaller, to the point of being about 4mm when you are in your 70s.

A pair of binoculars with an exit pupil that matches or is slightly larger than the diameter of your dark adapted pupil will allow the maximum amount of available light to be gathered and presented to your eye. Modern lens coatings also help increase the amount of light transmitted through the system. So you don't need fancy Night Vision Googles or Scopes, though they have their place.

If you haven't used a pair of good binoculars at night, go out and try it. They really help.