NavList:

I want input and your thoughts for a project.
The idea is to decrease dependents on out side source and place it to the Seaman. THE SEAMAN”S EYE and Closest Point of Approach.
When underway the seaman must always beware of surroundings, the seaman’s eyes are the main source for aware information.
To be safe at sea the eyes need assistance to know what to see and how to use what is seen.
Even using electronics the seaman needs background information on how to best use the eyes.
The Andrea Doria and MV Stockholm collided at sea in 1956, with many lives loss; even through both ships had radar.
Apparently the ships bridge crews didn’t know how to use the maneuvering board and did not follow the” Rules of the Road”.
Also, must not have properly used their always present equipment, the “seaman’s eyes.”
Presently radar and use of the maneuvering board is well known; “RADAR NAVIGATION MANUAL HO.PUB. 1310”
(Defense Mapping Agency).There are many shore base schools teaching the use of radar for Navigation and at sea safety.
Even with on board radar, the Seaman need to depend on his eyes to judge and make decisions at each change of course
for navigation or avoidance. The “Rules of the Road” places extra burden on the vessel using RADAR.
Distance at Sea.
The seaman’s eye needs to be able to estimate distance. The open sea appears very wide and distance is vast to the untaught eye.
Knowing the distance to the horizon enables a useable estimate of an object on it, but it is rare to see this occurrence. It is valuable to know
the horizon distance for all vessel decks and eye heights when at sea to best estimate target distance on, over or short of the horizon.
Table 8 in Bowditch vol 2 gives the “Distance to the Horizon” for the eye above the water- and formula: D= 1.1square root of eye height.
With the visible horizon distance as a reference, a superior and well-informed estimation can be determined.
A change of your eye height may help in the estimate. If your eye is 16 feet above the water and a ship is on the horizon at 4.4 nautical miles,
the 4.4 is good estimate. If another similar vessel to yours is hull down, and you can see the bridge, an estimate of 8 miles is fair.
If your eye is 25 feet the horizon is 5.5 and you see the top tower of a charted tower that is 100 feet tall or 10 miles to the horizon,
it is estimated to be 10 miles to the horizon; your estimated distance is 15.5 miles to the tower.
With practice and experience a seaman can estimate, not accurate, but usable object distance at sea. It may amounts to some rehearse and attention to improve accuracy.
Bowditch Vol 2 has other special cases that enable the seaman to estimate distance of dead in the water targets by doubling the angle on the bow
22.5 and 45 degrees, 45 and 90 and Distance by vertical angle using the sextant.
The seaman needs to be aware and use equipment on board. Even with the best and up-to-date equipment the eyes and how to use knowledge is more important.
The Seaman must be able to determine if a target is moving or still, or on a collision course, by observering the relative motion of the target, its bow angle and wake.
Using radar, collision course, is indicated by a steady or nearly steady bearing of the target and decreasing range.
The same holds true to the eye, a steady or near steady bearing by Compass or relative, and observed increasing target size.
If the target’s relative position is steady an uncomfortable Close point of approach is deemed possible and the rules of the Road may come to play.
In this case an early large change of course may be considered to avoid getting involved with the rules.
A quick way to determine a relative bearing, movement or steady, of the target, is to observe it against a far off land mass or slow moving cloud, this will give the eye
early and noticeable warning compared to taking bearings.
Distance and movement at sea is hard to judge for the seaman and especially the novice, so must be continuously practiced.
CLOSES POINT of APPROACH
Any time a target moving or still appears, the Closes Point of Approach (CPA) must be considered, the Seaman trained eye can give
good and safe information by observing the apparent relative motion of the target, but, to hold course or to change course, to wait, or do it now, is the question.
If a change of course to avoid collision or change for a destination is to be made the CPA is important and should be based on available information.
The Seaman eye may be the only available information, distance to the target needs to be measured or estimate. Desired CPA distance should be considered.
Radar and the use of a chart is always best suited to this situation, although most of the time on smaller craft the change of course is a
uninformed clue or guess or just a heading away from the target. The clueless change of course may works most of the time but it’s safer to think…
A better change of course or heading may be made simply by using the estimate distance and bearing to the target and the rule of sixty.
There are two ways to figure the CPA of your travel towards or away from the target and the distance of CPA that can be computed in your head or with the aid of pencil and paper.
No need for mathematician or tables, Background: Course change of one degree and a distance of 1000 yds will result in a right angle separation of 17 yds.
To (closely) get the CPA, a target at 8000 yds bearing 090 with a course of 100 will be 10x17 yds x8=CPA,1360. Where 10degrees is course difference
and 17yds, base, 8 is amount of thousand yds. Another may be easier, Divide the course change, 10 in to sixty=6. Divided the distance 8000yds by6 parts,
6/8000=CPA,1333. Either will work with a near correct CPA, if under 40 degrees with a reasonably accuracy. Considering other factors that, are in play such as:
how accurate is the measured or estimated distance and the ability to hold the heading track due to steering and currents and the bow angle and speed of the target?
The ease of taking a bearing and ease of computing CPA using either method is safer than blindly heading away from a target.



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