How far could the lookouts see ?


May 3, 2005
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I have always assumed that the men in the crow's nest could see as far to the horizon as the old rule of thumb.:
The distance in miles is equal to the product of a constant (I have seen both 1.2 or 1.55) times the square root of the height above sea level in feet ?
How high was the crow's nest on Titanic ? So how far could they see ?
I am also assuming the persons in the lifeboats could only see about 3 miles.
 
May 3, 2005
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I have always assumed that the men in the crow's nest could see as far to the horizon as the old rule of thumb.:
The distance in miles is equal to the product of a constant (I have seen both 1.2 or 1.55) times the square root of the height above sea level in feet ?
How high was the crow's nest on Titanic ? So how far could they see ?
I am also assuming the persons in the lifeboats could only see about 3 miles.
Found the answer:
Height: about 90 feet. Distance to horizon: about 12 miles.
If the mast head light was above the crow's nest, would a person in the lifeboat have seen it beyond the horizon before the person in the crow's nest have seen the lifeboats.....or vice-versa ?
 
A

Aaron_2016

Guest
Not sure about the measurements. A person can observe a further distance the higher one is above sea level owing to the curvature of the Earth. However as Captain Lord said - "It was a very deceiving night" as he was mistaking stars on the horizon for ships. Captain Moore of the Mount Temple saw a passing schooner that night. He was asked how far away she was. He replied - "I could not judge, because you cannot judge by a light at sea." Captain Rostron saw at least half a dozen icebergs that night before his lookouts.


Q - Your two men were on the look-out then in the eyes of the vessel?
A - Yes.
Q - No report had been made to you?
A - No.
Q - Who was it saw it first, do you know?
A - Yes, I saw it first.
Q - Before the look-out men?
A - Yes, we saw all the icebergs first from the bridge.
Q - I do not understand that. You were on the bridge with your officers, I presume?
A - Yes, the whole time.
Q - And each time, if I follow you, that an iceberg was seen, you picked it up first on your bridge?
A - Either one of my officers or myself, before the look-outs.
Q - Did you pick it up by sight, or by naked eye, or with binoculars?
A - At first with the naked eye.
Q - Do you find that you pick them up better with the naked eye than with binoculars?
A - It all depends. Sometimes yes, at other times not; it depends.
Q - How was it neither of the look-out men saw it or reported it to you? Why did not they see it before you?
A - Well, of course, they had all had warning about keeping a look-out for growlers and icebergs, previous to going on the look-out, and on the look-out also. You must understand, unless you know what you are looking for, if you see some very dim indistinct shape of some kind, anyone could take that as nothing at all - merely some shadow upon the water, or something of that kind; but people with experience of ice know what to look for, and can at once distinguish that it is a separate object on the water, and it must be only one thing, and that is ice.
Q - So that what it really comes to is this, if I follow you correctly, that it requires a man with some knowledge of icebergs, some experience of picking them up before he can detect them at night?
A - Precisely.
Q - That is to say, before he could detect them unless they were very close to him?
A - Yes.
Q - So far as you know, had any of these men any experience in being amongst icebergs?
A - Not to my knowledge, but I should imagine some of them must have had, because several of them have been in the Cunard Company for years.
Q - Does it mean that on your bridge you and your officers were quicker in detecting them than any of the men on the look-out?
A - Well, about 75 percent of the objects that are seen at sea every day or night are picked up from the bridge first. Naturally the officer will take more interest in these things than a look-out man. I always trust to the bridge preferably to the men.
Q - He relies upon his eyesight, assisted by the look-out?
A - Yes, that is the position; we are assisted by the look-outs.



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Dec 4, 2000
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The Bowditch text of the period listed the following "Distance of Visibility of Objects at Sea" in Table 6. I've selected the appropriate numbers for Titanic's bridge and crow's nest. Distances are in nautical miles to the horizon.

60' height 8.9 miles
65' height 9.2 miles
70 feet 9.6 miles
75 feet 9.9 miles
80 feet 10.3 miles
85 feet 10.6 miles
90 feet 10.9 miles
95 feet 11.2 miles

The same numbers for someone in a lifeboat. Note that the visibility distance to the horizon is much shorter than most people expect. This is especially true for people unfamiliar with the sea and the curve of the earth.

3 feet 2.0 miles
5 feet 2.5 miles
7 feet 2.9 miles
9 feet 3.5 miles

Keep in mind that visibility to the horizon is controlled by the height of the eye of the observer. So, a man with a height of eye of 5 feet standing on a deck 60 feet above the waterline would have the visibility for a height of 65 feet. Someone standing in a lifeboat might have a 7 foot height of eye.

To calculate the maximum distance at which a distant light can be seen it is necessary to first get the visibility for the height of the observer to the horizon. Then the height of the light is used to enter the table to get it's visibility to the horizon. The two distances are then added to get the total maximum distance that the light can be seen by the observer.

If the observer on a ship had a height of eye of 70 feet; and a survivor in a lifetboat held up a lantern at a height of 5 feet; that light could be seen at a maximum distance of 12.1 miles by the observer on the ship's bridge.

5 foot height Lifeboat Lantern Horizon = 2.5 miles to horizon
70 foot height of ship's observer = 10.6 miles to horizon

2.5 + 9.6 = 12.1 miles maximum visibility lantern to observer

On a night with a sharp horizon it is possible to "bob the light" by kneeling down and standing up, or rapidly moving from a higher to lower deck. If the light is visible from the higher position, but not the lower, the navigator can quite closely calculate his distance to the light. (Of course, a "sharp horizon" is seldom available when you need one, so this technique has limited practical application.)

-- David G. Brown
 
May 3, 2005
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Correction.
I should have said whether the lookouts on Carpathia saw the lifeboats from Titanic first or whether the persons on Titanic lifeboats saw the mast head lamp on Carpathia first. Would have to check on height of lookouts and mast head lamp on Carpathia rather than Titanic of course.