Georges Guay
Member
Titanic navigation lights range of visibility
Everyone knows by heart Article 2 issue forth the 1910 Regulations for preventing the collisions at sea. The masthead light had to be visible at a distance of at least 5 miles, the sidelights at a distance of at least 2 miles and the stern light from at least 1 mile. At least meaning not less than, at the minimum of, etc. If a candidate for the certificate of competency would present himself in front of a BOT nautical examiner and one of the questions to answer was; «According to the Rules, at what distance would you expect a masthead light to be seen in perfect visibility»; as of what I conclude from the evidences, the candidate would answer without hesitation 5 miles sir! Personally, I would not be entirely satisfied by that answer for the reason that a masthead light had to be visible at a distance of at least 5 miles onwards. There is quite a difference between could be seen and should or shall be seen. The range of visibility of a masthead light depends on the type of lantern (oil or electric), the type of lens (Plano convex or Fresnel), the intensity, the maintenance of the glass, the visibility, the height of eye of the observer, the observer visual acuity, the use of glasses, the abnormal atmospheric refraction, just to name a few.
Therefore, a masthead light had to be visible at a distance of at least, not less than or at the minimum distance of 5 miles in good visibility and virtually up to the geographical visible horizon in perfect visibility.
- Boxhall:
«I thought she was about 5 miles, and I arrived at it in this way. The masthead lights of a steamer are required by the board of trade regulations to show for 5 miles, and the signals (sidelights) are required to show for 2 miles. I saw the side lights. Whatever ship she was had beautiful lights. I think we could see her lights more than the regulation distance, but I do not think we could see them 14 miles.» Not to show for 5 miles but had to be visible at a distance of at least, not less than or at the minimum distance of 5 miles.
- Groves:
8419. What is the average range of an ordinary ship's sidelight? - Two miles.
8420. And the masthead light? - Five miles; that is the distance they are supposed to show.
8421. They do show a little further on a clear night? - Yes.
- Groves: about 5 to 7 miles,
- Gibson: 4 and 7 miles away,
- Stone: at about 5 miles distant,
- Lord: Pretty near south of us, 4 miles to the south
Lord who was the most experimented of all stated;
7120. Suppose the Titanic was 7 or 8 miles from you between 11.30 and 12 o'clock, would those on her bridge have been able to see your lights? - Easily.
Remembering that the yellow-funnel steamer Lord sighted on the southwest the next morning, beyond where this man had left, was even estimated at a mere 8 miles away!
In 1912, there was no way to establish with precision the distance of an observed vessel by her navigation lights alone. It seems that they were all using a sort of epoch rule of thumb inspired by «to show for 5 miles or to show for 2 miles» instead of had to be visible at a distance of at least 5 miles or at a distance of at least 2 miles. If only they would have had the chance to compare their rule of thumb estimations against accurate distances measured from Radar or AIS, they would confirm what I am trying to point out.
That range estimation of navigation lights is also very true today. The United States coast pilot states:
(159) The maximum distances at which lights can be seen may at times be increased by abnormal atmospheric refraction. In some conditions of the atmosphere white lights may have a reddish hue. Navigational lights should be used with caution because of the following conditions that may exist.
(164) The distance of an observer from a light cannot be estimated by its apparent intensity.
(170) Lights of equal candlepower but of different colors may be seen at different distances. This fact should be considered not only in predicting the distance at which a light can be seen, but also in identifying it.
The CCG List of Lights, Buoys and Fog Signals:
(12) Atmospheric conditions can have a considerable effect on light transmission and the visibility of lights. The distance to a light cannot be reliably estimated from its apparent brightness.
The American Practical Navigator, Bowditch:
The distance of an observer from a light cannot be estimated by its apparent intensity.
The List of Lights, Buoys and Fog Signals Luminous Range Diagram;
Intensity in candelas against range in nautical miles.
What Samuel came up with is that the incandescent light bulbs used in the electric lanterns were made of 2 filaments shining off 16 candelas each. The Fresnel glass had a magnification factor of 8.4 but an absorption lost of 10%. The sidelights had an additional filter loss of 2/5 (sidelight range ÷ masthead light range) due to the glass dye. 16 x 2 = 32 candelas or 402 lumens or the equivalence of an incandescent light bulb of 40 watts.
Masthead light intensity:
16 candelas x 2 = 32 candelas
32 candelas x [8.4 – 10% = 7.6] = 243 candelas
Visibility range = 19 miles
Sidelight intensity:
16 candelas x 2 = 32 candelas
32 candelas x [8.4 – 10% = 7.6] = 243 candelas
243 candelas x 2/5 = 97 candelas
Visibility range = 12 miles
In 1912, engineers knew well that the precision of calibration instruments would upgrade with time, thence every calculation integrated a margin of safety. To give an idea of such a margin, if you just add 2 candelas per filament or 5 watts per lantern, the masthead light range of visibility goes from 19 to 20 miles and the sidelights from 12 to 13. Notwithstanding the fact that United States Coast Pilot publication states that the maximum distance at which lights can be seen may at times be increased by abnormal atmospheric refraction; «Navigators, crew and passengers experimented a visibility rarely or never seen before. A most peculiar night. Very much refraction entered in weather log books. Witnesses stated that rockets bursting stars had color in it due to thermal inversion; a condition required for abnormal atmospheric refraction.»
To use the Luminous Range Diagram, we need to know the light intensity in candelas which was certainly not an information readily or easily accessible. Thanks Samuel for those data. The Nominal Range table given in the same publication is the maximum distance of a listed or a charted light, namely lighthouses, which can be seen when the meteorological visibility is 10 nautical miles. It does not really apply to ships navigation lights.
Geographical Range of Light Diagram:
The List of Lights, Buoys and Fog Signals or similar publications like Pilot Books, also present a Nomogram to determine the geographical range of a light. Why such coast guard publications would publish mathematical tools to determine the geographical range of a light? Just because when the visibility is unlimited, it is the most convenient tool to use. Titanic was a brand new vessel, up to highest standards and made to last. Her masthead light and sidelights lanterns were electric and her new Fresnel lens made the beam of light to focus. The weather of that moonless and pitch dark night was dead calm, dry and cold. Navigators, crew and passengers experimented a visibility rarely or never seen before.
As a result;
The minimum visibility range of Titanic navigation lights from the official Luminous Range Diagram was:
- Masthead light = 19 miles
- Sidelights = 12 miles
The maximum visibility range of Titanic navigation lights from the official Nomogram Geographical Range of a light was up to:
- Masthead light = 21 miles
- Sidelights = 17 miles
Geographical Range by calculations:
- Masthead light = 1.169 x [√(39+5) + √140] = 21½ miles
- Sidelights = 1.169 x [√(39+5) + √64] = 17 miles
Any mystery vessel with a depiction such as witnessed by Californian’s 3rd mate Charles V. Groves, located in between Lord subjective position and the Wreck location, would either sight the signaling lamp or hear the socket distress signals loud report or subsequently be swiftly identify;
«At about 11.30, I reported that vessel to Lord. I said that by her deck lights she was evidently a passenger steamer. Yes, a lot of light. There was absolutely no doubt her being a passenger steamer. Most decidedly I do believe that the passenger steamer was Titanic. The number of deck lights she was showing indicated me she was a large passenger steamer.»
Titanic masthead light was first seen from 19 to 21 nautical miles and her sidelights from 12 to 17 miles. Just far enough for the signaling lamp visible up to 10 miles to not be seen and just far enough for the socket distress signals loud report up to 13 miles to not be heard. The perfect distance apart at the very worst moment.
Everyone knows by heart Article 2 issue forth the 1910 Regulations for preventing the collisions at sea. The masthead light had to be visible at a distance of at least 5 miles, the sidelights at a distance of at least 2 miles and the stern light from at least 1 mile. At least meaning not less than, at the minimum of, etc. If a candidate for the certificate of competency would present himself in front of a BOT nautical examiner and one of the questions to answer was; «According to the Rules, at what distance would you expect a masthead light to be seen in perfect visibility»; as of what I conclude from the evidences, the candidate would answer without hesitation 5 miles sir! Personally, I would not be entirely satisfied by that answer for the reason that a masthead light had to be visible at a distance of at least 5 miles onwards. There is quite a difference between could be seen and should or shall be seen. The range of visibility of a masthead light depends on the type of lantern (oil or electric), the type of lens (Plano convex or Fresnel), the intensity, the maintenance of the glass, the visibility, the height of eye of the observer, the observer visual acuity, the use of glasses, the abnormal atmospheric refraction, just to name a few.
Therefore, a masthead light had to be visible at a distance of at least, not less than or at the minimum distance of 5 miles in good visibility and virtually up to the geographical visible horizon in perfect visibility.
- Boxhall:
«I thought she was about 5 miles, and I arrived at it in this way. The masthead lights of a steamer are required by the board of trade regulations to show for 5 miles, and the signals (sidelights) are required to show for 2 miles. I saw the side lights. Whatever ship she was had beautiful lights. I think we could see her lights more than the regulation distance, but I do not think we could see them 14 miles.» Not to show for 5 miles but had to be visible at a distance of at least, not less than or at the minimum distance of 5 miles.
- Groves:
8419. What is the average range of an ordinary ship's sidelight? - Two miles.
8420. And the masthead light? - Five miles; that is the distance they are supposed to show.
8421. They do show a little further on a clear night? - Yes.
- Groves: about 5 to 7 miles,
- Gibson: 4 and 7 miles away,
- Stone: at about 5 miles distant,
- Lord: Pretty near south of us, 4 miles to the south
Lord who was the most experimented of all stated;
7120. Suppose the Titanic was 7 or 8 miles from you between 11.30 and 12 o'clock, would those on her bridge have been able to see your lights? - Easily.
Remembering that the yellow-funnel steamer Lord sighted on the southwest the next morning, beyond where this man had left, was even estimated at a mere 8 miles away!
In 1912, there was no way to establish with precision the distance of an observed vessel by her navigation lights alone. It seems that they were all using a sort of epoch rule of thumb inspired by «to show for 5 miles or to show for 2 miles» instead of had to be visible at a distance of at least 5 miles or at a distance of at least 2 miles. If only they would have had the chance to compare their rule of thumb estimations against accurate distances measured from Radar or AIS, they would confirm what I am trying to point out.
That range estimation of navigation lights is also very true today. The United States coast pilot states:
(159) The maximum distances at which lights can be seen may at times be increased by abnormal atmospheric refraction. In some conditions of the atmosphere white lights may have a reddish hue. Navigational lights should be used with caution because of the following conditions that may exist.
(164) The distance of an observer from a light cannot be estimated by its apparent intensity.
(170) Lights of equal candlepower but of different colors may be seen at different distances. This fact should be considered not only in predicting the distance at which a light can be seen, but also in identifying it.
The CCG List of Lights, Buoys and Fog Signals:
(12) Atmospheric conditions can have a considerable effect on light transmission and the visibility of lights. The distance to a light cannot be reliably estimated from its apparent brightness.
The American Practical Navigator, Bowditch:
The distance of an observer from a light cannot be estimated by its apparent intensity.
The List of Lights, Buoys and Fog Signals Luminous Range Diagram;
Intensity in candelas against range in nautical miles.
What Samuel came up with is that the incandescent light bulbs used in the electric lanterns were made of 2 filaments shining off 16 candelas each. The Fresnel glass had a magnification factor of 8.4 but an absorption lost of 10%. The sidelights had an additional filter loss of 2/5 (sidelight range ÷ masthead light range) due to the glass dye. 16 x 2 = 32 candelas or 402 lumens or the equivalence of an incandescent light bulb of 40 watts.
Masthead light intensity:
16 candelas x 2 = 32 candelas
32 candelas x [8.4 – 10% = 7.6] = 243 candelas
Visibility range = 19 miles
Sidelight intensity:
16 candelas x 2 = 32 candelas
32 candelas x [8.4 – 10% = 7.6] = 243 candelas
243 candelas x 2/5 = 97 candelas
Visibility range = 12 miles
In 1912, engineers knew well that the precision of calibration instruments would upgrade with time, thence every calculation integrated a margin of safety. To give an idea of such a margin, if you just add 2 candelas per filament or 5 watts per lantern, the masthead light range of visibility goes from 19 to 20 miles and the sidelights from 12 to 13. Notwithstanding the fact that United States Coast Pilot publication states that the maximum distance at which lights can be seen may at times be increased by abnormal atmospheric refraction; «Navigators, crew and passengers experimented a visibility rarely or never seen before. A most peculiar night. Very much refraction entered in weather log books. Witnesses stated that rockets bursting stars had color in it due to thermal inversion; a condition required for abnormal atmospheric refraction.»
To use the Luminous Range Diagram, we need to know the light intensity in candelas which was certainly not an information readily or easily accessible. Thanks Samuel for those data. The Nominal Range table given in the same publication is the maximum distance of a listed or a charted light, namely lighthouses, which can be seen when the meteorological visibility is 10 nautical miles. It does not really apply to ships navigation lights.
Geographical Range of Light Diagram:
The List of Lights, Buoys and Fog Signals or similar publications like Pilot Books, also present a Nomogram to determine the geographical range of a light. Why such coast guard publications would publish mathematical tools to determine the geographical range of a light? Just because when the visibility is unlimited, it is the most convenient tool to use. Titanic was a brand new vessel, up to highest standards and made to last. Her masthead light and sidelights lanterns were electric and her new Fresnel lens made the beam of light to focus. The weather of that moonless and pitch dark night was dead calm, dry and cold. Navigators, crew and passengers experimented a visibility rarely or never seen before.
As a result;
The minimum visibility range of Titanic navigation lights from the official Luminous Range Diagram was:
- Masthead light = 19 miles
- Sidelights = 12 miles
The maximum visibility range of Titanic navigation lights from the official Nomogram Geographical Range of a light was up to:
- Masthead light = 21 miles
- Sidelights = 17 miles
Geographical Range by calculations:
- Masthead light = 1.169 x [√(39+5) + √140] = 21½ miles
- Sidelights = 1.169 x [√(39+5) + √64] = 17 miles
Any mystery vessel with a depiction such as witnessed by Californian’s 3rd mate Charles V. Groves, located in between Lord subjective position and the Wreck location, would either sight the signaling lamp or hear the socket distress signals loud report or subsequently be swiftly identify;
«At about 11.30, I reported that vessel to Lord. I said that by her deck lights she was evidently a passenger steamer. Yes, a lot of light. There was absolutely no doubt her being a passenger steamer. Most decidedly I do believe that the passenger steamer was Titanic. The number of deck lights she was showing indicated me she was a large passenger steamer.»
Titanic masthead light was first seen from 19 to 21 nautical miles and her sidelights from 12 to 17 miles. Just far enough for the signaling lamp visible up to 10 miles to not be seen and just far enough for the socket distress signals loud report up to 13 miles to not be heard. The perfect distance apart at the very worst moment.
Attachments
Last edited:
