Determining distance a bowlight can be seen in nautical miles?

[bostonwhalermontauk1965]

Hi guys
I know this question seems as if I stayed up late at night to dream up a silly question to throw at you - but here is my issue....
I just spent a lot of time restoring my late fathers 1965 Boston Whaler.I have to replace the bow light. I am trying to retain the original look as best I can. However , the bow light - which I have found an exact replacement - is very small. I really want to stick with the factory look but I found a similar one as a replacement known to be seen for 2 nautical miles. The direct Boston whaler replacement manufacturer cant tell me how far that one can be seen - but tells me it is up to OEM specs - which lets face it - back in 1965 wasnt too high. What are everyones thoughts on going with the aftermarket similar one for the known two miles - or what are the factors which make a light seen from further away? - Is it a larger lens, or more bulbs in fixture or what? - Also and thank you again in advance - For the same boat - what hight does my stern light have to be for it to be up to USCG standards? I have to put a new one on and want that to be correct and safe as well - I plan on installing one that can be seen for 3 nautical miles (Stern Light) Lets hope if it is just a matter of more bulbs to increase visibility - then two naut. miles on bowlight and three NM on sternlight with the motor off too long dosent run battery down too quick. - Thank you all again - Paul

 

[Silvertip]

Re: Determining distance a bowlight can be seen in nautical miles?

There are lots of things that determine how far a light can be seen. Here are just a few.

1) Quality of the light -- meaning the design of the reflector, the quality of the lens, etc.
2) Height of the light.
3) Bulb light output (intensity)
4) Weather conditions -- which relates to items 1, 2, and 3.

 

[Boatist]

Re: Determining distance a bowlight can be seen in nautical miles?

I agree with Silvertip.
Brightness is more important than size.
Lens design that directs light to the horizon and not up into the air very important.
The earth is curved so height is a factor. You will not see it if it is over the horizon.
Weather fog or rain and again the brighter the better.
The all around stern light must be high enough to be seen 360 degrees so not blocked by the cabin or any other structure.

 

[jhebert]

Re: Determining distance a bowlight can be seen in nautical miles?

Replies which mention the height of the lamp as a factor are not particularly interesting in this case. The required visibility for the sidelight of a vessel of less than 12-meter length is only one mile. Even on a small boat like a Boston Whaler the lamp will be at least two feet above the water. The distance to the optical horizon on earth is

d = (1.5h)^0.5

where
d is in distance to horizon in miles, and
h is in elevation in feet

A lamp 2-feet above the water has an optical horizon of 1.7-miles. Unless you plan to use the Boston Whaler on a lake on another planet, you will not have to consider the height of the lamp as an influence in complying with the Navigation Rules.

Also, the term "bowlight" appears nowhere in regard to navigation lamps. There are no requirements to show a "bowlight" and thus no visibility requirements for one. You are welcome to install any kind of light in the bow of your boat you wish, so long as it does not interfere with the visibility of the required lights.

 

[sasto]

Re: Determining distance a bowlight can be seen in nautical miles?

What wattage bulb are you using? 3 watts can be seen over 2 miles....by itself....not counting the colored cover plate or reflector.

 

[jhebert]

Re: Determining distance a bowlight can be seen in nautical miles?

Here is some more research on the visibility of navigation lamps of various colors. This was first published in 1892, about 118-years ago, but I do not think the Physics of the natural world have changed much since then:

http://query.nytimes.com/mem/archive-free/pdf?res=FB0A10FF3D5C17738DDDAF0994D9415B8285F0D3

A red light of 3.2-candlepower was found to be fairly visible at one mile.

The technical requirements of the Navigation Rules for lights is given in Annex I to the rules, which can be found at:

http://www.navcen.uscg.gov/index.php?pageName=navRulesContent

See the section on intensity of lights, at:

http://www.navcen.uscg.gov/index.php?pageName=navRule&annex=annex_1Intl#8

The rules use the term "candela" which is the modern replacement for candlepower. The rules specify for a lamp required to be visible at one mile the emitted light should be at an intensity of 0.9-candela.

If you plan to change the miniature electric lightbulb in a lamp there is not much concern about the increased consumption of electrical power. Most of these lamps only consume a small current. However, for incandescent lamps, more current through the lamp will produce proportionally more heat. The thermoplastic lens of the lamp may suffer if too much heat is created by the lightbulb.

Also, the Navigation Rules mention:

"The maximum luminous intensity of navigation lights should be limited to avoid undue glare."

You may not want to amp-up (as the kids like to say) the lamps too far.

 

[ChampionShip]

Re: Determining distance a bowlight can be seen in nautical miles?

Turn them on at the dock, swim out 2 miles and look back at the boat.....can you see the light? Kidding- but standard red/greens can be seen farther than people generally think. Have you considered a set of LED replacements? They draw less power and are generally brighter than incandescents.

-Champ

 

[bostonwhalermontauk1965]

Re: Determining distance a bowlight can be seen in nautical miles?

Thank You all for your input - Its amazing how much info a website like this can drum up - and I am having a lot of fun restoring this old boat and having it come out as really nice as it is - largely in part to info I receive from knowledgeable people like the cool guys that responded here. I do not know the wattage of bulbs of either replacement because neither seems to specify in either description - although the factory replacement bowlight I believe to have (1) 1157 type automotive bulb in it or similar eqiuvalent. I am thinking about installing both front and rear light as LED and am going to look into just that because they do last longer, draw less and are usually brighter as well. Thank you again - Paul

 

[twistedshadows]

Re: Determining distance a bowlight can be seen in nautical miles?

we have a led nav light on are boat. we got stuck one night and had to call seatow not having a gps with us we could only describe are location basicly and try to talk seatow in are direction. well they where having trouble finding us so we started flashing the nav light so they would have something to look for, the lady saw the flashing nav light about a mile and a half away i say thats a preaty good distance.
joe

 

[bostonwhalermontauk1965]

Re: Determining distance a bowlight can be seen in nautical miles?

Replies which mention the height of the lamp as a factor are not particularly interesting in this case. The required visibility for the sidelight of a vessel of less than 12-meter length is only one mile. Even on a small boat like a Boston Whaler the lamp will be at least two feet above the water. The distance to the optical horizon on earth is

d = (1.5h)^0.5

where
d is in distance to horizon in miles, and
h is in elevation in feet

A lamp 2-feet above the water has an optical horizon of 1.7-miles. Unless you plan to use the Boston Whaler on a lake on another planet, you will not have to consider the height of the lamp as an influence in complying with the Navigation Rules.

Also, the term "bowlight" appears nowhere in regard to navigation lamps. There are no requirements to show a "bowlight" and thus no visibility requirements for one. You are welcome to install any kind of light in the bow of your boat you wish, so long as it does not interfere with the visibility of the required lights.

Unless you plan to use the Boston Whaler on a lake on another planet, you will not have to consider the height of the lamp as an influence in complying with the Navigation Rules.

I did plan to use the Whaler on a lake on another planet - but I need to ask NASA if I can borrow a tow vehicle to get it there -