Nav' Lights Angles

[Cariadco]

Is there any reason why Nav lights have a masthead viewing arc of the red/green of 112.5, and the white of 135?
Why not nice round numbers of say for example110/110 and 140 or 120/120 and 120?
I have looked but no answers out there in Googleland.

 

[Sandy]

Look at points of the compass.

 

[john_morris_uk]

Is there any reason why Nav lights have a masthead viewing arc of the red/green of 112.5, and the white of 135?
Why not nice round numbers of say for example110/110 and 140 or 120/120 and 120?
I have looked but no answers out there in Googleland.

Because it’s very easy to divide off 22.5 degrees and 135 degrees.
Divide the circle into 90 degree quadrants. Divide a quadrant into two 45 degree sectors
Divide again = 22.5 degrees.

You don’t need a protractor or any angle measurement ability or instrument.

This and what Sandy said above.

 

[wonkywinch]

 

[Refueler]

Look at points of the compass.

And that for centuries mariners have spoken about points of the bow .. etc.

 

[Refueler]

But what I think is more important - is that so many boats with separate nav lights at side - when mounted on pulpits are wrong .... even those mounted on coachroof are often wrong as well.

 

[Cariadco]

I now, see the Light...!! So to speak.
Thank you all.
I'm gonna have some fun with this, and ask a few 'Ancient Mariners' I know. (now that I know the answer...)

 

[Blue Seas]

Two points abaft the beam on Port side round to Two points abaft the beam on the Stbd side - leaves 135 Deg - also defines your COLREG zones
eg. Overtaking arc etc.

 

[thinwater]

But what I think is more important - is that so many boats with separate nav lights at side - when mounted on pulpits are wrong .... even those mounted on coachroof are often wrong as well.

Seems like a good time to be specific. Which mountings do you find incorrect? For example:

• Power boat lights do not necessarily have the required vertical range to allow for heeling. The lights must be rated for sailboats.
• The lights must be mounted at the correct horizontal angles. Often they are angled up or down because of the angle of the hull or cabin side.
• The fore/aft angle is important as well, and this is often botched on cabin and hull mounted lights.

The first two errors can make them close to invisible. That last will alter the horizontal angles, possibly a lot.

 

[VicS]

But what I think is more important - is that so many boats with separate nav lights at side - when mounted on pulpits are wrong .... even those mounted on coachroof are often wrong as well.

Not often as wrong as one pulpit mounted bicolour I saw on a boat in a marina many years ago. It was mounted upside down ( IIRC) so that it showed red to stbd and green to port.
.

 

[Refueler]

Seems like a good time to be specific. Which mountings do you find incorrect? For example:

• Power boat lights do not necessarily have the required vertical range to allow for heeling. The lights must be rated for sailboats.
• The lights must be mounted at the correct horizontal angles. Often they are angled up or down because of the angle of the hull or cabin side.
• The fore/aft angle is important as well, and this is often botched on cabin and hull mounted lights.

The first two errors can make them close to invisible. That last will alter the horizontal angles, possibly a lot.

Take a walk around any marina and look at lights mounted on pulpits. The Dual lights such as I have on my 38 are OK as the light is mounted centrally. But individual lights are fitted to sides of pulpit - and the lights angles actually cross each other ..... Technically from dead ahead - both lights should be seen ... move slightly to one side and only that side should be seen ... but because of the pulpit design - the other light is still visible until a number of degrees offset.

Here I have tried to correct the horizontal division of light - but still the wedge is not enough to counter the pulpits angle. Also the lights are not perpendicular - needing further development of the wedge to correct.

On cabin sides - often the lights are placed where cabin sides are starting to angle toward centreline with no wedge correction. Plus a small amount of non vertical.

Its a common fault - nothing that prevents you being seen etc. - but in the case of the side lights sectors overlapping - this causes head on error ...

 

[Refueler]

Not often as wrong as one pulpit mounted bicolour I saw on a boat in a marina many years ago. It was mounted upside down ( IIRC) so that it showed red to stbd and green to port.
.

That is plain stupidity on part of the owner / installer. My point is fault of design. Pulpits angling in toward stem causing light sectors to overlap instead of being adjacent, as well as not being vertical.

 

[rogerthebodger]

My bicolor bow nave light has the same issue and I have considered fitting a shade to separate the two lights to shade each colour

The angle of separation of side lights beams is just bad design to as it only the brackets to be orientated correctly both vertically and horizontally with directions boards a seen on old sailing ships rigging mounted

 

[finestgreen]

Take a walk around any marina and look at lights mounted on pulpits. The Dual lights such as I have on my 38 are OK as the light is mounted centrally. But individual lights are fitted to sides of pulpit - and the lights angles actually cross each other ..... Technically from dead ahead - both lights should be seen ... move slightly to one side and only that side should be seen ... but because of the pulpit design - the other light is still visible until a number of degrees offset.

Here I have tried to correct the horizontal division of light - but still the wedge is not enough to counter the pulpits angle. Also the lights are not perpendicular - needing further development of the wedge to correct.

View attachment 181670

On cabin sides - often the lights are placed where cabin sides are starting to angle toward centreline with no wedge correction. Plus a small amount of non vertical.

Its a common fault - nothing that prevents you being seen etc. - but in the case of the side lights sectors overlapping - this causes head on error ...

The lights should overlap slightly - each should cut off between 1 and 3 degrees outside the specified sector

 

[Refueler]

The lights should overlap slightly - each should cut off between 1 and 3 degrees outside the specified sector

Slight mis-interpretation there ....

It is the INTENSITY of the light - not the physical angles.

IMO Statement :>

"In the forward direction, sidelights as fitted on the vessel shall show the minimum required intensities. The intensities shall decrease to reach practical cut-off between 1 degree and 3 degrees outside the prescribed sectors"

This is NOT physical overlap ... its a factor because the lights can be seen slightly outside their physical design ... and is why ships have matt black screen panel ahead of the side lights ...

IMO again :>

"The sidelights of vessels of 20 metres or more in length shall be fitted with inboard screens painted matt black, and meeting the requirements of section 9 of this Annex. On vessels of less than 20 metres in length the sidelights, if necessary to meet the requirements of section 9 of this Annex, shall be fitted with inboard matt black screens. With a combined lantern, using a single vertical filament and a very narrow division between the green and red sections, external screens need not be fitted."

Anyway - the angles I am highlighting in my post about errors are far more than 3 degrees and a walk round any marina will soon show up boats that have this problem.

 

[thinwater]

Please explain the distinction in the last sentence.

On a vessel of less than 20 meters in length the sidelights may be combined in one lantern carried on
the fore and aft centerline of the vessel, except that on a vessel of less than
12 meters in length the sidelights when combined in one lantern shall be
placed as nearly as practicable to the fore and aft centerline of the vessel.

To me, it reads that if you are less than 12 meters in length you can mount the combined light slightly off center. I can't think why you would do that, but there it is.

—INLAND—
Lights and Shapes
RULE 21
Definitions
...
(b) “Sidelights” mean a green light on the starboard side and a red light on
the port side each showing an unbroken light over an arc of the horizon of
112.5 degrees and so fixed as to show the light from right ahead to 22.5
degrees abaft the beam on its respective side. On a vessel of less than 20
meters in length the sidelights may be combined in one lantern carried on
the fore and aft centerline of the vessel, except that on a vessel of less than
12 meters in length the sidelights when combined in one lantern shall be
placed as nearly as practicable to the fore and aft centerline of the vessel.

 

[finestgreen]

Please explain the distinction in the last sentence.

On a vessel of less than 20 meters in length the sidelights may be combined in one lantern carried on
the fore and aft centerline of the vessel, except that on a vessel of less than
12 meters in length the sidelights when combined in one lantern shall be
placed as nearly as practicable to the fore and aft centerline of the vessel.

To me, it reads that if you are less than 12 meters in length you can mount the combined light slightly off center. I can't think why you would do that, but there it is.

—INLAND—
Lights and Shapes
RULE 21
Definitions
...
(b) “Sidelights” mean a green light on the starboard side and a red light on
the port side each showing an unbroken light over an arc of the horizon of
112.5 degrees and so fixed as to show the light from right ahead to 22.5
degrees abaft the beam on its respective side. On a vessel of less than 20
meters in length the sidelights may be combined in one lantern carried on
the fore and aft centerline of the vessel, except that on a vessel of less than
12 meters in length the sidelights when combined in one lantern shall be
placed as nearly as practicable to the fore and aft centerline of the vessel.

I believe those words are from the US Inland Rules, not the colregs

 

[thinwater]

I believe those words are from the US Inland Rules, not the COLREGS.

True, but that doesn't make it less a fair question of weird wording!

[BTW, for UK readers, the US Inland Rules are very similar to COLREGS, with >95% exactly the same. There are also a few river rules that differ in order to deal with large barge pushes coming down really big ribbers with really high flow current. The Mississippi in the spring can be unbelievable, but traffic can't stop.]

In fact, on my trimaran, the combined side lights are mounted ~ 10 inches off center on the pulpit. The reason is that the folding bowsprit would strike it if it were mounted dead center, unless I built a guard, and it would block more light than with it mounted to the side. I suppose the bowsprit blocks a small bit of the arc (7 degrees, slightly more than the permitted 6 degrees, but I'm guessing at the distance). Of course, two separate lamps would solve the problem. Perhaps one lamp used fewer amps, back in the day when incandescent ruled.

This is a very rare case of why off center can make sense.

Someday I may change it, but I barely ever sail at night. Daysailer.

[Not easy to see, but the wrapped section of the pulpit is where the bowspirt lands when folded up. The black blob to port on the same rail is the combined lantern. It's about 10-12 inches away, I think The bowsprit is hinged, the bobstay being adjusted by a cascade tackle and the jammers to the right.

(The international rule is the same but does not include the <12 meter part. My trimaran is 8 meters.)