What's the reason for requiring stern and masthead lights ?

[Boo2]

Hi,

For boats under power the general requirement is for a white stern light having an arc of 135 degrees and a masthead light with an arc of 225 degrees. Given that only one of these can ever be visible at one time, what is the purpose of the requirement for two separate lights ? (I know there are exemptions for small vessels but that's not the point of my question.)

Thanks,

Boo2

 

[Severnman]

What do the Rules say regarding the positioning of a masthead light? Think also sidelights, then think aspect...

 

[KellysEye]

Take a look at http://www.navcen.uscg.gov/?pageName=navRulesContent scrolll down to Part C. The regulations cover all types of boat and ship and size.

 

[rob2]

I think others have already hinted at the reason. These are not a full set of lights and taken in conjunction with the sidelights and vertical positioning it is possible from all the variations to tell the nature of the vessel and its aspect.

Rob.

 

[GrumpyOldGit]

Strange question

May be something to do with not getting mowed down in the dark by a huge commercial vessel...........

 

[Boo2]

What do the Rules say regarding the positioning of a masthead light? Think also sidelights, then think aspect...

I think others have already hinted at the reason. These are not a full set of lights and taken in conjunction with the sidelights and vertical positioning it is possible from all the variations to tell the nature of the vessel and its aspect.

Sorry to seem dim, but I still don't understand, it is only ever possible to see a single one of the two white lights :

• When viewed from abaft that is the only light visible.
• When viewed from forwards the single white light is visible over the appropriate coloured sidelight.

So why not just specify a single white light with a 360 degree arc set 2m above the sidelights ? Surely that would have exactly the same effect when viewed from forwards, and no-one abaft can see how high the stern light is above the sidelights anyway ?

Again, sorry if the answer is obvious, but I can't see it...

Boo2

 

[sailorman]

Sorry to seem dim, but I still don't understand, it is only ever possible to see a single one of the two white lights :

• When viewed from abaft that is the only light visible.
• When viewed from forwards the single white light is visible over the appropriate coloured sidelight.

So why not just specify a single white light with a 360 degree arc set 2m above the sidelights ? Surely that would have exactly the same effect when viewed from forwards, and no-one abaft can see how high the stern light is above the sidelights anyway ?

Again, sorry if the answer is obvious, but I can't see it...

Boo2

a single all round white is the rools for under 7m o/all
above that length steaming + bi / side lights + stern light
with an anchor light in the fore triangle

 

[alahol2]

Presumably there are circumstances (certainly on a sailing yacht) when the stern light is required when the steaming light is not. So you may as well have two lights. The bigger you get the further from the stern your stern light gets if it's midships.

 

[duncan99210]

As you approach a boat from the bow, you will notice a change in the position of the white light - from say mid mast to lower down at the stern. This will tell you that aspect of the boat - heading towrads you, away etc, as shown by the relative change in the lights. Hence the reason for the 2 lights as opposed to one, allowed for small, slow vessels....

 

[Pye_End]

So why not just specify a single white light with a 360 degree arc set 2m above the sidelights ?

the only place that you can do that is at the masthead which is allowed for under 12m. Any lower and you will have at least one blind spot unless you split up the white into two.

 

[VicS]

So why not just specify a single white light with a 360 degree arc set 2m above the sidelights ? Surely that would have exactly the same effect when viewed from forwards, and no-one abaft can see how high the stern light is above the sidelights anyway ?

From the colregs:-
A power driven vessel of less than 12 m in length may exhibit an all round white light and side lights
Rule 23 d (i)

I dont know why the concession only applies to vessels under 12 m. Vessels over 50 m of course exhibit two mast head lights

See Annex 1 for the exact height and vertical separation requirements

COLREGS

 

[alan_d]

Lots of people quoting the regulations but not answering the OP's question, which is why?

I don't know for sure, but the regulations have developed incrementally over time, so perhaps the sternlight came first and the masthead light was an addition for power-driven vessels to the already prescribed sternlight for sailing vessels.

 

[VicS]

Lots of people quoting the regulations but not answering the OP's question, which is why?

I don't know for sure, but the regulations have developed incrementally over time, so perhaps the sternlight came first and the masthead light was an addition for power-driven vessels to the already prescribed sternlight for sailing vessels.

It is because the regs define the stern light as "placed as nearly as practicable at the stern".
They also require that "When only one masthead light is prescribed for a power-driven vessel, this light shall be exhibited forward of amidships".

Now you cannot have a single light that satisfies both conditions!

The condition for the masthead light to be forward of amidships is relaxed for vessels under 20m giving rise to a single all-round light being allowed for vessels under 12m.
Technically I guess a combined light should be close to the stern rather than forward of amidships where it may be in the case of a sailing vessel under power.

 

[Stu Jackson]

So why not just specify a single white light with a 360 degree arc set 2m above the sidelights ? Surely that would have exactly the same effect when viewed from forwards, and no-one abaft can see how high the stern light is above the sidelights anyway ?

Again, sorry if the answer is obvious, but I can't see it...

Boo2[/QUOTE]

Because it can tell you the direction the vessel is heading.

And they're really steaming lights, many times, I think, incorrectly termed masthead lights.

 

[theoldsalt]

The ColRegs do seem to differentiate between a sailing vessel under power and a power vessel (under 12m).

Power vessels can display an all round white light but sailing vessels under power must show separate stern and steaming lights. There may be a good reason but the ColRegs don't give reasons.

 

[lenseman]

. . . . So why not just specify a single white light with a 360 degree arc set 2m above the sidelights ? Surely that would have exactly the same effect when viewed from forwards, and no-one abaft can see how high the stern light is above the sidelights anyway ?

Again, sorry if the answer is obvious, but I can't see it...

Boo2

There is no way you can fit an all-round white light to a yacht that is two metres above the starboard and port navigation lights as the mast and sails would obscure the light to the rear and therefore would not be visible.

These rules were created a long time before yachts with masthead lighting.

 

[onesea]

Hi,

For boats under power the general requirement is for a white stern light having an arc of 135 degrees and a masthead light with an arc of 225 degrees. Given that only one of these can ever be visible at one time, what is the purpose of the requirement for two separate lights ? (I know there are exemptions for small vessels but that's not the point of my question.)

Thanks,

Boo2

Think of the practicalities of placing one light on a vessel that can be seen all the way round?

Once you start getting over 40 or 50 foot, the top of the mast? It would be very high up and easily missed by smaller boats...

Once over 50m the second mast headlight requirement would make it even more difficult. Then many ships of 50m + in length have exemptions form second mast head light.

I am sure if some one asked the MCA they would grant a exemption for smaller boats to carry one all round white where practical....

As long as other vessels can see you and your aspect and what your status is (sailing or motoring in these forums?).

The rule of the road was not written from scratch, over night its generations of experience put together.

Personally crossing the channel I would happily put mast head light all round (If motoring) and side lights. Yet once I got into the Solent would switch to a low stern lights and side lights.

Reasoning:
Mid channel: Little scatter light high can be seen for good distance clear of waves etc..
Solent: More small boats and back ground scatter in line of sight of small boats. From a ships bridge the lower lights will appear below any shore lights sooner.

Might not be in the rules but makes sense to me.

 

[Pye_End]

The ColRegs do seem to differentiate between a sailing vessel under power and a power vessel (under 12m).

Power vessels can display an all round white light but sailing vessels under power must show separate stern and steaming lights. There may be a good reason but the ColRegs don't give reasons.

That power driven vessel viewed from the bow is not correct. The white is an all round, so should be viewed from the bow.

For the sailing boat, you would not expect to see two white lights at the same time, as in the view from the beam. They do not have two be two different lights as already discussed on this thread, assuming the vessel is less than 12m.

 

[prv]

And they're really steaming lights, many times, I think, incorrectly termed masthead lights.

Uh, no. The Colregs call them masthead lights, but they're often (incorrectly, if you like) called "steaming lights". The exact opposite of what you just said.

Pete

 

[aquaplane]

Uh, no. The Colregs call them masthead lights, but they're often (incorrectly, if you like) called "steaming lights". The exact opposite of what you just said.

Pete

And when you are in a chandlers wanting a stern light and he is trying to tell you that a steaming light will be OK it confuses them even more if you keep calling it a masthead light for when you are motoring as opposed to an all round white which would go at the mast head but is a different thing.