How to judge a nav light at two miles

[LONG_KEELER]

The regs say that all lights except the side lights must be seen at a distance of two miles for an under 12 metres boat.

How can I test mine ?

Sensible or silly answers acceptable.

Also, why the side lights ok at 1 nm when the rest are 2nm ?
Right answers only please.

 

[TLouth7]

Get someone in a dinghy to row 1 mile away and hold up a big mirror. You will want to check all the angles so have them row round you in a big circle.

 

[lw395]

I think that's translated to a measurable luminous intensity.
What's actually visible at 2 miles will depend on how dark the background is, the eyesight of the observer etc.
I'd imagine the sidelights are only required to be less powerful because a) coloured lenses will absorb a lot of the power, so a 10W bulb only gives 1M for a coloured lens or something?
And beyond 1M, the issue is mostly to know there's a small boat there, as chances are it will change heading before its covered a mile.

 

[LadyInBed]

Bow combo light is a 'Side Light' so it could well be too low to see it at more than a mile.
It's interesting that the Stern light, which is probably at the same height as the Bow light, needs a 2 mile viz light power.

How can I test mine ?

Radio a boat that you can see on AIS at just over 2M and ask him if he can see your lights?

 

[LittleSister]

I think that's translated to a measurable luminous intensity.

Annex 1 of the ColRegs translates the distance specifications into a luminous intensity specification, using a defined formula that assumes a certain meteorological visibility. (This means the user doesn't have to worry about how misty it is on the day, how dark the background is, etc. In fact it is prohibited to have variable intensity nav lights.)

The upshot is a 1 mile visibility is defined as 0.9 candelas, and 2 miles as 4.3 candelas.

Non-electric lights are required to comply 'as far as practicable'.

 

[[70521]]

In fits of the giggles here. Judging nave lights is this for technical ability or artistic impression?

I'll get my coat.

 

[Skylark]

Radio a boat that you can see on AIS at just over 2M and ask him if he can see your lights?

I was thinking along similar lines. Ask a (friendly) boat with radar to measure distance and note visibility of the lights.

 

[Uricanejack]

for the most part.
If you by a light from a reputable source. It will probably exceed the minimum requirements provided the condition of the wiring and the power supply are in good condition.
If the battery is low or the wiring and connections a bit corroded it won’t get the current and voltage it requires.

The light will probable have the requirement stamped on it. If in doubt check with a multi meter.

 

[Neeves]

Very sensible question

I'm not sure why you need to involve anyone else.

Anchor up. Find somewhere 2nm away (obviously on land) - your chart plotter will suffice). Switch on light(s). Fire up the O/B when its dark (using required lights all round white) and go an have a look). You can do the side lights at the same time.

You observation will be more valuable to you - than anyone else - as you will know what your own yacht looks like to others. Been there, done that.

Jonathan