Where the 112.5 degrees comes from...

[PuffTheMagicDragon]

And there was me thinking that the helmsman used to stand naked with his legs apart. The ship would head North or south. When the swell changed,, indicating a different latitude , he noticed the swing change in the nether regions . At that point he would turn east or west.

Are you sure that you're not confusing that with the original sundial?

 

[Buck Turgidson]

A fingerwidth is about 2% of an arm's length.
So a 10m boat being 3 fingers, 10m is 6% of the range so it's about 160m away.
I don't think degrees bring much to this particular party.

It's funny, we all use 1 in 4 or 25% for a steep hill, few people will talk about a 10degree hill (unless they mean a cold one...).

We are rather keen on gradients of climb and descent in my business. The rule book is full of them

 

[Sandro]

I think that the division in 360 degrees comes from ancient astronomers. One degree is the angular way made in one day by the sun on the background of the fixed stars (though not exactly).

Sandro

 

[skyflyer]

someone said it was internationally agreed for ships and aircraft - nope, aircraft are 110 deg

and there's the rub - its all theoretical claptrap because in real life the cut-offs arent that precise and its the relationship of the lights you see that matter not the precise angle.

 

[Refueler]

and there's the rub - its all theoretical claptrap because in real life the cut-offs arent that precise and its the relationship of the lights you see that matter not the precise angle.

Agreed but its why ships have their side lights set into boxes with not only the light casing itself set to the angle - but a board at front of the box that makes double sure light does not 'bleed' into change-over ... there's also a rear board to ensure rear cut-off.
Yachts of course don't have this and rely on the light case itself.

I love who ever designed pulpits with light plates ... I have a pulpit with plates to fit side lights to ... one each side. Problem is the designer forgot to have the plates aligned with the fore-aft line of the boat and so the lights need wedge inserts to correct them. Otherwise they angle inwards based on the pulpit line. 3D printer provided them as nothing could be found on shop shelf.

 

[Ohlin Karcher]

"..Agreed but its why ships have their side lights set into boxes with not only the light casing itself set to the angle - but a board at front of the box that makes double sure light does not 'bleed' into change-over ... there's also a rear board to ensure rear cut-off.
Yachts of course don't have this and rely on the light case itself..."

Mine does..although the new LED lights are tiny compared to the old paraffin ones, and I rely on the light fitting itself for the aft cut-off.
The spaces previously taken by paraffin lamps are now full of 'shrooms..

 

[Refueler]

Nice one ... but your light box has the forward bit missing ... on a ships light 'box' there is at front of box a vertical piece at 90 degrees to the rear wall that provides the cut off ...

 

[emandvee44]

Talking about fingers and angles.
Arab sailors navigating across the Indian Ocean had no octants or sextants. They had a 'Kamal', which consisted of a rectangular wooden plate, roughly the size of a cigarette packet. A length of string was fastened to it and had knots tied on it towards the end. A knot was held between their teeth and the Kamal was held vertically such that the string was stretched. Holding the bottom edge of the Kamal on the horizon, the height of Polaris was estimated in finger widths. The 'pilot book' would say, for example, to go to Calcutta "Go South until Polaris at two fingers and then turn East for five days when you will meet a change of current direction..."

Probably would end up on the rocks because that is not Polaris!

 

[Momac]

I wonder how many navigation lights are fitted with such precision as to be accurate relative to the axis of the boat within a fraction of a degree ?
The split of the 360 degrees of a circle into 32 makes sense if you think of the imperial measurements of length where 1/32nd of an inch isn't such an unnatural division.

 

[Refueler]

I wonder how many navigation lights are fitted with such precision as to be accurate relative to the axis of the boat within a fraction of a degree ?

Quite !

Reminds me of an old RAF joke ...

Instructor and student up in a training biplane ...

Instructor tells student :

Ins " 1 degree port lad...."

Student " We can't steer that accurate in this heap ... "

Ins " OK then 5 degrees port, 4 degrees stbd ... smartar** "

 

[Alan S]

emandvee44
the Dragon is correct, that IS Polaris.

 

[macd]

The split of the 360 degrees of a circle into 32 makes sense if you think of the imperial measurements of length where 1/32nd of an inch isn't such an unnatural division.

It may make sense, but I doubt that one is much to do with the other. It ultimately derives, surely, from their being four cardinal points, to which there's evidently reference in the Old Testament. (Although five cardinal points were favoured in ancient China...) The 32 point concept seems to have arisen in the Mediterranean in the Middle Ages. Such multiples didn't figure in Classical Greek/Roman measurements and the Middle Eastern ones from which they derived (they liked 28, amongst others ?). Ancient Greece and Rome used a 12-point wind rose.

 

[Ohlin Karcher]

emandvee44
the Dragon is correct, that IS Polaris.

Yes I thought the other side of the saucepan points up to Polaris?

 

[penberth3]

It may make sense, but I doubt that one is much to do with the other. It ultimately derives, surely, from their being four cardinal points,...

Agreed, its nothing more than binary division, like cutting up a Christmas cake.

 

[macd]

Yes I thought the other side of the saucepan points up to Polaris?

Except, of course, when it points down to it...

 

[Kukri]

Feeble little star. I always ask myself ‘is that it?’

 

[macd]

Feeble little star. I always ask myself ‘is that it?’

Then imagine what it might think of you. Or any of us.

 

[Kukri]

Then imagine what it might think of you. Or any of us.

So long as I can be certain that I have got the blighter and not one of its apparent neighbours, down to the horizon, I am happy enough. I don’t usually sail in latitudes where Polaris any use to steer her by.

 

[emandvee44]

Sorry - you draw an imaginary line from Merak through Dubhe
and it leads to Polaris.
The one shown in Magic dragon's pic. is Alkaid - but you all knew that from my diagram.
M.

 

[Alan S]

No. Alkaid is in Ursa Major. You are getting your Ursas in a twist! Puff the magic dragon's original illustration showed Polaris in Ursa Minor, different shaped "handle"
Here hoping you don'tend up on the rocks : )