navigation

alahol2 said:
....... does anyone plot in 'true' on a coastal chart?
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Yes. Its just simple arithmetic, it doesn't warrant aligning your plotter with any "special" mark for convenience. I believe that the use of "auto correcting" for variation on Portland Plotters and such like contributes to students not understanding the relationship between magnetic and true position lines. However, it is convenient to use this feature and I have used it confirm my arithmetic when very tired and my position lines don't appear as expected.

Normally I do the calculation as a column of numbers in my navigation log book and sum up a la primary school. I have monumentally messed up my navigation when doing mental arithmetic and now commit the arithmetic to paper for my own assurance.
 
JayBee said:
Unlike the "bow" type, they don't require the user to shift grip, alternately squeezing bow and legs when making small adjustments to the span.
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Operate single handed dividers by squeezing the bow with index finger and thumb and the legs with little finger and heel of hand. No need to change grip.

Quite Easily Done.
 
snowleopard said:
Operate single handed dividers...
Quite Easily Done.
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Entirely agree.
But I wonder how many people have ever been shown how to do it?
Just as I wonder how many people have ever been shown how to use the Captain Fields markings on parallel rulers? Judging by the number of people who seem to think you have to "walk" parallels all over the chart, I suspect the answer is "not many".
 
Just as I wonder how many people have ever been shown how to use the Captain Fields markings on parallel rulers
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Well i haven't for a start.

Now you have raised the issue you had better explain or post a link to the instructions.


As for the main discussion I'm certainly in favour of one of the square protractors whether you call it a Portland or a Breton plotter rather than the parallel ruler. Reserve that for the evening classes.

Didn't John Goode come up with some "improvements" to the basic design of the Portland protractor some years ago ... a good(e) few years ago!
 
Squeezing techniques

snowleopard said:
Operate single handed dividers by squeezing the bow with index finger and thumb and the legs with little finger and heel of hand.
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Having done that, and discovered some under-exercised muscles in your hand, you find that they won't open anything like as far as a pair of "straights" of similar size. Hey Ho - forget the squeezing technique and open them right out.

I rest my (dividers) case.
 
Parallel Rulers

timbartlett said:
.....I wonder how many people have ever been shown how to use the Captain Fields markings on parallel rulers? Judging by the number of people who seem to think you have to "walk" parallels all over the chart, I suspect the answer is "not many".
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Captain Field's parallel rulers were an innovation/improvement on earlier, mostly boxwood models, which were not engraved with a protractor scale and HAD to be "walked" between a printed compass rose on the chart and the points of interest.

What is the point of parallel rulers if they are just going to be used as a straightedge/protractor combo? Better to go for the "no moving parts option" and get a genuine (French) Breton Plotter, or a big Douglas Protractor, or a pair of navigational triangles, or some other gizmo that doesn't need a particularly level or stable work surface.
 
Back when I used to poke a pencil around a paper chart, I found a rolling ruler the best tool for transfering a bearing. But I must admit I'm astonished to hear that so many are still sitting below at a chart table with detailed nav calcs.

Does everyone have a full crew to sail for them then? Don't you like going on deck & looking to see where you are? Or do you lack knowledge of your home waters? Is your chartplotter unreliable? Do you sail in fog/ darkness without radar? Or is it that you don't often bother on the boat but like to show off on the forum?

Oooh, I think I feel another thread coming on . . .
 
Searush said:
I'm astonished to hear that so many are still sitting below at a chart table with detailed nav calcs.
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You've got me bang to rights guv. Haven't used a paper chart of the Solent in the last 4 or 5 years ever since I got my hand held plotter. Outside the Solent, the relevant chart is on the table and updated with positions even if I don't use it to navigate with. Got the implements and I think I could still use them in extremis.
 
There is a world of difference between navigating a chart table and navigating a boat

Searush said:
But I must admit I'm astonished to hear that so many are still sitting below at a chart table with detailed nav calcs. Don't you like going on deck & looking to see where you are?
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Why does this seem to assume that an interest and/or ability in basic navigation involves "sitting below at a chart table with detailed nav calcs"?
The only reason working out a course to steer should take more than a few seconds is if you don't know how to do it.
And the only reason working out a height of tide should take more than about three minutes is if you need to look up the instructions or if you try to work to a ludicrously high level of accuracy.
 
Tim,
I think that's the crux of my point. The level of accuracy required in a classroom is designed to make sure students understand the principles. It doesn't make sense to me to do that at sea - especially when solo.

Tidal calcs are down to the rule of 12ths - and should be possible in your head. I tend to do them as I walk to the bow & lay out the anchor chain prior to anchoring - or before choosing whether to cross or circumnav the sandbanks. The range of the current tide needs to be in my head at the start of any passage, but I experience 11m tides in N Wales.

I haven't done a classroom style calculation since I tried showing my son how it all works some years ago. Unfortunately, he wasn't interested enough to pay attention!
 
Come in kitcrazy (OP)

Over 1000 views and 49 replies so far! kitcrazy must be thrilled!

kitcrazy..........

kitcrazy...........?
 
in praise of parallels

JayBee said:
What is the point of parallel rulers if they are just going to be used as a straightedge/protractor combo? Better to go for the "no moving parts option" and get a genuine (French) Breton Plotter
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Agree with you that the French Breton is better than the English copies, but the advantage of parallels over Breton (for me -- I'm not criticising Bretons or those who love them) is that (a) you can get parallels oriented correctly and then adjust their position, rather than having to get orientation and position right in one go
(b) you can draw longer lines
(c) You don't have to fiddle about with the moving part in the middle.;)
VicS said:
Well i haven't for a start.
Now you have raised the issue you had better explain or post a link to the instructions.
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Well you did ask!...
The basic principle is that when the rulers are closed, they form one half of a rectangular protractor. The scale of degrees is along one long edge and the two short edges. The centre of the protractor (corresponding to the hole in the middle of a breton plotter or a Douglas protractor) is the tip of the "S" mark on the other long edge.
To draw a line in a given direction:
Place the closed parallels on the chart in roughly the right place, with the tip of the "S" mark just touching any convenient meridian.
Keeping the rulers closed and the tip of the S mark on the meridian, rotate the rulers until the required direction on the degree scale is lined up on the same meridian.
Hold one of the rulers in place by pressing it against the chart, and move the other one as required to get the line in the right place.
To measure the direction of a line
Place the parallel on the chart, lined up with the line
Holding the ruler with the scale of degrees in position, move the ruler with the "S" mark as required until the tip of the S mark is touching any convenient meridian.
Holding the S-mark ruler in place, close the other ruler up to it, and read off the direction of the line by seeing where the meridian cuts the scale of degrees.
 
Small confusion here

timbartlett said:
Agree with you that the French Breton is better than the English copies, but the advantage of parallels over Breton (for me -- I'm not criticising Bretons or those who love them) is that (a) you can get parallels oriented correctly and then adjust their position, rather than having to get orientation and position right in one go
(b) you can draw longer lines
(c) You don't have to fiddle about with the moving part in the middle.;)
Click to expand...

a) no problem with a bit of practice
b) genuine Breton Plotters come in several lengths and can be up to a metre long
c) genuine Breton Plotters don't have a moving part in the middle

see here:http://sufmarins.ifrance.com/reglecras.html
 
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Oops

timbartlett said:
That's a Cras plotter. And that's why the webpage you referenced is called "reglecras"
The Breton Plotter is here: http://www.rapporteurbreton.com/produits_MK1.htm
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On a point of nomenclature, you are right.

However, Admiral Jean Cras was a famous Breton and his plotter was the original - still to be found on every French ship and available in every French chandlery I've been into. The one with the rotating protractor part is just the yachtie version.
 
Absolutely agree: the Cras plotter would have had first claim on the name "Breton Plotter" if Admiral Cras had wanted to claim the name. But he never did, which is why the name was still available to be claimed by Captain Gueret for his plotter with a rotating protractor in the middle.

It only matters if you're in the kind of job where you can get sued for not knowing the difference between a Cras, a Breton, and a Portland.

Now, how many angels did you say could dance on the head of a pin? :)
 
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Searush said:
The level of accuracy required in a classroom is designed to make sure students understand the principles.
It doesn't make sense to me to do that at sea - especially when solo.
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Couldn't agree more, this summer (that seems a long time ago now) I visited ports previously unvisited such as Roscoff and for the first time, went in by putting WP's onto the chart plotter on the fly and running down a goto line.
Far more liberating and less stressful than having to pop up and down from the chart table like the now in vogue Meerkat :D
 
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