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timbartlett
06-05-10, 17:59
Most parallel rulers nowadays have Captain Fields markings.
But how many people know what they are and how to use them?
And how many actually do?

shmoo
06-05-10, 19:23
Use one with little knurled wheels.

sarabande
06-05-10, 19:39
I've seen the compass bearings (points) and protractor bearings on both roller parallels and parallel arms. Is there some extra special way such rulers can be used, apart from dividing the bacon sandwiches very accurately ? ;)

BlowingOldBoots
06-05-10, 19:55
Yes and yes. A very convenient solution to walking errors. Makes it very easy to use.

Searush
06-05-10, 20:37
Don't use parallel rulers - too susceptible to errors. Sometimes use a rolling ruler tho.

Rowana
06-05-10, 21:43
Most parallel rulers nowadays have Captain Fields markings.
But how many people know what they are and how to use them?
And how many actually do?

The parallel rulers on Rowana were in the chart table drawer when I bought her. I've never used them, so in answer to your questions - "No" and "No"

Am I missing some great navigational secret:confused:

Are you going to enlighten me, and show me the true path to follow?


I haven't hit anything yet, so I must be doing something right:D

timbartlett
07-05-10, 02:09
Am I missing some great navigational secret:confused:
Are you going to enlighten me, and show me the true path to follow?
It's hardly a great navigational secret, nor is it a matter of being "enlightened" or following the true path: it's just a matter of personal preference.

timbartlett
07-05-10, 02:15
I've seen the compass bearings (points) and protractor bearings on both roller parallels and parallel arms. Is there some extra special way such rulers can be used, apart from dividing the bacon sandwiches very accurately ? ;)


If you close the rulers you will see that the degree markings (mostly on one ruler) all point straight towards the end of the "S" mark on the other ruler.

So to draw a line in -- lets say-- 045/225 direction:-
(1) close the rulers and place them on the chart in roughly the right place
(2) align them by slithering them around until the tip of the S mark is touching a meridian (any meridian) and the 045/225 mark is touching the same meridian.
(3) hold one ruler down, and adjust the position of the other ruler until it is exactly where you want it to be
(4) draw the line.

It's a similar principle to using a Cras plotter.

jonjo5
07-05-10, 03:14
Could someone explain the Captain Fields pinch gesture on my iPhone touch screen?

john_morris_uk
07-05-10, 07:09
There wasn't an option of "Yes I know what they are, but I don't use parallel rules on small boats."

BlowingOldBoots
07-05-10, 07:12
Don't use parallel rulers - too susceptible to errors. Sometimes use a rolling ruler tho.

No more than other plotters in my opinion. The CF feature makes them as stable as any non moving plotter. I may not be the best person to comment on modern changes as I carry a slide rule on the boat!

nonitoo
08-05-10, 08:34
I may not be the best person to comment on modern changes as I carry a slide rule on the boat!

My father gave me a beautiful Castell Slydrool for my 21st - still got it around somewhere.

(Always had a problem with the decimal point when working out the - usually large - moment values in a longitudinal stability calculation to establish fore/aft trim with various cargo configurations).

Thank goodness for the arrival of calculators, even if the first one I had used Polish notation. Still better than nothing however.

Back to the original O/P - yes I do use parallel rules and the Field pattern all the time aboard, makes it all very easy.

Tom

VO5
08-05-10, 08:57
Many yachtsmen complain about difficulties in using parallel rulers.

Using them properly is an acquired skill, like for example using single handed dividers using only one hand to open, close them and set them and walk them.

I digress.

Make sure your chart table is dead flat. If it isn't, you will always have problems in walking the parallel rulers.

To walk them properly you have to alternate the downward pressure you use on them.

When they are set down, press firmly on the side which will not move. Open them. Exert pressure on the opened one relax pressure on the first. Close them. Now exert pressure on the first, relax on the second. Open the second. Exert pressure on the second, and so on.

Don't forget the Mnemonic "Firm grip - no slip"...:D

Krusty
08-05-10, 23:42
Parallel rules are fine on a steady chart table big enough to have space surrounding the chart, but on a typical small yacht table they are a pain.
Far better is the Navigation Triangle and Straight Edge; the same principle of taking an angle to or from a meridian and transfering it to the relevant point; but easier to manipulate and easier to read. The transfer is by sliding the Triangle along the firmly pressed Straight Edge. (Great for identifying headlands by tangential bearings!)
Most people find the degree markings much easier to read than a compass rose or a Capt. Fields parallel rule.
The most common objection I used to come across, and shared, was that the Straight Edge could be displaced, by a slight twist, as the triangle was slid along it.
SO; I devised an effective way to overcome that tendency by making a Straight Edge slightly arched to transfer the pressure to its ends; and to help it grip the paper by scoring the underside.
It performed very well indeed and often became the method of choice among trainee navigators: so popular that I found myself making them in half-dozen batches!
The material was quarter-inch Perspex/Lexan type sheet; cut by jig-saw with a fine blade at slow speed; emery-papered true on a flat worktop, and screwed to a concave manogany handle to give it a few millimeters arch. I could make a batch in a couple of hours, at material costs of about 2 each. (20 years ago)
My original rule and a triangle with the centre of its 'rose' on the hypotenuse edge, with a little indent for the pencil point, are still my favourites for chartwork.


http://i215.photobucket.com/albums/cc310/Piotaskipper/Nav%20ruler/P5080001.jpg


http://i215.photobucket.com/albums/cc310/Piotaskipper/Nav%20ruler/P5080003.jpg

boomerangben
10-05-10, 11:57
I've been to the Captain Field a number of times. It is marked by two oil platforms and an anchored tanker. Get a bit closer and one of the platforms is marked WPP, and the tanker FPSO. Oh and the platforms have white lights on each corner flashing morse code Uniform.

Or am I on the wrong tack?

Phoenix of Hamble
10-05-10, 12:38
I use parallel rules in preference to any other device... I carry a Portland plotter, but will always reach for the parallel rule when doing the chart work myself...

Just habit I guess.