hi, been reading up on basic navigation and i've got myself some charts to pratice on, but i need to get a parallel ruler and dividers. I've noticed there's diffent types, does it matter which ones or is it just down to personal choice?
Dividers are fairly standard; the type with a semi-circle (or 'bow') near the hinge, so that you can open and close it with one hand. Never stick the points into the chart, but lay the dividers almost flat against the paper to take measurements.
Go for brass with a stainless set of points - feels really good !
Parallel rulers are a different fish kettle. Lots of different types and some non-parallel ones as well.
The roller rule will wander all over the chart table and is pretty useless on a small boat under destroyer size.
I prefer the ones which are like two plastic rulers, joined by a couple of thin metal plates, so that you can zig zag them over the chart from a compass rose. They remain stationary when flat on their own.
Plotters
There are lots of other bespoke devices: e.g. Breton plotter, Portland plotter, etc., which all have a compass with deviation / variation adjustments, graticules, distances markings etc.
They can be quite addictive, and each has its army of followers. Probably the best all-round device, and cheapest !
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On the whole it's a matter of personal preference. I have Capt Field's parallel ruler (the one with a protractor drawn on it), but haven't used it for years. When I use one, which is not often these days, I have a gizmo attached by parallel tapes to a corner of the chart table which is easy to use, even one-handed (and also has a protractor built-in).
I don't use a Breton type plotter, though we have one since SWMBO went to classes. I only ever use it to line up screw holes before drilling, but I know a few people, some of them sane, who use one for navigation.
As a general rule get the best quality stuff you can afford. That goes for most things on board, if only for the greater pleasure in their use.
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Portland plotter and dividers were recommended at our nav course - have served us well and never needed anything further. You can get some nav exercise books which might give you some focus - nothing quite like the real thing though.....
As a recent 'dazed kipper' theory and practical student. I can vouch for the brass/stainless dividers and Portland plotter. IMHO they work well in the classroom and also for real when rolling around off St Alban's Head in the pitch black with no GPS.
I have worked with parallel rules as well but just find the compactness (is that a word?) and convenience of the Portland pretty good.
Tim
Last edited by emsworthy; 05-11-09 at 00:46.
Reason: Can't spell Parellel at this time of night right 1st time!
Absolutely Personal Choice - But Some Are Better Than Others Depending On The Job
A good Parallel Rule, a Douglas Protractor and a so called Breton Plotter (the rectangular device with the circular protractor in the middle). I actually prefer Standard Dividers as opposed to the bow type. My reasons are as follows: -
Parallel Rule
Easy to use for transfer of positions lines - running fix is a classic example.
Very easy transfer of Lat and Long from GPS to chart.
Buy the 12" size
Douglas Protractor
Great for setting up position lines directly from the object on the chart. Simply put the centre over the object (protractor aligned North) and mark the angle on the chart. Draw position line from object through mark.
No need to slide or position device to transpose angle.
Buy the 6" size
Breton Plotter
Great for laying off a course and measuring the bearing. Simply align on the course, twiddle the dial to North (make sure it overlays a Lat or Long line) and read the bearing.
Standard Dividers
I have never navigated in such a contorted position which only allows me to squeeze the bow types. The bow types allow you to squeeze to open and squeeze to close. However they always open up just short of the distance you want to measure. Bow type, in my opinion, have limited functionality compared to Standard Dividers.
Buy 9" size
Why Any of the above tools can do any of the plotting requirements when navigating so you only need to have one type and just practice. I have found that each of the angle measuring devices can be used in an optimal situation as described. This has been observed over many years of so called traditional Navigation.
If I Only Had To Choose One
12" Douglas Protractor. No moving parts, big enough to place in a useful position on the chart, long enough to use as a straight edge rule; 9" standard dividers.
Don't get too hung up about it. As another poster says, just practice.
Last edited by BlowingOldBoots; 05-11-09 at 01:12.
Reason: A bit of clarity on dividers
Just get a pair of STRAIGHT navigational dividers, as found on all ships' bridges. For people with the normal complement of fingers, these are much easier to use with one hand than the "bow" type, which look the part but don't do the job anywhere near as well.
Parallel rules belong on a large, flat and relatively steady ship's chart table - not much use on a yacht at sea. A Breton plotter or big Douglas Protractor will do the job better.
Personal preference, but it's worth trying with all of them until you can establish a preference, rather than using one and then slagging off all the others.
Personally, I prefer bow dividers (the big ones -- forget the fiddling little ones) over straight ones, and I prefer 12" or 15" Captain fields parallels over a Breton plotter. (a proper, thin flexible Breton, not the heavy, thick, brittle copies).
Most of the other contraptions come way down my list but I did have a fairly long-standing infatuation with an 8" douglas protactor look-alike.
But get what *you* like, and *enjoy it*: navigation is a hobby -- not a "chore".
Personal preference, but it's worth trying with all of them until you can establish a preference, rather than using one and then slagging off all the others.
Personally, I prefer bow dividers (the big ones -- forget the fiddling little ones) over straight ones, and I prefer 12" or 15" Captain fields parallels over a Breton plotter. (a proper, thin flexible Breton, not the heavy, thick, brittle copies).
Most of the other contraptions come way down my list but I did have a fairly long-standing infatuation with an 8" douglas protactor look-alike.
But get what *you* like, and *enjoy it*: navigation is a hobby -- not a "chore".
Spot on Tim. Find what you like. What works for you. If it works & you find ease using it & get the correct results then end of story. Each to their own...........as long as it works.
One correction. Navigation is not a hobby, it is a necessity. IMHO of course. Hee hee.
hi, been reading up on basic navigation and i've got myself some charts to pratice on, but i need to get a parallel ruler and dividers. I've noticed there's diffent types, does it matter which ones or is it just down to personal choice?
Very much personal choice - mine is for the ultra-simple and cheap two largish triangular setsquares. I find that holding one down firmly and sliding the edge of the other against it is very esay to know if anything slips, and you can usually move from compass rose to chart point or vice versa in one go, at worst two shifts. With parallel rules you often have several 'steps' to go, and each step increases the chances of something moving, as it's rather fiddly.
My second choice is a square portland protractor - the one with a hole in the middle. I've also tried the currently fashionable Breton plotters with adjustable buits in the middle, but reverted to the two setsquares.
As for dividers - I have a big brass pair, but actually prefer a good quality large compass with a pencil at one end. For some traditional nav tasks you need to draw arcs, and you can't do that with dividers.
In practice however nowadays I first LOOK carefully at the chart, then navigate on an electronic plotter, but I write down a GPS position every hour and I can go back to absolute basics if I need to.
I've taught nav for years. If the class want me to buy equipment in bulk for them, I always go for the bow type dividers and the Breton plotter. This plotter has the biog advantage that it works out the way to apply deviation and variation for you, and some people have difficulty remembering how to do that. I have occasionally had people turn up with Capn Fields or parallel rules and even one of those useless on a yacht roller thingies, but most have ended up using the Breton plotter.
As above, PORTLAND plotter (Breton is the original name), plus Dividers. Whichever dividers you prefer, beware the plastic type with no screw in the hinge, you want brass with stainless points, they will last forever. There are good deals on ebay for a Portland plotter and dividers - about £23 inc P&P.
All wonderful stuff for working in the classroom & planning courses to within a 1/2 deg.
However, when working in the cockpit of a small boat at sea when singlehanded, it's all about as much use as a chocolate teapot. By all means learn that stuff and make sure you understand the principles.
Then you can use your eyeballs, brain & chart folded on your knee to get a position & plot a course as you steer. Identify a landmark, point at it & then transfer that "bearing" to the chart, already orientated on your knee. Remember that & do the same for another landmark. Where the 2 cross is obviously your position - with a decent circle of uncertainty. You know where you want to go so use your eye & hand to transfer that bearing off the chart to the horizon & steer it. You will need to make some allowance for tide & leeway etc, but it works and you don't even need a pencil or a compass.
Of course, if you have the time & support to use all your equipment & books, then great, do it. It is very satisfying to navigate from below & hit a mark on the nose in fog, but safe singlehanding without instruments is not difficult & very useful. It can also provide a quick & simple "sanity check" on the info yoru navigator gives you.
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The first question is - why are you doing this? Is it for an exam, to use on board or just for interest?
If it's for an exam you need to be able to show you can do it the traditional way with parallel rules. In a real situation the Breton-type plotter where you set magnetic variation then forget it is far quicker.
The best instrument I ever had was a 24" gunmetal roller parallel rule but it needed a full-size chart table. Since those were stolen I now use a breton plotter for coastal work and a douglas protractor for plotting astro position lines.
I have seen all sorts of equipment used for plotting - parallel rules (roller or pivot-arm), Breton/Portland plotters, Douglas protractors and even a pair of set squares. Anything you can get on with is OK.
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'scuse my ignorance - but is there any difference between a Breton and Portland plotter?
In principle, nothing at all. That type of plotter was originally made in France, and called the 'Breton' plotter. When made in the UK by a different firm they had to use a different name.
A word of warning on dividers. As others have said, you want brass dividers with stainless points. I have seen brass dividers where the ends of the legs have been chrome plated; they look very similar, but the points rapidly bend or blunt. Look for a definite discontinuity between the brass and the stainless bits.
I need to get a parallel ruler and dividers.
I've noticed there's different types, does it matter which ones or is it just down to personal choice?
forget parallel ruler!
Get two pairs of dividers.
For plotting a position on a chart, I use two pairs of dividers (bow type). One to transpose Lat and one to transpose Long. It saves a lot of faffing around altering it for Lat and Long.
Plotters - as you say, it just down to personal choice.
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forget parallel ruler!
Get two pairs of dividers.
For plotting a position on a chart, I use two pairs of dividers (bow type). One to transpose Lat and one to transpose Long. It saves a lot of faffing around altering it for Lat and Long.
Plotters - as you say, it just down to personal choice.
Puzzled as to how you draw water track, tidal set & drift and ground track with dividers.
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One hull good, two hulls better.
I use a Portland plotter. I find no problem with it. There's *always* something on it you can line up with the grid. I've got a waterproof notepad for pilotage/nav notes when I know I'm gonna be stuck in the cockpit and not get to the nav table.
forget parallel ruler!
Get two pairs of dividers.
For plotting a position on a chart, I use two pairs of dividers (bow type). One to transpose Lat and one to transpose Long. It saves a lot of faffing around altering it for Lat and Long.
Plotters - as you say, it just down to personal choice.
Thats all very fine but with which do you draw course lines, tidal drift and such like.
My personal preference are Captain fields paralell rules, I have them in different lengths, I have both types of dividers but prefer my 8" brass and stainless compasses. I use a 24" straight edge for extended lines, and I also have a large chrome plated Brass roller Rule, but I tend not to use it at sea, only for planning.
Try the different options and use what ever you feel most content with.
hi, been reading up on basic navigation and i've got myself some charts to pratice on, but i need to get a parallel ruler and dividers. I've noticed there's diffent types, does it matter which ones or is it just down to personal choice?
As previously stated, its personal preference.
However, parallel rules are definitely for the bridge of a merchant vessel, particularly those with rollers.
Most important thing to remember, is that anything transferred from or onto a chart, MUST be in degrees TRUE! So learn how to apply variation/deviation correctly.
PS, another 'obvious tip' often forgotten - mention has been made regarding divider points becoming blunted, but how many times has the 2B pencil been blunted by putting them point downward in the chart table holder? They should always be put away point upward to preserve the point.
Not Dayskipper or YM Theory, that's for sure. I, and everyone else who sat it with me, used a Portland plotter. I used to teach DS classes and most people used Portlands - I don't recall any rules on what you can and can't use.
Michael Green (the Art of Coarse Sailing) did it with two nails in the foredeck.
Leslie Phillips took "Troutbridge" (Navy Lark) to New york on a street map of Brighton!
Simple navigation, tiller in one hand, cuppa in the other, no faffing about with dividers and parallel rulers, just a couple of nails to blearily sight along!
Failing that, follow someone else!
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I used to think wives and boats were a financial drain on one's resources, but that was before the kids became teenagers.
Not Dayskipper or YM Theory, that's for sure. I, and everyone else who sat it with me, used a Portland plotter. I used to teach DS classes and most people used Portlands - I don't recall any rules on what you can and can't use.
Perhaps I put that a bit strongly. I think you should be able to show that you can do Variation calculations rather than just dial it in on the plotter.
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One hull good, two hulls better.
In principle, nothing at all. That type of plotter was originally made in France, and called the 'Breton' plotter. When made in the UK by a different firm they had to use a different name.
A word of warning on dividers. As others have said, you want brass dividers with stainless points. I have seen brass dividers where the ends of the legs have been chrome plated; they look very similar, but the points rapidly bend or blunt. Look for a definite discontinuity between the brass and the stainless bits.
Variation is so small now in this neck of the woods, that it can be virtually ignored (tell it not in Gath).
I swear by Weems and Plath dividers. The advantage of this type is that you can, with a wheel, adjust them to an exact distance and this will be held, whatever the motion of the boat. £9.75 from RYA shop.
Regarding navigation notebooks which are water proof. I open up old tomato/orange juice cartons, wash them and then write my pilotage plans in indelible pen on them. Write with a medium thickness nib and you can read them at night without using a torch, using the compass light.
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Posts: 102
Trad Nav
I am interested to know why some people think roller Parallel rules are unsuitable in a yacht. They are so much more convenient, especially for passage planning and they more easily transfer over a large chart. For detailed work when doing chart corrections, I use a large Douglas. I also use a Douglas in conjunction with a set square for plotting star-sights.
Stainless steel points on dividers? I have missed out. Mine have tool steel and I keep them shoved into a cork, preferably one from a Grand Cru Classe. They have never rusted thanks to Ducru Beaucaillou.
If you should want to make your own plotting sheet, then adjustable set-squares are good.
How much of that is true and how much a leg pull?
I swear by Weems and Plath dividers. The advantage of this type is that you can, with a wheel, adjust them to an exact distance and this will be held, whatever the motion of the boat. £9.75 from RYA shop.
What happens when you simply want to quickly measure a distance on the chart between two fixed points? Do you hold on to them with one hand, while cranking the wheel with the other?
If so, seems like hard work and more suited to school geometry or a draughtsman's table.
In reply to Jaybee of 0923 this am. You do not need to "crank" the dividers using the wheel, but can open and close them easily with one hand. Work well at sea with one hand for yourself and one for the dividers!
Bow-type dividers have proved popular at sea since medieval times. In the classroom, however, for those ploughing through RYA or MCA shore-based courses, a draftman's type of compass with lead changed for a second "needle" would help achieve the degree of accuracy that keeps the examiner happy.
I like straight navigational dividers - brass, with stainless steel points, about 7 or 8 inches long and with a screw at the hinge keeping them together and allowing some frictional adjustment.
This could be a "personal" and possibly irrational prejudice, but I don't think so.
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. (Thinks: perhaps a YouTube video is required here.)
"Straight" dividers are to be found in their tens of thousands on the chart tables of merchant ships of all nationalities, whilst the sexy looking (medieval) "bow" types are almost never in evidence. As both versions cost about the same amount of money, I conclude that the overwhelming majority of professional navigators find the "straight" type easier and more convenient to use.
Used the bow type dividers for years and got really fed up with having to open them 'the wrong way' because they never seemed to open wide enough the right way. Anyway, last time I sold the boat I let the bow dividers go with it and bought a new set of straight ones. Much easier and less hassle.
And Portland plotter, does anyone plot in 'true' on a coastal chart?
....... does anyone plot in 'true' on a coastal chart?
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.
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.
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.
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One hull good, two hulls better.
Operate single handed dividers...
Quite Easily Done.
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
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!
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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.
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 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".
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 . . .
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I'm astonished to hear that so many are still sitting below at a chart table with detailed nav calcs.
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
Quote:
Originally Posted by Searush
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?
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!
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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
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.
Quote:
Originally Posted by VicS
Well i haven't for a start.
Now you have raised the issue you had better explain or post a link to the instructions.
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.
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.
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
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?
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.
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
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hi, been reading up on basic navigation and i've got myself some charts to pratice on, but i need to get a parallel ruler and dividers. I've noticed there's diffent types, does it matter which ones or is it just down to personal choice?
Personal choice.
I make my own, now to be known as the Doug748 plotting aid:
How is that for oneupmanship. Or is it a bit sad?
OK so it is a Douglas protractor stuck onto a bit of perspex. This is the mark three version, the mark one was made with a simple 360 protractor, and the mark two with the remains of the Goode................yep it is just sad.
navigation
Ocean Froggie 
Really?
Parallel Rulers
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