Special purpose protractor?

[Alan Mighty]

Originally Posted by kawaboy

Is this protractor used for some special purpose or is it like just any other protractor?

It's just like any other nautical set square aka nautical triangle.


Your 30-60 nautical triangle is, as others have said, part of a pair of nautical triangles.


It's true that a pair of isosceles (45-45) triangles are common. But 30-60 triangles do the job too. Humans are inventive. Many ways to come up with what inventors think is a better rat trap.


Yours is part of what's called the Inoue nautical triangle set. Or the 'Inoue type nautical triangles' if you and your search engine prefer. As opposed to Kent nautical triangles, adjustable triangles etc.


One source for Inoue nautical triangles is: https://mdnautical.com/inoue-type-tr...et-371007.html


Use of an internet search engine using "Inoue nautical triangle" should find you a dozen firms offering you mass quantities at lower prices.


Nothing "wonky" about the protractor circle or its markings. It's the same as an isosceles nautical triangle in its markings and its workings. Any of the vendors of isosceles nautical triangles will provide you with instructions, such as: http://www.davisnet.com/product_docu...M_ChartKit.PDF


Your missing triangle from the Inoue pair is the interesting one. And it's the secret of the Inoue plotting system.


Al

[Alan Mighty]

Originally Posted by Lodesman

Wow. I hope your pre-GPS navigation/piloting skills are good enough to explain how a 30-60-90 triangle is superior to the common 45-45-90?

The standard pair of set squares, or if you prefer 'plotting triangles', was one 30-60 right triangle and one isosceles triangle.


Reason: with both a 45-45-90 triangle and a 30-60 right triangle, you can quickly, easily and accurately construct angles of 15, 45, 75, 90, and 105 degrees. With two 45-45 right angle triangles, you can only quickly construct angles of 45 and 90 degrees.


So the standard pair of set squares, both for marine navigation and geometry/tech drawing in general, was a 30-60 right triangle plus a 45-45 right triangle.


Of course, a protractor triangle lets you construct more angles. The earliest set squares (around 1850) were opaque, not transparent. The technology to make transparent triangles and to engrave them with an accurate protractor arc came later.


You can find a big mob of folk and companies that each claim to have been the inventors or first manufacturers of protractor triangles. A lot of authorities reckon that the nod of approval goes to: https://www.aristo.at/produkte/navigation/

[Alan Mighty]

Originally Posted by Alan Mighty

The standard pair of set squares, or if you prefer 'plotting triangles', was one 30-60 right triangle and one isosceles triangle.

By about the 1960s, the standard 'Kent' set for chart table use was either one isosceles protractor triangle and a straight edge or two isosceles triangles, one plain and one with a protactor arc (with angles extended to the edges.


The Inoue set, was a 30-60 right triangle with an engraved protractor arc (with angles extended to the edges) plus a "danger bearing triangle". So the protractor triangle of an Inoue set could be used just like a the protractor triangle of a Kent set.


The 'danger bearing' triangle was the magic bit. This was in pre-GPS days, when getting an accurate fix was slower and less accurate than post-GPS days.


So the idea was to lay out the desired course. And in pilotage waters to identify dangers on either side of that course. Then to calculate danger bearings (usually to prominent features) that would allow the helmsman to avoid such dangers (i.e. Not More Than {NMT} bearings to port, NLT bearings to starboard).


If you lay the hypotenuse of an Inoue danger bearing triangle along one's desired course, you could quickly and easily translate the danger bearing into an angle off the bow. And that avoided that the confusion between NMT and NLT, or at least that is how I imagined Inoue san to have promoted his invention.

[UNCIVILIZED]

Alan Mighty (& others) thanks for filling in some of the blanks on THE BASICS of navigation. Which most have forgotten, or never got off of their backsides in order to learn.
It's saddening to see how far we've fallen. But it's what I predicted in my YW article, many years ago. At the ancient age of 28.

I'd forgotten about this thread, but yes, most of what's mentioned is correct. Plus there's a LOT more that you can do with these triangles, or the more standard ones for that matter. And much of the same things can also be done with both; parallel (linked) rules, & rolling ones, too. Ditto on hemispherical protractors.

I'm just not up for penning another treatise at the moment. However, I can say that there is a LOT of information & skills, in the old school nav. text books, that it would be wise for everyone to learn. As much of the time when I mention things like Danger Bearings, or Escape Bearings, people just look at me with glazed eyes.

If you want to learn, turn off your GPS (or Especially your chart plotter) for a few weeks, & practice/learn DR, plus the almost endless multiplicity of other ways of getting fixes. Ditto on dusting off your sextant, etc.
Let alone, learning how to navigate like the ancient's did...

[Lodesman]

Originally Posted by Alan Mighty

The standard pair of set squares, or if you prefer 'plotting triangles', was one 30-60 right triangle and one isosceles triangle.


Reason: with both a 45-45-90 triangle and a 30-60 right triangle, you can quickly, easily and accurately construct angles of 15, 45, 75, 90, and 105 degrees. With two 45-45 right angle triangles, you can only quickly construct angles of 45 and 90 degrees.

Thanks for your thoughts; I was unaware of Inoue triangles - I assume they're familiar to Japanese mariners? The danger line facility is interesting.

Unlike drafting I can't think of a reason a navigator would want to accurately construct standard angles as you mentioned. A pair of 45-45 triangles can easily be used to (quickly)walk a line (courseline, LOP, whatever) across the chart. As others stated, I prefer and am more comfortable with a Douglas (Portland) protractor, but have had an introduction to paired triangles.

[Alan Mighty]

Originally Posted by Lodesman

Thanks for your thoughts; I was unaware of Inoue triangles - I assume they're familiar to Japanese mariners? The danger line facility is interesting.

I think Inoue triangles were first produced by Uchida, a big Japanese stationery firm. The triangles are sometimes marketed as 'Uchida Inoue triangles' - for which see Amazon.com - as well as 'Inoue-type triangles' or 'Inoue formula triangles'.


What I called the 'danger bearing triangle' can also be used, of course, to plot leeway due to wind or current.


I have a memory that plotting the likely effect of leeway due to wind or current was the original reason for the Inoue triangle. I think (but don't know for sure) that Inoue san was a professor of naval architecture at Kyushu University and he did research on the effects of wind on the turning circle and course of cargo ships.


And my understanding is that prospective ship's officers in Japan were trained in the use of the Inoue triangles. In turn, Inoue triangles became standard chart table equipment on cargo ships in other East Asian economies.


I suspect that most Inoue triangles are now manufactured in China and likely not by Uchida.

Unlike drafting I can't think of a reason a navigator would want to accurately construct standard angles as you mentioned. A pair of 45-45 triangles can easily be used to (quickly)walk a line (courseline, LOP, whatever) across the chart. As others stated, I prefer and am more comfortable with a Douglas (Portland) protractor, but have had an introduction to paired triangles.

Your mileage might vary.


Being able to quickly construct a 30, 75, 105 etc degree angle can be useful for several jobs, such as drawing a tacking cone to optimise an upwind course and prevent overstanding. In flat water and steady wind, I might draw a tacking cone with laylines 10 degrees either side of the rhumbline. In shifting winds I construct the laylines of a tacking cone at 20 deg either side of the rhumbline, and move them out to 30 degrees either side in a developed sea.


I know racing skippers who have constructed tacking line protractors on each side deck to estimate ladder rungs, TWA etc.


There's lots of uses for angles on a sailing boat. Just like how the arcs on the 'danger bearing' triangle of the Inoue set can be used for danger bearings, leeway, offsetting wind sway when calculating the turn advance of a cargo ship and so on.


I don't argue that any one plotter, parallel rule, protractor etc is superior to others.


I was first taught chart work by the Aus military, using a large square or Douglas protractor. I thought the Douglas protractor was the ants pants, until I met what Dockhead and you call the Portland plotter.


The history of which is long (and perhaps interesting to one or two). To cut it short, let's start with Jean Emile Paul Cras, a rear admiral in the French navy who specified the Regle Cras (Cras ruler or Cras protractor) for chart work in the French navy. Yvonnick Gueret, a Breton seaman who worked on everything from recreational yachts (doing deliveries) to fishing boats and coastal freighters, set up a navigation school in the 1960s. Gueret found his students would make errors with the Regle Cras and he devised his own version, with a rotating protractor instead of a fixed one, that he manufactured and called the Rapporteur Breton (Breton Plotter) starting in the mid-1960s. Gueret did not patent his device (but its novelty may not have been significant enough for a patent, or it may be that he didn't have the resources to gain a patent). A UK firm copied the device (but without red and green markers, so the monochrome version was cheaper to make), calling it the "'Portland Series' course plotter" or "'Portland Series' Breton Plotter" . Much more recently Weems & Plath copied the UK version of the device, calling it the 'Weems Protractor'.


Gueret did get two French patents in 1991, but only for the red and green colour marks and reversed print on his original Breton Plotter. I've not seen either patent enforced.


You can find Jean Cras in Wikipedia, more for his musical work than his navigation and naval leadership.


Gueret has a slight mention in the English language version of Wikipedia.


Professor Inoue's work in the 1970s and 1980s is probably found in specialist academic libraries. He doesn't have much of a digital presence, to the point that I don't know his calling name (and Prof Inoue is likely not closely related to the other famous-to-cruisers Inoue, Inoue Takuzo san whose name is enshrined in the initial letter of the company name 'iCom' short for 'Inoue Communications').


As I mentioned earlier the 45-45 navigation triangle is now also known in the trade as 'Kent triangle', named after a UK stationery manufacturer (does Kent stationery still exist? I'm sure they would have produced more than 45-45-90 navigation triangles or set squares!?!).

[Dockhead]

Originally Posted by Alan Mighty

I think Inoue triangles were first produced by Uchida, a big Japanese stationery firm. The triangles are sometimes marketed as 'Uchida Inoue triangles' - for which see Amazon.com - as well as 'Inoue-type triangles' or 'Inoue formula triangles'.


What I called the 'danger bearing triangle' can also be used, of course, to plot leeway due to wind or current.


I have a memory that plotting the likely effect of leeway due to wind or current was the original reason for the Inoue triangle. I think (but don't know for sure) that Inoue san was a professor of naval architecture at Kyushu University and he did research on the effects of wind on the turning circle and course of cargo ships.


And my understanding is that prospective ship's officers in Japan were trained in the use of the Inoue triangles. In turn, Inoue triangles became standard chart table equipment on cargo ships in other East Asian economies.


I suspect that most Inoue triangles are now manufactured in China and likely not by Uchida.




Your mileage might vary.


Being able to quickly construct a 30, 75, 105 etc degree angle can be useful for several jobs, such as drawing a tacking cone to optimise an upwind course and prevent overstanding. In flat water and steady wind, I might draw a tacking cone with laylines 10 degrees either side of the rhumbline. In shifting winds I construct the laylines of a tacking cone at 20 deg either side of the rhumbline, and move them out to 30 degrees either side in a developed sea.


I know racing skippers who have constructed tacking line protractors on each side deck to estimate ladder rungs, TWA etc.


There's lots of uses for angles on a sailing boat. Just like how the arcs on the 'danger bearing' triangle of the Inoue set can be used for danger bearings, leeway, offsetting wind sway when calculating the turn advance of a cargo ship and so on.


I don't argue that any one plotter, parallel rule, protractor etc is superior to others.


I was first taught chart work by the Aus military, using a large square or Douglas protractor. I thought the Douglas protractor was the ants pants, until I met what Dockhead and you call the Portland plotter.


The history of which is long (and perhaps interesting to one or two). To cut it short, let's start with Jean Emile Paul Cras, a rear admiral in the French navy who specified the Regle Cras (Cras ruler or Cras protractor) for chart work in the French navy. Yvonnick Gueret, a Breton seaman who worked on everything from recreational yachts (doing deliveries) to fishing boats and coastal freighters, set up a navigation school in the 1960s. Gueret found his students would make errors with the Regle Cras and he devised his own version, with a rotating protractor instead of a fixed one, that he manufactured and called the Rapporteur Breton (Breton Plotter) starting in the mid-1960s. Gueret did not patent his device (but its novelty may not have been significant enough for a patent, or it may be that he didn't have the resources to gain a patent). A UK firm copied the device (but without red and green markers, so the monochrome version was cheaper to make), calling it the "'Portland Series' course plotter" or "'Portland Series' Breton Plotter" . Much more recently Weems & Plath copied the UK version of the device, calling it the 'Weems Protractor'.


Gueret did get two French patents in 1991, but only for the red and green colour marks and reversed print on his original Breton Plotter. I've not seen either patent enforced.


You can find Jean Cras in Wikipedia, more for his musical work than his navigation and naval leadership.


Gueret has a slight mention in the English language version of Wikipedia.


Professor Inoue's work in the 1970s and 1980s is probably found in specialist academic libraries. He doesn't have much of a digital presence, to the point that I don't know his calling name (and Prof Inoue is likely not closely related to the other famous-to-cruisers Inoue, Inoue Takuzo san whose name is enshrined in the initial letter of the company name 'iCom' short for 'Inoue Communications').


As I mentioned earlier the 45-45 navigation triangle is now also known in the trade as 'Kent triangle', named after a UK stationery manufacturer (does Kent stationery still exist? I'm sure they would have produced more than 45-45-90 navigation triangles or set squares!?!).

You are a font of knowledge!!

I learned a lot from your posts.

The so-called "Portland Plotter", which is my go-to device for chart work, is actually still called a "Breton Plotter" by many old timers over here. Giving credit where credit is due.

In my opinion, the Portland/Breton Plotter has more or less obsoleted set squares. I know how to use a set square, but just barely, and I don't keep one in my nav table (whereas I have a spare Portland Plotter as a backup ). It does "clearing bearings" (what you've been calling "danger bearings") and walks meridians, LOP's, etc., with ease.


Chart work is such a great pleasure -- I feel sorry, really, for those of us who are uninterested in working with paper.

[Hydra]

I prefer the Cras ruler/plotter because there is only one part to hold: on a small yacht in a seaway, it is sometimes difficult to manage the rotating protractor on a Breton plotter. I just imagine what it would be with a pair of set squares!

It seems that Pr Inoue calling name is Shosuke. See for example the 3rd reference here: http://www.koreascience.or.kr/articl...2003_v27n6_631

Alain

[belizesailor]

Originally Posted by Lodesman

Thanks for your thoughts; I was unaware of Inoue triangles - I assume they're familiar to Japanese mariners? The danger line facility is interesting.

...

Yes, thanks for the detailed info on the Inoue triangles. I've used the more common triangles, and lots of other plotting tools, but not the Inoue triangles.

Always more to learn.

[kawaboy]

Thanks to all for your thoughts and comments. It certainly has been informative. :-) Thanks again

I didn't think for a moment that this triangle would generate so much interest. :-)

Regards

Joe

[sophiedaisey]

Alan Mighty, WOW I certainly enjoyed this thread, navigation is so fascinating. Without it we would still think the Earth was flat!!!



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