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Old 08-03-2016, 22:40   #1
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Special purpose protractor?

Good day all

I was going through some boxes the other day and came across this protractor. I also found parallel rules and a standard protractor.

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

Cheers

Joe in Manila
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Old 08-03-2016, 23:48   #2
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Re: Special purpose protractor?

It'd make doing some of the more "advanced" DR, & Old School nav work easier/possible. But I don't see what about it is that you're calling special. Then again, I learned Nav a Long time ago, & am used to tools akin to that.
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Old 09-03-2016, 01:21   #3
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Re: Special purpose protractor?

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Originally Posted by UNCIVILIZED View Post
It'd make doing some of the more "advanced" DR, & Old School nav work easier/possible. But I don't see what about it is that you're calling special. Then again, I learned Nav a Long time ago, & am used to tools akin to that.
Hmmm
I can't quite work out what this thing is for. Can't find it readily in my nav texts. Any further elucidation appreciated.
The 30 degree angle appears military, but the markings appear nautical.
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Old 09-03-2016, 02:11   #4
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Re: Special purpose protractor?

I'm afraid that I have no further info on this item. Seems odd that the reciprocals are only on the East side.

Perhaps Uncivilized can enlighten us... perhaps a quick example of how this thing is used?
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Old 09-03-2016, 05:35   #5
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Re: Special purpose protractor?

It combines the function of a protractor, normally laid over a compass rose (the crossed lines at the bottom--long side) or the intersection of plotted log.-lat lines, with a standard triangle. With it, one can dispense with a separate protractor and perform ones plotting on a chart with two triangles alone.

FWIW...
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Old 09-03-2016, 07:51   #6
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Re: Special purpose protractor?

Exactly. It's half of a Set Square. You need one more of them.

It's used to find a courseline or bearing in relation to a meridian.

A pair of these allows you to "walk" the meridian over to the line you're trying to plot.

Works very well, but I prefer the PORTLAND PLOTTER.

The Portland Plotter is faster and more convenient, provided your chart has gridlines on it.
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Old 09-03-2016, 09:13   #7
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Re: Special purpose protractor?

http://www.davidburchnavigation.blog...triangles.html
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Old 09-03-2016, 18:17   #8
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Re: Special purpose protractor?

Well how about that...You learn something new everyday.

Thanks a lot to all.

Cheers

Joe
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Old 09-03-2016, 19:44   #9
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Re: Special purpose protractor?

I'm not convinced it's a navigation triangle. For one thing, nav triangles tend to be isosceles. While it could be used as such, it would be more cumbersome that a standard triangle for some tasks. And there must be a reason the inner circle is inverted and 90º out from the outer scale. I don't know what it is for - it's a mystery.
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Old 09-03-2016, 20:00   #10
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Re: Special purpose protractor?

Fine on flat paper on flat table but worry that the kind of folded charts we have to use could be ripped at the folds by the pointy end?

Haven't honestly used them for real since I learned how - should make more of an effort to practice the old skills I suppose.

Also prefer the Portland.
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Old 10-03-2016, 05:22   #11
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Re: Special purpose protractor?

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I'm not convinced it's a navigation triangle. For one thing, nav triangles tend to be isosceles. While it could be used as such, it would be more cumbersome that a standard triangle for some tasks. And there must be a reason the inner circle is inverted and 90º out from the outer scale. I don't know what it is for - it's a mystery.
True, I noticed that too. Sure looks like typical nav related markings on the scale though. Maybe a drafting tool that someone pressed into service for navigation use?

Any old school draftsmen here?
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Old 10-03-2016, 06:35   #12
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Re: Special purpose protractor?

Good Lord. Anyone that learned navigation/piloting before GPS knows that is a protractor triangle. The loss of basic knowledge/skills on such matters is appalling. For more information see Celestaire Plotting Protractor Triangle.
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Old 10-03-2016, 06:46   #13
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Re: Special purpose protractor?

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Good Lord. Anyone that learned navigation/piloting before GPS knows that is a protractor triangle. The loss of basic knowledge/skills on such matters is appalling. For more information see Celestaire Plotting Protractor Triangle.
Good Lord...that exact same product has already been posted several times on this thread. Its not the same as what the OP posted.
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Old 10-03-2016, 07:54   #14
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Re: Special purpose protractor?

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Good Lord...that exact same product has already been posted several times on this thread. Its not the same as what the OP posted.
No. His is evidently a 30-60-90 triangle with extended protractor degree markings conveniently etched along the straight edges making it even more useful than a simple protractor triangle for marking a bearing/LOP.
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Old 11-03-2016, 18:31   #15
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Re: Special purpose protractor?

Quote:
Originally Posted by svHyLyte View Post
Good Lord. Anyone that learned navigation/piloting before GPS knows that is a protractor triangle. The loss of basic knowledge/skills on such matters is appalling. For more information see Celestaire Plotting Protractor Triangle.
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? And as a master Vasco, I'm sure you can explain how one uses the wonky inner circle on the OP's triangle?
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