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08-03-2016, 21:40
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#1
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Registered User
Join Date: Mar 2009
Location: Manila Philippines
Boat: Rob Perry Tatoosh 42'
Posts: 59
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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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08-03-2016, 22:48
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#2
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Registered User
Join Date: Jun 2014
Location: Up the mast, looking for clean wind.
Boat: Currently Shopping, & Heavily in LUST!
Posts: 5,629
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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.
__________________
The Uncommon Thing, The Hard Thing, The Important Thing (in Life): Making Promises to Yourself, And Keeping Them.
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09-03-2016, 00:21
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#3
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Registered User
Join Date: Jul 2012
Posts: 197
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Re: Special purpose protractor?
Quote:
Originally Posted by UNCIVILIZED
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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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.
Lee
Sent from my GT-I9507 using Cruisers Sailing Forum mobile app
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09-03-2016, 01:11
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#4
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Registered User
Join Date: Mar 2009
Location: Manila Philippines
Boat: Rob Perry Tatoosh 42'
Posts: 59
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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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09-03-2016, 04:35
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#5
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Registered User
Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,961
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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...
__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
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09-03-2016, 06:51
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#6
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,764
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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.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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09-03-2016, 08:13
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#7
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Registered User
Join Date: Dec 2010
Location: W Carib
Boat: Wildcat 35, Hobie 33
Posts: 13,480
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Re: Special purpose protractor?
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09-03-2016, 17:17
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#8
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Registered User
Join Date: Mar 2009
Location: Manila Philippines
Boat: Rob Perry Tatoosh 42'
Posts: 59
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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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09-03-2016, 18:44
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#9
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Registered User
Join Date: Nov 2005
Location: At the intersection of here & there
Boat: 47' Olympic Adventure
Posts: 4,852
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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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09-03-2016, 19:00
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#10
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Registered User
Join Date: Jan 2016
Posts: 429
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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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10-03-2016, 04:22
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#11
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Registered User
Join Date: Dec 2010
Location: W Carib
Boat: Wildcat 35, Hobie 33
Posts: 13,480
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Re: Special purpose protractor?
Quote:
Originally Posted by Lodesman
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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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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10-03-2016, 05:35
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#12
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Registered User
Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,961
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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.
__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
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10-03-2016, 05:46
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#13
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Registered User
Join Date: Dec 2010
Location: W Carib
Boat: Wildcat 35, Hobie 33
Posts: 13,480
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Re: Special purpose protractor?
Quote:
Originally Posted by svHyLyte
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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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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10-03-2016, 06:54
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#14
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Registered User
Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,961
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Re: Special purpose protractor?
Quote:
Originally Posted by belizesailor
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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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.
__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
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11-03-2016, 17:31
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#15
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Registered User
Join Date: Nov 2005
Location: At the intersection of here & there
Boat: 47' Olympic Adventure
Posts: 4,852
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Re: Special purpose protractor?
Quote:
Originally Posted by svHyLyte
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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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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