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» Online Classroom   »   » Public Discussion of Inland and Coastal Navigation   » Parallel Rules vs Triangles

   
Author Topic: Parallel Rules vs Triangles
drlmk


 - posted March 09, 2007 08:53 AM      Profile for drlmk           Edit/Delete Post 
I was recently on a ship where the navigator used two plastic triangles for plotting, rather than parallel rules. He would effortlessly slide the rules against each other and move across the chart as he plotted positions, courses, etc. Looking over his shoulder, it wasn't clear to me exactly how he was doing what he was doing, but it seemed to work like a charm. His comment to me was that the ship didn't even have a set of parallel rules and once you got used to the triangles, you'd never go back.

So, my questions to you experts are 1) How do the triangles work? and 2) What are the advantages and disadvantages of triangles vs parallel rules?

Thanks for your help.

From: Spokane
David Burch


 - posted March 09, 2007 11:35 AM      Profile for David Burch           Edit/Delete Post 
These are a standard type of plotting tool used on some (by no means all) larger vessels. They have the advantage of yielding more accurate angles and therefore are often used for USCG tests. A sample of one is below. We will come back later and add a note on how to use them. It takes two of them two layout and transfer angles. They cost $14.95 each, with handles. You can also get them for less without handles and then go to the hardware store and pick out some even nicer handles for a custom set. Handles are recommended.

The only problem is that they do take some practice to get used to. We have found that most people tend to give up on them before they master them, and thus we have not used them in our course materials for general navigation.... however, if you do want the most precise hand plotting, these are the best solution.

 -

One popular source for these "navigator's triangles" or "protractor triangles" is Weems-Plath.com. we can also special order these. I checked their website and they have an instructions pdf for these, but it is not so useful, and in fact it does not show the way they are most commonly used. Thus we might write up some notes on these and post them here as soon as we get a moment and then share them with our good friends at Weems and Plath.

so please stand by on the instructions and if you do not hear from us here in a few days, please remind us.

Note that some mariners who might use these for a test will then switch back to using Weems parallel plotter or parallel rulers once underway on their own vessel.

From: Starpath, Seattle, WA
drlmk


 - posted March 09, 2007 01:43 PM      Profile for drlmk           Edit/Delete Post 
Thanks. I'll stand by.
From: Spokane
drlmk


 - posted March 26, 2007 08:51 AM      Profile for drlmk           Edit/Delete Post 
Got a set of the triangles and worked with them over the weekend. They do take a bit of getting used to, but once over that hurdle, they're slick! All you need is a meridian line and you're set to plot -- no compass rose necessary. The only disadvantage I can see is that you can only plot True bearings.

Can't say that I'll be throwing away my parallel rulers any time soon (I've had the same set for over 40 years), but I'm going with the triangles for now.

From: Spokane
David Burch


 - posted March 28, 2007 06:36 PM      Profile for David Burch           Edit/Delete Post 
Well in principle you can walk a line to or from the compass rose with these, just as you would with a weems plotter or parallel rules. In that sense, i would say they are similar to a Weems plotter in that the most convenient use is with true bearings on a meridian line, but can be used with a compass rose if desired.
From: Starpath, Seattle, WA
drlmk


 - posted March 29, 2007 10:29 AM      Profile for drlmk           Edit/Delete Post 
Sure. That makes sense. Thanks.
From: Spokane
chetco


 - posted April 12, 2007 11:48 AM      Profile for chetco           Edit/Delete Post 
I'm looking for the instructions you said you were going to offer regarding using two triangles vs a parallel. Is was back in late March when the question was asked.

Thank you,

From: oregon
David Burch


 - posted April 12, 2007 01:33 PM      Profile for David Burch           Edit/Delete Post 
I am sorry that we do not yet have anything formally written up on these, but here are a few tips for the basic application.

Problem: draw a line through Point A in direction 057 T.

Solution:

Step 1. Choose any point B on the nearest meridian line to point A, and orient triangle 1 (either one of them, they are the same) so that it points in direction 057 T. This will have the center point of the triangle on the meridian and then you rotate the triangle so the meridian crosses the 057 line on the protractor printed on the triangle. Double check by just looking at its orientation that it is about right... ie that you did not just line up some numbers without thinking of what the orientation was supposed to be. There are several scales on the triangle and you may have grabbed the wrong one if you do not look at the edge crossing the meridian to be sure it makes sense. You can do this alignment very precisely, relatively easily within ± 0.5°.

Note you are always using the degree marks on the outside edge of the triangle shown above. The inside scales are just there to show you the different orientations and subsequent meanings of the outside scales.

 -

Step 2. Holding triangle 1 firmly in place, align triangle 2 under it so you can slide 1 over to point A as shown below.

 -

Step 3. Slide 1 over to Point A and then draw in your line. If you have any doubt that you slipped some, then slide 1 back to the meridian to check it out.

 -

-------------------------

Reading the bearing of a line on the chart is just the opposite. Align one triangle with the bearing line, then put another under it to slide it to the nearest meridian to read the bearing.

-------------------------

Hope that helps for now.

From: Starpath, Seattle, WA
chetco


 - posted April 13, 2007 02:03 PM      Profile for chetco           Edit/Delete Post 
Thank you, that helps a lot.
From: oregon
SunriseBoy


 - posted December 10, 2013 09:57 PM      Profile for SunriseBoy           Edit/Delete Post 
Get a Yeoman Puck. Fantastic.
David Burch


 - posted December 10, 2013 10:37 PM      Profile for David Burch           Edit/Delete Post 
The yeoman puck plotter (http://www.yeomanuk.co.uk) is an interesting combination of electronics and paper charts, and it sounds like it works well from your note.

However at some $600 without accessories, one is left in a quandary.

For this much money, you can buy a notebook or tablet computer, and a blue tooth gps. Good echart programs are free and the echarts are free.

So if we want to take electronics into the plotting, why not go with this modest ECS combination that costs less, and you do not have to plot anything.... just watch the boat move across the screen. Measure range and bearing to anywhere at the click of a mouse or tap of the finger.

in the textbook we have a short section on how you can solve vector problems with an ECS display as well, so even when not underway you can solve plotting and other navigation problems electronically.

However, electronics *of any kind* put you onto a slippery slope. Once the camel has his nose under the tent....

From: Starpath, Seattle, WA


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