Triangular engineers scale for plotting

[dukes4monny]

Hi all, I'm just reading an American book about navigation, and the author Bill Brogdon advocates a method for measuring LAT and LONG on a small chart using a 'Triangular engineer's scale'.
Before I dash out and buy one of these, have any of the learned forumites used one these for this purpose? Is it any good?
He mentions getting one which is marked "10" "20" "30" "40" "50" "60" on it's six faces.......I assume that this is an imperial measure, so I'm guessing that I must ensure that I get an imperial version?

Thanks for any pointers.

 

[sailorman]

Hi all, I'm just reading an American book about navigation, and the author Bill Brogdon advocates a method for measuring LAT and LONG on a small chart using a 'Triangular engineer's scale'.
Before I dash out and buy one of these, have any of the learned forumites used one these for this purpose? Is it any good?
He mentions getting one which is marked "10" "20" "30" "40" "50" "60" on it's six faces.......I assume that this is an imperial measure, so I'm guessing that I must ensure that I get an imperial version?

Thanks for any pointers.

sounds like just another way to measure rather like a scale rule would be used

some protractor / plotters have a scale on the edges for this purpose

 

[Skysail]

Hi,

Its a long time since I saw one, but I think the 20, 30, 40, refers to divisions per inch, for use on engineers drawings, architects etc. I think it only comes in imperial scales.

IMHO, it is easier to use dividers to measure lat and long accurately, transferring them to the scale on the edge of the chart.

 

[late-night-lochin]

Triangular Scale Rules

Hi Dukes4monny

Yep, these are still used by engineers and architects for scaling drawings but were most commonly used by draftsmen for producing drawings in the days before CAD.

The scales you have quoted are strange though. The scales contained on a scale rule do vary but typically a metric scale rule would have scales of 1:10, 1:20, 1:25 1:50, 1:100 and 1 to 200.

An imperial scale rule would typically have scales 1 inch to 1 foot (1:12), 1/2 inch to 1 foot (1:24), 1/4 inch to 1 foot (1:48) 1/8 inch to 1 foot (1:96) etc.

They are probably still available from an office stationers but as a previous poster said, I can't see any advantage over dividers though.

 

[sarabande]

I can understand an engineer's (or architect's) triangular rule being useful if the imperial / metric scales on the ruler match or are an easily related function of the scales used on a chart.

However, most charts are not furnished with vertical and horizontal lines across the main graphic are, as the Ord Survey does. So there is a slight problem with getting a good right angle to mark the relevant units from the side of the chart.

However (again) I can see that if you need a clearance distance off on a bearing, and there's a scale of 1.250 on the ruler, and the chart is at, say, 1.2500, then using the rule might be easier than opening dividers, measuring from the Lat scale, then transferring to the bearing line. The mental arithmetic is always a potential source of error if you have been up all night and it's a bit choppy, so reducing the risk is important.

Plastic plotters in their many manifestations, and parallel rules seem simple in comparison. There must be a reason why triangular rules have not caught on as mainstream nav kit. I'd not bother buying a triangular ruler unless you are experimenting with eccentric navigation tools.

 

[VicS]

What one of these.

Sort of thing everybody has somewhere isn't it

Often wondered if I'd find a use for it. What's the book?

.

 

[dukes4monny]

Thanks for all the replies. It's obviously not a method that is much used. I think that it is a method that he devised himself, but seeing that one of the things that he is responsible for is positioning of channel markers etc., I don't doubt that it works.

As Skysail says, a 'Triangular engineers scale' appears to have divisions per inch rather than an architects one which has fractions.
I will try and expalin the method as I understand it:
To find the latitude of a waypoint (WP) on a (1:30,000) chart that has latitude lines marked every 2 minutes, and the WP lies between the latitude lines of 03°00' and 03°02', using an appropriate scale on the rule (50), place the 0 of the scale on the 03°00' line and the 20 of the scale on the 03°02' line (rule will be at an angle), with the edge of the rule touching the required WP, if the WP is exactly half way between the two lines, it will read 10 on the scale, so the position will be 03°01'.
If the WP was at 7.2 on the scale, this would give a 03°00.72' and so on......

The book is 'Boat navigation for the rest of us' by Bill Brogdon

 

[VicS]

Mine has (apart from one edge which is just a plain 1" and 1/16" scale) scales that are 3/32", 1/8", 3/16", 1/4", 3/8", 1/2", 3/4", 1", 1½" & 3" divisions each subdivided into 12 (presumably to give an inches and feet scaling) and then further divded into 2, 4 or 8 (to give fractions of an inch)

That's not going to be suitable but somewhere there's a flat more modern one. It'll be interesting to see how that's divided if I can find it, but if SWMBO comes home and finds that I have spent the morning looking for old scale rules instead of cooking lunch I'm going to be in trouble,

 

[Cliveshep]

Loads of scale rules here: http://www.blundellharling.com/products.asp?subcategory=Scale+Rules&category=Drawing+Products

 

[dukes4monny]

It would appear to be a common item in the US, but not over here. I had a look at that site Cliveshep, but they don't list this type of scale.
Here is an example: http://www.iteminfo.com/Product.aspx?id=11970574
I have e-mailed a UK based company to see if they can source them.

VicS, just blame me if you get in trouble.....I'm used to it