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Then I would put a dot anywhere on the line preferably in open water.

Then through that dot pointing somewhere west of north I would draw a line through the dot so that the angle between my northwest line and my south east line was 130 degrees.

Then I would use a parallel rule to find out the magnetic heading of this second line.

The difference between the magnetic heading of the second line and 300 is your deviation.

There are real navigators on this forum but maybe this will get you started.

This is how I thought about it.

If you see the lookout tower and the Island in line then you have to be somewhere on a line that connects those two.

The only question is where on the line and which direction you are pointing.

We don't know nor care where on the line but we know we are pointing 130 degrees west of the line because that is what the Pelorus says.

Now we can tell what our magnetic heading should be.

If it doesn't match our compass the difference must be the deviation.

It looks like the second question is the same as the first just different numbers.

I'm just guessing here but does this make sense?

the chart is a permanent fixture on the kitchen table, in the AM I will calculate your reply thanks

Then I would put a dot anywhere on the line preferably in open water.

Then through that dot pointing somewhere west of north I would draw a line through the dot so that the angle between my northwest line and my south east line was 130 degrees.

Then I would use a parallel rule to find out the magnetic heading of this second line.

The difference between the magnetic heading of the second line and 300 is your deviation.

There are real navigators on this forum but maybe this will get you started.

This is how I thought about it.

If you see the lookout tower and the Island in line then you have to be somewhere on a line that connects those two.

The only question is where on the line and which direction you are pointing.

We don't know nor care where on the line but we know we are pointing 130 degrees west of the line because that is what the Pelorus says.

Now we can tell what our magnetic heading should be.

If it doesn't match our compass the difference must be the deviation.

It looks like the second question is the same as the first just different numbers.

I'm just guessing here but does this make sense?

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5,097 Posts

Please expand on what the letters mean.

What is D C etc.

Oh I just remembered True, Varitation, Magnetic, devation, compass

Also please quote the problem exactly, word for word with nothing added or left out including exact punctuation.

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5,097 Posts

I suspect their is a missing piece of the puzzle.

In what way did he solve the puzzle with 299,05,314,003,317

To me the number 300 has to be in the mix someplace because according to the question the compass is 300 yes?

So one way or another if you have the calculated or plotted magnetic course and you have the compass you just subtract to get the D.

So in your solution where is my 300 compass which is the given.

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5,097 Posts

If you know the magnetic of the range then without a chart you can just go west 130 degrees and have a magnetic bearing.

The difference between magnetic and comp is deviation.

But unless you have the bearing of the range in either true or magnetic how do you start to calculate?

Maybe that number was part of the prior problem.

Letters are

T true

V variation ... difference between true and magnetic; in the charted region for the problem magnetic is to the left/west of true as you look north

M magnetic

C compass

D deviation, the difference between magnetic and your particular compass

Here's sort of a backwards way of looking at it:

In the first problem, boat was on heading 300 (compass) (roughly northwest).

The angle of the boat's heading to the range via pelorus angle measure was 130 to starboard, which I assume is measured from the bow (duh), so same as 40 degrees behind your starboard beam.

If compass direction were to have been the same as magnetic, then the range would have been on the line 300 + 130 = 430 minus the 360 you don't need is 70 degrees. Sighting straight down the range should have shown you a "70" and that would also have been its magnetic direction. If the magnetic direction of the range plotted off the chart was something different from 70, you'd have that much deviation... for this particular heading. (Do this lots of times for different directions and you could construct a "deviation card" and then be done with this sort of thing.)

But, to solve the problem, I think you need to know something about that range... either an observed compass bearing, or its direction after plotting a line for the range and walking it up to the compass rose, or a published bearing for the range... something.

I'm lazy and like to stay with magnetic, but maybe the navy and wanna-be navy folks like to have more numbers to play with and think that converting everything to True is intrinsically more virtuous or gives them better feng shui or something. That's fine on big ships, but simplicity is beautiful on a small, bouncing boat. Especially if squinting over a chart down below is risky to your feeling of well being.

Oh, and if you don't like the variation where you are navigating, just wait long enough and it'll change. Only a little in the short term (chart should show annual change in variation for its area), but give it 10 000 years or so and you just might see the big magnetic pole flip.

And another option is to just sail in Lake Michigan, Kentucky or Tennessee, Georgia, or parts of the Bahamas, where navigators don't have to worry about much steekeen variation.

A wicked thought... see just how good your instructor is by having him work problems like this while skippering a small, heeling, bouncing sailboat in a lively seaway while dodging holiday weekend traffic and keeping a good lookout. No doubt he'll always get perfect, textbook results. Yeah, right.

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9,378 Posts

If that is the case, the problem is solvable.

Edit. I just found my old copy of the practice chart 1210 Tr ( training) .

It indeed lists a lookout tower and not a windmill.

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9,378 Posts

Same place as the windmill?

Edit. I just found my old copy of the practice chart 1210 Tr ( training) .

It indeed lists a lookout tower and not a windmill.

Jack Lat I get 41.25.3 Lon is the same.... with a pair of triangles, on my living room floor.Same place as the windmill?

I can't fiddle with it any more tonight..have other work to do... OP should have his training chart..and can confirm.

I'm using chart 1210Tr...thanks davidpm, rgscpat, jackdale and tempest for helping me thru this, questions are 7 & 8 in the above link.

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