Using Radar for navigation..

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I'd go further and suggest that with a combination of radar and hand bearing compass you can very accurately plot your position from 1 recognisable charted object - the compass is excellent for what it's designed to deliver; the bearing. The radar will deliver the distance exactly.

Re plotter v radar etc - as has been said over and over again on here and in published material, continually cross referencing 2 or more sources of information is good practice; never forgetting the Mk 1 eyeball.

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In fact take note of charted coastline ... because radar only sees visible items and also does not return from soft material ... that coastline you see on radar may be inland of the actual charted coastline ... but a number of dist off of various land objects / marks etc. will soon indicate that ...
 
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I'd go further and suggest that with a combination of radar and hand bearing compass you can very accurately plot your position from 1 recognisable charted object - the compass is excellent for what it's designed to deliver; the bearing. The radar will deliver the distance exactly.

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Thats's an interesting point - I was fixated on "radar = poor visibility" - I hadn't thought about using it in good vis. as a supplement to the compass.
 
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I'd go further and suggest that with a combination of radar and hand bearing compass you can very accurately plot your position from 1 recognisable charted object - the compass is excellent for what it's designed to deliver; the bearing. The radar will deliver the distance exactly.

Re plotter v radar etc - as has been said over and over again on here and in published material, continually cross referencing 2 or more sources of information is good practice; never forgetting the Mk 1 eyeball.

[/ QUOTE ]I won't argue with that! I suppose what I had in mind was the situation where you can't see the charted object! Three distances from identified points gives a very good fix and is often overlooked by the novice navigator.

One might argue that ANY fix is better than no fix. The skill of the navigator (or experience) is to know what reliablityerror allowance to apply to the pencil mark on the chart. (Or the digits on the GPS come to that!) Its like the fix that is put down with hude certainty, that doesn't a square with the depth on the sounder. Something is wrong!

You are right when you say that the good navigator cross checks everything. It might just be a glance to make sure it all adds up and ties together. When something looks wrong, you know its time to have another look at what you are doing.
 
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why are you using the radar for bearings and not the hand-compass?..)


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If you were taught to use the radar for bearings on this course, somebody needs to be sacked. Even with a very accurate gyro feeding bearing information, the beamwidth on a yacht radar is such that closer than 10 degrees bearing would be a miracle. You should only be using it for accurate ranges from prominent points, and it is entirely possible to get a very nice three position fix this way (using a visual bearing as well preferably), and this used to be the prefered system over Decca positions, but is obviously dependent on radar horizon.
 
[quote Even with a very accurate gyro feeding bearing information, the beamwidth on a yacht radar is such that closer than 10 degrees bearing would be a miracle.

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I'd have to check my notes, but I'm fairly sure that the instuctor said that you'd be lucky to get it within 1 degree or so (and then, IIRC, an offset of half the beam width has to be added - annother approximation). He was emphasising (as others have here) that the range marker is a better tool.
 
Skents - Thanks for your excellent example, and great piccy. And thanks for recounting your experience.
I've seen a similar effect on the same type of equipment - ie working great, suddenly out by quite a large amount, then back on track... no problem with datum, no adjustments to settings... but I've seen it! Unfortunately didn't take a photogragh! And it was a lovely sunny day with good vis, and I knew where we were.
Being old-school, I've never relied on a plotter/gps... But I do think these modern small solid state radars are quite clever...! Shame I'm not a very good operator.
 
the best time to practice 'blind navigation' is in good weather ...... it gives confidence in the kit and yourself

I would recommend ppl practice navigating with radar for when the gps goes tits up, its another trick up ones sleeve.

IMO of course /forums/images/graemlins/cool.gif
 
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the instuctor said that you'd be lucky to get it within 1 degree or so

[/ QUOTE ] The beamwidth on a standard 18" antenna is in the order of abt 8 degrees (cannt remember the exact figure off hand) believing that you can get to even half of that is very dangerous even if you have decades of experience (I have) and then there is the issue of bearing accuracy between where you think the radar is pointing, versus the actual physical position, and finally the issue of gyro/radar accuracy - forget 1 degree - consider 10 degrees possible if you are an experienced user.

Then there is the probability that most people will be using head up displays and electronic bearing lines which means that your ten degrees of accuracy has just doubled unless it is a very flat ocean.
 
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why are you using the radar for bearings and not the hand-compass?..)


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If you were taught to use the radar for bearings on this course, somebody needs to be sacked. Even with a very accurate gyro feeding bearing information, the beamwidth on a yacht radar is such that closer than 10 degrees bearing would be a miracle. You should only be using it for accurate ranges from prominent points, and it is entirely possible to get a very nice three position fix this way (using a visual bearing as well preferably), and this used to be the prefered system over Decca positions, but is obviously dependent on radar horizon.

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I would have to consider about the error on bearing ... but would be surprised if beamwidth was that bad ... if it was and at the powers from yacht radar - would make it near useless ... half-beamwidth and all that is taught to us along with beamwidth extension etc. as Merch guys ...

I would be suprised if beamwidth error was more than 1 degree actually .... BUT total error due to non-steady course keeping, deviation, variation etc. accumulative on a Magnetic Compass equipped yacht ... yes could be getting on for 10 at times ...

It's actually why I proposed distance off in earlier post ...

Of course if you want to remove errors due to compass correction - you can use the radar bearings not as related to compass but as horizontal difference angles ... and quickest accurate way to plot horizontal angles to get position is to draw on a piece of tracing paper ... then place on chart and align to the land marks etc. then mark chart at intersection .... no compass errors etc.

isn't life wonderful !!
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quickest accurate way to plot horizontal angles to get position is to draw on a piece of tracing paper

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There is a purpose designed piece of equipment designed to do this, normally used to resolve horizontal sextant angles for survey work! Quicker and more accurate that the tracing paper, but a LOT more expensive!
 
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quickest accurate way to plot horizontal angles to get position is to draw on a piece of tracing paper

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There is a purpose designed piece of equipment designed to do this, normally used to resolve horizontal sextant angles for survey work! Quicker and more accurate that the tracing paper, but a LOT more expensive!

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I used to have a Tri-plotter ... left it in draw after getting good with the paper ! Accuracy in fact is debatable which is better ... as both use exactly same fundamental principle ...

But a pad of tracing paper is cheap !!
 
Skents - I too have a C80 and experienced this. I had mated it with an older gps and sometimes the gps lost datum. Or the plotter did. I cured it by upgrading to a new raymarine 125 gps - at least it hasn't recurred. I always do a sense check on power up since that time!
 
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I know a retired Destroyer Commander. He said they used to make navigators give instructions to take Destroyers out of Portsmouth blind. Said it kept them on their toes!

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And everyone else, I would imagine!
 
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I know a retired Destroyer Commander. He said they used to make navigators give instructions to take Destroyers out of Portsmouth blind. Said it kept them on their toes!

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They then promoted them to Skippers of Well Known Yacht Charter Co. !!
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And everyone else, I would imagine!

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