GPS Log

[Peter_Shipley]

With the increased accuracy of GPS has anyone thought of using a GPS in place of a traditional log. Apart from the speed variation due to positional error and the obvious problem with a USA shutdown, I cannot see any navigational disadvantages. And it is one less hole in the hull.

Thoughts?

 

[yoda]

Lack of redundancy and the inability to revert to traditional navigation when all goes wrong. Yes GPS is good but the sets still stop working from time to time. Conversly GPS is great when the log fails like mine has!

Yoda

 

[LadyInBed]

What's a 'traditional log' a paddle wheel, or throwing something overboard and using a stopwatch?
I use the GPS to log COG & SOG. The GPS records a position every 10 mins so looking back to the position the boat was at an hour ago, the distance is equivalent to my SOG and the back bearing of the course to that position gives me my COG.
I don’t log the speed through the water, I just do a 'snapshot' two or three times an hour to see what effect the current is having. As with comparing the ships head to the COG.

 

[Trevor_swfyc]

Peter,
I agree with you, a log paddle wheel is prone to barnicles and hence often fails anyway. I have a trailing log but on short trips its hardly worth the risk of reversing over it and wrapping it round the prop. So I get SOG from the GPS the boat will do 5 knots at 2,000 revs so it is obvious when the tide is with me or against. The reason for the LOG over GPS SOG is that if you are racing the gain of 0.1 knots from a minor sail trim is immediatly shown and is used in conjuction with SOG. Another thing a LOG gives is total distance covered since last set to zero not any good for oil change interval unless you own a motor cruiser and not a yacht.
The main answer that you cannot get away from is the ability to navigate without the GPS, you know that thing that points to magnetic north, a chart, echo sounder, pencil, dividers, parallel rule and you guessed it a LOG. Thank God for GPS!!
We have never had it so good.

 

[bigmart]

One thing to remember, if you do any RYA Qualifications, is that it is distance logged, (ie. throught the water & not over the ground, that counts for passage qualifications.

I must admit that I always feel uneasy when my log packs up, even though I have the super wonderful GPS as backup.

 

[VMALLOWS]

As posted several times before, I think paddle-wheel logs are a total waste of time.On a cross-channel trip you can be sure they'll clog up several times. Why do people say that 'you shouldn't rely on GPS' but are quite happy to rely on their little paddle wheel connected to a (usually rather antiquated) piece of electronics mounted in the wet in the cockpit.

 

[rich]

now't wrong with GPS, just don't foget how to do it the old way! i have used decca than gps for the last 20odd years, life just gets better.how else can we make it easya?

rich ) Why pay, when you can do it yourself?<P ID="edit"><FONT SIZE=-1>Edited by rich on Sun Jun 16 23:42:02 2002 (server time).</FONT></P>

 

[VMALLOWS]

You're right. Nothing quite beats that first pre-decca trip to France when you actually worked out tidal offsets and so on and wondered what that huge nuclear power station was. I have even been known to mistake Hengisbury Head for Hurst Castle!.

 

[Twister_Ken]

A log, of course, tells you speed through the water, while GPS gives you speed over the ground. The difference between these two tells you a great deal about tide and current effects - useful if you are either cheating or working the moving carpet and want to be in the best place. It matters a lot in a saily yacht, much less so in a 20+ kt power yacht.

 

[VMALLOWS]

But how did you know the speed over the ground before Decca/GPS?

 

[Twister_Ken]

By various methods of position fixing and doing sums. Much easier now. In fact, I'd have to think hard about how to do a running fix if I ever needed to do one again