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Old 03-08-2013, 16:22   #16
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Re: Taffrail logs - ?

The only way to get an accurate run to calibrate the log is to make a run over a known distance WITHOUT CURRENT effecting the time required. Could probably do the same thing with a GPS in still water. If you are really into Navigation, could build in a correction for current if you KNOW what the current is. As far as how to calibrate the log that's anyones guess. Have never heard of playing with the length of the line. Possibly might be necessary to lengthen it to avoid skipping if your boat is a fast multi. The Walker came with premeasured line for the propellor. No mention of messing with it in the directions to calibrate, IIRC.

Going distance travelled from noon sight to noon sight or a fixed time or distance with a GPS is prone to all sorts of errors from leeway, current, etc. That's why navigation was so interesting in the good old days. Used to say I was always lost, it was just a matter of how lost. Out of the box, the Walker has appeared accurate and has gotten me there from the old sextant days to the electronic navigation of today. FWIW, have found the GPS speed to be way out of line with the speed through the water and virtually useless for trimming the sails, etc. A knot meter works way better for that and way more fun to watch it hit 10k on a 25' water line boat.

Have never had a problem with the log propellor fouling even dragging down the kelp laden California coast. As far as the angle of attack, think it varies very little from 2 till it begins skipping out of the water surfing. The line may sink or rise with speed variations but the actual direction of pull on the line at the propellor is pretty much horizontal. Think catenary on an anchor. I've made passages with two different paddle wheel knotmeters that were calibrated to the Walker. Never more than a few 10ths of a mile difference in a hundred mile run. Doesn't mean the Walker is measuring the actual speed through the water but that it doesn't vary with speed in relation to a paddlewheel log. One of the logs was a B&G and the other a Raymarine ST60.
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Old 03-08-2013, 16:23   #17
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Re: Taffrail logs - ?

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Originally Posted by Pete7 View Post
I think David summed that up pretty neatly with his normal down to earth approach. The big tides found on NW sides of continents make it all guess work anyway. Sometimes our log reads the same as the GPS and sometimes it doesn't. Now is it the tide, a bit of weed or calibration of the log?

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You want perfect navigation, drive on the interstates.
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Old 03-08-2013, 16:27   #18
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Re: Taffrail logs - ?

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Raku:I noticed that no one has answered your question regarding how speed is measured.
Of course there is a counter that is attached to a braided line that is attached to a towed spinner that reads out in nautical miles covered , but there is also a opening in the housing that enables one to count the revolutions of the spinning flywheel and when armed with a stopwatch the navigator could reference a diagram that gave the speed thru the water in knots.
I towed one across the Atlantic and they are very accurate ,totally mechanical devices that use no electricity, fool proof and work well in all weathers but speed is not accurate in drifting conditions or very slow speeds while the distance run still continues to work accurately
As noted, one does not want it to become entangled with a fishing line since the two lines will then be wrapped around each other thousands of turns...If contemplating a voyage RTW I would probably keep it aboard since the modern yacht is only 1 lightening strike away from the 18th century. PM me if interested in purchase of a lightly used one complete with original wooden box and spare spinners( sharks think they're yummy).

Thanks -- you got the point; it's a backup. SHARKS like the spinners? that's funny!

I don't know what kind of device I want yet. I'm not contemplating any sort of round the world trip but I sometimes bring my own toys along when on someone else's boat. It's paid off more than once.
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Old 03-08-2013, 16:37   #19
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Re: Taffrail logs - ?

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Originally Posted by Vasco View Post
If I remember right you calibrate the log by lengthening or shortening the line. The trick is to match the log reading to the day's run. We used to enter the log reading at the end of every watch.
Thanks for that input.

However, if that is how they were calibrated, ie by comparing to a day's run as determined by celestial, then they are not very damn accurate!

Also, don't think that the length of the spinner line matters in that way... after all, once the twist is stable there must be one rev of the input shaft of the log for every rev of the spinner, or else the line would continue to twist up (or untwist.

Give it another think and see if anything else pops up, please.

Cheers,

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Old 03-08-2013, 16:49   #20
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Re: Taffrail logs - ?

I towed a Walker Log across the Pacific and around the islands for a few years. After each watch or on the hour we would log the distance traveled. The thing was very accurate and I would never have attempted to calibrate it since ther was no such thing as GPS.
I lost the whole log to something one night while off the coast of Washington about 600 miles out. Bang! It was gone along with a chunk of varnished mahogany taffrail.
It is a work of art and a "thing of beauty is a joy forever" - Keats.
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Old 03-08-2013, 17:09   #21
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Re: Taffrail logs - ?

The logs were as accurate as required in its day. It just helped in getting a DR position. Not really much good for anything else.

For those interested in this old stuff , you stream and hand the log.
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Old 03-08-2013, 18:51   #22
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Re: Taffrail logs - ?

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Originally Posted by Rakuflames View Post
Thanks -- you got the point; it's a backup. SHARKS like the spinners? that's funny!
Yes, the big game fish or sharks have plucked one off line in past, so make sure you have spare spinners for model you get.

Walker is the most popular but you can find other makes from time to time on EBay or such. It is convenient backup that does not take up much space and is totally mechanical. Got to love the olden days of simple technology.
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Old 03-08-2013, 19:50   #23
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I have one , lovely device , pity the Walker instrument company is long gone.


Those respondents looking for accuracy are missing the point , its helps working up a DR , DRs are inherently unreliable.

Dave
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Old 03-08-2013, 20:07   #24
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I have one and use it to check the onboard log before any long distance passages, hoping that the walker is pretty accurate. But how does anyone know how accurate their unit is?

And been there with the fishing line
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Old 03-08-2013, 20:34   #25
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Originally Posted by conachair View Post
I have one and use it to check the onboard log before any long distance passages, hoping that the walker is pretty accurate. But how does anyone know how accurate their unit is?

And been there with the fishing line
Yiu could check your daily runs against GPS assuming you are free from major local tides or currents. Only a certain accuracy is neccessary as DR plots are inherently inaccurate.

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Old 03-08-2013, 21:07   #26
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Yiu could check your daily runs against GPS assuming you are free from major local tides or currents. Only a certain accuracy is neccessary as DR plots are inherently inaccurate.

Dave
That's the point, from comparing daily runs on GPS log and through the water nowhere is free of currents. Round the Atlantic anyway. Plus measured miles don't exist in most of the world. Not that big a deal but would be nice the know just how accurate a walker trailed log is.


Interesting just how many eddies and local currents there are far out in the open ocean.
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Old 03-08-2013, 22:18   #27
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Originally Posted by conachair View Post

That's the point, from comparing daily runs on GPS log and through the water nowhere is free of currents. Round the Atlantic anyway. Plus measured miles don't exist in most of the world. Not that big a deal but would be nice the know just how accurate a walker trailed log is.

Interesting just how many eddies and local currents there are far out in the open ocean.
Yes but the accuracy so obtained is better then any DR accuracy you might plot, so once the trailing log is not the most inaccurate component , who cares.

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Old 03-08-2013, 22:58   #28
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who cares.

Dave
I do

Why bother having any kind of log if you have no idea how accurate it is.
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Old 03-08-2013, 23:13   #29
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Originally Posted by conachair View Post

I do

Why bother having any kind of log if you have no idea how accurate it is.
Sheesh , this pinpoint navigation fixation is all due to modern electronics.

Your celestial fix represents your best accurate fix, offshore , the Inaccurracy of that fix can be considerable. Since EP trumps DR , having a DR water distance method of greater accuracy is useless.

Check your trailing log against GPS 24 hour distance traveled ( not SOG ) that's way more accuracy then needed.

Or if you forsake GPS , check it against noon to noon sight runs.
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Old 03-08-2013, 23:36   #30
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Re: Taffrail logs - ?

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Got to love the olden days of simple technology.
In their day, the taffrail logs were the high tech instruments, and mariners were probably saying 'got to love the olden days of simple technology' (streaming a chip line and counting the number of knots in the line played out in the time the sand in a 15 second glass ran out).

I find taffrail or patent logs to be sufficient for DR and celestial work. If you are worrying about navigating to within a meter of your actual position, you are spending too much time fretting and not enough time enjoying the act of sailing.
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