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Old 18-02-2009, 13:01   #46
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See also the very simple paddle wheel tap test procedure at:
Testing Knot-Log Speed Instrument
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Old 18-02-2009, 20:49   #47
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I scrolled back too fast. You're right about Fairbanks' post being the source of the info.

Steve B.
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Old 18-02-2009, 21:21   #48
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Whew! Ya had me going there for a minute.
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Old 19-02-2009, 13:32   #49
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Thanks for the feedback Mark.

I had sometimes looked at mine and thought that the cable where it exits the transducer could be vulnerable due to the apparant lack of strain relief there so is nice to know there is a bit of wriggle room inside if the worst happens.

John
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Old 19-02-2009, 14:55   #50
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The Raymarine knot meter can be calibrated. Great to check against GPS in a location with minimal current. It not only provides estimated speed, but will give trip and total distance. Some will even provide water temperature. If you have GPS and the plot charter, it will also calculate current for you.

It can be a handy tool at times. There have been instances when my GPS has been unavailable and I have used it for dead reckoning. So, you can think of it as a good backup tool.

The ultrasonic sounds WAY better! If you forget to pull it out and replace with the plug when you're going to be away for a while, you tend to come back and it is plugged with mussels, barnacles and &^%. I guess the ultrasonic is a lot less worrisome. But $$$$?? And if you already have one.....

Good to know they can be patched, now, what do I do with that spare???
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Old 19-02-2009, 17:14   #51
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...It can be a handy tool at times. There have been instances when my GPS has been unavailable and I have used it for dead reckoning. So, you can think of it as a good backup tool...
A much better and FAR cheaper backup than a log in case of failure of one's GPS is a handheld GPS. In fact one can install a second mounted GPS as a backup for the same price as a log .
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Old 19-02-2009, 23:53   #52
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But No log means no boat speed info (as distinct from SOG), which I find fairly important, particularly in terms of set and drift.
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Old 20-02-2009, 03:23   #53
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But No log means no boat speed info (as distinct from SOG), which I find fairly important, particularly in terms of set and drift.
As explained in my post earlier in the thread, with a GPS one does not need to know the magnitude of set, drift and leeway.

If only a GPS one just creates a waypoint at or between one and the destination and then sail down the bearing to it (ie helm so the bearing to waypoint remains constant).

If have a plotter or an ECS on a computer one just sails towards the destination (or any point, not necessarily a waypoint, on the way to the destination) with the look ahead vector extended over it.

Both automatically correct for set, drift and leeway with no log.

One also soon gets to get a good feel for what these are just by the difference between the bearing to waypoint and the boat's compass heading, but the information is redundant as it is not required to navigate the boat.
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Old 20-02-2009, 08:09   #54
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But No log means no boat speed info (as distinct from SOG), which I find fairly important, particularly in terms of set and drift.
Amen!
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Old 20-02-2009, 12:34   #55
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Amen!
That seems to be a response based on faith rather than on facts .

Another area of instrumentation error that implicates the log that many don't seem to be aware of is in wind speed and direction, both true and apparant. If this is dependant on the log and compass heading rather than the GPS then the whole of the vector sum of set, drift and leeway is an error in it as is the log error too. The set, drift and leeway can be a substantial error so gives the situation of the wind instrumentation only tending towards accuracy when set, drift and leeway are nil, leaving only the still likely to be important error in the log.

This becomes especially important on race boats if sailing to polars. A friend, who has unfortunately unexpectedly died, developed professional nav systems and high end sailing instrument systems for racing sailboats which addressed both the navigation and wind errors introduced by avoiding use of the log and compass and using GPS.

The electronic charting system that I use for navigation seems to discard the log and compass heading information when calculating wind and uses the GPS SOG and course over ground but I have not had the incentive to delve into confirming that. Why I think it is so is that the wind vector rotates aimlessly when the boat is stationary. I don't know how common that is with other ECS's as again I have not had the motivation to check.

Note nowhere have I suggested a log is redundant, can be a salve to the body to see speed through the water but hopefully some will see that the faith that is put into it for navigation and wind is misplaced now that there are far more accurate ways of navigation based on GPS.
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Old 20-02-2009, 12:58   #56
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Originally Posted by MidLandOne View Post
That seems to be a response based on faith rather than on facts .

Another area of instrumentation error that implicates the log that many don't seem to be aware of is in wind speed and direction, both true and apparant. If this is dependant on the log and compass heading rather than the GPS then the whole of the vector sum of set, drift and leeway is an error in it as is the log error too. The set, drift and leeway can be a substantial error so gives the situation of the wind instrumentation only tending towards accuracy when set, drift and leeway are nil, leaving only the still likely to be important error in the log.

This becomes especially important on race boats if sailing to polars. A friend, who has unfortunately unexpectedly died, developed professional nav systems and high end sailing instrument systems for racing sailboats which addressed both the navigation and wind errors introduced by avoiding use of the log and compass and using GPS.

The electronic charting system that I use for navigation seems to discard the log and compass heading information when calculating wind and uses the GPS SOG and course over ground but I have not had the incentive to delve into confirming that. Why I think it is so is that the wind vector rotates aimlessly when the boat is stationary. I don't know how common that is with other ECS's as again I have not had the motivation to check.

Note nowhere have I suggested a log is redundant, can be a salve to the body to see speed through the water but hopefully some will see that the faith that is put into it for navigation and wind is misplaced now that there are far more accurate ways of navigation based on GPS.
And if Mount Everest does not move,
I am sure that it will prove ...
You can/cannot solder knot log leads.
(You can)
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Old 20-02-2009, 13:43   #57
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And if Mount Everest does not move,
I am sure that it will prove ...
You can/cannot solder knot log leads.
(You can)
Surely if one sets out to drift a thread onto set and drift then it is always on topic .

John
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Old 20-02-2009, 14:04   #58
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Surely if one sets out to drift a thread onto set and drift then it is always on topic .
Set is not really a factor since it's about where it drifts. Navigation in the CF forum defies instrumentation. You are apparently were where you appear to have been. Contrary to common assumptions the forum is flat and you can fall off the edge easily. We offer a push from time to time. After that it's out of our jurisdiction. We are finite.
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Old 20-02-2009, 14:30   #59
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We offer a push from time to time.
You mean like those big frightening creatures that one sees on old charts that stop one wanting to stray too close to the edge .
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Old 22-02-2009, 20:48   #60
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At last this thread is getting really interesting
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