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Old 15-02-2009, 19:45   #16
Hal
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Is "set and drift" like "heading and course"? I do not think that I would ever drill a hole in my boat below the water line. It sounds counter productive to staying afloat. If that thing breaks off, can you put a cork in the hole or will the boat fill up so fast that you only have time to launch the dingy?
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Old 15-02-2009, 20:22   #17
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Said with all possible kindness: if you don't know the answer to your question, you need to learn more about navigation. Nonetheless, the short answer is "set and drift" refer to how much a boat is set in some direction by current drifting the boat from her position in otherwise still water. A GPS will never tell you how much current you're moving with, against, or across, only the final speed over ground, which is not the same as velocity through water, save with no current at all. The consequences of not knowing set and drift can be significant.
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Old 15-02-2009, 20:49   #18
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Said with all possible kindness: if you don't know the answer to your question, you need to learn more about navigation. Nonetheless, the short answer is "set and drift" refer to how much a boat is set in some direction by current drifting the boat from her position in otherwise still water. A GPS will never tell you how much current you're moving with, against, or across, only the final speed over ground, which is not the same as velocity through water, save with no current at all. The consequences of not knowing set and drift can be significant.
Correct me if I'm wrong but does a knot meter tell you set and drift? I think we were comparing Knot Meter vs GPS vs ultasonic sensors.
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Old 15-02-2009, 21:02   #19
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A knot meter will tell you speed through the water, nothing more.
For example if you were sailing North at 5 knots according to your knot meter, and the GPS said you were moving North at 7 knots, (assuming the knot meter was correctly calibrated) you would know that the current of the water was also moving North at 2 knots. If however, in the above scenario your GPS said you were moving at 3 knots, you would know that the water was moving South at 2 knots. If you were sailing 20 miles or so it would make a BIG difference in time of arrival to your destination!

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Old 15-02-2009, 21:20   #20
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Well that's what I thought Steve. I'm not sure how set and drift ended up in the thread anyways. I think a few of us are ready to chuck knot meters in favor of a GPS.
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Old 15-02-2009, 21:55   #21
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Well that's what I thought Steve. I'm not sure how set and drift ended up in the thread anyways. I think a few of us are ready to chuck knot meters in favor of a GPS.
It wouldn't be the first time I misunderstood a point.... but, here goes nothing

I think the "set and drift" comment was made because during the whole thread, the current was assumed to be with or against you (as far as the stated examples went) if the current is diagonally affecting your boat, then scenery changes dramatically.... and it would be nice to know what the current is doing to you Perhaps I am wrong about this but data over ground doesn't necessarily provide the necessary navigational info.

Ok, I'll shut up now

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Old 15-02-2009, 22:07   #22
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I'm totally understanding the set & drift thing. I'm thinking a GPS tell you a lot more than a knot meter does and especially when link to a plotter. I will go out on the navigation limb here and say I don't think you need a knot meter if you use a GPS. I promise I will now wash my mouth out with soap...
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Old 16-02-2009, 00:39   #23
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Just to add to the confusion:
Why put a hoe in the boat just to measure speed through the water; don't you just toss a small bit of paper into the water at the bow and time the period it takes to pass the stern. Some simple maths converts this to knots - probably more accurate than a lot of paddle wheel meters in my experience .
Compare waterspeed and heading with GPS "groundspeed" and track - the difference is due to set and drift. In tidal areas, this will change hourly.

Anyway congrats. to MarkJ for fixing the unfixable.
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Old 16-02-2009, 00:43   #24
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Just to add to the confusion:
Why put a hoe in the boat
Why not??? Some of us like to have a hoe onboard...
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Old 16-02-2009, 01:24   #25
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Note to self: I must proof read, proof read and proof read before submitting the (w)hole post.
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Old 16-02-2009, 04:19   #26
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Anyway congrats. to MarkJ for fixing the unfixable.
Thank you I can't wait to try it out That will be tomorrow or wednesday when we head to Lady Musgrave Island - hopefully it will be out of internet range!
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Old 16-02-2009, 10:59   #27
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For example if you were sailing North at 5 knots according to your knot meter, and the GPS said you were moving North at 7 knots, (assuming the knot meter was correctly calibrated) you would know that the current of the water was also moving North at 2 knots.
Determining current set and drift is not that simple. The current could be moving faster at some other angle giving you the same readings. With heading and VTW input, a GPS can give accurate current set and drift.

Eric
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Old 16-02-2009, 11:34   #28
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What fairbanks56 said... a GPS does make sorting out set and drift super easy. There are other ways (look into dead reckoning for the details), but this is one place where GPS really shines. That said, GPS alone won't do the job, because it will not come up with VTW. It's the combination of GPS and some sort of knotmeter (even a chip log - no holes needed!) that works.
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Old 16-02-2009, 13:23   #29
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RBEmerson,

Your point well taken with no offense. All should heed. Although I have never sailed the ocean blue, except on Carnival lines as a passenger, I do have many years of navigation skills in my black bag of tricks. The question was rhetorical in nature. I am impressed with the repair job as far as functionality goes, but the hack job looks mighty scarey. I would repair the hole and use the GPS or one of the other gizmos that others have suggested. I remember an old technology standby that works when all else fails. It is a rope with knots tied every so often. You through a waited end over the stern and play out the rope for a specific period of time. Then count the knots.
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Old 16-02-2009, 16:38   #30
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Determining current set and drift is not that simple. The current could be moving faster at some other angle giving you the same readings. With heading and VTW input, a GPS can give accurate current set and drift.

Eric
I was just trying to keep it simple to make a point. In the Northern parts of Puget Sound, we get up to 6 knots of tidal current at times, so I use both a paddlewheel and a GPS Chartplotter to keep apprised of the above.

Re the "hack job":
The repair was done to the inside of that sender.
Take another look at the picture. You will see the O ring way down the shaft.
I have one exactly like it on my boat.

Steve B.
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