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Old 17-09-2010, 07:52   #61
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In my view a GPS device cannot be substituted for a reliable knotmeter. I have had the experience of sailing west, under the Golden Gate Bridge at 2 knots while running under a spinnaker, stearing 90 (M), and making 4+ knots through the water. (Likewise a GPS can tell you what direction one is going, but not what direction one is pointing, eh? Hence the old reliable compass.)

We have a Standard Horizon speed-log with a paddlewheel impellor. To keep growies off of the thing, I pull it out once a month or so, give it a bit of a scrub and give it a light coating of Neosporin (anti-bacterial cream) from the medicine chest.

While we have the knotmeter, to calibrate it properly, and to serve as a back-up should it fail, we have another inexpesive knotmeter that is very accurate--see Knotstick Sailboat Speedometers .

FWIW...
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Old 17-09-2010, 08:39   #62
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Originally Posted by SailFastTri View Post
You are absolutely correct, GPS readings would be the better calculation base rather than the speed/log.

But can you name a manufacturer's wind meter that give the option to use GPS readings (rather than speed/log) for calculating this when you push the button to change from apparent to true readings?
The B&G instruments I have will do it.
The bottom figures on the left are true wind angle and speed
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Old 21-09-2010, 11:26   #63
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Originally Posted by svHyLyte View Post
In my view a GPS device cannot be substituted for a reliable knotmeter. I have had the experience of sailing west, under the Golden Gate Bridge at 2 knots while running under a spinnaker, stearing 90 (M), and making 4+ knots through the water. (Likewise a GPS can tell you what direction one is going, but not what direction one is pointing, eh? Hence the old reliable compass.)

We have a Standard Horizon speed-log with a paddlewheel impellor. To keep growies off of the thing, I pull it out once a month or so, give it a bit of a scrub and give it a light coating of Neosporin (anti-bacterial cream) from the medicine chest.

While we have the knotmeter, to calibrate it properly, and to serve as a back-up should it fail, we have another inexpesive knotmeter that is very accurate--see Knotstick Sailboat Speedometers .

FWIW...
I'll have to try the neosporin.

I clean mine by pulling it and imediately putting in a plug with an O-ring on it, ( it has a hole drilled for the pin). It only takes a second, and I get very little water in. AND, .... it is great practice for the time I ran over someones Deck floating 1" UNDER the surface some months after the Hurricane Ike, It just hit the speed sensor and broke it and popped it out of the through hull. Fortunately the plug was hanging nearby ready to use. When I heard the bump and speed sensor went dead I knew exactly what had happened and dove the gangway, pulled the access panel, yanked the remains of the paddlewheel with the dangling wires, and inserted the (handy),plug, and watched as the bilge pump sucked down the spill. I was back at the wheel with a NON leaking hull before the boat had moved 10 yards.
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Old 21-09-2010, 14:05   #64
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Heh!

I forgot to put my log in place before we left the dock one day and decided to just do it while heading down the channel. Heh! At 4 knots or so the amount of water I saw was quite a shock. I didn't even get the plug all the way out. We stopped the boat to "do it right".

I guess I just want to know the difference between SOG and boat speed.

On Sunday coming back from Anclote to Hudson with NE 8-12 kts and a 1 kt counter current, I was able to make one tack and put us right on the outer marker. I did fall off 10deg that last mile though - I sorta try to do that too. It's better than another tack.
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Old 21-09-2010, 14:11   #65
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I guess I just want to know the difference between SOG and boat speed.
I differentiate between SOG and STW, the latter signifying speed through the water, which is commonly called "boat speed." If I'm sailing against a 1-knot floot at a STW of 7 knots, my SOG would be 6 knots.

If I'm sailing polars, my SOG is irrelevant, and my STW is everything.
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Old 21-09-2010, 15:08   #66
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Holy cow thats one expensive tansducer...

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Old 21-09-2010, 16:21   #67
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Especially so considering the Knotstick gives the exact same information for $49.95 (USD), eh?
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Old 21-09-2010, 16:37   #68
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Especially so considering the Knotstick gives the exact same information for $49.95 (USD), eh?

But given the amount of materials and technology they are both marked up by about the same percentage it seems.

I wonder how either would do with all the floating grass around here. Can't troll at all.
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