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Old 27-02-2012, 15:58   #1
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How Necessary is a Knot Meter ?

I'm sick of knot meters...I truly am! Half the time they never work due to the paddle fouling and their accuracy is terrible. Everyone I have ever had would be accurate at lets say 4 kts. But above it...say 5.5 kts, the boat would actually be doing 6.1 and when it read 1.5kts, I would really be doing .7kts.
It seems to me and I want to do this, that on my next haul-out, I will F/G over the hole and just use my GPS. Every watch, the speed and distance is entered in the log anyways and gives the data I need (Furuno GP30). How do others feel about this?
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Old 27-02-2012, 16:03   #2
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Re: How Necessary is a knot meter

what kinds of knot meter did you have?
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Old 27-02-2012, 16:10   #3
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Re: How Necessary is a knot meter

Not (had to say it).

I had one on my last boat; I stopped fixing it when I got GPS.

I have one on this boat. I keep the plug in, for the same reason.

Someone will argue they need speed-through-water to get apparent wind (though really, speed over ground may be more to the point). Some of the errors you see may actually be tide--that is one use--but only if it is quite accurate.

For most of us... forget about it.
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Old 27-02-2012, 16:11   #4
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Re: How Necessary is a knot meter

Don't leave it in the water. I have a paddle wheel type that goes through a thru-hull with a sort of flapper valve in it. I can remove it from within the boat (its in a settee locker) and clean it, or just leave it out of the water when not using it. I have a flat plug I screw back in its place. Easy peasy.

I should also mention that I mostly use it in marinas when approaching the dock - largely because after going fast for awhile my sense of speed gets off and the difference between an approach at 2 kts and 1 kt is really huge for me.
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Old 27-02-2012, 16:16   #5
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Re: How Necessary is a knot meter

I'd say it's useful but hardly necessary. Since it measures speed relative to the water, together with GPS it allows you to calculate the current set and drift. It's easier if it's a part of an integrated system that can do it automatically. Also, it's an independent measurement of speed and distance, so if GPS get wiped out by a solar flare (fairly unlikely) and you have a compass (highly recommended), you will still have a means of determining your dead reckoning position.

I pull mine out whenever I leave the boat on a mooring for a week or longer, and also paint it with transucer antifouling paint. That seems to control fouling to a tolerable level.
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Old 27-02-2012, 16:24   #6
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Re: How Necessary is a knot meter

If you like sailing to polars, a knot log is indispensable.

When working to weather, I will often dictate a STW for the person at my helm rather than a course. In other words, I might say, "Keep the boat at six knots." If they end up going faster than the ideal speed, I want them to sail higher. IF they end up sailing slower than the ideal speed, I want them to fall off.

This is a great way to get a rookie helmsperson to sail a higher VMG. But in a high-current area like SF Bay, it only works with a knotlog.
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Old 27-02-2012, 16:26   #7
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Re: How Necessary is a knot meter

I've never been able to keep one working more than a few days before something fouls it, and besides for cruising purposes the GPS speed is all you really need. Actually, if I've owned the same boat for awhile I find that my guestimate of speed is pretty close based on feel, wind speed, wake, etc.
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Old 27-02-2012, 16:30   #8
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Re: How Necessary is a knot meter

If you have a functional GPS you really don't need the knot meter except maybe in racing. I use an old taffrail log on occasion, but even a wooden triangle and a long length of appropriately knotted cord and stop watch would suffice for average cruising. On the other hand, if you have a systems failure, and are relying on DR, then knowing your speed is essential and a good functional knot meter or patent log would be just the ticket.
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Old 27-02-2012, 16:37   #9
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Re: How Necessary is a knot meter

I guess if you are the racer/ex-racer type like Bash you like your knotmeter.

On my first boat I never even put the paddle in the 2 years I had it and just left the plug in. My current boat the knotmeter worked for the first 2 months till it clogged up. But it always read low and I don't even think it is aligned correctly. When it clogged I never bothered to pull it and clean it and just use my GPS.

I guess the usefulness of the thing just depends on the way you like to operate your boat.

I wonder if you can coat the paddle wheel with something like propspeed etc?
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Old 27-02-2012, 16:52   #10
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Pulling the plug and putting the log in the water is just part of my get ready routine. Like switching on batteries, removing mainsail cover etc. it's a one monute job.

Leaving it in the water never worked out for me. 10 minutes to clean it after a week in the water.

It's not a necessity but for the reasons Bash stated and more it is a good tool to have on the boat. Especially in light airs and high current.
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Old 27-02-2012, 17:47   #11
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Re: How Necessary is a knot meter

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Pulling the plug and putting the log in the water is just part of my get ready routine. Like switching on batteries, removing mainsail cover etc. it's a one monute job.

Leaving it in the water never worked out for me. 10 minutes to clean it after a week in the water.

It's not a necessity but for the reasons Bash stated and more it is a good tool to have on the boat. Especially in light airs and high current.
I do the same thing. They're so easy to clean. 14 years on the same knotmeter. Had to replace the paddle wheel section once a while back though as it broke off from the upper part.
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Old 27-02-2012, 17:47   #12
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Re: How Necessary is a knot meter

If your GPS goes tits up, how are you going to DR without some idea how far and how fast you are going. To me, it's as important as a depth sounder for a back up should the real world ever intrude on my life. It's also invaluable in experimenting with trimming the sails and optimizing boat performance. The knotmeter reacts instantly while the GPS is a lagging instrument and next to worthless for that.

I've got a Raymarine ST60 and it's dead on accurate as long as I pull the paddlewheel when I'm done sailing. It's never fouled underway and has been underway for nearly a month at one time. Set it up against my Walker log. Once it was dialed in it's never varied more than a few tenths of a mile over a days run compared to the Walker.

Besides it was a hell of a lot of fun to watch it hit 9.1 knots sliding downwind in the trades.
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Old 27-02-2012, 17:49   #13
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Re: How Necessary is a knot meter

I'm a minimalist and do not find many instruments indispensable ,but most of us want to sail well and I find the speed log is the best instrument for any who want to get the best out of their sail trim and craft.
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Old 27-02-2012, 17:57   #14
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Re: How Necessary is a knot meter

[QUOTE=AuroraGH;897011]Don't leave it in the water. I have a paddle wheel type that goes through a thru-hull with a sort of flapper valve in it. I can remove it from within the boat (its in a settee locker) and clean it, or just leave it out of the water when not using it. I have a flat plug I screw back in its place. Easy peasy.
QUOTE]


We sail Lake Michigan. There is no fouling all season and it reads fast or slow depending on point of sail and speed. I don't even clean it when we haul out. It is only an instantaneous indicator of betterer or worser. There is so much turbulance and other hull effects that it is pretty much worthless except for amusement.
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Old 27-02-2012, 19:44   #15
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Re: How Necessary is a knot meter

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It's also invaluable in experimenting with trimming the sails and optimizing boat performance. The knotmeter reacts instantly while the GPS is a lagging instrument and next to worthless for that.
+1. I don't have a chartplotter but use a handheld GPS and a puck. Maybe these are not as accurate, but it drives me nuts watching the speed jump from 4.5 to 6.3 knots and back again when the boat has not changed speed. All the while my 30 year old knotmeter registers a steady 5.1 knots. On the other hand, my fastest speed to date on my Catalina 30 was 18.3 knots in 10 knots of wind as measured by my GPS.

Without the knotmeter it would be impossible to tell if my barberhauler did any good. As far as fouling, if it's not spinning I just look for a good patch of kelp. Gets the wheel spinning and takes the algae off the bottom on that side.
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