knot meter reads slow - SailNet Community
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post #1 of 13 Old 06-05-2008 Thread Starter
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knot meter reads slow

I finally located the speed transducer. It had been removed from the hull and plugged.

I installed it and took the boat out for a test.

It seems to read about half speed. I can't be precise because my GPS wasn't working but I know what six knots looks and feels like on this boat.

The most I got out of it was 3.4

I figured it might be in backwards or sideways.

I checked more closely. the transduced will fit snugley and not leak no matter which way you stick it in but there is a slot in which it seats a little further down and the wheel is parralel to the boat in that position.

I don't have the manual for the ST50 /ST4000 stuff.

In over my head?
First Boat, a well-equipped 1977 Camper Nicholson 31
What is all this stuff and how does it work?
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post #2 of 13 Old 06-05-2008
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Two things,

It may be in backwards, there is a little arrow molded in the top transducer that should point forward (front of the boat).

Lubrication, try plummer's grease.
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post #3 of 13 Old 06-05-2008 Thread Starter
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I tried it in several positions, backwards and frontwards.

The wheel spins freely- i mean, you can flick it with your finger and it will spin for a few seconds.

thanks

In over my head?
First Boat, a well-equipped 1977 Camper Nicholson 31
What is all this stuff and how does it work?
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post #4 of 13 Old 06-05-2008
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You may need to calibrate the unit. see attached link

Raymarine Marine Electronics - Retired ST50 Manuals

Raymarine has the ST50 manuals on line.

I have the ST60 and had to calibrate once I installed the unit.

Best of luck,

Patrick

S/V "Fat-Kat"
C&C 32, Hull #237
Mt. Hope Bay
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post #5 of 13 Old 06-05-2008
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Could also be you were surfing with the current. If so then your SOG, if reported by the inopperable GPS, would be higher than your speed over water, as reported by the speed transducer.

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sold the Nauticat
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post #6 of 13 Old 06-05-2008
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I'd recommend reading the manual and going through the calibration procedure. I think Gui has done this to make sure his knotmeter is about 30% fast.

Be aware that when checking your knotmeter against SOG on a GPS, the GPS will not be affected by any currents, where the knotmeter will be.

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post #7 of 13 Old 06-05-2008
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Heck, when my nephew comes down to sail with me, I adjust the calibration factor all the way up. Then when we get back to the mooring, I reset it back to 1.4 so it reads correctly. He always would complain we are going too slow, he is used to being 6 inches off the water and not four feet, totally Different feel of speed. It stopped the complaints, and the wife and myself get a laugh out of it.

Patrick

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post #8 of 13 Old 06-05-2008
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Have you tried the Evelyn Woods Speed Reading Course? Helps everyone/thing read faster

It's probably calibration, might be fouled already (mine fouls in less than a week), and might be needing some lube.
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post #9 of 13 Old 06-05-2008
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We'll have to remember this when viewing any videos you post.

One downside of owning and sailing a multihull is people often don't realize just how fast you're going... Doing 12 knots on a monohull, unless it is a really big bastage, is going to have the sails all loaded up, and the boat heeled over, and the rigging making all sorts of noise... on my boat, we can do twelve knots with just the genny up... and it doesn't heel way over... and it's actually pretty quiet relative to a monohull...so it can be very deceptive. We don't have to have rail meat hiked out over the high side...

See the video located here—click on the video link at the top of the page, or see this video to get an idea of what I'm talking about.




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Originally Posted by pfatyol View Post
Heck, when my nephew comes down to sail with me, I adjust the calibration factor all the way up. Then when we get back to the mooring, I reset it back to 1.4 so it reads correctly. He always would complain we are going too slow, he is used to being 6 inches off the water and not four feet, totally Different feel of speed. It stopped the complaints, and the wife and myself get a laugh out of it.

Sailingdog

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a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Last edited by sailingdog; 06-05-2008 at 08:24 AM.
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post #10 of 13 Old 06-05-2008
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Hi
This might help, there are different paddle wheels and some have one, two, or four magnets in them.
Is the boat new to you? Has some one fitted an incorrect paddle wheel in the past?
The calibration will only give you a certain %age of adjustment.
Check you have the correct paddle well for the transducer.
Good luck
Michael
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