[C38] Knot meter location

S Orton ssorton at hotmail.com
Fri Jan 14 18:05:50 EST 2011


Chuck,  I have Raymarine (about 10 years old) and it still works fine.  It comes with a screw in plug, with o-rings, which I use when ever tied up for long periods.  The kit comes with a finger nail bottle of instrument antifouling paint.  Following instructions, the paddle wheel remain free to this day.
Cheers, Steve O 


Date: Fri, 14 Jan 2011 11:34:09 -0500
From: charles at finn.ws
To: listserve at catalina38.org
Subject: Re: [C38] Knot meter location


I will be installing my third version of the knotmeter early this spring.  When I upgraded last time to Navman, I could not get the original (flush mount) paddle wheel out.  It seemed to be almost welded in and I gave up after heating and hydraulic force wouldn't budge it.  Plus, the Signet hole was larger than the Navman.   I am currently installing Raymarine which of course is a different hole size (larger).   My research at the time was extensive, but came down to essentially two observations.  First was that the paddlewheel should be located where there is as little laminar flow disruption as possible.  Generally this is as far away from your bow waterline as you can get, but not so far back as to be disrupted by the pressure wave generated by the keel, which is rather small and angled due to the raked design of our keel.  Second is the preferred location is on the centerline of the boat, but varying a bit to either side does not make much difference.  So, I think your boatyard probably made the right call regarding location although I would have a real problem with them varying from explicit instructions! 

I have to admit that I probably keep installing a knot meter more out of sentiment and for emergency purposes than usefulness these days (I still have a lead-line on board and actually do use it).  Frankly, it was quite disappointing ten years back when I first got GPS to discover how variable the readings are based upon boat speed, slime, etc.   My chart plotter is so much more accurate regarding VMG, SOG, etc. that I seldom refer to the knotmeter other than to get excited when we are flying because it invariably reads faster than we are really going.  But for the moment, what's the harm in believing you are doing 13 knots!  I do agree with Tom's point regarding tides and this can be important at times, but I tune with my chartplotter.

Chuck Finn
Mighty Quinn #114 (1981, with the knot meter just aft of the water tank right inside the access door on the vee berth)

On 1/13/2011 10:46 PM, Steve Smolinske wrote: 

Does anyone have any knowledge on the location of the knot meter on the centerline?  Peregrine is in the yard having mushroom mounts removed and replaced with flush mounts.  I instructed in writing to the yard along with a photo to place the knot meter on centerline 33% of the distance from the keel to the waterline entry point.  They have placed it 1' in front of the keel and stated that is the perfect location and any further forward it will be subject to disturbance from the bow wave.  (yes they went ahead without contacting me first)   We are going to talk about it tomorrow morning and Im hoping someone has some definitive information I can use. Grrrr  Thanks
 
Steve
#312 Peregrine
Seattle
  
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