[Rhodes22-list] transducer thru-hull

[bgreenwald at optonline.net]

Roger,

Your description of the problem is accurate - the whole thru hull is out of alignment.  Based on your information, I will try to take an acccurate reading of the misalignment and, if, as I suspect it produces immaterial reading errors, I'll just let it go.  Thanks much.  And thanks to everyone else who responded so promptly to both questions.

Bruce Greenwald
S/V Ruach II

----- Original Message -----
From: Roger Pihlaja <cen09402 at centurytel.net>
Date: Sunday, March 28, 2004 4:41 pm
Subject: Re: [Rhodes22-list] transducer thru-hull

> Bruce,
> 
> I have the Autohelm ST-50 tridata system, which is the immediate 
> predecessorto your ST-60 system.  Assuming your ST-60 transducer 
> is like mine; then,
> the thru hull has a key which prevents inserting the transducer 
> out of
> alignment.  When you say your transducer is out of alignment, I 
> presume you
> mean the entire thru hull is installed such that the alignment of 
> the keyed
> transducer is not parallel with the centerline of the boat.  
> Assuming we are
> on the same page, there is no reason why one couldn't unscrew the big
> flanged nut on the thru hull, break the caulk loose, remove the 
> thru hull,
> clean up the old caulk, & reinstall the thru hull in the correct 
> alignment.In the stern area of the hull under the cockpit, there 
> is a nice handy CL
> molded into the hull running from the back of the shoal draft keel
> practically back to the cockpit drain.  A chalkline from the 
> transducer thru
> hull & running parallel to this molded-in CL would ensure transducer
> alignment to less than 1 degree of [Error].  The existing transducer
> misalignment will not affect the water depth or water temperature
> measurements.  However, the knotmeter and knotlog will be off by the
> following amount:
> 
> [Error] = 1 - cos(Theta)
> 
> Where: (Theta) is the misalignment angle in degrees between the 
> boat's C.L.
> & the transducer axis
> 
> For example, suppose (Theta) = 10 degrees:
> 
> [Error] = 1 - cos(10 deg) = 1 - 0.9848 = 0.01519 or about 1.52% low
> 
> Note that this transducer misalignment will always cause the speed &
> distance measurements to be in error on the low side.  I leave it 
> to you to
> decide if 1.5% error is enough to worry about.
> 
> The Seatalk system is Autohelm's proprietary communications bus which
> enables all the instruments connected to the bus to share and 
> display data.
> 
> Hopefully, this helps, Bruce.  Good luck.
> 
> Roger Pihlaja
> S/V Dynamic EQuilibrium
> 
> ----- Original Message -----
> From: <bgreenwald at optonline.net>
> To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> Sent: Sunday, March 28, 2004 1:19 PM
> Subject: [Rhodes22-list] transducer thru-hull
> 
> 
> > Hi all,
> >
> > I have an ST-60 tridata with a thru-hulll speed transducer,
> > installed in the lazarette by GB 2 years ago on my then
> > new 2002.  I have had some troubles since the beginning
> > achieving accurate readings  - I tried various fixes until
> > last summer when the whole thing failed - sent it back to
> > Raymarine for a cable replacement.  In that process, I
> > discovered that the thru-hull is not aligned perfectly with
> > the center line of the boat - its probably off 5-10 degrees
> > fro parallel.  I am curious if this is a material problem in
> > accurately recording speed and, if so, if there is any way
> > to remove the thru-hull and reseat it on the proper line.
> > Any suggestions would be appreciated.  Thanks.
> >
> > Bruce Greenwald
> > S/V Ruach II
> >
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> >
> >
> 
> 
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