[C320-list] Speed log problems

[Graeme Clark]

Warren

Good question! I guess my main reason is that we have a high tidal range in Falmouth (up to 15ft or more) and as you might imagine that can generate some 'interesting' tidal currents. In order to work out the current our chart plotter needs an accurate speed through the water (although I guess what it actually woks out is the combined effect of current and leeway?)
However we can look at current predictions from the charts or the plotter, so that is not essential; although I don't race, on longer passages and beats upwind, I do end up tweaking  and adjusting this and that trying to get a better hull speed and SOG isn't quite the same. However I agree it is not worth spending a lot of money on!

The idea of a quick underwater localised scrub to see if that restores the reading (i.e. if it is hull fouling) is a great idea -  shame that the water here is only about 55F, but I'll manage somehow!

Graeme

> 
> 
> Message: 3
> Date: Thu, 4 Jul 2013 14:35:53 -0400
> From: Warren Updike <wupdike at hotmail.com>
> To: <C320-List at Catalina320.com>
> Subject: Re: [C320-list] Speed log problems
> Message-ID: <BAY156-DS20B52AF312143CB47EC6EDBE7C0 at phx.gbl>
> Content-Type: text/plain; charset="us-ascii"
> 
> Graeme, why do you need it?  Racing maybe?  I gave up on mine: a pain to
> insert and remove, and would readily be clogged with critters.  Now, I rely
> solely on SOG from GPS.  Yes, I don't get true wind; but, then I've never
> had it (different story.)  If you really want/need true wind, for about $100
> you can get a device that will use SOG and output STW on Sea Talk and forget
> the headache with the transducer.  If interested, let me know and I'll dig
> up the product info.
> 
> Warren & Pattie Updike
> 1994 C320 #62 "Warr De Mar"
> 
> -----Original Message-----
> From: Graeme Clark [mailto:cg at skyflyer.co.uk] 
> Sent: Thursday, July 04, 2013 5:37 AM
> To: c320-list at lists.catalina320.com
> Subject: [C320-list] Speed log problems
> 
> Our original fitted instrumentation (#303, 1996) was ray marine ST50+
> Tridata and two years ago we fitted a replacement Ray transducer
> paddlewheel. This is located directly beneath the two smaller drawers in the
> forepeak cabin, pretty much on the centreline, with the depth transducer
> next to it.
> 
> I am having a real problem calibrating the instrument. earlier in the year
> we set a calibration factor of around 0.80 and now it has had to be change
> to 2.00 to get anywhere near a sensible reading.
> 
> I regularly withdraw the transducer and clean it for any fouling and other
> marine life and even pushed out the axle pin, to enable a really thorough
> cleaning and gave everything a squirt of silicone spray lubricant before
> reassembly, but still the calibration changes
> 
> I can only come up with two theories: (1) the instrument or transducer is
> faulty or (2) other fouling and marine growth on the hull in front of the
> transducer is affecting the water flow over the paddle wheel as the season
> progresses.
> 
> I'd be grateful for any other suggestions and also for an efficient way to
> trouble shoot without simply replacing every single item piece by piece!  I
> guess a haul out and scrub would initially show whether the hull fouling was
> a factor, but (where I am) that is the bets part of $500. A new transducer
> is about the same and a replacement  instrument (ST60+ is nearest available
> type that is compatible) would be $3-400 I think. If I end up doing all
> three that is and expensive trouble shooting exercise!
> 
> Graeme
> (Simia, #303, Falmouth, England)
> 
>