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GPS log vers paddle log

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stownsend View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stownsend Quote  Post ReplyReply Direct Link To This Post Topic: GPS log vers paddle log
    Posted: 09 May 2016 at 22:11
Evening, this may be a silly question but here goes...
 
I took the boat out for a blast on Sunday in Cardiff Bay, fresh water barraged bay, minute amount of flow and a mile or so wide by several. My paddle log was out by around 2 knots compared to my gps. Any ideas and can the paddle log be calibrated?
 
Cheers
 
Stu
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Wayne's World View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Wayne's World Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2016 at 08:40
Stu,

I gather your paddle wheel log was around 2 knots slower than your GPS? If this is the case your paddle wheel may have growth on it which is slowing it down. Give it a clean and it should be close to your GPS reading with no current.

If the paddle wheel log is showing 2 knots more than your GPS you can calibrate it via one of your Triton displays -press the arrow key to enter the menu, then select Setup, then select Calibration and you then have two choices to do the calibration.
 
Wayne W
Cruising, currently in the Caribbean and will head across the Pacific early 2024
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stownsend View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stownsend Quote  Post ReplyReply Direct Link To This Post Posted: 11 May 2016 at 07:02
Hi Wayne
 
Thanks for your reply, the log is much slower, when she comes out this year i'll clean it all up underneath.  I've got a Simrad IS15 set so will have a read of the instructions to see if as a temp fix add a couple of knots.
 
Cheers
 
Stu
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bitbaltic Quote  Post ReplyReply Direct Link To This Post Posted: 11 May 2016 at 12:28
I replaced my IS15 with an IS20 (and an airmar transducer) partly for an N2K system upgrade but also partly because the paddlewheel seemed to be chronically under-reading in the bay when compared to SOG. The bay is perfect for calibration so if the wheel is reading slower than the GPS, something is out of spec for sure.

The IS15 should have a calibration factor somewhere. I can't remember what I did when troubleshooting mine- I probably ramped it up to the maximum offset and still couldn't get it to read SOG in the bay, so replaced it. I had the feeling the wheel was worn out.

Alternative possibilities:

Have you recently changed GPS? My present IS20 log is calibrated to my Garmin 128 GPS, but a recently installed Simrad NSS7 sees a SOG 0.1-0.2kn higher than the Garmin. This is so little as to be within the error of the log measurement so I haven't re-calibrated, but if you have changed GPS it could explain sudden differences- but perhaps smaller differences than you are experiencing.

If you have not experienced this lag issue before and it has appeared this season, I would also in the first instance suspect growth- probably just slime in the bay. I've found that I can get at the paddlewheel (more or less) with an ordinary deck brush by leaning off a finger pontoon with the boat brought close alongside. Worth a try? If you are more brave and have the IS15 blanking plug, you could pull the transducer out even when it's in the water (only a cupful or so of water will come in when you do it). Then clean off the slime, spray on a bit of WD40, and replace before trying another calibration run.
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Sea-U View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sea-U Quote  Post ReplyReply Direct Link To This Post Posted: 11 May 2016 at 13:48
My experience with paddlewheels is that they are too narrow.
I had an old Silva log where the paddlewheel was 1.5 cm wide. Worked allways.
Upgraded to Autohelm and problem started. It got stuck and also slowed down quickly. Same with this airmar stuff.
Should probably go for separate for log and echo, and get a transduser with a wide paddlewheel. 


Edited by Sea-U - 11 May 2016 at 13:48
Sea-U is a 370e #532 located SW Norway
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