Ask SAIL: Paddlewheel Knot Log Problems

I'm trying to figure out why my paddlewheel knot log is registering incorrectly. The plug is clean, and the wheel turns freely. Yesterday my GPS showed my speed over the ground was 5 to 7 knots, and the speedo registered 0 to 0.8 knot. It does this periodically to irritate me.  
Author:
Publish date:

Ben Wilcox of Naples, Florida asks:

I'm trying to figure out why my paddlewheel knot log is registering incorrectly. The plug is clean, and the wheel turns freely. Yesterday my GPS showed my speed over the ground was 5 to 7 knots, and the speedo registered 0 to 0.8 knot. It does this periodically to irritate me.

Don Casey replies: 

Generally when a knot-log display under-registers or reads 0.0, the problem is with the transducer or its cable. If it works fine sometimes, fouling is likely your problem. You can test the transducer out of its through-hull housing by watching the display as you spin the paddlewheel in the air. It should spin easily and smoothly. To thoroughly clean it, push the axle pin out with a stiff wire to release the paddlewheel. Be sure to note which way the paddles face. Polish the axle and the sides of the wheel with a Scotchbrite pad.

DonCasey_1

If you still have problems, try resetting the unit to the factory settings. Your manual will show you how to do that. You’ll have to recalibrate the unit afterward, but resetting can clear up electronic glitches. If the unit continues to show 0.0 or some ridiculously low value, the transducer may be defective. You can do a rough check by turning off the unit and disconnecting the screen and the green conductors from the head. Use a multimeter to measure continuity between these two conductors while you turn the paddlewheel. A good transducer will show the circuit opening and closing with each quarter turn of the wheel. 

Got a question for our experts? Send it to sailmail@sailmagazine.com

Related

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com No chafe, safe stay  If you’re leaving the boat unattended for a longish period, there’s a lot to be said for cow-hitching the shorelines, as this sailor did. They’ll never let go, and so long as the ...read more

belize600x

Charter Special: Belize

It would be hard to imagine a more secure spot than the Sunsail base on the outskirts of the beachside community of Placencia, Belize. The entire marina is protected by a robust seawall with a channel scarcely a few boatlengths across. It’s also located far enough up Placencia ...read more

DSC00247

DIY: a Top-to-Bottom Refit

I found my sailing “dream boat” in the spring of 1979 while racing on Lake St. Clair in Michigan. Everyone had heard about the hot new boat in town, and we were anxiously awaiting the appearance of this new Pearson 40. She made it to the starting line just before the race ...read more

01-oysteryachts-regattas-loropiana2016_063

Light-air Sails and How to Handle Them

In the second of a two-part series on light-air sails, Rupert Holmes looks at how today’s furling gear has revolutionized sail handling off the wind. Read part 1 here. It’s easy to look at long-distance racing yachts of 60ft and above with multiple downwind sails set on roller ...read more

HanseCharles

Video Tour: Hanse 348

“It’s a smaller-size Hanse cruiser, but with some big-boat features,” says SAIL’s Cruising Editor, Charles J. Doane. At last fall’s Annapolis Boat Show, Doane had a chance to take a close look at the new Hanse 348. Some of the boat’s highlights include under-deck galleries for ...read more

amalfitown

Charter Destination: Amalfi Coast

Prego! Weeks after returning from our Italian flotilla trip last summer, I was still feeling the relaxed atmosphere of the Amalfi Coast. It’s a Mediterranean paradise, with crystal-clear waters, charming hillside towns and cliffside villages, plenty of delicious food and wine, ...read more

image005

Inside or Outside When Sailing the ICW

Last April, my wife, Marjorie, and I decided to take our Tartan 4100, Meri, north to Maryland from her winter home in Hobe Sound, Florida. This, in turn, meant deciding whether to stay in the “Ditch” for the duration or go offshore part of the way. Although we had both been ...read more

MK1_30542

SailGP: There’s a New Sailing Series in Town

San Francisco was the venue of the biggest come-from-behind victory in the history of the America’s Cup when Oracle Team USA beat Emirates Team New Zealand in 2013, so it seems only fitting that the first American round of Larry Ellison’s new SailGP pro sailing series will be ...read more