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:
Updated:
Original:

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

Beneyteau-Excess12

Boat Review: Excess 12

Groupe Beneteau, builder of Lagoon catamarans, has introduced a new multihull line called Excess. The first of the boats to reach U.S. shores at the Annapolis boat show was the Excess 12, a 38ft 6in design based on the popular Lagoon 40. The thought process behind this new boat ...read more

Spindriftracing

Extreme Sailing: No Piece of Cake

It can be easy to take for granted the incredible performance of today’s most cutting-edge grand prix racing boats. The latest crop of full-foiling 75ft America’s Cup monohulls, for example, were all up on their foils and even successfully tacking within hours of their first ...read more

Solar-Dinghy-pump-photo

Gear: Solar Powered Dinghy Pump

Tired of forever finding your dinghy or open daysailer filled with water when you arrive to go sailing? For years, sailors and engineers have sought a solution to this seemingly eternal problem, and now it appears the folks at Sea Joule Marine may have finally found it in their ...read more

BestBoatPromo-03

Best Boats 2020

How’s this for a thought experiment: imagine setting a diminutive Tiwal 2 inflatable dinghy alongside a Catalina 545 cruiser? It would be hard to imagine two more different watercraft, and yet they are both still very much sailboats. They are also both winners in this year’s ...read more

Hanse-675

Video Tour: Hanse 675

This past fall at the Annapolis Sailboat show, we had a chance to catch up with Hanse’s  Maxim Neumann, who kindly provided us a tour of the company’s new flagship, the Hanse 675. An impressive, well-built production yacht that boldly ventures into maxi-yacht territory, the ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com Be thrifty with propane  If you like to cook on board, the propane tanks supplied as standard with many modern yachts won’t get you far. Whether we bake bread or not, the one thing we all do is boil ...read more