Updated:
Original:

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:

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.

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

03-IMG_0590

Bill Tilman’s Simple Sailing

Like an ostrich on a bad day, I’m head-down in the lazarette of Nellie, my Beneteau First 42, dealing with the propane tank. My wife taps me on the shoulder, and I rise to see a pair of foiling catamarans accelerating onto their carbon-fiber wings. As the blood drains from my ...read more

01-LEAD-210801_PM_Tokyo20_22825_5540

Olympic Sailing: Where to Now?

It’s official, not only is the United States no longer an Olympic power when it comes to sailing, it’s fast beginnings look like an also-ran—albeit an also-ran with loads of potential. What other conclusion is there to draw from the fact that for the second time in three ...read more

244526945_394104495768313_1401658800642145082_n

Return of the Annapolis Boat Show

After a hiatus in 2020, the United States Boat Show in Annapolis, Maryland returned in full force last weekend. “Pent up demand” was the name of the game for visitors and exhibitors alike. Queues to get in each morning stretched around the block, and the docks were congested ...read more

Untitled-1

Sailing Hall of Fame Inducts Class of 2021

This weekend, the National Sailing Hall of Fame has inducted eleven new members to make up the class of 2021. “The remarkable achievements of this year’s class exemplify excellence and an unwavering dedication to our sport,” said National Sailing Hall of Fame president Gus ...read more

ed3b8ae9-b65d-2941-47ec-cd0277bfcbe8

Mirabaud Voting Open to the Public

Photos from the industry's top photographers are in, and the 12th annual Mirabaud Yacht Racing Image competition is underway. An international panel of judges has selected this year's 80 finalists, which have been published online. The panel will also select the winner of the ...read more

P1320232-copy

Annapolis’ Boat Show is Back

After a year off in 2020, the United States Boat Show in Annapolis is back. From the diminutive Areys Pond Cat 14 XFC to the massive Lagoon Sixty 5, many of the SAIL’s 2022 Best Boats Nominees are on display for the public to get a firsthand look at, and SAIL’s Best Boats panel ...read more

05-Squall-in-the-ITCZ

Close-Hauled to Hawaii

The saying “Nothing goes to windward like a 747,” is one of my favorites. I actually once took a 747 upwind, retracing my earlier downwind sailing route across the Pacific. I’ve also done a fair bit of ocean sailing to windward. The 747 was a lot more comfortable. But then ...read more

01-LEAD-IMG-2106

Refurbishing Shirley Rose: Part 3

If you missed the first installment, click here. The hull and deck of Shirley Rose had been repaired, but what kind of sailboat would she be without a sturdy rig? I was told she was ready to sail, and that the owner replaced the standing rigging a few years before. Shirley Rose ...read more