Skip to main content

Ask Sail: Tachometer Gone Wild

My sailboat is equipped with a Yanmar diesel. Often while motoring, the tachometer suddenly pegs out beyond the highest value. At these times there is no change in the engine itself; it is not racing.

Chris Bosworth, Newport News, VA

A: My sailboat is equipped with a Yanmar diesel. Often while motoring, the tachometer suddenly pegs out beyond the highest value. At these times there is no change in the engine itself; it is not racing. The only solution seems to be to kill the engine and turn the key off. (Simply killing the engine does nothing for the tachometer until the ignition key is turned off.) Might this be an intermittent bad connection? If so, should I look at the engine or behind the instrument panel?

Nigel Calder Replies
A: Yanmar has two types of tachometer: one of them (the GM series, which I suspect is what you have) employs a sensor screwed into the flywheel housing; the other (which is found on most other models) takes information from the alternator. The alternator type senses the frequency of the three-phase output of the alternator before it is rectified to DC current to charge your batteries, and when it fails it will likely default to zero, which is why I think you have the other type. The flywheel type could potentially go to full rpm if shorted. (Full disclosure: I am not entirely certain of this.) According to Yanmar, the most likely problem with this kind of tachometer is the connection plug on the wiring harness, though this doesn’t seem to fit your having to turn off the ignition to reset things. Still, I recommend you check this plug, as it is easy to do. If this doesn’t fix things, find the sensor on the flywheel, unscrew it, clean it and check all the connections and wiring, including those at the gauge end. The following website has some useful information on tachometers and more: yanmarhelp.com/s_tach.htm.

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

Related

thumbnail_Jump-1

The Marblehead-to-Halifax Ocean Race Returns

It’s been four years since racers last sailed the cold North Atlantic in the venerable Marblehead-to-Halifax race—and finally, the wait is over. The Boston Yacht Club and the Royal Nova Scotia Yacht Squadron have announced the 39th Marblehead-to-Halifax Ocean Race set for this ...read more

Wendy-2048px

Meet Wendy Mitman Clarke, Editor-in-Chief of SAIL magazine

Learn more about how she and the magazine’s team are committed to building on SAIL’s legacy of more than 50 years as an authentic voice about the sport and the sailing life, delivering stories that educate, inspire and inform. ...read more

maintenance-02

Cruising: Old Sailors Never Die

“Old sailors never die, they just get a little dinghy.” It may be a hoary old joke, but one of my problems at age 79 is I can no longer get easily in and out of a little dinghy, and neither can my (several years younger than me) wife. For this, and various other reasons I will ...read more

01-LEAD-DSC_0953

The Mighty Compass

Here’s to the humble magnetic compass, without a doubt the sailor’s most reliable instrument onboard. It’s always there for you and with the rarest of exceptions, always operational. Yes, I love my chartplotter, autopilot, radar, and AIS. They help me be a safer and more ...read more

02-En-route-Jost-Van-D

Chartering: Swan Song in the BVI

Joseph Conrad once wrote, “The sea never changes.” And while this may or not be true, something most definitely not open for debate is the fact we sailors, “wrapped in mystery,” as Conrad put it, are continually changing—whether we like it or not. I found myself thinking these ...read more

220307FP51_1JML0332

Boat Review: Fountaine-Pajot Aura 51

If you can sell more than 150 catamarans off-plan before the resin has even hit the fiberglass, you must be doing something right. Despite costing around $1.1 million once fitted out and on the water, Fountaine-Pajot’s new 51 has done just that. The French yard has been at it ...read more

00LEAD-IMG-9035

Ready to Fly a New Sail

It’s a typical humid, southern Chesapeake Bay summer day when I show up on the doorstep of Latell & Ailsworth Sailmakers in the one-stoplight, one-lane-roadway, rural tidewater town of Deltaville, Virginia. I’m late getting here to work on a new jib for my 29-foot, Bill ...read more

m5702_RACE-AREA-6

Dates for the 2024 America’s Cup Announced

Ever since making the controversial decision to hold the next America’s Cup in Barcelona, Spain, instead of in home waters, Defender Emirates Team New Zealand has been hard at work organizing logistics for the event.  The Racing Area for the Challenger Selection Series and the ...read more