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.
Author:
Publish date:

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.

Calder_0

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

Related

01-Opener-P1090199-copy

The Great Schooner Race

I arrived in Rockland, Maine, on an early afternoon in July with a backpack, my camera and little else. Though traveling to an unfamiliar place to race with a crew of strangers has been a common theme in my sailing career, I had no idea what to expect from the massive wood and ...read more

westonsquallpic

Cruising: Camaraderie in the Squall

Darkness had fallen and the howling wind almost drowned out the voices coming over the VHF radio. “Lights on! Blow horns!” “Make noise to alert the crew!” “Shine the spotlight on the cat by the shore, it’s dragging dangerously near our bow.” These were calls to action, not ...read more

Lagoon-50a

Boat Review: Lagoon 50

Anyone under the impression that change in today’s production catamarans is about little more than cosmetics needs to check out the Lagoon 50—an all-new design that went on to become the winner in the 40 to 50ft cruising multihull category in SAIL’s 2019 Best Boats awards. ...read more

shutterstock_543237994

The Slow Route to Cabo

Each November, cruising boats start leaving California for “a winter of fun in the sun down Mexico way.” And having spent the summer and autumn on a leisurely passage down the West Coast on board Distant Drummer, our Liberty 458 sloop, my husband, Neil, and I were now in San ...read more

MHS-GMR_3549

New Multihulls 2018

Farrier F-22 New Zealander Ian Farrier ushered in a new genre of sailing with his folding-ama trailerable trimarans, the best-known of which are the Corsair designs. Farrier’s last project before he passed away last year was this sweet little tri. Available in three versions, ...read more

shutterstock_373701682

Cruising: Island Comeback

The U.S. Virgins Islands have surged back from the devastation of the 2017 hurricanes, with new infrastructure plans that will benefit charterers and cruisers alike. After hurricanes Irma and Maria roared through the Leeward Islands in September 2017, it was impossible to ...read more