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:
Updated:
Original:

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

grenadapromo_0

A Grand Grenada Charter

I have often sailed in the swath of more accessible West Indian islands that lie between Antigua and Puerto Rico. But I had never before cruised around any of the islands south of Antigua, so I jumped at the chance last April to step aboard a Lagoon 380 catamaran from Horizon ...read more

SunFast-600x

Video tour: Jeanneau Sun Fast 3300

Jeanneau America's Mike Coe takes SAIL aboard the brand new Sun Fast 3300 for an exclusive tour. This mid-sized stripped-down racing boat has a perfect balance of amenities and weight-saving simplicity to make it a blast to sail. Though it boasts sleeping space for up to six, ...read more

furlex2

Know-how: Installing an Electric Furler

Push-Button Reefing Boats have never been easier to sail, and yet, designers and builders still strive for that extra iota or two of convenience. A case in point is the growing acceptance of powered headsail furlers. Roller-furling headsails are ubiquitous not only on cruising ...read more

New-Lead

Know-how: Modify a Blackwater System

My dissatisfaction with the head and holding tank plumbing arrangement on our 1987 Sabre 38 had grown as we cruised the boat away from the comforts of a marina for longer periods of time. When we are tied up at a marina, the use of regular bathrooms generally trumps the ...read more

01-LEAD-Suzuki-55f19d31e297c

Choosing the Right Outboard

Two of the most indispensable items on board a cruising yacht are a dinghy and an outboard motor. At anchor or on a buoy, of course, they are your only means of getting ashore. They also have a thousand other uses. For example, they can allow you to motor across to friends’ ...read more

2019-giftGuide

2019 Holiday Gift Guide

Sailing America Rizzoli International Publications has released this striking portrait of American sailing by nautical photography legend Onne van der Wal just in time for the holidays. Featuring 200 stunning photographs spanning the length and breadth of the sailing scene—from ...read more

01-Sailing-La-Vagabonde,-Outremer-48

Cruising: the Vagabonde Life

Once upon a time conquering your dream of sailing off into the sunset was enough, but these days it seems like you have to be popular on social media too. Balancing the stresses of sailing around the world while keeping a successful—not to mention financially lucrative—social ...read more

191114

Video: 11th Hour Racing Arrives in Brazil

Team 11th Hour Racing finished in fourth place this past week among the 29 IMOCA 60s competing in the 4,335-mile doublehanded Transat Jacques Vabre race from Le Havre, France, to Salvador de Bahia, Brazil. Aboard were American Charlie Enright and French sailor Pascal Bidégorry, ...read more