Accurate Digital Tachometer

rengnath

Cadet
Joined
Feb 15, 2015
Messages
20
Hello,

I'm having a hard time finding a digital tachometer with good reviews for my boat. Long story short, I have a Mercruiser 3.0 with a carb that I troll with. We needed the ability to make fine adjustments to adjust our speed down to a tenth of a mile. We have successfully rigged up a servo to the carb linkage to adjust RPMs by 30 revs or less verified by a timing light/shop tach. We were never able to make these types of fine throttle adjustments with the throttle lever. The biggest issue is we can't hear the change in RPM's since the adjustments are so fine. The Faria tachometer on the dash is already inaccurate and no differences are shown there either.

I'm looking for a digital tachometer that I can permanently install that has an accuracy of +- 10 RPM. I found some cheap ones on Amazon, with less than perfect reviews. I have also found a waterproof tachometer by Longacre (52-46863) for about $150, but there are limited reviews on the unit. My other option is to install a Actisense EMU-1 to convert analog signals to NMEA 2000 to display on my Raymarine Axioms, but that is a $600 investment and seems a little excessive for my purposes.

That being said, can anyone recommend a dependable digital tachometer that reads within +- 10 RPM that will work with a 4 cylinder 4 stroke (2 PPM)?
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Tiny tach are the go to brand for this. Widely used on jet skis to accurately tell rpm. Very simple to install too.
 

GA_Boater

Honorary Moderator Emeritus
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May 24, 2011
Messages
49,038
You need to look at the speedo or GPS to measure speed, not a tach. A tenth of a MPH could be a 30 or 300 RPM change due to wind, water condition, currents, number of folks in the boat, how much gas is left, catching some big fish, how much beer is left, etc.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
If still want to go for any of both reputed induction tachs :.

Hardline Pros : meets the +,- 10 rpm request, doesn't need a ground wire to read rpm accurately, can replace the internal battery when shot, the pick up signal cable can be trimmed to required size if with excessive cable leftover after installing meter to plug wire.

TT Cons : Isn't known if meets the +,-10 rpm request, requires a ground cable to read rpm accurately which will eventually break with prolongued motor vibration, that's from personal experience in outboard installations. Pick up cable is fixed, can't be trimmed without modification, battery case is sealed.

Happy Boating
 

Bondo

Moderator
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Apr 17, 2002
Messages
70,468
You need to look at the speedo or GPS to measure speed, not a tach. A tenth of a MPH could be a 30 or 300 RPM change due to wind, water condition, currents, number of folks in the boat, how much gas is left, catching some big fish, how much beer is left, etc.

Ayuh,..... Having trolled for 1,000s of hours, for various species, I find it hard to believe such a finite throttle control to be necessary, for the various reasons stated above,.....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
Messages
47,306
The 3.0 changes +/- 30 rpm on its own.

Trying to control the throttle, especially on a 3 liter that tight is a fools errand
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Surely you'd just use a GPS to verify your boat speed remains at the set point. A tacho is just a display of the rpm to get you at that speed. It's Knots you're interested in, not rpm.

And I have to ask, what are you doing that requires such fine speed control? When I troll, for fish, about 1400rpm gives me ABOUT 6 knots, and that works just perfectly. I control the throttle by hand, but I make adjustments based on boat speed, not engine speed... Boat too slow, more throttle, boat speed too fast, less throttle. I don't care about the engine speed, just the boat speed.

And if your servo is doing the job based on boat speed, a tacho accurate to +/-10rpm is a bit pointless.

Chris......
 

Bondo

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Apr 17, 2002
Messages
70,468
When I troll, for fish, about 1400rpm gives me ABOUT 6 knots, and that works just perfectly.

Ayuh,.... Trollin' for walleyes, we run 1 mph to 'bout 1.5 mph,.....

At idle, I toss a drift sock over each side, 'n put my over-sized Bennett trim tabs full down,.....

That gives me 'bout 3/4 mph, 'n I bump the throttle from there,.......

There's still always variation in the speed caused by climbin', 'n fallin' off the waves,.....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,306
I prefer pan-fried moments after filleting. Not deep fried.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Superb...if you like your fish beer battered and deep fried. Otherwise, not so good....lol

I’ll stick with fresh Tuna, Striper, Flounder and Mahi

Ohhhh, a man after my own heart. Fresh Mahi-mahi, very little can top that. We're right in the Mahi-mahi season now, and we're not allowed to go fishing. :mad:
 
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