Tachometer readings

[swordfisherman]

My tachs seem off. Which should i believe is right?

 

[Fred]

When my previous boat did this, I found the sync gauge to be correct.
Then by previous knowledge of my boat I was able to tell which tach was correct based on boat speed.
Also my tachs were obviously wrong at idle. Moving the switch on the back of the tach fixed the problem.
It was a gas powered boat.

 

[swordfisherman]

Thanks Fred. I will look at the back of my tachs if i could find that switch too. I have diesels.

Ive also read here that sea ray tachs are unreliable

 

[peterkvs]

I'd bet money NONE of them are correct. Before I switched to the Aetna Digital tachs I had no idea what my true rpm was. I would sync by ear, which is very accurate. After installing the digital tachs, which are accurate to less than 1 rpm, I learned that one tach was 50 rpm low and the other was 150 rpm low. Also learned that my sync guage (which is adjustable behind the dash) was off 25 rpm to the Starboard. Surprisingly the Glendenning synchronizer can typically hold the engines within 2-4 rpm when engaged.

Pete

 

[Mike Blake]

I always go by the sync gauge and the speed on the GPS

 

[swordfisherman]

Peter that was your thread i read about. But those tachs are a bit pricey too. So mike, I should follow the sync gauge?
What do you mean by speed on the gps?

 

[peterkvs]

Best thing to do is learn to use your ear. With a bit of practice and close listening you can get the engines within 10 rpm of each other just by listening to the beat frequency of the engines. Or if you really want to know what is going on, then borrow or purchase a photo tach, make some measurements of the actual RPM vs what the gauges say and make a mental note. My experience is that none of the OEM gauges are very accurate, so hard to say which one to trust.

Pete