Originally Posted by raymond.goff
Hi all. I only have about 10 hours on my new to me 78 Marin Trader 34. I am still trying to find the "sweet" spot for cruising RPMs. So any advise for that one.
But main question for this post: I noticed my upper helm gauge is showing 200 Rpm more than lower gauge. They both "stick" a bit upon start up as well. Before I start chasing down wiring etc. I wanted to see if others have had similar experiences.
Not sure if original gauges, but the look like they maybe.
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1978 Marine Trader 34
don't know why but it seems to be very common that lower and upper tachs differ.
When purchased our AMS we noticed that the upper reading is in the range of only 75-80% of the reading at the lower helm. At the end I checked both by a stroboscopic measurement of the real engines rpm and found that the lower tach shows 115% and the upper tach 90% of the engine rpm, so both are somehow misleading.
Signals come from the alternators, not from the mechanical tachometer adopter as on our previous boat. Was unsure whether the readings at constant engine rpm will change with the load condition of the batteries but couldn't measure any significant changes during some random checks.
Instead of an calibration of the tachs (don't know if it is even possible) I just prepared two tables "translating" the readings to engines rpm, one for the lower and one for the upper helm. Works fine ...
We prefer to run our twin FL120 in a range of 1300-1750 rpm.
And yes, the above given figures of reading differences are average values of starboard and port engines, there is also a deviation between both sides ...
best regards / med venlig hilsen