2012 Hunter 39 Tachometer Issue

[canuck]

We have a Yanmar 3JH5E (40 HP) with a 3 blade prop and have the Electromaax 120 amp upgrade. At 2900 RPM we are only hitting 6 knots. Our bottom is clean. We can hit 7.3 knots but tach shows 3800 rpm. Obviously we cannot cruise at that rpm. I am of the opinion that the tach is calibrated incorrectly and/or the optional alternator is affecting the tach. Has any body experienced similar issues with or without the optional alternator.

Should this engine max out at 3200 rpm with a properly spec'd prop?

Thanks

 

[Don12364]

So easy to check your tachometer with one of these. Just stick a piece of white tape on the rim of your engine pulley and shine the laser of this instrument on to it whilst the engine is running.
RPM accuracy 0.05%

http://www.ebay.com/itm/Digital-Las...696?pt=LH_DefaultDomain_0&hash=item2ec334c3a8

On my 3JH2E my tacho reads 6% too low so when it reads 3,400 the actual engine speed is 3,600 rpm.. On my older engine setup the Yanmar tacho is not digital though
For $12 you will never regret this purchase just for the peace of mind it provides

 

[Hello Below]

This item received some pretty good ratings on Amazon.com. But have some reservations sending any amount of money to someone with "toymodel888" in the email address . . . but did anyway. Thanks for the link.

 

[Marc14857]

Tach Issue

Had what sounds like a similar issue on my H44 with the optional alternator. The tach gets its signal from the alternator and various alternators have a different number of poles which generate pulses read by the tach. You need to set up the tach to match the number of poles. About two years ago I think I posted the VDO instruction sheet on how to accomplish this. Pretty straight forward. It might be in the archives. If not google VDO who made the tach for the Hunter control panel at least the 2005 model year. I would forward it but I don't recall where I stored the instructions..maybe on the boat which is still in hibernation.