Proper RPM by sound?

[George H260]

My 1978 h27 came with the Yanmar SB8 and no tach (or buzzer!) in the A panel. I constanly feel as if I am running at too low a % of power most of the time since at higher RPMs a one-banger gets pretty noisy, and I tend to subconsciously equate high-revvying noise with engine strain. In terms of throttle lever travel, should I not be afraid of pushing the stick well forward?My engine did not have a tach sender option installed. Will an electrical tach wired to the alternator (?) be of good use? And I'll REALLY have to wire-in a buzzer of some sort! A while back, when I really needed to be looking, I didn't notice the water temp light come on until way too late! But, no worries, Torresen (Thanks for all your help Kathleen!) had all the parts and advice I needed, and now I'm back in business. (The upside - after so many months without an engine,I can now fetch a mooring or a slip under sail blindfolded!)

 

[David Foster]

Same question

I've got the same question for my '77 H27.

 

[Gordon Torresen]

SB8 RPM

Your SB8 is rated 8 HP at 3200 RPM or the max. you would ever want to turn it. You'll get 6 HP at 2600 and 5 at 2200. Some where at 2600 or less would be a comfortable, long term, speed. Although I would have to confirm availability, a tach and sender appear to be still obtainable, at a cost of about $350.00. Listening to the sound would be a more economical option. You could obtain a hand held tach (rent, borrow or buy) to get the sound at various speeds. You could correlate those RPM with boat speed for a check. An electric tach is also available and I believe there is an AC output on your alternator to drive it. This would also require the use of an external speed measuring device to get proper calibration. Thank you for the complement. I'll make sure that Kathleen hears about it.

 

[George H260]

SB8 RPM, thanks for your reply, and...

I agree, at $350.00 I'd rather listen!Correlating RPMs (with a handheld tach) to speed through calm water and marking the throttle lever position, along with "memorizing" the pitch of the engine sound, seems the way to go.Once this is done, I could look into a buying an electric tach as I would have a reference point for rough adjustment. It need not be exact, an indication of relative RPM changes would suffice.Could you tell me which terminals I would hook up the portable tach to? Same applies to the electric tach if I get one. (If you happen to know the layout of the stock alternator that came with this engine...)Thanks!