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Took out our new (to us) Sakonnet with the aforementioned motor and am curious what voltage should I expect - I understand that too low and battery may not be charging - too high and it would be bad for battery.
TIA
Wayne

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A battery at 100% full charge is 12.6 standing voltage (not being charged). I have found that analog style volt meters used in boats typically are up to 1/2 volt off in actual reading. My depth finder seems to be the most accurate for reading voltage when compared to a digital volt/ohms meter. For your engine, which I have one on one of my boats it typically reads 12.9 volts at idle and 13.9-14.2 volts above 3000 rpm's. This is charging voltage, not the actual battery voltage. As I mentioned, the actual battery voltage is measured at rest, accessories off and standing for at least for 1 hour after being charged. I prefer to have them sit overnight after being charged to measure their actual state of condition. One thing I've learned about batteries, when you are buying a replacement make sure you get newest date code/sticker that says when it was manufactured. Ask to have the battery voltage measured and you want to see 12.5-12.6 volts in a new battery. If the battery shows a date sticker over 6 months old, don't buy that battery because as batteries sit, they lose voltage and a lead acid battery sitting for months partially discharged will ruin the battery. I learned this the hard way.

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Thanks fitz for that comprehensive reply. Your reply was just what I was looking for.
My concern is that our new Garmin fish finder was reading 14.5 volts while we were cruising (we don't have a working tach) - I'm a little concerned that this reading may be too high. My ROT for car alternators has always been 13-14.2 volts during driving.
BTW- i am using a relatively new car battery, not a deep cycle or anything special, in the boat - it was handy.
Do you think 14.5 should be of concern?

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Not a major concern, but I would consider it at the high limit of charging voltage, my 60 Merc will occasionally hit 14.5 volts at high RPMs. My twin 115 Mercs on my '73 22-2 Aquasport also run about the same voltage at high speed and settle back down to 12.9-13.2V at idle so there is consistency even in different engines and applications. Check your battery water level after a couple of trips to make sure its above the plates. If your not using a lot of water in the batteries from being overcharged consider everything OK.

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Cool - thanks for your insights!

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Remember that many older motors had no regulation in the charging circuit, so it was common to see voltages well above what would be considered normal in a car, for example. If memory serves, my old 1989 Johnson 70 would show north of 16V at high speed, once the battery was fully charged. It only put out 6 watts total, so that did no harm to the battery, but I can well imagine newer electronics might not be happy. I did buy an external regulator before installing a GPS, but then ended up replacing the motor before I ever used it.

So in general, I would not sweat the readings you're seeing, but you might want to check the motor specs to be on the safe side.

Tim

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These engines are regulated 16 amp stators.

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In that case, I'd echo the previous poster - the voltage is a little high; not a major concern at 16A, but check the water level from time to time just to be on safe side.

Tim