If your boat engine is a 4 stroke type using a standard ignition
configuration, an automotive electronic tach should work. Take care that the
automotive type may not be as water and weather resistant as the boat type.
It also may not be as heavy duty for taking the waves and bumps that you
will get in a boat, therefore the readings may not be as stable. There is a
very good reason for the big price difference.

If you check out the tachs used for competition vehicles, you will see tachs
going in to the many hundreds of dollars. These will not be water resistant,
but will be very accurate and stable with hard use. There is good reason for
the price difference.

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Greetings,

Jerry Greenberg GLG Technologies GLG
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WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
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"RB" wrote in message
. ..
My boat tach just quit. I have a 115hp Johnson '77. An OEM replacement
goes for about $130.

There are automotive units commonly available for down around $30, and I'd
love to be able to use one of these el cheapos if it will work.

Most auto tachs have a switch on them for selecting 4/6/8 cyl use. I think
putting the switch on the 8cyl setting (4 cycle, of course) would cause the
scale to read right for my 4 cyl 2 cycle boat engine.

Both tachs seem to be triggered by a 12v pulse from the electrical system.

If I'm right on the above, then it seems I can get away with using the
automotive tach. Thoughts/comments...