Two vs. Three Bladed Prop
Sister Ships
The two bladed prop's, boat speed was derived from Garmin GPS - 12.
The engine RPM was obtained from a Tiny-Tach     
with a 6mm sending unit on the #1 injector line.

The three bladed prop's, boat speed was derived from a GPS and verified by timing between marks.  The engine speed was derived by monitoring the prop coupling RPM with a hand held optical tachometer similar to the Cen-Tech unit.  The tach numbers were then multiplied by 2.14 to derive the engine RPM.

All work was done in calm waters with no wind.  Note that just one foot waves can decrease top speed by 0.3 Knots. 
Tach is velcroed
to the instrument
panel when
needed for now
The 6mm transducer is
attached to first injector line.
Used Olympus, Camidia 
D340 R with 1.3 Megapixels
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Engine Temperature
Boat Speed
This page was last updated on: July 7, 2016
Created  September 15, 2002
zeroed on Oct. 5, 02'
Nicer looking digital tachs with greater precision are available from Aetna Engineering in Grand Rapids, MI