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PROPELLER TUNE-UP BRINGS BIG IMPROVEMENT
By Robert Hale
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While the boat was hauled out last fall we had Kruger & Sons, in Seattle, check the props for balance and consistency of pitch. The props checked okay, but naturally they could be made better. Kruger's MRI (Measurement Recording Instrument) showed that the blades varied considerably in pitch and other measurements. Ron Kruger told me that bringing the props to ISO Class I (high accuracy) standard from ISO Class III (wide tolerances) standard would result in more top speed, greater fuel efficiency at cruise, and noticeably smoother running.
I had heard the same statements from Jon Hall, at Premier Propellers in Bremerton. Premier Propellers has similar measuring equipment, and, like Kruger, a list of positive comments from happy customers.
Persuaded but skeptical, I told Kruger to bring the props to Class I standards. Each year we try to add something to make the boat better. For the 2000 season we added the engine synchronizer. For 2001 it would be the propeller work. This was in addition to the mega-expense of ridding the bottom of osmotic blisters.
The blister repair -- read, new bottom -- was completed in mid-February, and Marilynn Hale and I took the boat out to Lake Washington for sea trials. As we built to our 2400-rpm, 16-knot cruise speed, Marilynn and I awaited the familiar vibrations. We had always assumed that the vibration was from the two diesel engines hammering away under the cabin sole. The vibration hadn't been bad. We'd grown accustomed to it.
This time, the vibration wasn't there. The boat was smooth. The vibration hadn't been from the engines but from the props. With the props brought to Class I tolerances the change in ride was amazing. The word that comes to mind is electric. We are extremely pleased.
I have no report on top speed. We had not run at wide open throttle since before Selective Availability was removed from GPS. Top rpm had been 3200-3300, but I didn't write it down. We didn't run past 2500 rpm on our sea trial. Two passes on the Evergreen Point floating bridge's measured mile put our 2400 rpm speed at 16 knots exactly, in line with what the GPS said and essentially unchanged from before. I would not be surprised, however, if we now use a little less fuel at 16 knots. Lacking flow meters, though, any change would have to be dramatic to be detectable.
Our boat is equipped with Michigan 22×22-inch 4-blade nibral propellers. The propeller work came in a little under $1000 total. Since the boat already was hauled and the propellers and shafts removed in readiness for bottom blister repair, I don't include any yard charges.
This upgrade falls into the category of being kind of expensive when we're writing the check, but really appreciated afterward. I'm glad we did it.v
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