Vibration within certain RPM range

[Robert Moretti]

Last year, I changed from a two-blade fixed prop to a two-blade feathering prop. Generally, I'm glad I did. Engine performance and speed suggest that my new prop is pitched correctly. However, at about 2400 RPM there is a new vibration that disappears at about 3000 RPM. The vibration is best described by thinking of a wave. That is, the vibration increases in intensity, then falls away, then increases, etc. At 2400 RPM, the vibration occurs with a period of about 1.5 seconds. The period shortens with increased speed, until the vibration disappears. I don't know where to start to figure out the cause. Any ideas? Thanks!

 

[Jeff Bacon]

Try This

Robert:Many of use have had vibration questions over the years, and many fixes apply to different boats. My vibration problem was 75% solved by tightening the motor mount bolts. They were not "obviously" loose, but a 1/2 turn or less on each mount eliminated a lot of my vibration.Good Luck ......... Jeff

 

[John O'Donald]

simular problem

I have a two blade feathering prop with simular problems. What brand is yours and what boat/engine

 

[kevin]

check track

Hello Robert, The cycle waves you describe sound like harmonic vibrations. In the case of a Max-Prop we see these types of problems pop up when: Shaft angle is to great, pitch is to great, prop is out of balance or track, tip clearance is shy. I’m NOT BASHING your propeller, but of the few that have come through my shop for repair we do take them and better the balance. I would first start by working with the person you bought the prop from to get them to confirm that the unit is in balance and that the blades are tracking while the vessel is still out of the water. I would confirm, when you can that, the tack is reading accurate and that the Rpm’s you achieve are in fact the real numbers. If the system was out of alignment and your cutlass was bad, you should experience problems through the whole range of Rpm’s. It has happened before with all prop people, that you may find the best system for your boat is not a two blade but a three. That of coarse is one of the last things we would put you through. Hope this helps. Kevin