Just purchased a new lund 1400 fury with 30hp e-tec tiller and I really like the motor it idles smooth and quiet and wide open throttle it is smooth and quiet but its the in between rpm ranges that I get a vibration or more like a "buzz" through the boat it is very annoying and the more weight I put in the boat the worse it gets. Is this a common occurance in the e-tecs or do I possibly have a bad motor mount. I called the dealer that I bought it from and they said that thats the way they are. Just was curious if anyone else has the same issue.
09-26-2013 11:26 - edited 09-26-2013 11:32
You may be noticing the small rpm range usually above fast idle and before the boat is up on plane that is known as the transition area between the "lean burn" stage and the power stage, to put it in non-technical terms. A good tech can tweak TPS adjustments and the use of a different propeller often minimizing the situation. Traditonal carburetor motors also had the same roughness in that range due to the engine running richer than normal as the carbs were changing from the low speed circuits to the mid and high speed circuits. Those older motors were noisier and not as smooth as today's motors so the shaking was not as noticable.
You may also be describing a harmonic vibration that occurs in your boat or from something loose in the rig. The same motor on a different make boat may be super smooth and buzz free. A trained tech can distinquish between the situations and may be able to help.
We run a 1973 14' Alumacraft with a 25 ETEC and had the same buzzing noise due to vibration. Bluewater Bill hits it right on the head. In our boat it was caused by the position of some of the gear in the boat and moving the gear removed the vibration-related buzzing at those transitional RPM's. I love experimenting with propellers and found that switching to a four bladed prop actually reduced the vibration-related buzz considerably. The 4 bladed prop also feels smoother in the tiller. I believe the added blade reduces total blade loading on each blade which smooth's out the thrust pulse (the driving force behind the buzz) sent from the lower unit through the transom and into the boat to a different frequency. This new frequency falls outside the threshold of the buzz-inducing frequency in our boat and we noticed the noise is reduced or eliminated. I have switched back and forth between three and four blade props with surprising results. The buzz is audible while running the three blade prop and greatly reduced or gone while running the 4 blade prop. If moving stuff around in the boat doesn't help this idea might.
Thanks for sharing your experience with us. I am sure it will be helpful to others in the future.
We tested several props on our boat (see below). We settled on a 12 inch pitch 4 blade Aluminum prop from Solas. It was the smoothest running prop we tested. We wish we had a 4 bladed 13 inch pitch to test as well. We think it would have yielded the best overall performance AND lowered WOT RPM closer to our target of 5770. If you extrapolate from the data below you should see our point. We hope this helps!
Thank you for posting your prop results. That will help other readers in the future.