Vibration solution

[Engineer6]

We have a 2000 Albin 36 TE single screw that encountered vibration at 2,000 rpm in a sea trial. We went through the usual problem-solving steps of prop tuning, shaft alignment, bearing replacement, shaft log adjustment to some improvement but not a total solution. We then heard from Gary at Snead Island Boatworks of a past project that entailed the "feathering" of the trailing edge on the keel.

The Albin single keel is flat at the rear and almost seven inches across at the top and tapers to five inches above the shaft bearing. It then further tapers from five inches to about three inches at the skeg. This flat trailing edge creates a dead zone at the rear at high (for a trawler) speeds. this does not sound like a lot of dead zone but for a 24 inch prop (75 inch circumference) the 12 inches of dead zone is 15% of the total swept area; not allowing for spreading turbulence.

The fix was to add a tapered extension to the trailing edge of the keel. This creates a slightly pointed rear edge. The added section is above and below the shaft bearing. The keel structure and shaft bearing were untouched. The new trailing edge is extends 3 to 5 inches to the rear of the old flat keel edge and is smoothly faired into the existing keel. The radius of the new trailing edge is about 1/2 inch. The improvement in flow is marked. The boat now is vibration free up to the engine WOT of about 2,600 rpm.

Interesting that Albin may have realized this since most people operate at 75% of WOT as a working maximum. That equates to about 2,000 RPM. It was only above 2,000 RPM that the vibration started. We never operate the boat above that level so never saw the vibration. It only became apparent when the engine was taken to WOT as part of a sea trial.

My thanks to Gary at Snead Island Boat Works for his advice on this and to Peter at Marsh Harbor Boat Works for the excellent work.

[Carl]

Any pictures of before and after?

[jcollins]

Thanks for posting this information. I'm going to try and condense it and add it to our library of information. I'm curious. We had another member that was looking at a 36. The deal did not complete because of the vibration issue. Is this the same boat? Single 450 if I recall?

Anyway, welcome to AOG. Post some pictures when you get a chance.

[Engineer6]

To J collins,
I have "before" pictures and have asked boatyard for "afters". None have showed up yet. I will be sure to send along when they are available. I don't know if this is same boat you are referring to or not.