Vibration Below 800 rpm

[nussbda]

I'm considering moving from a Hunter 30 to an Albin 28, and sea trialed a 1996 28 with a Cummins 250 last week. Below 800 rpm in gear there was a lot of vibration. At 800 rpm hull speed was over 5 knots, which was awfully fast for navigating in the marina (at least for me). There was no noticeable vibration over 800 rpm. The surveyor said the prop might need to be balanced, but the broker said "that's the way they are", and just take it in and out of gear to go slower. What should I expect at idle speed in gear? Should it idle at 600 rpm in gear (it was idling at 750 in neutral)?

Thanks for your feedback.

Dave

[Pitou]

The following is a reference from my B Series Aftercooled (Family M10TA) Technical File Bulletin Revision from 10/2000.
Engine Model: 4B-250 - idle speed range / 625-675 ; rated engine power 250hp at 3000 rpm. high idle 3300-3400

First off I'm assuming that all of the motor mounts are in good shape. The vibrations you're experiencing can come from shaft alignment, bent shaft, a worn cutlass bearing in the stern tube and from the prop. All should be "in tune". I'd start with the alignment 1st and then work your way to the wheel. All very solvable. When I first took delivery I had deck vibration at idle speeds and started with the alignment which was right on, but found a worn cutlass bearing and the prop needing to be tuned. After all that things flattened right out and no more shake. If you pursue this boat, try to negotiate the tune into your offer.

As far as being a little too fast around the dock, my 370 Cummins liked to do 6 knots in still water at idle. Bumping in and out of gear was my initial norm around the docks until I installed a trolling valve. I've found that it's not only handy when fishing, but the trolling valve calms things down around the fairway.

Good luck on your journey to acquiring a 28 TE.

[jleonard]

I'm considering moving from a Hunter 30 to an Albin 28, and sea trialed a 1996 28 with a Cummins 250 last week. Below 800 rpm in gear there was a lot of vibration. At 800 rpm hull speed was over 5 knots, which was awfully fast for navigating in the marina (at least for me). There was no noticeable vibration over 800 rpm. The surveyor said the prop might need to be balanced, but the broker said "that's the way they are", and just take it in and out of gear to go slower. What should I expect at idle speed in gear? Should it idle at 600 rpm in gear (it was idling at 750 in neutral)?
Thanks for your feedback.
Dave

750 in Neiutral to 600 in gear seems like too big of a hit to me.
Was the tachometer calibrated?
What was the WOT rpm?
Was the vibration comming from the prop, from the engine (motor mounts), or from the damper plate (aka "gear rattle")?
I have never heard of a prop causing a vibration at that low of an RPM (except for one that was actually missing a blade), that is why I am asking these questions.
You should be able to pinpoint the source of the noise or vibration rather easily...or at least the surveyor should be able to.

[Russell]

When I purchased my 97 model it had the same problem. New motor mounts made a tremendous improvement. Once I am out in the main channel of our harbor I kick up the RPMs to 900 where the engine sounds much smoother and I am at around 5.5 knots. Coming from a sailboat you are going to have a learning curve to move around the docks. I too was a sailboater for 30 years and was surprised at the difference. The large rudder on a sailboat is made to give control at very low speeds. The rudders on power boats are nearly useless in neutral and you have to learn how to use prop walk and prop wash over the rudder to get low speed control. It is actually quite easy once you understand it and practice a little bit.

[dkircher]

Dave,

I wouldn't believe that broker, since in my experience, that is not the way they are!

My 28TE with the 330 Cummins is fairly smooth at idle after warm-up. Extremely smooth at 800+ RPM once I am out of the marina.

I do move along in gear at about 5 knots at idle, and take the transmission in and out of gear as necessary. I have a short run in and out of the marina, so generally that isn't much of a problem. I could use the trolling valve. So far that hasn't been necessary.

I agree with the others that the boat may need engine mounts or some other repair. I suggest that you find a good mechanic to advise you.

I hope you find a great TE.

[Chris & Dale]

Dave,
You might consider a 28TE w/a Yanmar 300 or 315....don't idle near that fast. Makes it a lot more managable in the marina docking. Regardless, you will love the boat. One Man's Opinion.

[Nancy]

Dave, we bought a 1995 28 with a Cummins 250 last spring. (One of the boats we looked at in MD matches your description - probably the same one. We liked the broker - thought he was a straight-up guy with an interesting background that included a stint in Vermont. But I digress.)

We're new to the 28 and to diesel engines. Ours behaves at low idle (750 rpm) much as you describe and smooths out beautifully at 850. Engine mounts are good, cutless bearing is good. We changed the pitch and cup of the prop after winter haul-out (because we weren't getting rated rpm's + ~100 at WOT) , so will be interested to see how she behaves when we launch.

Our experience has been that every boat has a range that it doesn't like. On the 28, it just seems like there's a lot of iron under that hatch, and at low idle, loose components rattle - stowed hatch covers, cabin door, etc. We quickly learned to compensate by wedging in some styrofoam packing material - problem solved. It's not like we're feeling vibration in the cockpit sole, steering wheel, etc., and as I said, above 750 all is well, so we're inclined to think it's just an rpm range that the boat doesn't like.

As for the velocity at low idle, yes, it's a lot faster than any previous boat - about 5 knots as you observed. I learned years ago that neutral is my friend at the dock, and it's really true in this boat. We've gotten used to it.

[nussbda]

Thanks everyone for the feedback. It sounds like I'll have some learning to look forward to.

Dave