Aquadrive thrust bearing very hot

[sailingmonica]

Our sailboat is equipped with an Aquadrive system (CV 15 with a B10 thrust bearing) made in Sweden by GNK. The thrust bearing area gets hot while under power (4 knots) and gets so hot it starts to smell if we increase the speed to 6-7 knots. Then, if we reduce the speed the smell is gone, so I assume the temperature goes down a bit. Still, it is so hot you cannot touch it.

Then, last year we actually ordered a new bearing and replaced it. Still, it is as hot as ever.

If it matters, I even changed the transmission from a 2:1 to a 3:1 to reduce the number of RPM to the shaft hoping it will keep the Aquadrive temperature down. It did not change anything.

We asked around and were told these systems do get hot, and it's OK.

I was wondering, however, if anyone on this forum has experienced this.

Welcome back Monica!

Probably Baeckmo can tell you more about that setup!

Wait if he chimes in.

Regards
Richard

[baeckmo]

Well, don't expect too much.... Nice to hear from you though!

Bearings get hot mainly from two reasons: 1/Too much lube grease, and 2/Overloads. Provided you still run the same setup as before, the net thrust is well within the acceptable range for this bearing unit. Since it is "permanently" lubricated, "overgreasing" is not the cause of heat either.

My first guess is then an overload due to the thrust plate (in the hull) not beeing absolutely perpendicular to the shaft. Even a small deviation from 90 degrees, particularly in the horizontal plane, will cause a remarkable load increase for the bearing unit. In my opinion, the installation instructions are not clear enough on this issue. Vertically it's not quite as critical for the smaller units with only two mounting bolts.

Assuming the rubber thrust pads are correctly inserted, I suggest that you loosen the bolts a few turns (engine off), while rotating the shaft slowly by hand. Carefully observe if the bearing housing will "seek a new position" with one mount easing off from the thrust plate. Shim as necessary and reassemble. Now check that the intermediate driveshaft can move slightly in axial direction, so that it is not jammed too close between cardan units (check nominal installation dimension)

A weak thrust plate will give away under load, so having checked installation unloaded is just the first step, then you have to make shure there is no flexing in the arrangement under load.

Reasonable temperatures during run-in might be ~50 deg C, later ~40: "smelling hot" is certainly an indicator of having a cat onboard.


And, as an afterthought: have the mounting bolts worked loose at any time? If so, the metal inserts in the rubber pads may be different length, or their meeting surface pitted, causing the bearing housing coming out of true.

Hmm,

nothing beats first hand experience.


except maybe "both hands experience".....

[baeckmo]

....or, as one of my first chiefs put it, while debarking for an offduty weekend with fluids and ladies galore: "The head should work and the fingers assist, not the other way around"!

Must spread some reputation around...and so on, you know.

[sailingmonica]

Baeckmo, I will never cease to be amazed at the thoroughness and clarity of your answers, at the immense knowledge you accumulate and your willingness to help. All my good friend Apex1 had to do was summon you. Are you a genie?

Seriously, I am extremely grateful for your superb input. Will go over the check list and come back with the results.

And thank you, Apex1

Monica

[baeckmo]

Mmm, aah, oooh, I love it when you scratch my back like that....... but maybe let's wait with the celebrations till the problem is definitely solved??

[sailingmonica]

...the bolts were loose...

Originally Posted by sailingmonica

...the bolts were loose...

Hmmm................

no comment.

But at least it was the cheapest repair we could expect..............

[baeckmo]

Originally Posted by baeckmo

........And, as an afterthought: have the mounting bolts worked loose at any time? If so, the metal inserts in the rubber pads may be different length, or their meeting surface pitted, causing the bearing housing coming out of true.

Sic!

Now use some extra care when retightening; check that the bearing housing is not forced ascew due to uneven mating surfaces. Good luck!