Stern gear worn with aquadrive

[Roadrunner]

We have just had a survey report back for a boat we are buying. Hull is in excellent condition however there is substantial play in the prop shaft and the stern tube is oval shaped. It was an external survey only and the surveyor suggested that the engine mounts may need to be replaced. I don't believe that he knew it had an aquadrive and its my understanding that these mean that alignment is not such a big issue, I'm just curious as to how this wear may of occurred. It's our first boat, I'll learn eventually

[ditchcrawler]

As I understand it to a certain degree, not sure what would happen if the engine was say half an inch to low

[RLWP]

As I understand it to a certain degree, not sure what would happen if the engine was say half an inch to low

 

Nothing, the Aquadrive will accommodate that

 

Richard

[bizzard]

Possibly the boat has spent most of its life operating without an aquadrive or any other form of double UJ, the propshaft being coupled direct to a rubber mounted engine and beerbox which wore the shaft and bearing, the aquadrive being a later addition.

 

Incidentally, is the stern tube of the conventional greaser gland type or the water lubricated rubber cutless bearing Vetus type ?

Edited October 21, 2015 by bizzard

[SUIGENERIS]

I have one of these fitted and as I understand it the aquadrive has the thrust carried on to two ( on bigger ones more) rubber pads which locate the thrust bearing in alignment with the shaft. Then there is a CV joint between that and the engine/gearbox which can accomodate quite a considerable lack of alignment of the engine. But if the thrust plate or the rubber pads are defective then the shaft is flexing and could easily be the cause of the wear on the stern tube.

[bizzard]

I have one of these fitted and as I understand it the aquadrive has the thrust carried on to two ( on bigger ones more) rubber pads which locate the thrust bearing in alignment with the shaft. Then there is a CV joint between that and the engine/gearbox which can accomodate quite a considerable lack of alignment of the engine. But if the thrust plate or the rubber pads are defective then the shaft is flexing and could easily be the cause of the wear on the stern tube.

Or the thrust plate bearing was not accurately aligned with the shaft when fitted.

[Bee]

The Aquadrive is a bit like a car drive shaft with 2 constant velocity joints and a hefty thrust bearing that should be firmly fixed to the boat. They do a very good job and will protect the drive train from the Aquadrive to the gearbox but I think they need to be installed with a bit of care from the Aquadrive to the propeller shaft. I think that the prop shaft should be carried in a plummer block or it will go round in an ellipse. Not too sure, someone will know. edited cos Bizzard just said that.

Edited October 21, 2015 by Bee

[Guest]

How many hours on the engine?

Any chance of a pic of the setup?

Edited October 21, 2015 by Guest

[Bloomsberry]

If the stern tube is eliptical then surely this must mean that there is a greater chance of leakage into the bilge.

 

So what is the stern gland leakage like when the boat is in the water ?

[Flyboy]

The Aquadrive is a bit like a car drive shaft with 2 constant velocity joints and a hefty thrust bearing that should be firmly fixed to the boat. They do a very good job and will protect the drive train from the Aquadrive to the gearbox but I think they need to be installed with a bit of care from the Aquadrive to the propeller shaft. I think that the prop shaft should be carried in a plummer block or it will go round in an ellipse. Not too sure, someone will know. edited cos Bizzard just said that.

With an Aquadrive the thrust bearing is effectively a plummer block which supports the prop. shaft.

[dor]

THe aquadrive (and similar Python Drive) should have a plate with a thrust bearing on it. This has to be mounted very accurately so that the bearing is in line with the stern tube and exactly square to it. If this is not fitted correctly it can cause wear to the stern tube. The thrust bearing is attached to the plate by two bolts which should be tensioned properly (measured by how much the rubber bushes are squashed up). If these bolts are loose the thrust bearing can move and this can cause excessive wear to the stern tube.

 

The drive part between the thrust bearing and the gearbox consists of a short shaft with a CV joint on either end. There should be about 7 degrees of intentional misalighnment between the two CV joints to ensure the grease is circulated within the sealed CV joints. If they are exactly in line it can cause excessive wear. This shaft allows the engine to move quite a bit without that movement being transmitted to the stern tube. The thrust bearing means that the prop thrust is taken up by the plate not by the engine mounts, so this should reduce wear in the rubber mounts. However the mounts still have to be set up properly and this is not an easy task. The usual mistake is when the engine can rock on the diagonal because the mounts are not aligned properly in pairs. It is something that a lot of "engineers" in marinas don't understand or don't know how to do properly. If they are not set up correctly the mounts will be subject to excessive movement. This causes them to heat up due to frictional forces within the rubber causing degradation. This can often be identified by a soft sticky 'soot' around the mounts.

 

Aquadrives and Python Drives are a great way to connect the prop to the gearbox but, contrary to what some believe, they still need to be set up carefully.

[Guest]

THe aquadrive (and similar Python Drive) should have a plate with a thrust bearing on it. This has to be mounted very accurately so that the bearing is in line with the stern tube and exactly square to it. If this is not fitted correctly it can cause wear to the stern tube. The thrust bearing is attached to the plate by two bolts which should be tensioned properly (measured by how much the rubber bushes are squashed up). If these bolts are loose the thrust bearing can move and this can cause excessive wear to the stern tube.

 

The drive part between the thrust bearing and the gearbox consists of a short shaft with a CV joint on either end. There should be about 7 degrees of intentional misalighnment between the two CV joints to ensure the grease is circulated within the sealed CV joints. If they are exactly in line it can cause excessive wear. This shaft allows the engine to move quite a bit without that movement being transmitted to the stern tube. The thrust bearing means that the prop thrust is taken up by the plate not by the engine mounts, so this should reduce wear in the rubber mounts. However the mounts still have to be set up properly and this is not an easy task. The usual mistake is when the engine can rock on the diagonal because the mounts are not aligned properly in pairs. It is something that a lot of "engineers" in marinas don't understand or don't know how to do properly. If they are not set up correctly the mounts will be subject to excessive movement. This causes them to heat up due to frictional forces within the rubber causing degradation. This can often be identified by a soft sticky 'soot' around the mounts.

 

Aquadrives and Python Drives are a great way to connect the prop to the gearbox but, contrary to what some believe, they still need to be set up carefully.

I have always used the "scissor jack" trick that you once described and it works a treat.

[Roadrunner]

I'll have a look next week once we've actually bought her and get a few pics, it has occoured to me that it was the sales bloke that told us it has an aquadrive, its not mentioned on the details, just says shaft drive. Well I'll find out soon

[Sea Dog]

I have always used the "scissor jack" trick that you once described and it works a treat.

That's sounds interesting. If you can remember where it might lurk, could you post a link please?