centraflex or aquadrive

[simon boden]

we are in the process of having a new 62 foot narrowboat built, and we have decided to put a Beta BV1903

43 hp engine on flexi mounts into it. Could any one give us some advice on whether to fit a centra flex coupling or to go for the more expensive aquadrive. e.g. does the centraflex take out as much vibration as the aquadrive?

Thanks for helping Simon Boden

[dor]

Can't give you any advice about the Centaflex, but I do have a python drive fitted on mine. This is a similar concept to the Aquadrive, but at the time I bought it (about three years ago) it was shorter than the Aquadrive and considerably cheaper. (I believe the Aquadrive has been updated since.)

 

It made a huge difference to the amount of noise both inside the boat and coming up through the ruiser stern deck. It is fully sealed, needs no maintenance and hasn't given any trouble.

 

Some of the smaller centaflex couplings are just flexible couplings. The key thing about the Python Drive & Aquadrive is that the thrust is taken directly by the hull rather than through the gearbox/drive plate/engine mounts.

[Gary Peacock]

Do you really need to spend the money?

 

A simple R&D coupling is very effective if the engine is installed properly.

[John Orentas]

Simon.

 

I tend to agree with Gary, there are several options of doing the installation, what your two options have in common is that both allow for angular and linear alignment and not just in a static form. When an engine is running on flexible mounts it will move around (or want to move around) in 3 dimensions and with all kinds of rotation thrown in, if your drive chain does not allow for all this, massive unnecessary loads will be placed on components not designed to take them, you will be storing up all kinds of problems for the future.

 

Even here on this forum you will read reports of premature failure of gearboxes, stern-gear and other components and of others suffering excess vibration and transmission noise, people for various reasons will be very reluctant to seek out the underlying cause.

[khaffra]

I personally think Aquadrives work extremely well as they allow for the use of much softer engine mountings and when we fitted one there was a noticeable difference in the lack of vibration transmitted to the boat.

Fitting an aquadrive on its own will only have a marginal effect it needs fitting as a package including the mounts and you will also have to make sure there is some flexibility to any pipes etc attached to the engine.

They are not the easiest thing to fit retrospectively so if you want one fit it from new.

[John Orentas]

I personally think Aquadrives work extremely well as they allow for the use of much softer engine mountings and when we fitted one there was a noticeable difference in the lack of vibration transmitted to the boat.

Fitting an aquadrive on its own will only have a marginal effect it needs fitting as a package including the mounts and you will also have to make sure there is some flexibility to any pipes etc attached to the engine.

They are not the easiest thing to fit retrospectively so if you want one fit it from new.

 

 

Yes the main problem is that a certain amount of fabricating and welding is required in order to fit the thrust bearing and constant velocity joints and is often necessary to move the engine to allow space. It is an expensive job as a retrofit and a bit beyond most D I Y 's.

 

For anyone who wants to cut costs, another very efficient method is to use an industrial 'Rubber Tyre' drive, I did this many years ago and it is still going strong at a fraction of the price. Let me know if you want details.

[dor]

My Python Drive was retro-fitted without major work. A plate was welded across the bilge with a cutout for the drive to bolted to it. It is fairly short, which is why I went for the Python drive at the time, and all the thrust is taken directly by the hull.

 

As I mentioned above, the whole point of these drives is to transfer the thrust to the hull rather than pushing it through the drive chain and engine mounts.

 

This is a completely different approach to just putting in a flexible coupling, and I would do it again sa I think it is well worth the effort. Fitting in a new build should be very simple and not cost much more than the cost of the coupling itself.

[Alastair]

For anyone who wants to cut costs, another very efficient method is to use an industrial 'Rubber Tyre' drive, I did this many years ago and it is still going strong at a fraction of the price. Let me know if you want details.

 

My boat has a home-built connection using car CV joints. However, I'd like to replace it with a new fitting.

 

Can you tell me more about your "industrial 'Rubber Tyre' drive"? Is it suitable for handling large torque?

[khaffra]

My Python Drive was retro-fitted without major work. A plate was welded across the bilge with a cutout for the drive to bolted to it. It is fairly short, which is why I went for the Python drive at the time, and all the thrust is taken directly by the hull.

 

As I mentioned above, the whole point of these drives is to transfer the thrust to the hull rather than pushing it through the drive chain and engine mounts.

 

This is a completely different approach to just putting in a flexible coupling, and I would do it again sa I think it is well worth the effort. Fitting in a new build should be very simple and not cost much more than the cost of the coupling itself.

 

I would fit one again but mine was not simple to fit but mainly due to the lack of room available around the engine and between the gearbox and the stern tube and it did mean lifting the engine nearly out of the boat, it was though done on the side of the canal not at a boatyard with just the brackets fabricated inland.

I agree in a new build you would hardly notice the extra cost and it would be very simple.

[John Orentas]

My boat has a home-built connection using car CV joints. However, I'd like to replace it with a new fitting.

 

Can you tell me more about your "industrial 'Rubber Tyre' drive"? Is it suitable for handling large torque?

 

 

Hi Alastair.

 

Bearing in mind all the bits were purchased and the work was done many years ago, I checked all torque requirements at the time and I allowed a safe margin. The 'Rubber Tyre' drive is about 10 inches diameter with an 1.5 Colet connector on one side and a standard 4 hole connector at the other which fixes directly to the gearbox output flange, made by Fenner I think .

 

For the thrust bearing I used a standard Plummer housing and a 'spherical' bearing, 1.5 inch dia. with grub-screw pilots. In the early 90's the whole lot cost less that £200.

 

The only maintenance it has ever had is a few pumps of grease into the thrust bearing every year.

[Alastair]

Does the spherical bearing accomodate the shaft not being aligned with the gearbox?

[John Orentas]

Does the spherical bearing accomodate the shaft not being aligned with the gearbox?

 

 

No. The rubber tyre does that. But you must align the plummer bearing by shimming, much more simple than it sounds.

 

Not sure now if 'spherical' is the best description. 'Double row angular contact' might be better given that it must take thrust in both directions. Bearing suppliers are good at advising about such things.

[DHutch]

Yes the main problem is that a certain amount of fabricating and welding is required in order to fit the thrust bearing and constant velocity joints and is often necessary to move the engine to allow space. It is an expensive job as a retrofit and a bit beyond most D I Y 's.

Dont forget this is a new build.

- So fabrication is less of an issue. And certainly the possition of the engine is very much negotinable.

 

 

Daniel

[Alastair]

No. The rubber tyre does that. But you must align the plummer bearing by shimming, much more simple than it sounds.

 

Not sure now if 'spherical' is the best description. 'Double row angular contact' might be better given that it must take thrust in both directions. Bearing suppliers are good at advising about such things.

Hmm. I already have a thrust bearing. it's the two CV joints between the thrust bearing to the gearbox that I'm thinking of replacing. Maybe two of the 'rubber tire' jobs would do the trick. They sound similar to a fitting that I had on an old bedford van.

[John Orentas]

Hmm. I already have a thrust bearing. it's the two CV joints between the thrust bearing to the gearbox that I'm thinking of replacing. Maybe two of the 'rubber tire' jobs would do the trick. They sound similar to a fitting that I had on an old bedford van.

 

 

Alastair,

 

You only need one 'rubber tyre' job the only thing they won't do is take thrust. You are probably thinking of the inboard U/J's that were fitted to Hillman Imps and others, they were bonded one piece units. What I have in mind are very much larger jobs which can be taken apart for maintenence.

[Alastair]

The bedford one could be taken apart - it was like a rubber disk with about 6 holes in it. The outer part of the rubber disk bolted to a flange on one shaft, and the inner part bolted to another flange on the other shaft. It soaked up vibration.

 

My current system is like this:

 

| | / \ |

| ------ |/----------------------------\ |

| | \ /|

thrust flange shaft flange

Bearing welded & CV

to Bolted to gearbox

CV

[edit]

Blast - it makes sense in the edit window.

 

Anyway, starting from the thrust bearing, there is a flange welded to a CV. This has a car drive shaft coming out of it, with the end of another drive shaft welded to that. That end goes into another CV, which is welded to another flange, bolted to the gearbox.

 

So I don't need anything to take thrust, just to absorb vibration and some misalingement.

Edited March 6, 2006 by Alastair

[John Orentas]

The bedford one could be taken apart - it was like a rubber disk with about 6 holes in it. The outer part of the rubber disk bolted to a flange on one shaft, and the inner part bolted to another flange on the other shaft. It soaked up vibration.

 

My current system is like this:

 

| | / \ |

| ------ |/----------------------------\ |

| | \ /|

thrust flange shaft flange

Bearing welded & CV

to Bolted to gearbox

CV

[edit]

Blast - it makes sense in the edit window.

 

Anyway, starting from the thrust bearing, there is a flange welded to a CV. This has a car drive shaft coming out of it, with the end of another drive shaft welded to that. That end goes into another CV, which is welded to another flange, bolted to the gearbox.

 

So I don't need anything to take thrust, just to absorb vibration and some misalingement.

 

OK sounds to me like you have a perfectly good system, a sort od DIY aquadrive.

 

The canvas disc types, they used them in the pre-war Austin seven they worked well but would only take angular misalignment, you need two of then for linear.

[Alastair]

It's ok at normal speeds, but overheats when running at speed - I think one of the CV's might have been distorted by the welding when it was originally made. So pootling about on the river is fine, at anything up to 6knots.

 

When there is a flood on, I need to be able to confidently motor at higher speeds. It's ok atm, as long as I keep a close eye on the grease levels in the CVs.

 

What do you mean by linear misalignment?

[DHutch]

| | / \ |

| ------ |/----------------------------\ |

| | \ /|

thrust flange shaft flange

Bearing welded & CV

to Bolted to gearbox

CV

[edit]

Blast - it makes sense in the edit window.

You need to write it as code with

 tags (minus spaces) around it, then it doesnt remove the spaces, and you get a fixed-width font.

Like this [code]
|		  |  /						\  |
| -------- |/----------------------------\|   
|		  | \						   /|
thrust	   flange		 shaft			flange
Bearing	  welded						  & CV
		 to CV						   Bolted to gearbox

 

Daniel

[enigma]

The engine and drive train of a boat are very important, don't skimp on the quality. You will not regret having an Python Drive fitted. It must reduce vibration and noise problems.

Edited March 7, 2006 by enigma

[Alastair]

Retro fitting an aquadrive may not be the best solution, if the existing installation isn't conveniently designed for one.

 

The drive train components that John is talking about are heavily used in the haulage industry, they aren't a 'low quality' option. They have the massive advantage (over aquafax), of being user serviceable. This will make them easier by far to adapt to an old boat.

 

As I said before, my existing system is fine for pootling on still water. I'd like to improve it so that it can cope with long trips on fast flowing water.

[John Orentas]

It's ok at normal speeds, but overheats when running at speed - I think one of the CV's might have been distorted by the welding when it was originally made. So pootling about on the river is fine, at anything up to 6knots.

 

When there is a flood on, I need to be able to confidently motor at higher speeds. It's ok atm, as long as I keep a close eye on the grease levels in the CVs.

 

What do you mean by linear misalignment?

 

 

Angular misalignment. Imagine 2 shafts one driving the other, a single universal joint connecting the 2 will allow the drive to be transmitted but only if the shafts intersect at the centre of the joint, though as long as they do the angle can change.

 

Linear (or parallel) misalignment.

In the case of a soft mounted engine/gearbox driving a prop-shaft which passes through a rigidly mounted stern tube. The driven shaft will move in a random sort of way, the two shafts will not always intersect and they will move, up/down, side to side, twist left/right up/down. You will need a short intermediate shaft and an extra u/joint.

 

Very few types of universal joint will transmit thrust.

[simon boden]

we are in the process of having a new 62 foot narrowboat built, and we have decided to put a Beta BV1903

43 hp engine on flexi mounts into it. Could any one give us some advice on whether to fit a centra flex coupling or to go for the more expensive aquadrive. e.g. does the centraflex take out as much vibration as the aquadrive?

Thanks for helping Simon Boden