Possible redesign of Theodora's engine arrangements

[Theo]

I have posted a thread in General Boating about Theodora's seized engine.   Long standing readers may remember that Theodora has an unusual arrangement in her engine hole.  The engine is mounted back to front with the gearbox on the forward end. 

 

The order of units from aft to forward is Engine --> Gearbox --> stub shaft rotating between two plummer blocks with a triple V pulley between them.

 

The V belts connect with the propshaft which runs under the engine to a water cooled sterngland and then the propeller.

 

Problems:  1.  The engine is mounted on wooden bearers which are very effective in transferring vibration to the hull and throughout the boat.

2.  The two Plummer blocks and the gearbox need to be accurately aligned with each other.  Any movement of the engine means that there are problems with the bearings.  I last changed the stub shaft about 2,000 engine hours ago.

 

Jason Pinder suggests doing away with the belt drive, turning the engine around and mounting it about a foot lower in the engine hole.  To me this seems a massive undertaking and would mean that the alternator and raw water cooling pump belt would be less accessible.  He suggests rubber engine bearers to reduce transmitted vibration.

 

My favoured option is to leave the general arrangment as it is and fit something like a Python (I'm  looking at the P60-B) drive between the gearbox and the stub shaft.  The Python drive will mean that the engine would have to be moved aft a bit.  I am not near the boat so I can't, at this stage say how much and whether it could be moved back far enough.

 

Are there any other flexible drives on the market that might take up less room?  Jason mentioned something called Ultraflex but a Google search hasn't reavealed anything like a fexible drive.

 

All comments gratefully read!

 

Nick

[jonesthenuke]

How about hydraulic drive? No engine to prop alignment issues then.

[Tony Brooks]

The Cetaflex B claims to allow for both angular and radial misalignment, but I suspect it is severely limited when compared with an Aquadrive or Pythondrive.

 

 

FWIW, I very much doubt he meant rubber engine bearers, probably rubber (flexible) engine mounts.

[Theo]

10 minutes ago, Tony Brooks said:

The Cetaflex B claims to allow for both angular and radial misalignment, but I suspect it is severely limited when compared with an Aquadrive or Pythondrive.

 

 

FWIW, I very much doubt he meant rubber engine bearers, probably rubber (flexible) engine mounts.

That's probably what he said.  I may well have misremembered.

[ditchcrawler]

24 minutes ago, Theo said:

I have posted a thread in General Boating about Theodora's seized engine.   Long standing readers may remember that Theodora has an unusual arrangement in her engine hole.  The engine is mounted back to front with the gearbox on the forward end. 

 

The order of units from aft to forward is Engine --> Gearbox --> stub shaft rotating between two plummer blocks with a triple V pulley between them.

 

The V belts connect with the propshaft which runs under the engine to a water cooled sterngland and then the propeller.

 

Problems:  1.  The engine is mounted on wooden bearers which are very effective in transferring vibration to the hull and throughout the boat.

2.  The two Plummer blocks and the gearbox need to be accurately aligned with each other.  Any movement of the engine means that there are problems with the bearings.  I last changed the stub shaft about 2,000 engine hours ago.

 

Jason Pinder suggests doing away with the belt drive, turning the engine around and mounting it about a foot lower in the engine hole.  To me this seems a massive undertaking and would mean that the alternator and raw water cooling pump belt would be less accessible.  He suggests rubber engine bearers to reduce transmitted vibration.

 

My favoured option is to leave the general arrangment as it is and fit something like a Python (I'm  looking at the P60-B) drive between the gearbox and the stub shaft.  The Python drive will mean that the engine would have to be moved aft a bit.  I am not near the boat so I can't, at this stage say how much and whether it could be moved back far enough.

 

Are there any other flexible drives on the market that might take up less room?  Jason mentioned something called Ultraflex but a Google search hasn't reavealed anything like a fexible drive.

 

All comments gratefully read!

 

Nick

That is what I have between my hydraulic motor and the prop shaft I am still on the same shaft packings after 22 years. Sorry its not a uk page but it shows the unit nicely 

[Mike Tee]

Another vote for hydraulic drive - I have no engineering knowledge or skill, but ours works fine, and obviously the only thing connecting the engine (BD3) to the gubbins that drives the prop is two thick hoses. So it doesn't matter how high or which direction the engine points. Although I don't know how much one would cost, am guessing not cheap!

[Theo]

Thanks Mr Ditchcrawler!

 

Here's a website for it.  I looks as if it takes up much less room than the Python and is a small fraction of the price.

 

That's what Jason suggested but he couldn't remember the name at the time.

 

N

[IanD]

40 minutes ago, Mike Tee said:

Another vote for hydraulic drive - I have no engineering knowledge or skill, but ours works fine, and obviously the only thing connecting the engine (BD3) to the gubbins that drives the prop is two thick hoses. So it doesn't matter how high or which direction the engine points. Although I don't know how much one would cost, am guessing not cheap!

Several thousand quid IIRC... 😞 

 

(that was for an efficient long-life bent-piston pump/motor, inferior ones like vane pumps may be cheaper -- you also need a cooling system for the oil, which I think dissipated something like 20% of the engine power)

Edited October 1 by IanD

[Tony Brooks]

26 minutes ago, IanD said:

you also need a cooling system for the oil, which I think dissipated something like 20% of the engine power)

 

That will depend upon pump and motor design, and the fitter getting an adequate pipe and hose bore. I suspect piston moors and pumps will better that, while gear pumps may be worse.

 

It will also need a reservoir, PRV, and control valve.

[ditchcrawler]

I was lucky with mine, the original ARS company was a few miles away so I was able to visit the works and talk to the two fellers who owned it. The end result was a pump from a scrapyard which the checked over for me and a second hand motor they had on the shelf, held as a spare for a company that didn't even have a mark on the output shaft. The pipework cam from a Lowestoft company under the arrangement of take this real home , run it in and mark the length, bring it back and we will put the ends on. So I ended up with a reasonably prices job.

[Mike Tee]

It's a heavy (15mm bottom) 70' boat - and goes as fast as I need, also stops in it's own length from normal cruising speed, so if it is 20% down on power, it doesn't matter!

[Tony Brooks]

30 minutes ago, Mike Tee said:

It's a heavy (15mm bottom) 70' boat - and goes as fast as I need, also stops in it's own length from normal cruising speed, so if it is 20% down on power, it doesn't matter!

 

But that also implies a worse fuel consumption than a boat with a normal transmission. I suppose that if one decides that is worth it, then it depends upon how you think fuel prices will move.

[magnetman]

I did this once. Bought a narrow Boat which had a perkins 4236 on an elevated mounting running triple belts to the propeller shaft. I can't remember what gearbox it was but I took the whole thing out and fitted a Sabb twin on lower beds with a gearbox and I had a custom made cardan shaft for it. I didn't need any welding doing as the original shell had been supplied with ordinary engine beds. It was a 1970s Boat. At some stage someone had fitted the belt drive system for some reason perhaps because of the engine not being marinised. 

 

Its could be worth checking the engine beds in case the installation with the belts was added rather than being the original design. 

 

 

 

 

Edited October 1 by magnetman

[Mike Tee]

38 minutes ago, Tony Brooks said:

 

But that also implies a worse fuel consumption than a boat with a normal transmission. I suppose that if one decides that is worth it, then it depends upon how you think fuel prices will move.

I don't think one litre an hour average cruising is excessive so maybe mine was set up efficiently from new. Just the cost of boating.

[Theo]

Theodora averaged 1.21 litres per hour over 2928 hrs while we wre living aboard.

 

N

[ditchcrawler]

26 minutes ago, Theo said:

Theodora averaged 1.21 litres per hour over 2928 hrs while we wre living aboard.

 

N

That is about what I get, I can't do a long term measurement as I also have the diesel cooker so its only the fillups where the cooker hasn't been used and the the measurement of the diesel used is only within about 10%

[alan_fincher]

On 01/10/2024 at 16:39, Theo said:

Problems:  1.  The engine is mounted on wooden bearers which are very effective in transferring vibration to the hull and throughout the boat.

 

I'm a little surprised by this.  I've found that hard mounting an engine on to hardwood bearers can do quite an effective job in reducing vibration.

 

Are you confident that the engine is n good order, and firing reliably on all cylinders?