Conversion of Alwyn Vintcent to Hydraulics & Diesel Power 1996
From Anton – Cape Town
I did part of the conversion when the Alwyn Vintcent was converted to hydraulics and diesel power in 1996. I did all the mechanical works as a design, fabricate and install sub-contract to Hytec who were the main contractor. Hytec provided the hydraulic motor, diesel driven hydraulic power unit and hydraulic controls.
Unfortunately I no longer have any of the drawings or details of what we did so I will just tell you from my memory.
The AV, as I am sure you will remember, had a steam engine which drove the propeller via a 6” tail shaft that came from the engine room through the stern accommodation flat (in a bilge channel) and out the hull at the stern via a stuffing box.
Working backwards from the stern end of the bilge channel where the tail shaft goes through the stuffing box there was a bolted flange just forward of the stuffing. Between this flange and the bulkhead to the engine room there was about a 2.4 m long shaft which bolted onto the flange from a stub shaft from the engine room. This stub shaft from the engine had a radial and thrust bearing inside the engine room. The thrust bearing took the thrust from the propeller to the hull.
About a metre forward of the stern stuffing box there was a radial bearing in a plummer block housing that supported the shaft.The bearing incorporated a white metal split bush in an oil bath.
We removed the 2.4 m shaft and its radial bearing and replace it with a new 8” shaft about 1.5 m long.This shaft was turned down to 6” in the position of the radial bearing mounting to give a 1” annular shoulder; and we replaced the radial bearing with a new combination thrust bearing and radial bearing.
The old shaft and bearing unit were taken to the museum but they have subsequently been lost.
The new bearing which I supplied had a split-housing and contained a bronze bush either side which projected beyond the housing to provide a thrust face to bear on the 1” annular shoulder. The grease was pumped into the housing between the two bushes to lubricate both the radial and the thrust faces.
Moving forward from the bearing in the revised arrangement we have the new bearing, with the new shaft extending forward marginally to a flanged mounting for the hydraulic motor front face, and bolted on the back end of the hydraulic motor is an upstanding torque plate. Welded to this torque plate is a stub end of a 6” pipe with a termination flange.
Onto the top of the 6” pipe flange a 6” pipe torque arm was bolted which extended to the top of the accommodation flat where it was secured with a rubber mounting.
The diesel engine and hydraulic power pack used to be down below next to the hydraulic motor but is now gone, and the controls were on the bridge which were just variable speed of the motor either forward or aft. Steering remained by operating the rudder.
In a nutshell:
* The 2.4 m long 6” intermediate shaft and the supporting radial bearing were removed;
* A new combination thrust and radial bearing was installed on the same bearing mounting. This bearing had grease grooves to feed grease to the radial as well as the thrust faces;
* A new 1.5 m long 8” shaft was made up compatible with the tail shaft flange, the new thrust/radial bearing, and the front flange of the hydraulic motor;
* This new shaft was installed inside the bilge channel;
* The new hydraulic motor (radial piston motor I think) was bolted onto the new shaft;
* The torque plate and 6” pipe stub flange was bolted to the back of the hydraulic motor;
* The torque arm 6” pipe was installed between the torque plate and the roof; and
* The diesel HPU was installed and piped up to the motor with the controls taken to the bridge.
The performance of the tug I believe was identical to what it was when she was steam operated (the hydraulic motor delivered the same speeds with the same available torque and obviously the same power).
When we initially installed the system we did not have the extended torque arm, just the torque plate extending downwards into the bilge to increase the available space. I was unfortunately not there for the initial sea trials as I was managing the construction of the new harbour in Port St Francis. During the trials the bearings severely over-heated with smoke billowing from the bearing. On later inspection the thrust faces were seen to be completely damaged.
I reviewed the matter telephonically with a colleague, a Mechanical Engineer in Cape Town, and we came to the conclusion that because the thrust face was destroyed there must be a lubrication starvation on this face. We researched thrust bushes and identified the best way of lubricating a thrust face was to incorporate a tapered land face (rather than the set of simple radial grooves that I had initially employed).The tapered land bearing apparently could introduce the lubricant onto the bearing face much as a radial bearing does in the small annular space between the shaft and the bearing.
We machined and installed new bushes which had a tapered land face to hopefully improve the lubrication issue.
We then embarked on the second trial with heat sensors installed to see what was happening with the grease temperature, and alas the same thing started to happen. We stopped the trials straight away, before damage could set in, and removed the bushes.
It was fortunately just before the Easter Weekend (’96) so I drove to Cape Town to discuss and attempt to resolve the matter.On inspection of the bushes I was surprised to see that the initial heat bluing was not on the thrust face but on the radial face - and the penny immediately dropped. The radial loads on the bearing due to the torque application from the motor were too great because of the shortness of the lever arm on the hydraulic motor torque arm (something I had omitted to check). The solution was then obvious – extend the length of the torque reaction lever arm.
The torque plate was turned around to point upward, the 6” pipe was added using a rubber mounting anchorage on the roof, and from then the system worked wonderfully.
For the original conversion from steam to hydraulics I used Allwright Engineering to do the mechanical fabrication as a sub-contractor, but they no longer exist.
The works which we are now considering doing together with TEC Engineering is to take out the new shaft and hydraulic motor, convert the existing bearing unit back to a greased radial bearing only and fabricate and install a new 2.4 m tail shaft. At this stage we are pricing this conversion.