The Axiom Propeller Saga

It was in April 2011 that I had Stronghold lifted out by The Locker Company at Parvis Wharf for blacking and Stuart and Julia did a fine job on their tiny wharf. Strangely enough, at the same time, I was in a dry dock at Grendon blacking the two Narrow Boat Trust boats – was I mad or what? Anyway, I had bought an Axiom propeller to replace my chipped and bent prop and Stuart fitted it, though with a lot of effort to remove the old one. I had done a lot of research on the internet with people who had taken the plunge with an Axiom and apart from one, they all agreed that it was the ‘ mutts nuts’. Funny that, after I contacted one boater, I was networked to several others  with the same propeller – almost impossible without the internet – the electronic towpath telegraph.

I had contacted Alan and David Watts some months earlier with all the details of my boat and engine, so they were able to recommend the size and pitch of propeller to suit from their vast resources and experience. I was delighted with the performance, notably its power to stop from full speed in half the length of the boat, instead of one and a half times the length with the old propeller. Reversing in a straight line is far easier and it is possible to steer in reverse with some practice. Prop wash is greatly reduced when mooring and stopping in locks, but all these properties are as advertised. It is prone to collecting leaves in the Autumn though and I think this is due to the sharp corners on the inner edges of the blades, but a quick reverse soon clears the obstruction.

All was going well, or so I thought, until an Autumn trip to Oxford and back caused some concern over the fuel consumption. My consumption with the old propeller was about 1litre/ hour and now I was getting only 1.6 litres/hour – not up to Axiom standard, as they advertised an  improved consumption from 7% to 15%. I immediately contacted the Watts and they came back with a considerable list of things that would cause the increase, like cruising upstream, wind velocity, depth of water, fuel quality, etc. I countered all of these arguments and had a reply offering me a total refund. However, I did not want to return to the bad habits of my original propeller and asked if there were modifications that could be done. The reply was in the affirmative and so the boat was lifted out once again and the Axiom removed and taken to Thrapston.

I was given a very warm welcomed by Alan, who showed me around his garage workshop and told me his personal history of the boats he has owned and how his passion is the Axiom design. He offered to dress and balance the original propeller, free of charge, and then run it up on his dynamometer and take appropriate readings every 100 revs. After which, he would run the Axiom and match it to the characteristics of the original prop. He proposed to reduce the diameter by a small amount and reduce the shear, but refused to tell me how he intended doing that – trade secret! I can only assume that he removed some metal behind the blades, because in my opinion it would be almost impossible to alter the blade angle. I collected it the following day and it was re-fitted the following weekend.

 I now found the engine to be far more free revving and peaking under power another 100 rpm. There is no ‘sweet spot’ in the rev range - it was ‘sweet’ all through the rev range. I could cruise the canal at 4mph at 1400 rpm without any breaking wash. This had never been possible with this boat before. The reversing and stopping characteristics remained the same. Speed on the Thames remained at 5mph at peak revs, both upstream and down.

However, things were not as they appeared. The fuel consumption was just the same and I was not happy after a couple of short cruises up the Wey. As usual I check the lubricating oil level before every trip and suddenly it had increased by about 1 inch on the dipstick – horror of horrors! How could this happen? Further research on the internet revealed a leak of diesel into the sump of the engine and the most likely place was through the diaphragm of the lift pump. OK, get a new one from E-bay and fit it with the assumption that the diaphragm had a hole in it – false! The following weekend the oil level was again up by 1 inch, so what was left? I should at this point tell you that the engine is a BMC and the only possibility for diesel to enter the sump is through the lift pump and the injector pump, which are driven by shafts inside the engine block, so the injector pump was all that was left. Advice was sought from my local diesel service agent and my worst fears were confirmed. So, it was off with the injector pump the following weekend, which took a good four hours, having to pump out the sump and change the fuel filters yet again as well as removing the starter motor and oil filter to get access to the injector pump.

Fuel Lift Pump

I took the offending pump to Automarine Diesel Services, Portslade and they renovated it with new seals and re-calibrated it on their very expensive testing equipment for about £240. On re-fitting the engine started first time and ran very well after bleeding the system through – I was getting very good at this! All went well, until I decided to cruise up to the water point about 100yds away, when the engine refused to rev up. At first thought, it must be a broken throttle cable, but that was intact, so what was amiss now? As it happened, my friend Richard the diesel engineer, was on the scene, but could not offer a solution, recommending that I phone Automarine the following day. They were also at a loss as to why this had occurred and suggested that I return the pump, so off it came yet again, in an hour this time.

Injection Pump in situ.

After Treatment by Automarine.

The diagnosis, done in twenty minutes, was that there was a piece of dirt inside the  pump that stopped the throttle from opening fully. This was almost certainly down to me as there is so much loose paint on the engine. So, back to re-fitting yet again in thirty minutes this time – I really was getting good! This time it worked fine and it has not faltered once. The fuel consumption is now back to 1 litre/hour after 65 hours cruising and maybe even better over a longer period.

All in all, it was a salutary lesson – don’t always assume the obvious! It was also expensive and probably unnecessary to have taken off the Axiom to be modified. On the other hand, I did learn a great deal about the workings of a BMC diesel engine and you don’t usually gain experience without cost, one way or another. Finally, for all you sceptics out there, you won’t know about the Axiom until you have tried it. I would certainly never go back to the original propeller now.