Waterways World July 2009 - Narrowboat Editorial
Axiom Marine Propellers are a radically different design compared to conventional marine screws. We report on the first test in August 2008’s WW, Mark Langley investigates more closely.
The boat used the was a 58ft narrowboat, but on the wide, deep River Nene – not everyone’s typical cruising territory. Axiom have since evaluate their props on different narrowboats across the canal system and we were keen to see how they compared in more typical surroundings. Alan and David Watts, whom designed the propellers, invite us to follow up on our experiences and to engage in a more comparative test.
The Axiom design is more spade-like than ordinary marine screw type propellers. The core idea is that the thrust is equal both ahead and astern, with greater efficiency. The benefits are supposed to include improved stopping power, easier handling and less wash: there have been suggestions that fuel consumption may be reduced, but he data for this is very difficult to prove either way.
UK Boat Hire, who have a base at Gayton Marina, at the top of the Northampton Grand Union, kindly provided two boats for the test. The two Grebe class boats, from the Avechurch fleet are identical as any narrowboats can be: both 49ft and powered by the same Isuzu engine and gearbox. One boat had its original marine screw propeller, and the other an Axiom. The axiom prop had been tailored to give the same phasing as the original to make the test as fair as possible.

It was on a very cold, wet weekend in December that we assembled a crew of experienced narrowboaters to test the boats, on a run from Gayton, through Blisworth Tunnel, to Stoke Bruerne top lock. We left a decent gap, of around 300m between boats, to reduce any effects of turbulence between boats.
It was son obvious that, even on tickover past the many moored boats, The Axiom boat (Slavonion Grebe) that went of first, was moving slightly faster than the traditional screw boat (Pied Grebe). Following the Axiom boat, we could make out that the turbulence from the thrust of the prop surfaced much further behind the boat, than the traditional prop – which is what we expected from the Nene trials.
In the tunnel, the Axiom boat powered ahead, and despite maintaining the same engine revolutions, ending up moored a good five minutes ahead of the other boat outside the Waterways Museum. We then winded each boat and took it in turn back up the tunnel mouth, to use the winding hole for further photographs and reversing practice. Once this had been completed the crew swapped around (after a brief rest indoors, away from the torrential rain!) to take the boats back through the tunnel, this time with the conventional screw boat first.

One of the first striking differences which showed even when winding the boats was the Axiom propeller gave far more thrust astern. The conventional boat stopped in just over half its length from a fast walking pace: the Axiom managed it I under half a boat length. Slavonian Grebe was able to steer more confidently astern, while the marine screw boat required constant corrections in forward gear to maintain direction.
Looking at the water patterns around the boat while they were underway explained another aspect: the Axiom allowed the boat to sit virtually level underway. Both boats had full water tanks, yet the marine screw boat adopted a more bow-up posture when cruising. The suction hollows that occur behind the bow wave were much reduced, as was the bow wave itself, with the Axiom. The dip in the waterline level that occurs at the stern was also reduced. Presumably the Axiom, pushing the water out in a tighter arc, does not push the stern down as much.
Once back in the marina, the crew exchanged notes and comments. Both commented on the stopping power of the Axiom boat. Handling was definitely more positive, with less feedback on the tiller, plus reduced vibrations – though both boats were commendably vibration free inside the cabin.

One of the previous testers had noted that his boat behaved differently in tunnels with the Axiom fitted than without, and our test bore this out. The reduced suction hollows at the bow and stern probably mean that the boat does not pull towards the side as the conventional screw. When viewed from above, the Axiom boat shows slightly less wash, despite moving quickly. However, the height of the stern wash was lower, probably due to being run almost level. This may also explain that moored boats moved less on their lines as we passed with the Axiom powered boat, than the conventional prop.

It does appear that the Axiom propeller gives advantages over a standard marine screw: stopping power, handling astern, and the boat running level. Time will tell whether boaters consider the premium for this design to be worth paying for.