Narrowboats are notoriously difficult to manouver
due to their length, poor hydrodynamic qualities,
and propulsion design - a fixed prop and a large
rudder mounted behind it.
A rotatable ducted prop would have considerable
The proposal would be to remove the existing prop
shaft (closing off the stern gland) and the
rudder. This is replaced with a ducted prop with a
set of vanes, mounted directly below the rudder
The prop is powered by a hydraulic motor; the
working fluid is plain water. The shaft bearings are
water-lubricated ceramic and some leakage is
anticipated. Flow and return connections run
through the downshaft which passes through the
aperture for the former rudder shaft. A
conventional tiller bar is fitted to the top of the
Clean water is pressurised by an engine-driven
pump. It passes down the shaft to operate the
motor. Most of the water, now at much reduced
pressure, returns to the feed tank through a filter.
As the water is admitted and retrieved via banjo
couplings, the tiller can be rotated through 360
degrees while under full power. It is as efficient in
full reverse as full forward.
Water can be diverted to operate a reversible
hydraulic bow thruster if desired.
There are no lubricants to leak and contaminate
the canal water. The below-water componenents
are fabricated from stainless steel and phosphor
bronze, both corrosion-resistant.
The propulsion unit can be removed for
maintainance without drydocking the boat.
A tank of clean "prop water" is needed to ensure
the level in the hydraulic system is maintained.