Advances in superyacht propulsion
by Roger Marshall
Many of new drives tout space savings in the engine room, perhaps leaving extra space for an SCR unit and the urea storage tanks needed to reduce NOx emissions.
Whether they will save enough space is doubtful, but these newer drives could change the entire engine room concept by putting gearboxes and propulsion units outside the hull, eliminating steering systems and using the extra space for environmental controls.
Smaller craft also have seen performance efficiencies from various styles of drive trains: Volvo Penta’s IPS system led the way, followed by Zeus and now Fortjes.
The Fortjes system is squarely aimed at larger craft. Rumour has it that the Volvo Penta IPS system also will be available soon for larger vessel’s up to 36.5m.
The Fortjes Drive System
From Reintjes Gears in Germany comes a new pod drive propulsion system. The pod drive has propellers at either end of the unit, one pushing and one pulling, and splits the engine power between both props.
According to Reintjes, this results in a lower blade loading on the prop, less noise, less cavitation and better high-speed thrust. The drives are not rotatable and come with their own rudders.
As expected from a gearbox manufacturer, the gearbox for the drive system is integrated into the housing at the top of the drive, making for easy installation. Reintjes claims it takes about four hours to install.
The thrust line is horizontal, which improves boat speed and handling.
The drives are available for vessels up to 2,000 kilowatts (about 2,800 horsepower) making them one of the largest yacht drives available.
The Voith Linear Drive
Lying somewhere between a ducted propeller (Kort nozzle), with its low-speed, high-towing capability, and a water jet, with its high-speed but lack of low-speed manoeuvrability, is the Voith Linear drive.
By combining the two concepts, Voith has come up with a drive that has the advantages of both a jet drive and a Kort nozzle with low-speed manoeuvrability and high-speed, fuel-efficient potential.
According to Voith, the drive is capable of propelling a vessel at speeds up to 40 knots.
Like a pod drive, it sits outside the hull, saving space that would normally be taken up by the transmission (and maybe freeing up space for an SCR unit). Unlike a conventional ducted propeller, the unit has highly skewed propeller blades contained within a shroud, rather like the jet engine on an aeroplane.
It is steerable and has far higher speed capabilities than a Kort nozzle, plus it has high fuel efficiency. Voith says that the first Voith Linear drive will be placed aboard a wind-powered support vessel later this year.
The engine manufacturer Wärtsilä has suggested that even more changes will be coming to cut fuel consumption and emissions.
Wärtsilä sees lighter vessel construction, the use of interceptor planes for faster craft (the US Navy already has fitted wedge-shaped hull extensions on many frigates and destroyers and cut fuel consumption by several percentage points), counter-rotating propellers (similar to those used on the Fortjes drive system and Volvo Penta IPS), computer-operated pumps to reduce start-up loads and overall consumption, low-wattage lighting throughout the vessel and other systems that reduce house and engine loads.
In other words, Wärtsilä sees a totally integrated house and engine control system designed to cut emissions by keeping energy usage low.
For yachts, this could mean a far greater integration of key systems, multiplexing of all lighting functions and a huge reduction in the yacht’s carbon footprint.