Main Fleet Features Voith Schneider Units


Voith Schneider® Propellers
Over 75 years ago a new propulsion system, then the only one of its kind in the world was developed by Voith from an idea by the Austrian engineer Ernst Schneider. It allows thrust of any magnitude to be generated through 360º quickly, precisely and in a continuously variable manner. It combines propulsion and steering in a single unit, with only the propulsion blades protruding out beneath the vessel's hull.

This solution is relatively straightforward: on this revolutionary system, a rotor casing, sitting in the ship's engine space, and which ends flush with the bottom of the hull is fitted with a number of axially parallel blades and rotates about a vertical axis. To generate thrust, each of the propeller blades performs an oscillating motion about its own axis. This is superimposed on the uniform rotary motion of the main casing. Blade excursion determines the amount of thrust, while the phase angle of between 0° and 360° determines its direction. As a result, the same amount of thrust can be generated in any direction, making a useful variable-pitch propeller - especially for double-ended drive through ferries like the Loch Class. Both variables - the magnitude and the direction of thrust - are controlled by a mechanical kinematic transmission, controlled by the ship's master.

Voith Schneider Propeller

Sectional Drawing of Unit
A CalMac Loch Class Voith Unit

The ideal combination:  
It is suggested that the quickest and safest ferry route is always the shortest. Increasing safety, economy, profitability and environmental compatibility demands call for vessels designed specifically for ferry traffic on their particular route. Many of the shorter routes on the CalMac network require a ferry that shuttles back and forth between the terminals - essentially acting like so-called 'floating bridges'. The Loch Class are a perfect example of this design, bringing with them drive-through capability as well as being highly manoeuvrable.

The reliability of a bridge is determined by its pillars. in the same respect it has been said that the "pillars" of CalMac's Loch Class ferries, from Loch Striven, the first of the original four 'Baby Lochs' to the 1991-built 'Super Lochs' Loch Fyne and Loch Dunvegan, are the Voith Schneider® Propellers: the combined propulsion and steering system adopted. They allow the vessels to berth with speed and ease, unload and reload vehicles without having to use mooring ropes to hold them in position and allow the ship to sail in either direction without having to back away from the berth and spin round. Tight locations are also not a problem - for example a ship the size of Loch Fyne can turn easily in the narrow confines of Lochaline, the Loch Buie can spin round in her own length while at the same time avoiding the sandbanks in the Sound of Iona, and the Loch Alainn can negotiate easily the tight approach round the end of Largs pier to the designated slipway.

In the CalMac fleet, it is not only the Loch Class ferries that use this propulsion system. The Streakers also use this revolutionary system to great effect. Not being of drive-through design, they have to spin round to use their stern or side ramps. Thanks to the high manoeuvrability allowed by the propulsion units down-below, tight turns can be made on the approaches to Gourock, Wemyss Bay, Dunoon and Rothesay - a factor that helps to keep the timetable on the Cowal and Bute routes as accelerated as possible.

CalMac vessels fitted with Voith-Schneider Units:


Loch Striven, Loch Linnhe, Loch Riddon, Loch Ranza, Loch Dunvegan, Loch Fyne, Loch Buie, Loch Tarbert, Loch Alainn, Isle of Cumbrae, Loch Shira

Keppel, Kyleakin, Lochalsh, Jupiter, Juno, Saturn

Left: Jupiter displaying her capability to travel in any
direction as she moves off Rothesay sideways using
her Voith Units.

Sequence Below: Loch Buie shows how easy it is
to 'spin' on the spot as she rotates 180' at her
Fionnphort berth.

Diagrams and Article Text From VOITH. Additional text and photos by Ships of CalMac

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