The purpose of this invention is to enable sailing boats and the like to steer sideways directly by the application of side thrust when navigating in confined waters e.g. when docking with a quay or manoeuvring through narrow passages.

The conventional method for achieving this is to mount a propeller in a tunnel across the boat and below the waterline. Such a thruster tunnel can be mounted at the bow or the stem of the boat, and is disclosed, for example, in document NL 9402184.

Modern hulls, especially for sailing boats, are often designed with a planing hull, which needs very shallow draft at the bow, which means that a conventional tunnel is often mounted close to or above the water surface (fig 3). To counter this the tunnel can be moved closer to the centre of the boat but this gives a lower turning effect for a given power input.

This invention makes it possible to place the propeller under the water surface, even at the shallowest part of the hull, whilst also reducing the volume of internal space required for a conventional thruster tunnel.

The invention achieves these objectives by the features of claim 1, namely by swinging down the propeller and the propeller housing through a recess in the bottom of the boat, to which a flexible ring is attached, that is arranged around the propeller carrying arm; thus the propeller will be placed under the water surface (fig 1)

The invention is best described and understood by reference to the attached drawings.

• Fig 1. Illustrates the main principles of the invention; showing how the propeller, and its housing / shroud is swung down from a recess in the bottom of the boat.
• Fig 2. Shows an example of the conventional design; a propeller in a thruster tunnel.
• Fig 3. Shows a more typical profile of the bottom of modem boat hulls.
• Fig 4. Shows the pivot point around which the propeller assembly swings.
• Fig 5. Shows how, when fully deployed, the propeller housing locates to the boat structure so that the side forces are not directed through the pivot point