NO20181547A1

NO20181547A1 - Propulsion for hydrofoil vessels

Info

Publication number: NO20181547A1
Application number: NO20181547A
Authority: NO
Inventors: John Martin Kleven Godø; Jarle Vinje Kramer
Original assignee: Norwegian Univ Sci & Tech Ntnu
Priority date: 2018-11-30
Filing date: 2018-11-30
Publication date: 2020-06-01

Description

PROPULSION FOR HYDROFOIL VESSELS

This invention relates to propulsion for hydrofoil vessels, and in particular is concerned with the use of a water jet propulsion system for hydrofoil vessels.

It is known to use water jets for propulsion of various marine vessels. It is widely held that the greatest amount of thrust is achieved with the water jet above the water line, i.e. with the jet being emitted into air rather than into the water. In the case of hydrofoil vessels it is typical to have a water intake that extends below the hull of the vessel in order to keep it submerged whilst the vessel is elevated by the action of the hydrofoil. The water is lifted from the intake into the hull by a pump or similar, and then expelled from an outlet at a rear end of the hull. The inventors have identified a need for improvement of the efficiency of such systems.

Viewed from a first aspect, the invention provides a hydrofoil vessel, the hydrofoil vessel comprising: a hull; and a water jet propulsion unit; wherein the water jet propulsion unit includes a water inlet arranged to be located below the water surface whilst the hydrofoil vessel is in motion, and a water outlet arranged to be located above the water surface whilst the hydrofoil vessel is in motion; and wherein the water outlet is placed outside of a main body of the hull and below the rear end of the main body of the hull.

With this arrangement water jet propulsion unit is placed at a vertical position which is below the surrounding part of the hull, and connected to a water inlet that is in a position below the water surface when the vessel is in motion.

The inventors have made the non-obvious realisation that the water jet propulsion of hydrofoil vessels with the water outlet in the main part of the hull involves a propulsion efficiency loss due to the need to lift water vertically from the water surface all the way to the hull in order to convey it to the outlet opening. Energy is lost through two independent mechanisms:

‐ Energy needed to lift the water vertically from the free water surface to the height of the water jet outlet.

‐ Energy needed for overcoming the inner resistance of the pipe/strut/channel leading from the water intake opening to the water jet outlet opening.

Both of these mechanisms lead to less efficient propulsion and thereby increased power and energy requirement for propelling the vessel at a given speed or a certain distance respectively. By placing the water outlet below the rear end of the hull the vertical distance from the inlet to the outlet is reduced compared to prior art arrangements where the water outlet is within the main part of the hull and water is propelled through the rear end of the hull, and the passageways used to convey the water from the inlet to the outlet can be made shorter. The propulsion system therefore becomes more energy efficient.

The water outlet may be placed within an extension of the hull that protrudes downwards from the main body of the hull at the rear end of the hull. This extension of the hull may be an integral part of the hull, or it may be a separate hull element that is joined to the outside of the main body of the hull.

The vessel may be arranged so that the water outlet is at least 20 cm below the bottom of the rear end of the hull, or at least 50 cm below the bottom of the rear end of the hull. It will be appreciated that there are benefits from any lowering of the outlet compared to placing the outlet in the rear part of the hull, whilst the maximum benefit can be achieved by arranging the downwardly protruding extension of the hull to place the water outlet as close as possible to the water surface, whilst avoiding contact with the water surface to avoid impeding movement of the hydrofoil vessel. Typical hydrofoil vessels might fly 20-100 cm above the water surface, and the vessel may be arranged in order to place the water outlet below the rear end of the hull and within the 20-100 cm space. The location of the water outlet may be defined herein with reference to the lowest part of the water outlet.

The downwardly protruding extension of the hull should have a length shorter than the overall length of the hull and may be narrower than the hull in the surrounding areas. The length of the downwardly protruding extension of the hull may for example be less than 10% of the total length of the hull. The width of the downwardly protruding extension of the hull may for example be 50% or less of the width of the main body of the hull.

The water jet propulsion unit can use a conventional arrangement for the passageways between inlet and outlet as well as for the motive force for the water jet, which may for example be a pump. In some examples the water jet propulsion unit is identical to known water jet propulsion units aside from the location of the water outlet relative to the hull. A conventional placement of the water inlet may be used in some cases. What is significant is that the water outlet discharges water through the rear end of the lowered extension part of the hull, and this is at a vertical position which is lower than what would have been the case if the water jet propulsion unit was placed inside the remainder of the vessel hull, as with the prior art.

The vessel may have a single hull or multiple hulls, such as being a catamaran or trimaran hydrofoil vessel. Where the vessel has a plurality of hulls then there may be a similar plurality of water jet propulsion units, such as one for each of the hulls. Each water jet propulsion unit advantageously has its outlet placed outside of a main body of the respective hull and below the rear end of the main body of the respective hull. Thus, for a vessel with two hulls there may be a first hull and a second hull with associated first water jet propulsion unit and second water jet propulsion unit, with the first water jet propulsion unit having an outlet outside of a main body of the first hull and below the rear end of the main body of the first hull, and the second water jet propulsion unit having an outlet outside of a main body of the second hull and below the rear end of the main body of the second hull.

The hull design may be similar to known hull designs. The hull has a rear end at the stern of the vessel, and an underside running from the base of the rear end along to the bow. The underside of the hull defines the lowest extent of the main body of the hull, and thus since the water outlet is placed outside of a main body of the hull and below the rear end of the main body of the hull then the water outlet is below the line of the underside of the hull at the rear end of the hull, although it will be appreciated that depending the form of the hull the underside may dip lower than the rear end as the line of the underside extends from the base of the rear end and along to the bow of the vessel. Thus, with the current proposal the water outlet is always placed lower than would be possible with placement of the water outlet in the rear end of the hull, but this may not be fully beneath the vertical height of the entirety of the hull.

The hydrofoil vessel may include wings similar to those used with known vessels, such as a main wing extending across the width of the hull and located below the main body of the hull. In the case of a multiple hull vessel the main wing may extend across the width of all of the hulls as well as spanning the width between the hulls. The hydrofoil vessel may include a wing attached beneath the water jet propulsion unit. The water inlet may be supported on a downwardly extending element mounted beneath the water jet propulsion unit, with a wing attached to this downwardly extending element, for example at the base of the downwardly extending element. The downwardly extending element optionally incorporates a control surface for providing steering control to the vessel, e.g. a rudder surface.

Certain example embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 shows a side view of a hydrofoil vessel with a water jet propulsion unit set below the main body of the hull;

Figure 2 shows a close up of the rear of the vessel of Figure 1;

Figure 3 is a stern view of the vessel of Figure 1, showing two catamaran hulls and the extended parts of the hulls;

Figure 4 is a similar view to Figure 3, with the main wing of the hydrofoil omitted;

Figure 5 is a close up perspective view of the rear of one of hulls of Figure 3, showing more details of one of the water jet propulsion units; and

Figure 6 is a perspective view from the front and side of a similar part of the hull to that shown in Figure 5.

The Figures show an example relating to a catamaran hydrofoil vessel. It will be appreciated that the proposed arrangement of the water jet propulsion unit, with the outlet outside of the main part of the hull and below the rear end of the hull, could be used for various forms of hydrofoil vessels. The main features of the example, as shown in Figures 1 to 6, are as follows:

Vessel 2,

(Catamaran) hull(s) 4,

Main hydrofoil 6,

Extension 8 to the hull 4 below the rear end of the hull 4

Water jet propulsion unit 10,

Water outlet 12 for the water jet propulsion unit,

Water inlet 14 for the water jet propulsion unit,

Downwardly extending element 16,

(Secondary) wing 18 on the downwardly extending element 16,

Control surface 20 on the downwardly extending element 16,

Controllable nozzle 22 at the water outlet 12.

The inter-relationships between these parts will be apparent from the drawings as well as from the other discussion herein. The drawings also show a representation of the water surface 24, which is depicted at a typical level below the vessel 2 and under the base on the hulls 4 to show the location of the water surface 24 during forward motion of the vessel 2. The underside of the hull(s) 4 sits at a level above the water surface as indicated by the line A in Figures 1, 2 and 3. The water outlet 12 of the water jet propulsion unit is below this line A, sitting within an extension 8 to the hull 4 that protrudes below the underside of the hull.

The water inlets 14 are equipped with horizontal hydrofoils 18 that can act as elevator wings for the vessel 2 and vertical control surfaces 20 that can act as rudders for the vessel 2, although it will be appreciated that advantages from placing the water outlet 12 beneath the rear end of hull 4 can be achieved with or without these features. The water inlets 14 might hence not be equipped with such hydrofoils 18 and/or control surfaces 20. The shape of the water inlet 14 is one example of how this might look, but any suitable form can be used.

Increased propulsive efficiency is achieved through two principles:

‐ Reduced lifting height from the water surface 24 to the water jet outlet opening 12. This leads to a reduction of power loss connected with vertical lifting of water.

‐ Reduced length of the inner channel of the pipe/strut/channel leading from the water intake opening 14 to the water jet outlet opening 12. This leads to a reduction of power loss connected with inner resistance in the pipe/strut/channel.

Claims

CLAIMS:

1. A hydrofoil vessel, the hydrofoil vessel comprising: a hull; and a water jet propulsion unit; wherein the water jet propulsion unit includes a water inlet arranged to be located below the water surface whilst the hydrofoil vessel is in motion, and a water outlet arranged to be located above the water surface whilst the hydrofoil vessel is in motion; and wherein the water outlet is placed outside of a main body of the hull and below the rear end of the main body of the hull.

2. A hydrofoil vessel as claimed in claim 1, wherein the vessel is arranged so that the water outlet is at least 20 cm below the bottom of the rear end of the hull, or at least 50 cm below the bottom of the rear end of the hull.

3. A hydrofoil vessel as claimed in claim 1 or 2, wherein the water outlet is placed within an extension of the hull that protrudes downwards from the main body of the hull at the rear end of the hull.

4. A hydrofoil vessel as claimed in claim 3, wherein the downwardly protruding extension of the hull has a length shorter than the overall length of the hull and is narrower than the width of the hull in the surrounding areas.

5. A hydrofoil vessel as claimed in claim 4, wherein the length of the downwardly protruding extension of the hull is less than 10% of the total length of the hull.

6. A hydrofoil vessel as claimed in claim 4 or 5 wherein the width of the downwardly protruding extension of the hull is 50% or less of the width of the main body of the hull.

7. A hydrofoil vessel as claimed in any preceding claim, wherein the vessel comprises a plurality of hulls and a plurality of water jet propulsion units.

8. A hydrofoil vessel as claimed in any preceding claim, wherein the vessel comprises two hulls including: a first hull and a second hull with a first water jet propulsion unit and a second water jet propulsion unit, wherein the first water jet propulsion unit has an outlet outside of a main body of the first hull and below the rear end of the main body of the first hull, and the second water jet propulsion unit has an outlet outside of a main body of the second hull and below the rear end of the main body of the second hull.

9. A hydrofoil vessel as claimed in any preceding claim, wherein the vessel comprises a main hydrofoil wing extending across the width of the hull(s) and located below the main body of the hull(s).

10. A hydrofoil vessel as claimed in any preceding claim, wherein the vessel comprises a secondary hydrofoil wing attached beneath the water jet propulsion unit(s).

11. A hydrofoil vessel as claimed in claim 10, wherein the vessel comprises a downwardly extending element mounted beneath the water jet propulsion unit, with the water inlet being supported on the downwardly extending element and the secondary hydrofoil wing attached to the downwardly extending element.

12. A hydrofoil vessel as claimed in claim 11, wherein the downwardly extending element incorporates a control surface for providing steering control to the vessel.