Field of the Invention; The present invention relates to powered marine craft, and more particularly the high speed varieties. Specifically it is directed to high speed water craft which use a surfacing propeller mounted in a propeller tunnel. The prior art can be located in Class 440, subclasses 66-70.

Summary of the Prior Art; The use of propeller tunnels is not new. This is true in both water craft and even the shrouding of aircraft. The propeller tunnel permits recessing the propeller at least in part interiorly of the projected area of the hull. Numerous problems arise with current surfacing propeller applications including dangerous exposure of the propeller. Another problem relates to the steering torque and avoiding the same. Most importantly, however, at low speeds there is cavitation and low thrust and water pile up at the transom in reverse. Accordingly achieving a planing configuration consumes considerable excess power, results in inefficient fuel consumption, and delays the boat when used as a pursuit ship or racing ship in getting up into a planing- configuration and reaching the maximum intended speed. Examples of the prior art patent may be seen in the following: U.S. Patent Nos. 2,434 700; 3,702,485 RE23,105; RE38,522; 130,391; 807,769; 815,270; 1,081,876 1,117,357; 1,262,942; 1,401,963; 2,138,831; 3,450,090 4,031,846; 4,363,630; 4,383,828; 22,080; Japanese Patent No. 55-156795(A) ; British ^' Patent No. 769,307; British Application Nos. 2,075,452 and 2,055,080. In particular the patents 2,434,700 and 3,702,485 relate to the type of tunnel involved.

Summary of the Invention: The- present invention is directed to a marine craft having a propeller tunnel in

which the sidewalls of the tunnel are essentially parallel and vertical and mate with a descending upper surface of the tunnel which optionally can be divided into a transom plate portion, engine plate portion, and bottom plate portion. The bottom plate portion mates with the bottom of the boat hull in a sharp line intersection. A surfacing propeller and associated drive shaft is mounted in the tunnel with a rudder positioned aft of the surfacing propeller. Baffles are provided on the lateral sides of the tunnel and terminate in a forward portion aft of the bottom plate portion of the tunnel. Optionally the exhaust can be vented onto the bottom plate portion of the tunnel to augment the flow of air, quiet engine and draw exhaust from engine. The method of the invention is directed to forcing the flow of air inside a surfacing propeller tunnel on a boat to the end that baffles provided on the lateral side are fed by air from the transom portion of the baffle and induced by the forward motion of the boat as well as the pneumatic effect of the surfacing propeller portion which is not in the water to force the air to go into the tunnel portion and thereby minimize any negative pressure build-up which would otherwise occur absent of venting. In addition the method optionally contemplates augmenting the pressure within the tunnel by directing the exhaust to a forward portion of the tunnel .

In view of the foregoing it is a principal object of the present invention to provide a vented boat tunnel in which the tunnel utilizes a surfacing propeller and venting the same to supply ambient air circulating to the forward portion of the tunnel and then rearwardly over the non-submerged portion of the surfacing propeller.

Another object of the present invention looks to the development of a tunnel for a surfacing propeller in which

-3- ^" the major portion of the surfacing propeller is within or adjacent the tunnel, and in . which baffles provide for venting the tunnel to permit accelerating the boat and maintaining planing speeds. 5

Yet another object of the present invention looks to the provision of a surfacing propeller tunnel which permits reducing the angle with horizontal that the drive shaft for the surfacing propeller makes thereby reducing the 10 component which would tend to drop the bow portion of the - boat into the water when underway.

Brief Description of the Drawings: Further objects and advantages of the present invention will become apparent 15 as the following description of an illustrative embodiment proceeds, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of the rear portion of a boat 0 having a surfacing propeller and tunnel mount for the prope1ie ;

FIG. 2 is a side view of the same boat as shown in FIG. 1 in essentially the same scaie; 5

FIG. 3 is a bottom view in enlarged scale of ther boat shown in FIGS. 1 and 2 focusing on the construction of the tunnel and showing the flow of air in alternative forms, the form when cruising, and the form when idling; 30

FIG. 4 is a longitudinal section view, in part, showing the interior of the propeller tunnel and the engine mount in the slow speed configuration;

5 FIG. 5 is a view from the same perspective as FIG. -but showing, the boat, in its planing o- - crusing configuration; ajTc-

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FIG. 6 is a perspective view taken from underneath and behind the. surfacing propeller showing the interior portions of the tunnel.

5 FIG. 7 showing venting from upright tubes taking air from hull interior or deck.

Description of the Preferred Embodiments:

~ ~ Apparatus; In FIG. 1 it will be noted that a boat 10 is shown having a relatively conventional transom 11, and curvilinear sides 12 above keel 13 moving forward to a bow 14. The underneath portion of the boat is a V-bottom 15 with a keel 13 and rudder assembly 16 exterior and aft of

15 the transom 11. The rudder assembly 16 includes the cantileverly supported rudder 18 which depends from a rudder mount 19 which, in turn, is mounted to the transom 11. The rudder can be of any convention means.

0 A tunnel 20 is provided underneath the V-bσttom 15. Turning now to FIGS. 5, 6 and 7, it will be seen that the tunnel has an upper surface which includes a transom plate portion 21, an engine plate portion 22 which slopes downwardly from the transom plate portion 21 which is es- 5 sentially parallel to the path of travel, and terminating in a bottom plate 24 which intersects the V-bottom 15 of the boat in a relatively sharp line, particularly as seen in FIG. 6.

0 A surfacing propeller 25 is mounted interiorly of the tunnel and is driven by a drive shaft 26. The drive shaft

26 is mounted by a shaft mount to the transom plate

. portion 21 of the tunnel 20. A stuffing box 29 in the engine plate portion 22 of the tunnel 20 provides access 5 to the drive assembly interiorly of the boat hull.

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In accordance with the invention baffles 30 are provided at either side and the top of the tunnel 20, and intersect the tunnel sides 31 of the tunnel. The interior portion of the baffles includes a baffle channel 32. The front portion of the baffle channel 34 is located aft of the bottom plate 24 of the tunnel 20. As noted particularly in FIG. 6, the baffles 30 are trapezoidal in configuration with the rear portion opening through the transom 11. The forward portion of the baffle 34 opens at a position slightly above the plane of the drive shaft 26 and scoops water at slow speeds, but is proportioned to always be above the water at higher speeds.

As noted interiorly of the boat in FIGS. 4 and 5 an engine 40 is mounted above the engine plate 22 of the top of the tunnel 20. An engine drive shaft 41 extends forwardly to a gear box 42. Optionally, as shown in FIG. 4, the engine exhaust 44 is routed to the forward portion of the engine plate 22 of the tunnel 20, and as shown in FIG. 6, exhaust ports 45 are located just aft of the bottom plate 24 of the tunnel. Also shown in phantom lines is the outline for a drive package and tunnel insert for conversion of existing boats.

Center of Gravity: When establishing the center of gravity for this type of craft there are several important considerations. The surfacing type propeller has significant lift and effects the dynamic center of gravity. The absence of the bottom in the area of the tunnel as well as the levei of the water and the air pressure in the tunnel have an effect on the dynamic "center of gravity. The aerodynamic, hydrodynamic and drag forces are similar to other planing hulls. When the differences are considered this type of system requires a nominal center of gravity of oniy 20 to 30 percent of hui i length forward of the transom. This changes wi h hull design., speed of craft and horsepower.

Plate Lengths; The length of the plates mentioned are proportioned to the size of craft and vary with the following considerations:

Bottom Plate 24: The bottom plate intersects the bottom at an angle greater than 30 degrees to promote separation of the flow stream at slow speeds. The length of the plate is appropriate to accommodate the shaft log with a minimum recommended vertical height of 25 percent of the propeller diameter.

Engine Plate 22: The engine plate length and angle are tailored to the engine configurations. The angle may be less than the bottom plate to parallel to the bottom of the hull terminating at the transom plate.

Transom Plate 21: The transom plate angle is to be parallel to the hull bottom at an elevation that allows 60 percent of the propel lor diameter vertically from the keel line to the bottom of the plate. The length of the transom plate is determined by the rudder, strut, .and propeller location. It is terminated at the forward end at the engine plate. The transom plate may terminate at its intersection with the bottom plate if the engine configurations allow. The rudder may be installed in the conventional manner under the hull if room permits or aft of craft.

Overall Tunnel 20 Length: The nominal tunnel 20 length for this type of system is 300 percent of the propeller diameter. Shorter configura ions will inhibit acceleration and reduce tracking stability gained from the tunnel walls. Longer configurations will increase propeller submersion reducing top speed.

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Propeller Location: The propeller is located to meet several of the following conditions:

1. The spray from the propeller must not cover the baffle inlets.

2. The minimum distance from the leading edge of the tunnel to the rear face of the propeller circle is to be 300 percent of the propeller diameter.

3. The nominal elevation of the propeller center line is to be coincident with the keel line. Up from this position increases top speed and craft crab angle. Down from this position has opposite effect.

4. Under dynamic conditions the propeller lift is included in the dynamic center of gravi y and allows tuning of the craft for a window of speed. For speeds other than this window the attitude of craft can be adjusted by conventional trimming techniques.

Tunnel and Vent Areas: The area of the tunnel 20 and the vents (baffle channels 32) are to be constructed with the following considerations:

1. The venting area required is a minimum of 25 percent of the propeller circle area when the vents are in communication with ambient air. This venting area can be divided between the baffles and the vent tubes or contained entirely by one venting system.

2. The total area of the tunnel including the rear vents in the plane of the transom of the boat is to be 80 percent of the propeller circle area.

The Method: The method of the present invention is directed to the flow of air interiorly of a surfacing

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propeller tunnel in a water craft. The method is performed by directing a flow of ambient air from the transom forward to the front portion of the surfacing propeller tunnel. Thereafter the air is permitted to reverse rearwardly and be engaged and accelerated by the non-submerged portion of the surfacing propeller which is in the air. Optionally the negative pressure tendency of the propeller tunnel is offset by confining the engine exhaust and directing the same interiorly of the tunnel.

Although particular embodiments of the invention have been shown and described in full here, there is no intention to thereby limit the invention to the details of such embodiments. On the contrary, the invention is to cover all modifications, alternatives, embodiments, usages and equivalents of the subject invention as fall within the spirit and scope of the invention, specification, and the appended claims.