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A boat including a propeller tunnel portion formed in a hull of the boat in which a propeller rotates on an output shaft that extends from the propeller tunnel. A protrusion having a curved portion terminates in a tip portion. The protrusion extends from the propeller tunnel portion and the tip port

A boat including a propeller tunnel portion formed in a hull of the boat in which a propeller rotates on an output shaft that extends from the propeller tunnel. A protrusion having a curved portion terminates in a tip portion. The protrusion extends from the propeller tunnel portion and the tip portion terminates near the aft plane of the propeller. The placement of the protrusion in the propeller tunnel portion can be shown to improve propulsion efficiency.

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1. A boat comprising: a propeller tunnel portion formed in a hull of the boat;an output shaft extending from said propeller tunnel portion;a propeller comprising a plurality of blades, said propeller rotating on said output shaft, said propeller defining an outer diameter, a forward plane perpendicu

1. A boat comprising: a propeller tunnel portion formed in a hull of the boat;an output shaft extending from said propeller tunnel portion;a propeller comprising a plurality of blades, said propeller rotating on said output shaft, said propeller defining an outer diameter, a forward plane perpendicular to said output shaft and defined by a forward-most extension of said blades of said propeller, and an aft plane perpendicular to said output shaft and defined by an aft-most extension of said blades of said propeller;a protrusion having a curved portion that terminates in a tip portion and provides a cowl around at least a portion of said propeller, said protrusion inwardly extends a distance from a surface of said propeller tunnel portion and said tip portion terminates at or abaft said aft plane, and wherein said cowl has an edge disposed at or abaft said aft plane of said propeller,further wherein said propeller tunnel portion defines a contoured portion configured to serve as an inflow opening ahead of said forward plane, wherein said contoured portion defines a maximum radius (RI) according to the formula, RI=RPslipwhere (RP) is a radius dimension of said propeller, and (slip) is a ratio of the propeller speed of advance divided by the product of a shaft rotational velocity and a pitch of said propeller. 2. The boat of claim 1 wherein said curved portion defines a surface that longitudinally becomes closer to said output shaft. 3. The boat of claim 1 wherein said curved portion defines a surface that longitudinally becomes closer to said propeller. 4. The boat of claim 1 wherein said propeller tunnel portion converges longitudinally about said output shaft. 5. The boat of claim 1 wherein said protrusion extends from said hull of the boat as an annular structure providing said cowl around an entirety of said propeller, said cowl having an annular edge defining a minimum inner diameter, said annular edge disposed at or abaft said aft plane of said propeller. 6. The boat of claim 1 further comprising a second propeller tunnel portion formed in said hull of the boat in which a second propeller rotates on an output shaft that extends from said second propeller tunnel portion, said second propeller comprising a plurality of blades and defining an outer diameter, a forward plane perpendicular to said output shaft and defined by a forward-most extension of said blades of said propeller, and an aft plane perpendicular to said output shaft and defined by an aft-most extension of said blades of said propeller; and a second protrusion having a curved portion that terminates in a tip portion, said second protrusion inwardly extends a distance from a surface of said second propeller tunnel portion and said tip portion of said second protrusion terminates at or abaft said aft plane of said second propeller. 7. The boat of claim 1 wherein said protrusion produces a cone-shaped zone rearward of said aft plane of said propeller, said cone-shaped zone contains air and is partly devoid of water. 8. The boat of claim 1 wherein said protrusion is fixed to said propeller tunnel portion. 9. A boat with a deck on which occupants can travel on water using the propulsive force of a propeller rotated on an output shaft, the boat comprising: a hull having a first portion forward of a second portion;a surface of said first portion that diverges from or is parallel to the deck;a surface of said second portion defines a propeller tunnel portion in which the propeller rotates on the output shaft, said propeller tunnel portion includes a portion that converges toward the deck;a protrusion inwardly extending a distance from a surface of said propeller tunnel portion and having a curved portion that terminates in a tip portion and provides a cowl around at least a portion of said propeller, said curved portion diverges from the deck, wherein the propeller comprises a plurality of blades and defines a forward plane perpendicular to the output shaft and defined by a forward-most extension of said blades of the propeller, and an aft plane perpendicular to the output shaft and defined by an aft-most extension of said blades of the propeller, wherein said tip portion is disposed at or abaft said aft plane of the propeller. 10. The boat of claim 4 wherein said propeller tunnel portion defines a contoured portion having an inlet section, a transition section, and a converging section. 11. The boat of claim 10 wherein said contoured portion defines a maximum radius at or ahead of said forward plane. 12. The boat of claim 1 wherein said tip portion terminates at a position rearward of said aft plane. 13. The boat of claim 12 wherein said tip portion terminates at a position outside of said outer diameter of said propeller. 14. The boat of claim 12 wherein said tip portion terminates at a position inside of said outer diameter of said propeller. 15. The boat of claim 1 wherein said tip portion is longitudinally aligned with said aft plane. 16. The boat of claim 1 wherein an entirety of said forward plane of said propeller is configured to be fully covered by water. 17. The boat of claim 9, wherein said propeller tunnel portion defines a contoured portion configured to serve as an inflow opening, wherein said contoured portion defines a maximum radius (RI) according to the formula, RI=RPslipwhere (RP) is a radius dimension of said propeller, and (slip) is a ratio of the propeller speed of advance divided by the product of a shaft rotational velocity and a pitch of said propeller.