Powerboat with disappearing tunnel

Abstract

A shallow draft boat has a hull that protects a propulsion propeller within a tunnel that passes only partially through the hull from stem to bow. The hull has a mechanism, such as a flap for selectively permitting or blocking water flow access to the tunnel from under the boat. The boat also has a lift mechanism for selectively positioning a propeller of a propulsion unit substantially directly behind the tunnel or below the tunnel. The boat can operate in two modes. In one, water access to the tunnel is permitted and the propeller is positioned above the bottom of the hull and behind the tunnel. In the other, water access to the tunnel is blocked and the propelles is positioned below the bottom of the hull. This construction permits selective operation in a shallow draft mode, in a normal draft mode or in between. In the shallow draft mode, the boat prevents propulsion unit malfunction by keeping obstacles, such as debris, crab pots and mammals such as manatees from contact with the propeller.

1 . A boat, comprising: 
 a. a hull having two channels allowing water flow through the two channels substantially from bow to stern, and an intermediate tunnel passing through only a portion of the length from bow to stern; and    b. a mechanism for selectively permitting or blocking water flow access to the intermediate tunnel from under the boat.    
   
   
       2 . The boat of  claim 1  further comprising: 
 c. a propulsion unit and    d. a lift mechanism to position a propeller of the propulsion unit so that it selectively operates substantially directly behind the tunnel or below the tunnel.    
   
   
       3 . The boat of  claim 2  in which the hull and the tunnel protect the propeller from obstacles when water flow access to the tunnel is permitted and the propulsion unit is positioned behind the tunnel.  
   
   
       4 . The boat of  claim 1  in which the mechanism for selectively permitting or blocking water flow access to the tunnel from under the boat comprises a moveable flap.  
   
   
       5 . The boat of  claim 4  in which the flap is hinged to permit or block water flow access to the tunnel.  
   
   
       6 . The boat of  claim 4  in which the position of the flap can be controlled by an electric, pneumatic, or hydraulic device.  
   
   
       7 . The boat of  claim 2  in which the lift mechanism is electrically controlled.  
   
   
       8 . The boat of  claim 2  in which the lift mechanism is pneumatically or hydraulically controlled.  
   
   
       9 . The boat of  claim 2  in which the a mechanism for selectively permitting or blocking water flow access to the tunnel from under the boat and the lift mechanism are commonly controlled so as to position the propulsion unit substantially directly behind the tunnel when water access to the tunnel is permitted to position the propulsion unit below the hull when water access to the tunnel is blocked.  
   
   
       10 . A method of designing a boat, comprising the steps of: 
 a. providing a hull having two channels allowing water flow through the two channels substantially from bow to stern, and an intermediate tunnel passing through only a portion of the length from bow to stern; and    b. providing a mechanism for selectively permitting or blocking water flow access to the tunnel from under the boat.    
   
   
       11 . The method of  claim 10 , further comprising: 
 c. providing a lift mechanism to position a propeller of a propulsion unit so that it can selectively operate substantially directly behind the tunnel or below the tunnel.    
   
   
       12 . A method of reducing a boats draft, comprising: 
 a. providing two channels allowing water flow through the two channels substantially from bow to stern, and an intermediate tunnel in the hull extending only part way from stern to bow;    b. providing a mechanism for selectively permitting or blocking water flow access to the tunnel from under the boat; and    c. providing a lift mechanism for selectively positioning a propeller of a propulsion unit substantially directly behind the tunnel or below the tunnel.    
   
   
       13 . The method of  claim 12  further comprising: 
 d. a control mechanism to simultaneously control the mechanism for selectively permitting or blocking water flow access to the tunnel from under the boat and the lift mechanism.