Tractor-type drive for boats with trim plane

Abstract

A drive for a boat includes a gear case and a propeller rotatably mounted to a front of the gear case. The drive also includes a drive support for mounting the gear case to the boat. The drive support allows at least a portion of the gear case to pivot about a trim axis to adjust the boat's trim. A trim plane is formed as part of, or added to, the gear case between a lower portion of the gear case, usually underwater in use, and an upper portion of the gear case. The trim plane has sufficient exposed lower surface area to apply a downward force on the water to assist trimming of the boat.

We claim: 
     
         1 . A tractor-type drive for a boat, comprising:
 a gear case;   a drive support for mounting the gear case to the boat, the drive support configured to allow at least a portion of the gear case to pivot about a trim axis;   a pulling-type propeller mounted on a propeller shaft extending forward from a front of the gear case;   wherein the gear case comprises a trim plane between a lower portion and an upper portion of the gear case, the trim plane configured to apply a downward force on the water to assist trimming of the boat.   
     
     
         2 . The drive of  claim 1 , wherein the trim plane has an upper surface and a lower surface, wherein the lower surface has a surface area of at least about 70,000 mm 2  exposed to the water. 
     
     
         3 . The drive of  claim 2 , wherein the lower surface has a surface area of about 90,000 mm 2  exposed to the water. 
     
     
         4 . The drive of  claim 1 , wherein the trim plane has a first width at a forward end thereof and a second width at an aft end thereof, and
 wherein the first width is less than or equal to the second width.   
     
     
         5 . The drive of  claim 4 , wherein the first width is less than the second width such that the trim plane tapers from back to front. 
     
     
         6 . The drive of  claim 1 , wherein the drive support is configured to allow at least a portion of the gear case to pivot about a steering axis to steer the boat, wherein the trim plane pivots with the gear case about the steering axis. 
     
     
         7 . The drive of  claim 1 , wherein the trim plane has a front end, the front end of the trim plane begins rearward of the pulling-type propeller. 
     
     
         8 . The drive of  claim 1 , wherein, when mounted on a boat, the drive support is configured to position the pulling-type propeller substantially rearward of the boat's transom. 
     
     
         9 . The drive of  claim 1 , wherein the trim plane has an upper surface configured to be above the water and a lower surface configured to be at or below the water, the lower surface being planar. 
     
     
         10 . A boat, comprising:
 a hull; and   a drive attached to a stern of the hull, the drive comprising:
 a gear case; 
 at least one propeller rotatably mounted at a forward end of the gear case; and 
 a drive support mounting the gear case to the stern of the hull such that the gear case is able to pivot about a trim axis, 
   wherein the gear case comprises a lower portion and an upper portion and a trim plane between the lower portion and the upper portion, the trim plane has a lower surface with an exposed surface area of at least about 70,000 mm 2  to apply a downward force on the water to assist trimming of the boat.   
     
     
         11 . The drive of  claim 10 , wherein the lower surface has a surface area of about 90,000 mm 2  exposed to the water. 
     
     
         12 . The drive of  claim 10 , wherein the trim plane has a first width at a forward end thereof and a second width at an aft end thereof,
 wherein the first width is less than or equal to the second width.   
     
     
         13 . The drive of  claim 12 , wherein the first width is less than the second width such that the trim plane tapers from back to front. 
     
     
         14 . The drive of  claim 10 , wherein the drive support is configured to allow at least a portion of the gear case to pivot about a steering axis to steer the boat, wherein the trim plane pivots with the gear case about the steering axis. 
     
     
         15 . The drive of  claim 10 , wherein the trim plane has a front end, the front end of the trim plane is positioned rearward of the at least one propeller. 
     
     
         16 . The drive of  claim 10 , wherein, the drive support is configured to position the at least one propeller substantially rearward of the transom. 
     
     
         17 . The drive of  claim 10 , wherein the trim plane has an upper surface configured to be above the water and a lower surface configured to be at or below the water, the lower surface being planar.