Boat motor stern walk direction stability spoiler.

Abstract

A boat experiencing stern walk, that is, when travelling at displacement hull speed, the water rushing in to fill the hollow left at the stern of the boat, pushes the boat to either port or starboard, requires constant steering correction. My invention of an aluminium direction stability spoiler, attached directly above the gearbox on an outboard motor, prevents the boat from being pushed from side to side by this displacement water and enables the boat to travel exactly as directed by the boat's steering. Intended for boats travelling only at displacement hull speed. Direction Stability Spoiler - Greg Meyer 20 25 20 26 12 14 A pr 2 02 5 A B S T R A C T 2 0 2 5 2 0 2 6 1 2 1 4 A p r 2 0 2 5 Page 3 of 3 Direction Stability Spoiler – Greg Meyer Figures 1 & 2 Here are the dimensions of the top and bottom plates of the spoiler. Figures 3 & 4 Here is a cross-section of the spoiler in Figure 3 and a side view in Figure 4. Specific dimensions are given. GREG 13-4-25 Figures 1 & 2 Top View Here are the dimensions of the top and bottom plates of the spoiler. 13-4-25 Figures 3 & 4 REAR Here is a cross-section of the spoiler in Figure 3 and a side view in Figure 4. Specific dimensions are given. BOTH SIDE Views 460 mas Page 3 of 3 Direction Stability Spoiler - Greg Meyer 20 25 20 26 12 14 A pr 2 02 5 G R E G M E Y E R 1 3 - 4 - 2 5 4 0 0 m m 2 0 2 5 2 0 2 6 1 2 1 4 A p r 2 0 2 5 4 6 0 m m S C A L E 5 : 1 G R E G M E Y E R 1 3 - 4 - 2 5 2 B O L T S T H R O C K S H M o s e e F i r s t 4 m m 5 0 m m A L U M I N I U M 8 0 m m F I N 4 0 0 m m B O T H S I D E V i e w s 4 6 0

Description

TECHNICAL FIELD The present invention relates to an improvement in the stability of the direction a boat is pointed in when travelling at displacement hull speed, to ease the burden of constant direction corrections required by the skipper. BACKGROUND OF THE INVENTION The reason for this invention was because after attaching a pod to the stern of a 6 meter planning hull fiberglass boat and downsizing the motor horsepower so that it only achieves displacement hull speed it was found that the action of the water back-filling the displacement hollow left at the stern of the boat caused the phenomenon described as ‘stern walk’. In other words, the direction in which the boat moved, under motor, was determined by this water back-filling the displacement hollow and would randomly and continuously swing the boat to port or starboard. If not corrected, the boat would travel in a circle. It was a constant effort adjusting the steering wheel to point the boat in the desired direction. Immediately upon attaching my invention to the existing fin directly above the gear box of the 25 horsepower engine, the boat was able to travel in a straight line without requiring the skipper to make any adjustments to the steering wheel. It has also enabled the boat to complete sharper turns when the wheel is turned from full lock left to full lock right and vice versa. As far as I am aware there is no other product that assists or stabilises the directional ability of a boat travelling at displacement hull speed or at planning speed. There are products 2025202612   14 Apr 2025 available that attach to the fin of an outboard motor, but they are only designed for uplift and have no directional stability ability, for example, the expired Patent #1985048552, and this type of hydrofoil attachment: https: / / www.boathardware.com.au / hydrofoil-se-sport-200-high-performance-turbo-grey. SUMMARY OF THE INVENTION My invention of a direction stability spoiler, to overcome the problematic phenomenon of ‘stern walk’, builds upon the basic outboard motor attachment design of already available products used for hydrofoil (as mentioned above). My aluminium spoiler, attached to the existing fin of an outboard motor, gives a boat traveling at displacement hull speed, directional stability using bent edges, that stabilise the motor’s movement through the water. The spoiler is made of two aluminium plates with bent edges, pop-riveted together, cut and shaped to slide over the fin of an outboard motor, and once slid on, then bolted to the motor. The left- and right-hand edges of the top and bottom plates are bent vertically (as seen in Image 4 and Figure 4) and, which are key to the spoiler’s direction stability capability. The action of the water passing the spoiler’s bent edges enables the motor to determine the direction of travel, rather than the direction of travel being determined by the water backfilling the displacement hollow (i.e. the boat succumbing to ‘stern walk’). Thus far, the spoiler has only been tested on displacement hull speed boats. The figures below, show the dimensions of the spoiler. Dimensions specific to the cut-out and flutes will be different for different sized and shaped motors (see Figures 1 & 2). The spoiler is made by cutting out the top and bottom plates from a 4mm sheet of aluminium. The cut-out sections are sized to fit a specific motor and cut out of each plate. Flutes on the top plate are also sized to fit a specific motor and bent into the top plate. The top and bottom plate edges are then bent vertically. The top and bottom plates are then pop-riveted together, Page 2 of 3 Direction Stability Spoiler - Greg Meyer 2025202612   14 Apr 2025 as in Image 2 and Figure 3. The spoiler is then slid onto the fin of an outboard motor, just above the gear box. Once snuggly fitted, the spoiler is then bolted and pop-riveted to the outboard motor. DETAILED DESCRIPTION OF EMBODIMENTS Descriptions are as above.

Claims

As previously stated, there are products designed for other purposes that attach to an outboard motor fin in a similar manner. My invention is designed specifically to overcome the problem of ‘stern walk’ as described above. The claim that I am making here is that it is the bent edges, on my spoiler, that give a boat, travelling at displacement hull speed, directional stability.Page 1 of 1Direction Stability Spoiler - Greg Meyer