Troubleshooting Guide: Boat In Reverse Goes Forward

If your boat goes forward when you put it in reverse, it could be due to a number of reasons. Firstly, it could be an issue with the control box being hooked up incorrectly, or there might be an issue with the propeller or lower unit installation. For example, if the control cables are hooked up incorrectly inside the control box, the boat may go in reverse when the control handle is shifted to forward. Additionally, the use of a wrong propeller or lower unit can also cause this issue. It is important to ensure that the correct type of propeller, either right-handed or left-handed, is installed, as it directly affects the direction of the boat. Another factor to consider is the speed of the boat when shifting gears. At idle speeds, shifting from forward to reverse typically does not cause any harm to the transmission or engine. However, shifting into reverse while moving fast in the forward direction or applying full throttle in reverse can put excessive stress on the engine and transmission, potentially causing serious damage.

The issue may be caused by the incorrect installation of the control box, propeller, or lower unit

If your boat moves in reverse when you put it in forward, it could be due to incorrect installation of the control box, propeller, or lower unit.

Control Box Installation

The control box uses either "push" or "pull" control with the cable. When you shift the control handle, the cable moves in or out, which shifts the lower unit. If the cables are hooked up incorrectly inside the control box, shifting into forward might push the cable instead of pulling it, resulting in the boat moving in reverse. This can be fixed by reversing how the cable is hooked up in the control box.

Propeller Installation

Another reason for this issue could be the installation of the wrong propeller. There are two styles of propellers: right-handed and left-handed, also known as standard rotation and counter-rotation, respectively. A standard or right-handed propeller is designed to spin to the right when in forward gear, while a counter-rotation or left-handed propeller spins to the left. If you install the wrong type of propeller, your boat will move forward in reverse or vice versa.

Lower Unit Installation

The engine's lower unit plays a crucial role in determining the direction of the boat. The lower unit shifts the boat into forward or reverse, and its rotation must match the style of the propeller installed. If the wrong lower unit is installed, it will result in the boat moving forward when the engine is in reverse.

To resolve this issue, it is important to ensure that the control box cables are connected correctly, the appropriate propeller style is installed, and the lower unit matches the propeller's rotation. Incorrect installation of any of these components can lead to the boat moving in the wrong direction.

The boat's drive system and transmission type play a significant role in this scenario

The type of transmission in a boat will determine how well it can handle shifts in direction. For instance, at slower speeds, you may not even stall the engine when shifting into reverse, while at higher speeds, you can cause serious damage. The design of the transmission also matters; some are built to handle the load of the boat going forward at higher RPMs, while others are not.

Additionally, the lower unit, which is found on outboard, inboard-outboard, and I/O engines, plays a crucial role in shifting gears. The lower unit contains four main gears, including the pinion gear attached to the driveshaft from the engine. When shifting from forward to reverse, the clutch dog moves back and forth to connect with either the forward or reverse gear. However, shifting at high speeds can cause significant stress on the clutch dog, leading to potential damage or failure.

Furthermore, the propeller also influences the boat's direction. There are two types of propellers: right-handed and left-handed, or standard rotation and counter-rotation, respectively. Installing the wrong propeller can result in the boat moving forward when the engine is in reverse and vice versa. This issue is common in twin-engine applications, where one engine typically has a counter-rotation lower unit and the other a standard rotation lower unit.

In summary, the boat's drive system, transmission type, lower unit, and propeller all play significant roles in determining the boat's direction and its ability to shift gears smoothly. Each component must work in harmony to ensure safe and efficient operation.

The speed and severity of the shift from forward to reverse can impact the potential damage to the boat

The speed and severity of the shift from forward to reverse can have a significant impact on the potential damage to the boat and its components. While slower speeds may result in a loud thud or a stalled engine, higher speeds can lead to more serious issues.

At high speeds, a sudden shift from forward to reverse can cause excessive stress on the lower unit, potentially leading to its destruction or damage to the engine. This is particularly true for boats with sterndrive or outboard transmissions, which are more susceptible to damage compared to inboard transmissions. The transmission in most inboard boats is designed to handle the shift better, and as long as the shift is not made regularly, the transmission will typically bear the brunt of the propeller's change in spin direction, causing the engine to stall.

The severity of the shift is also crucial. A gradual shift from forward to reverse allows the system to adjust and reduce the potential for damage. Conversely, a rapid shift can lead to a hydraulic lock-up of the transmission, resulting in the engine stalling. Additionally, the force exerted during a sudden shift can cause damage to the lower unit, including snapping or exploding, leaving the boat without shifting ability.

Furthermore, the engine itself can be affected. A sudden stop in forward motion, followed by a shift into reverse, can cause the back of the boat to squat in the water, leading to water intake through the engine's exhaust. This can result in serious engine damage, including bent valves and broken rods.

While these issues can be concerning, it is important to note that they are relatively rare, as they require multiple factors to align, such as speed, boat weight, and water conditions. Regular maintenance and careful operation can help mitigate these risks and ensure a safer boating experience.

The lower unit and engine may be damaged, with the potential for engine failure

If you accidentally put your boat in reverse while driving, there is a possibility that the lower unit and engine may be damaged, with the potential for engine failure. This is more likely to occur in boats with sterndrives or outboards, as these boats do not have transmissions to handle the shift in gears. Instead, they rely on lower units to shift between forward and reverse gears, which can be damaged by the sudden change in direction and speed.

Lower units are found on outboard engines and inboard/outboard (I/O) engines. They contain four main gears: the pinion gear, which is attached to the driveshaft from the engine and spins continuously when the engine is running; one forward gear and one reverse gear, which connect to the pinion gear and ride on the propeller shaft; and the clutch dog, which is fixed to the propeller shaft and slides back and forth when the control lever is shifted, engaging with either the forward or reverse gear.

When a boat is travelling at speed and suddenly shifts from forward to reverse, the small clutch dog goes from spinning one way to a sudden stop, then immediately starts spinning in the opposite direction. This can cause the clutch dog to snap or explode at high RPMs, resulting in a loss of shifting ability. Additionally, the force of the water on the propeller can prevent the lower unit from shifting at all, leading to further damage.

In some cases, the lower unit may develop a hole or experience internal damage, leading to potential engine failure. If the boat is travelling at high speeds and suddenly shifts into reverse, the back of the boat will squat in the water, pulling the rear into a wall of water. This can cause water to enter the engine through the exhaust, leading to serious engine damage, including bent valves, broken rods, and even catastrophic engine failure.

Prop walk may be causing the boat to swing in a certain direction when reversing

Prop walk, also known as the paddlewheel effect or asymmetric blade thrust, is a phenomenon that occurs when a propeller and its shaft are not perfectly parallel to the water's surface. When the shaft is angled downward, as is common, the propeller blades travel a greater cylindrical distance on their upstroke than on their downstroke. This pushes more water, generating greater thrust on that side. This, along with lateral deflection off the hull, pushes the boat's stern sideways, pivoting the vessel.

Prop walk is more noticeable in reverse, especially at slow speeds and high RPMs. It can be challenging when docking or manoeuvring in tight spaces. However, understanding and anticipating prop walk can help you make it work to your advantage.

Here's how prop walk may be causing your boat to swing in a certain direction when reversing:

First, it's important to know the direction in which your boat's propeller turns. Most propellers are right-handed, meaning they turn clockwise when viewed from astern. If your propeller is right-handed, it will push the stern of your boat to port when reversing. On the other hand, if you have a left-handed propeller that turns anti-clockwise, it will push the stern to starboard when reversing.

When reversing, the wash from the propeller is no longer going over the rudder, which results in a loss of steering. This, combined with the increased thrust on one side due to the prop walk effect, causes the boat to swing in a certain direction.

Additionally, the shape of the propeller blades contributes to this sideways force. The blade design creates a small amount of sideways force, which further influences the turning effect on the boat.

To determine the direction of your propeller's rotation, engage astern while securely tied to the berth and observe which side of the boat the wash comes out. If it exits to starboard, you have a right-handed propeller; if it exits to port, it's a left-handed propeller.

By understanding the prop walk effect and the direction of your propeller's rotation, you can use this knowledge to your advantage when manoeuvring your boat, especially in tight spaces.

Frequently asked questions