High Pressure / High Volume Steering Systems

Hydraulic Steering System Basics

Basic hydraulic steering systems have a helm that pumps fluid when a person turns it—basic hydraulic steering works for small to medium cylinder sizes. When steering forces increase, the cylinder displacement (measured in cubic inches or cc’s) grows to keep the work of turning the helm to a tolerable level. Meaning more helm turns to move the rudder the same amount; this works up to a point. 

A larger hydraulic steering system will use an electric or engine-driven pump to move higher fluid volumes to the steering cylinders. A boat with a large cylinder or multiple cylinders will require more liters per minute of flow to keep the steering responsive (have a faster “lock-to-lock” time, the time it takes for the rudder to be moved all the way from one side to the other).

These pump-driven systems are known as “hydrostatic steering systems.” Some examples in the marine industry are the Mercury Verado, Char-Lynn, and UFlex MasterDrive. The helm is no longer pumping fluid. Instead, it is a valve directing flow from the pump. These systems frequently use higher pressures than basic hydraulic steering systems. Because more force is required to move more fluid through the same size hose, the liquid must flow from the pump to the helm, then back to the steering cylinder. As the hose increases, more pressure is needed to move the fluid at a high flow in a large boat.  

How do Garmin autopilots interact with hydrostatic steering systems? 

The first problem is the total displacement size of the steering cylinder(s). Due to the larger steering cylinder size, the autopilot will need to pump more fluid than a basic hydraulic steering system to control the boat. Of Garmin pumps, the SmartPump has the highest flow rate. The SmartPump is designed to handle hard work with improved efficiency and heat management.   

The second problem is the same one faced by the steering system. If the pump needs to pump at higher flow rates, it produces higher pressure to get it through the hose. Installing the pump near the cylinder helps a lot with the high-pressure requirement. Less hose means the pump uses less force to push the same amount of fluid than it would if the hose is longer. SmartPump is the best pump for creating pressure to push the higher flow rate. 

Low-to-Mid Pressure / High Volume Steering Systems

A basic hydraulic steering system may have a high-volume steering cylinder. When the helm is turned, it pumps fluid. It will take a lot of turns of the helm to push the rudder lock-to-lock. These boats will often have a power-assist pump to help out. An example will be the SeaStar Power Assist, which detects flow from the helm and uses a pump to join in decreasing the number of turns of the helm to move the rudder lock-to-lock.

If a boat has multiple steering cylinders, add the displacement of the cylinders to get the total displacement.

When total cylinder displacement starts going above ten cubic inches (163 cc), that starts getting into the high volume category.

The autopilot page (https://www8.garmin.com/marine/PDF/Autopilot_Guide.pdf ) lists cylinder displacements and pump recommendations.