If you're shopping for trim tabs, chances are you're wondering about the differences between the two major types on the market - hydraulic and electric.
Bennett Marine manufactures the leading hydraulic system. What most people don't know is that electric trim tabs are not new but have been around for many years. In fact, Bennett Marine originally manufactured an electromechanical system. But in the best interest of the boater, Bennett changed to hydraulic due to its many advantages.
Separating Fact from Fiction
We encourage you to ask your fellow boaters and check out the boating forums online. (Such as some of these recommended forums to the left.) To help you get started in your research, here is a side-by-side comparison on the key differences between both systems:
The motor for the whole trim tab system, the Hydraulic Power Unit, is installed inside the boat in a dry environment.
Hydraulic actuators do not rely on a seal where the shaft enters the cylinder body. Instead the seal is made on the piston face inside the cylinder where no marine growth can occur. Even if a barnacle grows on the shaft, it will not cause a leak.
If a seal on a hydraulic actuator should break, its replacement cost is about $1.00 compared to the cost of replacing an entire electric actuator.
By placing the electric motor underwater inside the actuators, the electromechanical system is prone to failure. Electromechanical actuators rely on shaft O-rings to maintain the watertight integrity of the system.
Sand, grit or marine growth on the actuator will cut the O-ring seal letting water into the system. When the shaft of the electromechanical actuator is extended out of the cylinder body, it creates a vacuum inside the actuator. When a vacuum is pulled underwater the result is inevitably water being sucked in to fill the void. Once water enters the actuator, the boat will need to be taken out of the water and the actuator replaced.
With all systems, the trim planes, actuators, wiring and control switch have to be installed. With hydraulic trim tabs, a hydraulic power unit (pump) must be installed inside the boat. A few additional minutes spent installing the pump will give you years of trouble-free operation.
By placing the electric motor and gear system outside the boat, the electromechanical system can be slightly easier to install. However the time saved during installation is offset by the risks of placing electric components under water.
Durability is the biggest advantage of hydraulic over electric systems. Common sense tells you that electrical components are more susceptible to damage when submerged. If the O-rings inside an electric actuator fail, water will flood the actuator.
Bennett has chosen to create a system without this vulnerability so the boater doesn't have to worry.
Bennett hydraulic systems are capable of making the precise adjustments needed for smooth safe control of the trim tabs. Hydraulic systems start and stop instantaneously. There is no lag time.
Free-wheeling ball screw, gears and electric motors create considerable lag time from the time you take your finger off the control until the trim tab stops moving. This "actuator overrun" means that even momentary presses of the switch will result in the trim tabs running too far down or too far up. This overrun creates unpredictable and erratic control of the trim tabs that is confused with "fast action."
Again, there is no lag time with hydraulics - they start and stop right away. That said, fast moving trim tabs are not a desirable feature for exact control, particularly at high speeds. A hydraulic system is responsive and provides the boater with more control over the trim tab movement.
Some claim that electric actuators are "incredibly fast and responsive." The truth is they are only marginally faster than a Bennett system. It has 3/8" less travel time than the Bennett system. The shorter travel time accounts for the majority of the difference.
Small, incremental adjustments of trim tabs are the key to getting the best results, particularly at high speeds. In applications where precise and reliable control is important, hydraulic systems are the only choice. It is no accident that racing power boats use hydraulic trim tab systems.