 RE: hydraulic vs. Electric
Ok,
Here on this forum I will debate the two systems. As I mentioned on the main forum, regardless of the type you decide one get Tabs that are 12" x 12", 18" x 9" or what I would specifically suggest from our company 10" x 12" M120s. Tabs in this size range will give you the best results.
Trim Tab Systems
Hydraulic Vs Electromechanical
There are two major types of Trim Tab systems on the market, hydraulic and electromechanical. Both systems have been around for many years. In fact in the '60s Bennett Marine manufactured an electromechanical system later changing to the hydraulic system due to its many advantages.
Lenco is currently the most recognized electromechanical system. While both types of systems are designed to accomplish the same basic purpose there are significant differences in both performance and durability. It is very interesting to note that Lenco is not new technology; they have been around since the '70s.
Below is a side by comparison of design, construction and performance.
Durability
Electromechanical: By placing the electric motor and gear system out side the boat the Electromechanical system is a slightly easier system to install. However the time saved during installation is offset the poor reliability resulting from placing the electric components under water. Electromechanical actuators rely on shaft O-rings to maintain the watertight integrity of the system. Any fouling of the piston shaft by marine growth, sand or grit will result in a cut O-ring and total failure of the system. Relying on shaft O-rings compounded by the fact that as the shaft of the electromechanical actuator extended it creates a vacuum in the actuator. When a vacuum is pulled underwater the result is water being sucked into the actuator. The design of the system limits Lenco to offering a three year warranty on the actuators. According to an article in Trailerboats Magazine Lenco will not honor the warranty on the trim tabs if they fail due to being left in an extended position.
Hydraulic: The Bennett Hydraulic Power Unit (HPU) is housed inside the boat. While it takes a few minutes longer to install the result is years of trouble free service. Bennett 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, protected from contamination. The evidence of this attention to design is a 5-year warranty.
Accuracy and Control
Electromechanical: The design of the Lenco system's free wheeling ball screw results in 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. Recently Lenco introduced new control switches that provide an electrical brake for their system that makes them start and stop instantly, just like hydraulic systems.
Hydraulic: The Bennett hydraulic system is capable of making the small precise adjustments needed for smooth safe control of the Trim Tabs. Hydraulic systems start and stop instantaneously. There is no lag time. The result is reliable control at all times. In applications where precise and reliable control are important hydraulic systems are the only choice. It is no accident that racing power boats use hydraulic Trim Tab systems. High performance aircraft such as fighters rely on the swift and failsafe control that only a hydraulic systems can provide.
Speed of Operation
Electromechanical: One of the major selling points of Lenco's system is that "Electric actuators are incredibly fast and responsive. . . "
Hydraulic: The speed at which a Trim Tab moves is key element the ability to effectively and safely control the boat's running attitude. Fast moving Trim Tabs are not a desirable feature for exact control, particularly at high speeds. But of course Trim Tabs that move too slowly would not be a good idea. Actually comparing the speed of travel of the two system yields surprising results. The Lenco system is only marginally faster than the Bennett system. It is important to note that the Lenco system has 3/8" less travel than the Bennett. This shorter travel accounts for the majority of the speed difference. The speed of travel advantage claimed by Lenco is irrelevant when it comes to providing proper control of the boat. Yes the Lenco Tabs do travel a bit faster than Bennett, however it is worth noting we choose the speed to be the best for overall control and that we actually make "slower" systems at some boat builders request to give better fine tuning adjustment. It is also interesting to note that the other Electric trim tab manufacture LectroTab has come out with a system that is slower then their original system, and it is the speed we use!
Fast correcting Trim Tabs are not always a good idea, as most of you know that Tabs are most often used in short bursts, and too much movement results in overshooting the trim you want.
Safety
Electromechanical: When an electromechanical system fails the actuator will lock the Trim Tab in place. If the Trim Tab is in the deflected position when a failure occurs the only way to retract it is to haul the boat out of the water and replace the actuator. This can result in a potential dangerous situation. With one or both Trim Tabs locked in a deflected position the boat can not be run safely in a following sea or at higher speeds. This can spell disaster if a boat is 20 miles offshore and has to run home in a following sea or run an inlet.
Hydraulic: A failure in the Bennett system does not result in locked up Trim Tabs. Simply removing pressure from the system results in the Trim Tabs retracting to the full up position. With the Trim tabs in the full up position the boat may be safely run at high speed and in following seas.
Additionally since the hydraulic power unit is located inside the the boat repairs may be made without the expense and downtime involved in hauling the boat.
Exposed Wiring
Electromechanical: Lenco's electrical wires are exposed outside the boat where they may be damaged. The wires from each actuator pass through a hole in the upper hinge and through the transom with no positive seal or strain relief. Lenco's instructions call for holding the wire in place with sealant. Without strain relief any movement of the wire will break the seal resulting in a leak as well as water intrusion into the core of the transom.
Hydraulic: The Bennett hydraulic actuator connections are made inside the boat with the mounting portion of the actuator providing a positive seal and strain relief. When properly installed this design eliminates the risk of leaks and water intrusion into the transom core.
Trim Tab Design
Electromechanical: Lenco's advertising claims that the Trim Planes are "12 Gauge stainless steel planes and hinges." Actually most of their trim tabs do not have 12 gauge hinges, rather they are much lighter gauge piano hinges welded on to the Trim Planes. Welding stainless steel alters the properties of the metal making it more susceptible to corrosion. The pin used in a piano hinge is also prone to corrosion. Additionally piano hinges allow water to squirt through the hinge creating mist behind the boat.
Hydraulic: Bennett utilizes an exclusive interlocking hinge that is not welded, does not have a pin to corrode, and does not allow water to pass through. This type of hinge is much stronger and more durable than a welded piano hinge.
Lenco: Lenco Trim Tabs have the inboard and outboard edges of the Trim Tabs bent upwards at a shallow angle. This upward bend does not significantly contribute to the stiffness of the Trim Tab. Bending the edge of the Trim Tab up at a shallow angle creates low pressure along the edges of the Trim Tab. These areas of low pressure cause much more water to be lost out of the sides of the Trim Tabs compared to "flat" Trim Tabs.
Bennett: Bennett Trim Tabs carry a flat surface out to the edge of the Trim Tabs. This maintains the highest pressure across the surface of the Trim Tab for maximum lift. On some Trim Tabs Bennett turns the sides up 90 degrees to increase the stiffness of the Tab. Only when you put a 90 degree fold in the Trim Tab will you significantly increase its stiffness. On some other Trim Tabs Bennett folds the edges down 90 degrees to capture water that would normally be lost out the sides of the Trim tabs and channel it aft to produce additional lift.
I hope this is helpful and would hope that you pose the same questions to Lenco.
Tom McGow
Bennett Marine | 
