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Trim Tabs and Interceptors. The Ultimate Guide to Automatic Trim and Stabilisation for 20-45 foot boats.

Humphree Lightning interceptor

Every boat owner wants their craft to perform at its best on every trip and ensure the comfort and safety of passengers in all conditions. 

Yet despite their importance, trim and stabilisation are concepts many boat owners need to understand more fully. While individual boat designs lean more towards speed or comfort, automatic trim and stabilisation technology can transform a boat's safe and comfortable performance.

Table of contents


    Understanding trim and list – the basics

    Trim controls the boat's pitch – the relative height of the bow or the level of the boat from bow to stern.

    Pitch Illustration

    List is the boat's heel or how level the boat sits from beam to beam.

    Boat List Illustration

    What are trim tabs on a boat? 

    Trim tabs are either mechanically or electronically controlled horizontal flaps. They are attached to the boat's transom, allowing the skipper to adjust its pitch by creating lift at the stern. 

    Operating trim tabs independently will adjust the boat's list to compensate for a side wind or uneven loading when underway.

    Traditional Trim Tabs illustration 1280px

    The difference between trim tabs and interceptors

    An interceptor is an innovation in trim technology. First developed by Humphree, the Humphree interceptor system uses a blade that moves up and down on a vertical axis rather than a horizontal flap rotating around its leading edge. It uses hydrodynamic pressure that creates a triangular high-pressure effect in front of the interceptor blade to replicate the effect of a trim tab. The energy required to move the blades is much less than needed to move a trim tab, which has several benefits we'll cover later.

    hydrodynamic lift

    The Humphree Lightning interceptor system


    Taking it to the next level with automatic trim and stabilisation

    Automatic trim and stabilisation control are relatively new to recreational boats. The technology uses gyro sensors to detect the boat's bow-to-stern and beam-to-beam attitude in the water. The system uses the measurements to activate the trim control automatically.

    In its most basic form, automatic trim control performs the same function as manual trim tabs. But it does so automatically in response to the boat's acceleration, speed, weight distribution and the effects of wind.

    The most advanced systems take automation further by enabling dynamic stability control. These systems are dynamically responsive to uneven conditions in real time.

    The top tier of stabilisation technology is called coordinated turn. It keeps the boat flatter when turning, providing a true turn feel and enabling sharper turning at speed.

    Dynamic stabilisation control is where the best automatic systems come into their own. 


    The benefits of automatic trim and stabilisation
    Performance, Comfort and Safety

    Benefit 1. Getting up on the plane

    The benefit of automatic trim starts from the moment of acceleration from a standstill. When maximum lifting force is applied as the boat begins to move, the boat will come up out of the water onto the plane at a lower speed and significantly sooner. The bow of the boat will not rise as high, improving visibility. The result is better acceleration, comfort, efficiency and safety.

    Read more about Humphree Trim Tabs.


    Benefit 2. Optimised cruising

    Automatic trim maintains the boat's pitch at all speeds and levels of acceleration. The boat's hull design can function as intended. It all adds to better performance, passenger comfort, efficiency and lower fuel consumption.


    Benefit 3. List control

    When using automatic trim, sensors detect the boat's list – if it is leaning to one side or the other due to uneven loading or cross-winds. Trim is automatically applied to level the boat, resulting in a safer, more comfortable ride.


    Benefit 4. Greater performance, comfort and safety through swell and chop

    Every boat owner knows the uncomfortable and potentially unsafe experience of pounding into a sharp swell or chop. The boat launches off peaks and often slams down onto the water's surface. The discomfort is caused by the flatter rear planing section of the hull contacting the water first, meaning the sharper dead-rise of the hull at the bow isn't doing its job of slicing into the water.

    Automatic dynamic pitch control maintains a more level pitch angle in swell and chop, allowing the bow to slice into the water, creating a smoother ride. Passenger comfort and safety are significantly improved.

    This benefit is only realised by the very best systems that can respond quickly enough to change. Not all systems are equal.

    Pitch Animation

    Automatic Dynamic Pitch Control reduces the amount of bounce and keeps the boat more level in choppy seas.


    Benefit 5. A more comfortable ride with less sea sickness in cross or following swells

    Often, the least comfortable and safe part of a journey is when travelling across a swell or chop or when traversing a following swell. The roll and steering effect this type of water surface has on the boat is the one most likely to cause sea sickness and a potentially dangerous lack of stability.

    Automatic dynamic roll stabilisation, like pitch control, adjusts continuously to changes in water surface conditions, wind gusts and passenger movement across the boat. The boat remains far more level. It's a complete game-changer for passenger comfort, safety and the level of safe speed that can be maintained.

    List Animation

    Automatic Dynamic Roll Stabilisation reduces roll and keeps the boat more level in cross swells and following seas.


    Benefit 6. Superior boat handling and maneuverability

    The dead-rise angle of a boat's hull (its V-shape) helps the boat cut through the water's surface to create a smoother ride for occupants. 

    However, there is a side effect. When turning, the boat leans over to the dead-rise angle, which is uncomfortable and reduces the boat's cornering ability.

    Automatic coordinated turn is the highest level of automatic stability control. It maintains a flatter attitude when cornering, giving the boat a true turning feel. The effect is greater comfort, sharper turning and superior boat handling at speed.


    The critical things to know about trim stabilisation systems

    When buying a trim and stabilisation system for your boat, there are some essential things to know... 


    Should you choose traditional trim tabs or interceptors?

    Traditional trim tabs have limitations. 

    • They take a lot of force to operate, making them slower to respond in dynamic applications
    • Their bulk and the protrusion of unprotected flaps make them more susceptible to damage.
    • The limitations of traditional trim tabs led Humphree to develop the interceptor trim and stabilisation system. 


    The advantages of interceptors are:

    • Interceptors require less energy to move and have the potential to move faster and be more responsive and reliable.
    • Interceptors are very efficient. The flat blade creates a hydrodynamic pressure effect that simulates the diagonal lifting force of traditional trim tabs.
    • The relative mechanical simplicity of the interceptor-type system, with fewer protrusions, makes them less suspectable to damage.


    Not all interceptor trim stabilisation systems are created equal

    Several main factors determine the effectiveness, performance, efficiency and durability of interceptors:

    • Motion sensors and digital processing. The system's built-in sensors must detect pitch and roll in real time and use that data to drive the interceptor blades instantly. The speed and precision of the system provide the foundations of effective performance.

    • Hydrodynamic effect. While the width of the interceptor blade contributes to lifting force, blade depth is critical. A vital specification often overlooked is blade stroke, which determines how far the blade penetrates the water surface. Also important is the widest possible mounting position on the transom. 

      When the mechanical effect is optimised, boat movement control is more effective, and the response can be virtually instant.

    • Nothing puts hardware of all types to the test like harsh marine environments. The Interceptors' design, materials and manufacturing quality are central to reliability and durable performance. It pays to check reviews because out-of-water repairs are inconvenient and add considerably to the cost of ownership.
    Humphree Lightning stands apart for performance and durability

    Lightning is not your ordinary trim tab. No matter what propulsion system you use - outboards, electric, stern drive, or inboard – Humphree Lightning is the perfect trim and stabilisation choice for newly built boats or as an upgrade. It will take your boating experience to the next level. 

    The Lightning trim tab will increase speed and reduce fuel consumption and CO2 emissions.

    They are specifically designed for 20 – 45 foot boats.


    Humphree Lighting on the transomStabilisation experience

    Humphree has over 20 years of trim and stabilisation experience that is central to Lightning's technology, design and refinement. Lightning boat stabilizers bring advanced technology, superior reliability, and system flexibility to 20 FT - 45 FT recreational boat owners.


    Outstanding reliability and durability

    Humphree Lightning has mechanical components engineered to stand the test of time. Lightning delivers industry-leading reliability and durability using high-quality materials and robust and powerful actuators. 


    Superior performance, comfort and safety

    Humphree Lightning features a long 50mm interceptor blade stroke. This extended blade depth provides an optimum hydrodynamic effect to maximise lift. The blade stroke combines with powerful actuators that respond instantly to boat movement, ensuring optimised performance, comfort and safety. 

    Furthermore, Humphree Lightning is designed to be fitted wide on most boats' transom; a chine version is also available. The widest possible mounting position also has a very positive impact on stabilisation performance. 


    Advanced trim and stabilisation 

    The control and automation of trim and stabilisation of Humphree Lightning delivers a breathtaking impact on your boating experience.  

    The Lightning hardware and software-based feature packages, control trim, and stability delivering dramatically improved boating performance, comfort, and safety.

    • Auto Trim. Activated from the first moment of acceleration, Auto Trim gets you up on the plane sooner and at a lower speed. It applies optimum trim control across all speeds and levels of acceleration.

    • Auto List. Auto List automatically levels the boat heel or lean to compensate for uneven loading or cross-winds.

    • Pitch Control. Automatic Pitch Control smooths the up-and-down motion or bounce when planning in choppy conditions. The boat remains more level, adding comfort, speed, and safety. It can be considered a dynamic version of trim control that compensates for an uneven water surface in real time.

    • Roll Stabilisation. Automatic Roll Stabilisation compensates for side-to-side motion caused by a chop or rolling swell coming across the boat. It dramatically improves comfort and reduces the risk of seasickness.

    • Coordinated Turn. Automatic Coordinated Turn controls the inward heel angle when turning and actively contributes to the boat’s cornering ability. Keeping the boat flatter gives the boat a true turn feel and enables improved cornering at speed while enhancing comfort and safety.

    • MFD Integration. Integration with leading display systems such as Garmin, Simrad and Navico is easy. It adds to the seamless integration of Humphree Lightning into your boat control and navigation systems.

    • Over-the-Air Feature Upgrades and Options. The Humphree Lightning system consists of two primary elements – the Lightning Interceptor hardware and control software.

      Installation of Humphree Lightning hardware is less invasive and complex than traditional trim tab systems. Once installed, over-the-air software updates activate feature upgrades and options.


    The benefits of the Humphree Lightning system include:

    • Your boat only has to come out of the water for initial installation.
    • Buy only what you want, when you want it.
    • The Humphree hardware is built to last and not made down to a price to compensate for the software cost.
    • Periodic improvement of system performance is available without hardware upgrades.
    • Under Water Light. Underwater lights add something very special to your look after dark. It can also be a brilliant add-on for fishing.

      Available as an over-the-air option, underwater lighting enables powerful 10W RGM LED lighting with adjustable colours.


    Trim is essential

    The impact that effective trim has on the performance, comfort and safety of your boating experience cannot be underestimated. It's a genuine game-changer.

    Contact us today to learn more about fitting Humphree Lightning to your boat.