Why Do Boats Need Trim Tabs?

by admin

There are some very simple ‘things’ that trim tabs assist. For example as your boat slows from maximum speed, it begins to settle at the stern or “squat,” creating an inefficient, untrimmed condition. Or as you push the throttle down and the boat moves forward you have that period of transition from off the plane to on the plane. A “hill of water” is created and in this bow-high position, visibility is limited and the hull is experiencing increased drag as it climbs over the hump.

Uneven weight distribution is the cause of your boat listing to one side, but so too are the wind effect on hardtop boats. It is surprising just how much resistance a hard top gives as it predominantly leans into the wind.

Tabs are designed to fix all those issues, be they a very simple fixed manual unit to the new breed of highly sophisticated electronic self levelling controls. Tabs are now designed to sync with your boat’s drive system and take the guess work out of trim set up, to give your boat the best possible riding attitude.

How Will Tabs Effect My Boat

While, in the past, trim tabs were most often found on cabin cruisers and sport-fishers over 7m, today they have become common equipment on boats 5m-6.5m. You see trim tabs on everything from open tiller steer to bow riders, ski boats, cabin and hardtops. Many still believe that trim tabs are less important on smaller boats, but, in fact, the opposite is true. Trim tabs improve the ride of even the largest planing hulls, but on a smaller boat you will notice the difference much more. For instance, bigger boats are much less affected by weight distribution than smaller boats.

A simple, quick touch of a tab will bring a small boat back onto the right fore and aft or lateral trim angle to make a better ride. Trimmed correctly a boat will offer a softer and more comfortable ride. After decades of use on the water, it’s been proven that all boats, large and small, benefit from trim tabs for the same reasons – they improve planing and although probably only marginally, fuel efficiency. They also correct for uneven weight distribution, and they improve the speed, safety and overall boat performance.

If you have a fast boat then trim tabs help you get up on plane quickly without digging the stern down deep in the water and the bow sky high. Put the tabs down and the boat will literally pop up on plane. As you gather speed, you accordingly alter the angle of the tabs for the sea conditions.

Standard tabs on the family runabout allow the boat to pull heavier or multiple skiers, and slow down for the smaller kids without going bow high. Safety is a real advantage with tabs here. You can use your tabs to improve visibility and avoid running over something you did not see. If you do not have a lot of fat sacks aboard to weigh the boat down when wakeboarding, a second option is to run with the tabs hard down and the engine trimmed right in. This tends to bury the bow and cause a greater wake. Not very fuel efficient, but then the speed you go towing a wakeboarder is not going to use a heap of fuel.

When it comes to larger cruisers, these are now often set up with the engine package, so all the hard work is done for you, Even the new breed of pod drives are available with auto trim systems. Tabs on larger and heavier cruisers certainly help in both transition to the plan and handling in big seas.

Buying Trim Tabs?

Before purchasing trim tabs, make sure there is room to place the tabs. Check the design of the transom and measure for clearance around swim platforms or ladders. You’ll need at least 30cm along the bottom of the boat and 30cm vertically from the point in the centre of the tab. While your local dealer can install trim tabs for you, just about anyone who is handy with a drill and screwdriver can install trim tabs. Depending upon the size and construction of the boat, it shouldn’t take more than a few hours.

Determining Trim Tab Size

Installing undersized trim tabs is one of the more common mistakes. A tab that is too small will have to be deflected more in order to create sufficient lift. Just remember, the larger the trim tab, the more lift it will produce with the least amount of drag. Most manufacturers supply a sizing guide, to make your choice a lot easier.

Many factors affect the choice of properly sized trim tabs, and the ultimate responsibility for the selection is up to you. These sizing recommendations are based on an average performance. Your choice may vary based on power, engine configuration, weight distribution, type of boat, and use. The greater the surface area, angle of deflection and/or speed of the water flowing under the trim tab, the greater the lift. When making a choice between trim tab sizes, remember that the largest trim tabs that will comfortably fit on the transom will be the most efficient.

Whenever possible, choose a 22cm chord (fore & aft measurement) trim tab, and gain lift through a longer span(side to side measurement). The span of the trim tab has more of an effect on the amount of lift. However, a longer chord can be used effectively, and there are situations where you may need to use a 30cm chord.

This is especially applicable when there is limited transom space with a twin engine set up. Also, slower boats (less than 25 km/h), semidisplacement hulls, boats over 15m, outboard brackets or boats with any other feature that increases the need for lift aft benefit from the 30cm chord. The 30cm chord provides greater surface area, thereby utilising more water flow and providing more lift.

How Do I Use My Trim Tabs?

The key to getting the best results from your trim tabs is to operate them in short half-second “bursts” and let the boat react before making another adjustment. The amount of time between corrections is influenced by the size of the trim tabs and the boat’s speed.

Operating your tabs this way will help avoid over-trimming, which occurs when you’ve deflected the tabs too far. An over-trimmed boat will “plow” or “bow-steer.” If you over-trim the boat, simply press “Bow Up” and the bow of the boat will rise. Your boat may have been built to avoid this situation. Bennett’s hydraulically-adjustable trim tabs, for example, enable a boat to be designed and rigged, so it never runs in an over trimmed condition even at the top end of its speed range. This avoids the hazardous combination of high speed and unpredictable handling.

When steering from a bridge or tower, a good trimming method is to watch the bow spray, stern wake, or the rooster tail. An untrimmed boat will produce more spray aft of the bow and it will produce a larger wake. When trimmed, the bow spray is farther forward, the wake is reduced, and the rooster tail is smaller and farther behind the boat. You’ll also notice that the engine RPM will increase when the boat is properly trimmed.

As a result of uneven weight distribution, prop torque or wind, a boat can run with a list. Deep “V” and hardtop trailer boats hulls are particularly vulnerable to this condition. You can easily bring the boat level using your control. If the port bow is high, push the port side “Bow Down” direction (this lowers the trim tab on the starboard side). If the starboard bow is high, push the starboard side “Bow Down” direction until the boat is level (this lowers the trim tab on the port side).

Properly sized trim tabs can significantly reduce the time needed to get up on plane. They also allow the boat to keep its bow down and stay on plane at lower speeds. As the throttle is advanced, the stern of the boat begins to squat, lifting the bow. As the boat accelerates, push the bow down position of the helm control in short bursts. The boat reacts by the stern lifting, the bow coming down, speed increasing and the engine labouring less.

Using Your Power Trim and Trim Tabs Together

It is a common misconception that if a boat has power trim on the outboard or outdrive it does not need trim tabs. Yes, power trim can be used to adjust the boat’s attitude, but it is highly inefficient. This is because a propeller is designed to force the boat forward. When trimming the boat with the prop, the prop must not only push the boat forward but raise the stern, as well. In this situation, prop slippage is greatly increased thereby wasting RPMs. Power trim also cannot correct listing and is ineffective at slower speeds.

For increased speed and power, use your trim tabs WITH your power trim. The trim tabs trim the hull, while the power trim adjusts the prop. The result is optimum performance and efficiency not attainable by the use of power trim alone. To achieve maximum performance:
1. Adjust the trim tabs to achieve a planing attitude.
2. Use the power trim to position the prop path parallel to the water flow.
3. If necessary, re-adjust the trim tabs to “fine tune” your tabs. In other words, use your trim tabs to trim the boat and your power trim to trim your prop.

Changing a Boat’s Attitude to Match Sea Conditions During Take-Off

Properly sized trim tabs can significantly reduce the time needed to get up on plane. They also allow the boat to keep its bow down and stay on plane at lower speeds.

As the throttle is advanced, the stern of the boat begins to squat, lifting the bow. As the boat accelerates, push the bow down position of the helm control in short bursts. The boat reacts by the stern lifting, the bow coming down, speed increasing and the engine labouring less.

Choppy Head Sea

For the most comfortable ride, when running into a head sea you want to trim the bow down, so the sharp forward sections of the boat do their work cleaving the waves. This will bring the “V” of the hull in contact with the waves rather than having the waves pound the hull – and your passengers.

Following Sea

For best manoeuvrability and maximum steering control, trim tabs should be fully retracted in a following sea, or when running an inlet. Keep the tabs up so the tide or current won’t push the stern from side to side. Stern lifting, the bow coming down, speed increasing and the engine labouring less.

Beam Sea

Boats operating with waves approaching from the side often throw spray up on the windward side. This spray often is carried aboard by the wind (particularly on smaller vessels). Trim tabs are used to raise the windward side of the boat, blocking the spray that blows over the boat, resulting in a drier ride.

Correcting Porpoising

Porpoising is a condition more common in faster, performance boats. As speed increases, the bow repeatedly rises out of the water until gravity overcomes lift and the bow bounces down. Press “Bow Down” in half second bursts. As the trim tabs deflect, the porpoising subsides and your speed should remain the same or increase. Only a slight amount of trim tab deflection should be necessary.

Backing Down

When operating the boat in reverse, both trim tabs should be fully raised. The trim tabs produce drag if they are left down in reverse. This puts a strain on the tabs as well as affects the boat’s handling in reverse. Additionally, if one tab is deflected more than the other in reverse, the boat tends to pivot around the deflected tab. Properly installed tabs, fully retracted have no effect on backing down.

Trim Tab Enhancements & What’s Available

There are quite a few brands available on the local market to suit a variety of boat sizes and styles. To help your buying decision, the following will give you a brief indication of what each of the leading brands offers.

Bennett Marine offers a number of trim tab accessories that will enhance the performance of your system. Their patented Auto Tab Retractor automatically retracts the trim tabs when the ignition is turned off.

Trim Tab Indicators are now commonplace with most systems, but some are a little more sophisticated and precise than others. Bennett Marine offers three kinds of indication. One of them, the Electronic Indicator Control, includes the Auto Tab Retractor and connects easily to the Auto Tab Control.

The only thing better than a performance-enhancing trim tab system is one that runs itself! Auto Tab Control (ATC) does exactly what it says it does – it automatically adjusts your trim tabs to changing conditions and maintains the optimum running attitude for your boat.

Lenco has the Auto Glide Boat Control System, which controls your trim tabs from the time you leave your shore until you come home again! The Auto Glide uses engine data and GPS data to drive your boat to the most efficient running angle by adjusting the trim tabs as needed. This optimum running angle is determined during the set up process upon the installation of the Auto Glide system. They also offer a range of trim indicators, including the older style in line rocker switch with trim motor and switch the load directly without any controller. The Lenco up/down switch panel with LED Indicators is supplied with waterproof connection plugs and includes an electronic controller and switch panel.

Boat Leveler Co’s Insta-Trim Boat Leveler Tabs employ the force of hydraulics for smooth trimming action. When the trim tab rocker switch is pressed, electrical current is sent to the hydraulic motor pump unit. This signal activates the electric motor, creating fluid pressure. Valves on motor pump unit open, channeling the required amount of fluid to the actuators. When the trim tab rocker switch is released, the valve close, capturing the fluid in the actuators hydraulic cylinders. Thus, trim tabs hold their position. Insta-Trim Boat Leveler Tabs operate in reverse of what you might think. The port trim tab lifts the port stern which lowers the starboard bow.

Lectrotab uses an electromechanical trim tab system, with non hydraulic actuators. The unit ensures very accurate tab positioning, provides maximum lift force, and is totally self-contained for easy installation. An internally designed friction brake prevents unwanted tab retraction when underway or backing down. The actuator assembly is packaged in a non-metallic permanently sealed housing. No components need to be installed inside the boat. Most importantly, unlike hydraulic trim tabs, there is no oil to leak out.

The actuators incorporate either a standard or low profile transom mounting bracket and is available in 12V and 24V DC with standard, short or heavy duty style housings. Lectrotabs are made in the USA.

Quantum’s Archer – (Advanced Ride Control High Speed Extendable Retractable) – provides pitch, roll and trim control for high speed yachts using retractable winglets built into active trim tabs.

The design incorporates a hollow section trim tab with a hydraulically actuated and electronically controlled extendable winglet which extends from inside the trim tab and retracts inside the tab when not in use. Archer is intended for vessels in the 24-60m range with speeds of 25 – 50 knots, and is in development for larger yachts and commercial vessels up to 76m in length.

When sea conditions demand enhanced roll and pitch control, selecting “full deployment mode” extends the foil section winglets to increase the control forces. This activates the acceleration sensor and control for pitch, the angle and velocity sensor and control for roll, and the trim tab attitude control for trim.

Megatech is an hydraulically operated trim tabs system, made in Italy designed for fast boats from 10m to 30m and top speeds from 25 knots up to 100 knots and more under specific enquiry. They have no external hydraulic connections and fittings and suit any transom inclination up to 15deg.

Ultraflex’s trim tab system comes complete with an innovative joystick control that makes it ultra-easy to trim the boat, regardless of the conditions. Aptly named Easyjoy, Ultraflex’s joystick trim tab control works just the way everyone expects it to work. Completely intuitive, Easyjoy is a single lever control. It automatically operates either a single tab or both tabs together, quickly returning the boat to a level attitude. Each Ultraflex tab also features an electromechanical ram complete with totally encapsulated wiring system. Completely sealed with thermoplastic resin, dual seals and the added protection of rubber bellows, the Ultraflex tabs simply have no external glands or exposed wiring; they are always totally protected. Ultraflex trim tabs also feature automatic tab retraction.

Hydrotab interceptor trim tabs use an innovative patented design to provide fast and efficient trimming for your boat. Hydrotab units are controlled with precision by a small air compressor that offers a plug and play installation without the use of hydraulics and electric motors.

Designed to be an open self cleaning system, there are no sealed units and are offered with a 5 year warranty on the tab units Volvo Penta Boat Trim System (BTS) with its patented interceptor technology gives you perfect control over pitch and heel with rapid response, quicker onto plane and more comfortable ride. With the addition of the Automatic Boat Trim option, your boat is kept correctly trimmed – automatically! The Automatic Boat Trim option compensates for changes in speed, wind or people moving about on board.

Thanks to the integrated GPS receiver, it also senses change in course and does not compensate for heeling in turns. The trim system, recommended for speeds up to 45 knots, has all the same performance qualities as conventional trim tabs plus the additional benefits of quicker response, less drag and compact design. Unlike conventional trim systems using hydraulics, the system is operated electronically. As no hydraulic oil is used, there’s no risk of oil leakage in sensitive marine environments.

Smart Tabs are a system that requires no internal electronics or hydraulics and reacts to water pressure, boat speed, and payload. They are completely automatic requiring no operator adjustment while underway. The unique feature of Smart Tabs is that they are adjustable to the needs and requirements of the boat and owner. The system is active at all time without helm controls and pilot interface. At slow speeds, they deploy downward which increases stern lift. At cruising speeds, they are pushed up by the water pressure, but remain under a load creating ride control as shock absorbers.

Smart Tabs use a nitrogen gas actuator to hold the plates down during acceleration and provide lift to the stern. The plate size and actuator resistance (pressure) are determined by the boat size and horsepower at the time of installation. Smart Tabs target market is 3m to 7.6m with OB or I/O from 10hp to 250hp.

ACS tabs by Mente Marine was the first in the world to create an electronic trim system (ACS) based on “mems” sensors that measure the movements of the boat. It was released in 2002, followed by product refinements over the years. Today, everything is built into the control panel making it very easy to install. Changing from ordinary trim tab switches to an automatic system is just a question of changing the panel. The system fits all popular trim tabs on the market, both electromechanical and hydraulic. It automatically controls the boat in the roll axis (listing) and in the pitch axis (Bow up-down) depending on the product version. After the initial setup, the ACS is fully automatic. It goes on when speeding up and off when slowing down. While turning, the boat is allowed to lean inwards and automatic corrections are prevented. It shows tab position estimation and it also retracts the trim tabs after the drive.

related articles