Bennett Trim Tabs Overview & Selection Guide
Why Use Trim Tabs?
Trim tabs bring a multitude of advantages, by reducing bow rise you get on the plane faster, improving fuel efficiency and thus reducing costs. As well as improving visibility and the associated safety benefits they also correct listing and porpoising, reducing rolling motion and bouncing, resulting in a more comfortable ride.
- Get up on plane quickly, and plane at lower speeds
- Increase performance and fuel efficiency
- Increase visibility, improve safety
- Adjust the boat’s attitude for changes in speed, sea conditions, and shifting weight
- Correct listing on either side of the boat
How Trim Tabs Work?
Trim tabs apply downward pressure on the water which in turn creates upward pressure on the boat’s transom area, raising the stern and lowering the bow. As trim tabs are located on both the port and starboard sides they can impact each bow side, the port trim tab lowers the starboard bow, and the starboard trim tab lowers the port bow. This means when connected to a control switch next to the helm all the driver needs to do is press the button in the direction you want the bow to move, when the port tab is lowered independently, an upward force at the port stern of the boat is created. The inverse applies when lowering the starboard tab independently.
How To Select Your Trim Tabs
To estimate the trim tab size you require, the following is a good guide. For a boat with a maximum speed of 40mph (34.7knots) you will require a minimum of 1” (2.54cm) trim tab span (width) on each side of the boat for every foot in boat length. For example, a 22-foot boat would use a 24” (span) * 9” (chord) trim tab system.
The wider (span) the trim tab is the greater the lift you will get, so as a general guide you will fit the widest span tabs possible on your available transom area. A 9” (22.86cm) chord (front to back measurement) trim tab normally delivers the best result, however if transom space is limited you can fit a shorter or longer chord length tab and increase or decrease the span length to deliver the same total trim tab area.
Choose the approximate tab size for your boat using the sizing chart below. Make sure the tabs will fit your transom using the diagrams shown as a guideline. When measuring, disregard the strakes and follow the Vee of the hull.
Note: For boats with top speeds over 40mph we would recommend using either the Bennett Performance, or Bennett Premier Line trim tab systems.
Note: A 9” (22.86cm) chord trim tab is used in most applications. A 12” (30.48cm) chord trim tab can be more effective in the following circumstances:
- Limited Transom Space – Boats with twin outboards or twin I/Os, or boats with transom configurations that limit trim tab span, can use 12″ chord tabs to achieve maximum lift. Using the measuring guideline above, fit the maximum span tab and use the 12″ chord.
- Slower boats (less than 15 mph) – Semi-displacement hulls, boats over 50 feet, outboard brackets or boats with any other feature that increases the need for lift aft benefit from the 12″ chord. The 12″ chord provides greater surface area, thereby utilising more water flow and providing more lift.