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What Size Trim Tab is Right for Me?

Many factors affect the choice of properly sized trim tabs, and the ultimate responsibility for selection is up to you, the boat owner. To help you decide, Bennett Marine offers you a few guidelines below.

Trim Plane, Span, and Chord

General Guidelines

These sizing recommendations are based on 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.

As a rule, choose at least one inch of trim tab span (per side) for every foot of boat length. (Examples: 22-foot boat = no less than 24" x 9", 36-foot boat = no less than 36" x 9".

Span = side to side measurement
Chord = fore to aft measurement

Whenever possible, choose a 9" chord trim tab, and gain lift through a longer span. 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 12" chord. Click Here to See When to Use a 12" Chord

Measuring

Choose the approximate tab size for your boat using this sizing chart. Make sure the tabs will fit your transom using the diagrams below as a guideline. When measuring, disregard the strakes and follow the Vee of the hull.

Boat Length Engine Configuration Trim Tab Size
(span x chord)
15'-19' (4.5-5.8 m) Single I/O, Single Outboard or Inboard 12" x 9" (30 x 23 cm)
17'-19' (5.2-5.8 m) Single Outboard 8" x 10" (20 x 25 cm) M80
19'-24' (5.8-7.3 m) Single I/O, Single Outboard, or Inboard 18" x 9" (46 x 23 cm)
19'-24' (5.8-7.3 m) Limited Transom Space or Extra Lift 12" x 12" (30 x 30 cm)
20'-23' (6.0-7.0 m) Single I/O or Single Outboard 10" x 12" (25 x 30 cm) M120
22'-27' (6.7-8.3 m) Single I/O or Single Outboard 24" x 9" (61 x 23 cm)
22'-27' (6.7-8.3 m) Twin I/O or Twin Outboard 18" x 12" (46 x 30 cm)
25'-30' (7.6-9.1 m) Single I/O or Outboard 30" x 9" (76 x 23 cm)
25'-30' (7.6-9.1 m) Limited Transom Space or Extra Lift 30" x 12" (76 x 30 cm)
25'-30' (7.6-9.1 m) Twin I/O or Twin Outboard 24" x 12" (61 x 30 cm)
28'-34' (8.5-10.4 m) Inboard 36" x 9" (91 x 23 cm)
28'-34' (8.5-10.4 m) Limited Transom Space or Extra Lift 36" x 12" (91 x 30 cm)
28'-34' (8.5-10.4 m) Twin I/O or Twin Outboard 24" x 12" (61 x 30 cm)
32'-38' (9.7-11.6 m) Inboard 42" x 9" (107 x 23 cm)
32'-38' (9.7-11.6 m) Limited Transom Space or Extra Lift 42" x 12" (107 x 30 cm)
36'-44' (11.0-13.4 m) Inboard 48" x 9" (122 x 20 cm)
36'-44' (11.0-13.4 m) Limited Transom Space or Extra Lift 48" x 12" (122 x 30 cm)
42'-50' (12.8-15.2 m) Inboard 54" x 9" (137 x 23 cm)
50'-60' (15.2-18.3 m) Inboard 54" x 12" (137 x 30 cm)
60'-65' (18.3-19.8 m) Inboard 60" x 12" (153 x 30 cm)
65'-70' (19.8-21.3 m) Inboard 66" x 12" (168 x 30 cm)
70'-80' (21.3-24.4 m) Inboard 72" x 12" (183 x 30 cm)

Installation Requirements

Trim tabs should follow the Vee at the junction of the transom and the bottom of the boat. For maximum side to side control, trim tabs are generally mounted 3-4" from the chine and run towards the keel.

In case of inboards, the complete run from chine to keel may be utilized if it is an unbroken span of the same angle. Protrusions, such as strakes, may be bridged provided there is no change in angle on both sides.

On boats powered by inboard/outboards (I/O) or outboards it is necessary that the trim tabs not be placed too close (8" minimum) to the lower unit(s) to avoid disturbing the water flow to the propeller.

When to Use a 12" Chord

The 9" chord is used in most applications. However, in certain circumstances the 12" chord may be more effective:

Trim Tab Mounting - Two types of Mounting Hinges are Available:

Standard Transom Mount

Bottom Mount:

Performance Boats

Many factors determine the appropriate size and type trim tabs for "faster" boats. Special consideration is required when selecting trim tabs for performance applications.

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