Trim Tab Sizing Guidelines
Many factors affect the choice of properly sized trim tabs, and the
ultimate responsibility for selection is up to the boat owner.
These sizing recommendations are based on average performance.
Your choice may vary based on power, engine configuration, weight
distribution, type of boat, and use. 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.
General Guidelines
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
Measuring
After choosing a general trim tab size (see chart below), double check the
size by measuring the transom using the diagrams. When measuring, disregard
the strakes and follow the Vee of the hull.
12" Chord
The 9" chord is used in most applications. However, in certain applications
the 12" chord may be more effective: 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 in minimum
area. Using the measuring guideline above, fit the maximum span trim tab and
use the 12" chord. Extra Lift Slower boats (less than 15 mph), semi-displacement
hulls, boats over 50 feet, outboards on 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 utilizing more water flow and providing
more lift.
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 the 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.
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.
You may wish to contact Bennett Marine to discuss your particular application.
Bennett Sport Tabs are available for boats in the 40-60 mph range.
| Boat Length |
Configuration |
Trim Tab
Size (span x chord) |
|
| 15' - 19' |
Single I/O,
Single Outboard, or Inboard |
12" x 9" |
| 17' - 20' |
NEW |
M80 Sport Tab for Trailered
Boats |
8" x
10" |
| 19' - 24' |
Single I/O,
Single Outboard, or Inboard |
18" x
9" |
| 20' - 23' |
NEW |
M120 Sport
Tab for Trailered Boats |
10" x
12" |
| 19' - 24' |
Limited Transom
Space or Extra Lift |
12" x
12" |
| 22' - 27' |
Single I/O or
Single Outboard |
24" x 9" |
| 22' - 27' |
Twin I/O or
Twin Outboard |
18" x
12" |
| 25' - 30' |
Single I/O or
Single Outboard |
30" x 9" |
| 25' - 30' |
Limited Transom
Space or Extra Lift |
30" x 12" |
| 25' - 30' |
Twin I/O or
Twin Outboard |
24" x 12" |
| 28' - 34' |
Inboard |
36" x
9" |
| 28' - 34' |
Limited Transom
Space or Extra Lift |
36" x 12" |
| 28' - 34' |
Twin I/O or
Twin Outboard |
24" x 12" |
| 32' - 38' |
Inboard |
42" x
9" |
| 32' - 38' |
Limited Transom
Space or Extra Lift |
42" x 12" |
| 36' - 44' |
Inboard |
48" x 9" |
| 36' - 44' |
Limited Transom
Space or Extra Lift |
48" x
12" |
| 42' - 50' |
Inboard |
54" x 9" |
| 50' - 60' |
Inboard |
54" x 12" |
| 60' - 65' |
Inboard |
60" x 12" |
| 65' - 70' |
Inboard |
66" x 12" |
| 70' - 80' |
Inboard |
72" x 12" |
