The intent of this document is to provide a clearer understanding of the operational differences between a stepped-hull vessel and a traditional mono-hull style boat. Specific attention is provided herein to the uses and adjustment of engine trim. As such, this guide assumes that the reader and/or boat operator has experience using throttle-based engine trim controls and is performing the recommendations herein under favorable weather and water conditions. Towards this end, any reference to “trim” or “trimming” within this documents speaks directly to the outboard engine’s angle in the water, not the use of exterior-mounted trim tabs.
Benefits of a Stepped Hulls
A stepped hull design generally grants a boat with a larger degree of deadrise the ability to ride flatter in the water with a cruising height of approximately 3° bow up attitude. The inclusion of steps assist the vessel in achieving more speed, with less horsepower, and improved fuel efficiency versus traditional hulls with the same horsepower. Speaking purely on physics, when on plane, a stepped hull decreases the total wetted surface due to less contact points with the water and thereby lowers overall drag. Given this, while in a turn, the reduction in drag will produce a smaller wake. The end result, a stepped hull will generally be more efficient, use less fuel, and obtain a higher top-end speed.
Default Trim Position at Cruise
When operating a stepped hull, engine trim should be set to 50-60% out for maximum efficiency as this puts the cavitation plate parallel with the water. In contrast, a traditional hull would run with an approximate 25% trim.
When backing off the throttle and as the boat begins to settle, start trimming your engine into the zero-trim position. The zero-trim position should be consider the default and used for the starting point for acceleration.
Accelerating to Plane
To rise up to plane, increase the throttle briskly and begin trimming the engine outward within just a few seconds of acceleration. As speed increases, the operator should continue to add trim until reaching the 50-60% position and an approximate cruising speed of *30 to 40 MHP. *This will vary from vessel to vessel and engine horsepower.
Turning On Plane
Once on plane, trim the engine ‘as needed’ until the steering feels light and responsive. Understanding ‘feel’ is subjective, it is recommend taking multiple test runs to determine where your boat performs best.
Eliminate Bow Lift
Ideally, as the operator adds speed and trim simultaneously, the vessel will hold a 2° to 3° attitude. Translating from degrees to inches – from the helm position and looking forward, the forward-most point of the boat could be expected to rise approximately 6”. When properly trimmed, the vessel should not exhibit any bow lift on the hole shot.
Trim & Turning
With a mono-hull, it’s common to trim the engine inward (tucked in) to increase bow bite. In contrast, a stepped-hull should stay closer to the normal running position of 50-60% as not to dig into the water. The reason for this is during harder turns, the steps will lose their air induction within the inside hull vents and thereby increase wetted surface and cause drag. When this occurs, the operator should correct by adding throttle and keep the bow up.
Unless the vessel is experiencing wind induced heel, a need to correct a ballast heel, or the need to create a heel in windblown spray conditions, the operator will rarely have a need to use externally mounted trim tabs.