Most boats handle best when running parallel with their resting waterline. However, trimming your boat for different conditions can improve its ride, handling and safety.
Slight bow-up trim increases a planing hull’s efficiency but in excess increases slamming in a chop and impedes visibility. A little bow-down trim can give a more comfortable ride and better steering at slow speeds, but it can increase spray, cause bow steering or bury the bow in following seas.
Trimming your drives
Outboards and stern drives provide powered adjustment for the drive unit’s trim angle. When the drive is trimmed out—away from the transom—the bow rises. When the drive is trimmed in, the bow falls.
Trim the drive in for steering, visibility and wave handling at slower speeds unless you need bow-up trim to counterbalance weight in the bow.
Using trim tabs
A trim tab is a hinged plate mounted at each side of the transom’s bottom edge. In the raised position—flush with the bottom—the tab has little effect. When lowered, the tab lifts its side of the stern and depresses the opposite bow.
The tab’s angle is hydraulically controlled from rocker switches at the helm. Each tab is controlled separately, so you can adjust side-to-side as well as fore-and-aft trim.
When both tabs are trimmed down, the stern rises and the bow drops. Essential for getting an inboard boat to plane, this can also augment a trimmed-in outboard or stern drive. Once on plane, adjust the tabs to suit. Raise them to decrease drag, keep the bow up in a following sea, or fall off plane again; lower them slightly to maintain planing at a lower speed or to reduce slamming in a chop.
If your boat is unevenly loaded, you can level it side-to-side using one trim tab. Similarly, if you’re heeling into a crosswind, incrementally lower the tab on the side of the boat you want to raise. Gauge the effect of the trim before lowering the tab farther.
To learn more about proper powerboat handling, take the Boat Handling under Power seminar. Find a seminar near you.