Trimming your sterndrive engine properly has many benefits, including helping your boat to plane faster, perform better and use fuel more efficiently. If you are used to driving an outboard-powered boat, you will find that trimming a sterndrive boat is very similar. The difference is that unlike with an outboard, the sterndrive is hidden beneath your swim platform where you can’t see it. So, you need to rely on the trim gauge mounted at the helm to show you the angle of the drive. As you get more experienced at trimming the drive, you will be able to do this by feel.
You trim the sterndrive in and out using the “Up” and “Down” buttons located on the left-hand side of the throttle control. When you are idling out of the marina or away from the boat ramp, make sure the drive is all the way down in the water. In that position, the propeller is angled down and away from the transom. Once you reach an area where you can run at planing speeds, open up the throttle. When the drive is all the way down, the thrust from the prop will lift the transom, helping the boat to get on plane more quickly. Like a child’s seesaw, lifting the stern also will keep the boat’s bow down, preventing excessive bow rise that can block your view of the water ahead.
As you accelerate, gradually trim the drive up with your thumb. Continue trimming it up to the point where the gauge indicates it is midway between “Up” and “Down,” but no higher.
“Observe how the boat is behaving. If you trim the drive up too high, the boat may start ‘porpoising,’ with the bow bouncing up and down. In order to avoid that happening, be sure not to trim the drive higher than horizontal to the waterline initially,” said Reinhard Burk, MerCruiser® senior director of global inboard and sterndrive categories.
Burk continued, “The point just before the boat starts to porpoise is the most efficient position for the drive. The bow is raised high enough into the air to lower the resistance from the water, which increases the boat’s speed and reduces fuel consumption. But, if you trim the drive too far up, there is nothing to prevent the boat from porpoising.”
Alternatively, Burk points out, if your boat is equipped with a MerCruiser sterndrive with proprietary Active Trim technology, Active Trim can automatically trim the drive to the optimal position as the boat accelerates without you having to do a thing. “All you have to do is engage Active Trim,” he said.
Using Active Trim in conjunction with the MerCruiser Adaptive Speed Control system further improves control, with Adaptative Speed Control automatically holding the engine’s speed (RPM) as load or water conditions change or when the boat makes a tight turn.
“When you head into a tight turn, engine RPM and prop speed will drop. If you are trimming the drive manually, you need to lower the drive all the way down and accelerate into the turn. With the MerCruiser 4.5 and 6.2 engines, Adaptive Speed Control and Active Trim work together to do this automatically,” Burk said.
Whether or not you are driving a MerCruiser-powered boat, it is important to understand how to trim your sterndrive properly, and to practice the procedure until you can do it by feel without needing more than take a quick glance at the trim gauge. However, with a MerCruiser sterndrive equipped with Auto Trim and Adaptive Speed Control, this innovative Mercury technology automatically will ensure that your boat is performing efficiently, freeing you up to enjoy the ride.