Tilt and trim are mentioned frequently when discussing outboard motors, but whilst they are functioning on the same part of the engine, they are very different.
Tilt: Tilt angle raises and lowers the engine in and out of the water, mainly used when docking or in shallow waters to avoid bottoming the propeller out. Consider Tilt as the MAJOR adjustment.
Trim: Trim angle adjusts the position of the propeller shaft to the boat. Changing the trim angle will determine whether the boat is bow up, bow down or neutral. Trim position is important for a smoother ride and improved speed and/or efficiency. Consider Trim as the MINOR adjustment.
Trim angle is usually from roughly 0 to 20 degrees, whilst tilt can be 0-90 degrees to ensure the motor is fully removed from the water.
Typically, you will come across these 3 terms;
Positive Trim: The angle of the motor is slightly upwards, which will cause the bow to rise.
Neutral Trim: This is the ‘default’ angle, where the prop shaft is on the same plane (parallel) to the water.
Negative Trim: The angle of the motor is slightly downwards, which will cause the bow to drop.
Understanding this concept means that when we look at trimming up or trimming down, the basic concept of the propeller and prop shaft angle in relation to the boat makes sense. Trimming the engine down will raise the stern, which in turn pushes the bow of the boat down, this is negative trim. Trimming up does the opposite, where the stern is pushed down, causing the bow to rise. This is a positive trim.
Why is tilt and trim important to understand?
Understanding trim is important for optimizing journey efficiency. In general, trimming up pushes more of the boat out of the water, reducing water drag, and increasing speed and efficiency. Whilst trimming down will push more of the boat into the water, which increases drag, requiring more fuel, when on choppy waters being trimmed down can prove a more comfy ride. However, there is such a thing as too much trim.
Trimming up too much can cause the propeller to break the water surface. If the propeller is cutting through both water and air, it creates prop slip, as the propeller is designed to push around the resistance and weight of water. By having it in the air, the prop is not gripping constantly. This can slow the boat down, which then reduces fuel efficiency and speed.
Tilting up when stopped is also important. Of course, for large engines and inboards, etc., trimming up isn’t necessarily possible, but for the smaller outboard motors, trim up wherever you can. Leaving the propeller and engine down in the water for extended periods without moving can create a build-up of debris and growth, which can damage the propeller, shaft and the engine itself.
So why tilt and trim?
The ability to measure and record tilt & trim to improve fuel economy and handling of outboard engines has been a requested feature by our customers around the globe. Our team are pleased to be bringing this powerful feature to our popular EMU-1 Engine Monitoring Unit, which will allow users to collect that data and share it across their NMEA 2000 network.
More information about this exciting new feature to come soon!