If you’re new to boating, trimming the engine is something you will still be getting to grips with. Trimming the engine is one of the most effective ways to improve a boat's overall performance. Experienced boaters barely notice they are automatically adjusting trim because, over time, it becomes second nature to make tiny adjustments as you move through the water. The water state and weight of the vessel will affect how you maneuver the boat by using the trim. Ultimately, learning to use the trim effectively will help you maintain control of your boat, improving safer sea handling on all your boat trips.

Some boats have a trim gauge on the dashboard to help give you a visual aid so that you know where the engine is without having to keep turning around and looking for it. Otherwise you’ll have to keep a mental note of how far up or down you’ve trimmed the motors and know when to adjust based on environmental factors around you.

The trim affects the running angle of the boat in the water, which affects the depth of the propeller, general water flow and where on the hull the water hits the hull (i.e. the waterline). The trim system can change the angle of the outboard motor and the propeller angle - the normal operating range is usually about 20 degrees relative to the boat transom.

If you are new to boating and your course instructor tells you to “adjust the trim,” what you are doing is either raising or lowering the bow to change the way the boat moves through the water. Once you understand how to use the trim effectively, you can optimize speed, comfort, and fuel efficiency. Trimming your outboard can be done, either at stationary or while moving through the water.

How Does A Boat's Engine Trim Work?

Older model boats or small, utility boats with tillers may not be equipped with a power trim system, so you will have to adjust the angle of the motor by hand, which can require some brute strength. Fortunately, most modern recreational boats have a power trim system that utilizes electrically-controlled marine hydraulic actuators (otherwise known as tilt and trim rams). The trim rams are for fine-tuning the angle of your outboard, while the tilt rams are more for trailering. The complexity of your power tilt and trim system depends on your outboard power package and controls.

You can control the trim (and tilt) by using a toggle button on either the throttle lever or via a switch on the dashboard, depending on your model. The trim button will raise or lower the engine thus changing the angle of the outboard engine and the angle of the propeller shaft relative to the boat’s transom (the section on the stern of the boat that the engines mount to).

Trimming Up = Bow Up

When we trim up, we tilt the forward top of the engine towards the boat, which lifts the propeller on the bottom of the engine up higher in the water and further away from the stern of the boat, creating a force that presses downwards into the body of water. This force pushes the stern down and tilts the bow upwards.

Trimming Down = Bow Down

By trimming down, we tilt the forward top of the engine back, until it is parallel with the transom (or zero trim). This pushes the propeller towards the boat, pushing the water straight back away from the vessel and leveling out the boat’s hull. If you’re trimmed up to begin, when you trim down, the bow will lower. Of course you must be underway for this to work, if you are stationary, or moving at a very slow rate of speed, the effects of the trim may be negligible.

Top Tip: Remember that when you are running, the boat’s bow will move in the same direction as you press the trim button.

How To Trim On Plane

For planing hull boats, when getting onto a plane, the propeller should be ‘trimmed in’ (which is the same as having the trim down).
As the boat speeds up and the bow comes down slowly (this means that you are planing), you can start to ‘trim out' (trim up) if you’d like, in order to raise the bow slightly, which can, in some cases, reduce the amount of hull in contact with the water and thus increase your top speed.
When the bow is relatively level, and you have a clean wake behind you, you're on a plane, which means you are riding the boat as high up on the water's surface as possible. Every boat has a different ideal trim position for the hull’s design which can vary based on weather, wind and sea state.

Generally speaking, the faster the boat goes, the more you can trim the engines out (trim up) while still staying on a plane.

Boa- Wake-at-Long-Beach-Harbor

Find Your Boat’s Sweet Spot In The Water

As you drive the boat, the water state is likely to change. Once you become aware of how the boat's trim affects your boat, you can make automatic adjustments. Any skilled boater will factor in waves/sea state and what type of boat, outboard set up, and weight (passengers on board). Over time acquire a feel for your boat and how it reacts to engine trimming.

Using The Trim When Turning

When preparing for a turn, trim the outboard in (trimming down) for maximum handling. As you come out of the turn, you may find that trimming down and increasing throttle will improve your boat's planing capability. Once your boat begins to follow a straight line again, start trimming the outboard out (trimming up) slowly, and continue driving at your most efficient cruising speed.

Adjusting Your TrIm In Choppy Water

Depending on your hull design, trimming down all the way can be advantageous when cruising through choppy water because it positions the hull to slice through the water to allow for a smoother ride. Having your bow tipped up in the air is not going to work to your advantage in terms of speed and fuel efficiency and in some instances can be unsafe. On the other hand, if you’re worried about taking waves over the bow, you can trim up slightly to position the bow a bit higher into oncoming waves, as long as you stay on plane.

Adjusting Your Trim In Shallow Water

When you need a boat to float in as little water as possible, or travel very slowly, you should trim the engine up as far as possible, but always ensure the propeller is still underwater to pick up water for cooling. One easy way to check this is to make sure the water is circulating through the motor and exiting the water pump indicator hole (aka the "pee hole") in a steady stream. If you see this stream reduce or stop altogether, you either have the engine trimmed up too far, or your cooling system is clogged.

However, keep in mind that when the motor is trimmed all the way up in shallow water, if you give your boat too much throttle you will force the bow up, and the transom down, thus pushing the propeller into the ground. So when the motor is trimmed all the way up, you need to travel very slowly. If you know for sure that you have enough water under you to go fast, and you aren’t in a “no wake” zone, then you should keep your boat on a plane (with the engine trimmed down) as that is the highest position that your propeller will float in the water while underway.

Red Flag!

When you are driving your boat, look out for:

  • Porpoising. This is when the bow bobs up and down, caused by over-trimming (trimming too far up) at cruising speed when there’s no longer enough hull in the water to support the boat's weight. If this happens, trim down quickly to lower the bow.

Need a Helping Hand? Invest In An Auto Trimming Device

Old school boaters generally believe that you have to earn your stripes out at sea, and mastering the art of trimming is part of the parcel. But if you would prefer to take the easy route, consider purchasing Mercury® Active Trim system, which takes the guesswork and effort out of trimming a boat. Active Trim sure makes driving a boat easy, with an integrated GPS speed-based automatic engine trim system that continually adjusts engine trim based on boat speed and maneuvering changes. The Active Trim system is compatible with most Mercury four-stroke outboards from 40hp and up, Mercury two-stroke outboards with SmartCraft® system capabilities, and SmartCraft-capable MerCruiser® and Mercury Diesel sterndrive engines.

Q&A Boat Trimming Lingo

There are many ways to slice an onion and many ways to refer to repositioning your boats outboard. Here are some common terms you might hear in regards to trimming.

Trimming Up (Out)

When the outboard is “trimmed up” it raises the propeller, pushing the bow upwards.

Trimming In (Down)

When the outboard is “trimmed down” the propeller is lowered and the bow is pushed downwards.

Negative Trim

When the trim is all the way down, resulting in the bow dipping downwards towards the water, which can lead to “nose dives”.

Positive Trim

When the trim is all the way up, resulting in the bow lifting out of the water, which can lead to too much air getting under the hull.

Neutral Trim

Neutral trim, or zero time is when the engine has no angle and is parallel with the boat’s rear wall (transom). The propeller shaft sits evenly against the waterline, which is good for fuel efficiency and speed.

Written by: Emma Coady
Emma Coady is a freelance writer and marine journalist who creates content for many household names in the boating industry, including YachtWorld, Boat Trader and boats.com. She also writes for several boat builders as well as charter and rental companies and regularly contributes to Greenline Hybrid yachts, TJB Super Yachts and Superyachts Monaco. Emma is the founder of Cloud Copy and enjoys traveling around Europe, spending as much of her spare time as possible in or on the water.