7 Reasons To Use Boat Power Trim and Trim Tabs

Tom Wiesen

Nov 26, 2021

Many people have asked when to use power trim on a boat motor and when to use boat trim tabs? The fact is that they work in tandem, and the answers to these questions are demystified here.

Let’s start with the trim of your boat motor. Some boats only have this type of trim, and it basically tilts the motor up and down. All the way down is called trim in (because it’s close to the stern), or when the engine is tilted up, this is called trim out. It’s a switch that’s located on the dash, or on the shifter, and it has an up position, and a down position.

trim your motor boat

When at cruising speed, trim your motor out to raise the bow so there’s less drag or resistance, and greater efficiency.

When your boat is in deep enough water and you are ready to take off and get going, you’ll want to start with your engine trim all the way down. This gives you the greatest ability to get your boat up onto a plane quickly because with the trim positioned in, it forces the bow down as you come up to cruising speed.

What does getting a boat up on a plane mean?

As you take your boat from idle and then accelerate to put your boat into motion, the bow of the boat rises and the stern of the boat squats low in the water as the The boat climbs up and over the displaced cushion of water called the bow wave.

boat accelerate

Upon acceleration from idle, the boat must climb over the bow wave. When the bow lowers, the boat is on a plane.

Once the boat accelerates sufficiently to clear the bow wave, your bow comes down and the boat flattens out and accelerates. At this point the boat is on a plane.

Adjust your Boat’s Power Trim for Efficiency

Once you are up and running on a plane and cruising at speed, it’s time to trim your engine out. The general rule is to use the switch in half-second bursts until you find the sweet spot. Your objective is to raise the bow slightly so less of the boat’s bottom is in contact with the water thereby reducing drag while increasing speed and efficiency.

cobalt bow rider

Trim your motor out using half-second bursts on the switch until you find the sweet spot.

What happens if the motor is trimmed out too far?

If the motor is trimmed out too far, it will begin to suck air, known as ventilating, the RPM’s will go up, and your speed will decrease. Trim your engine back in using a half-second burst until your propeller is getting a full bite into the water and the ventilating has ceased.

Trim The Boat Motor Back in Once You Come to a Stop

Once you decelerate and bring your boat back down to idle, it’s a good time to trim your motor back in, so it’s in ready position for the next time you take off. If you leave your trim up and take off, your bow will remain high and it will take a long time and a lot of power to get the boat up onto a plane.

white mercury motor boat

Trim the motors back in when you come back to idle. Otherwise, when you go to take off, it’ll take forever to get on a plane.

So When Do You Use The Trim Tabs? 

Experts agree to use the boat motor trim as described above to adjust for maximum efficiency. So now introduce a boat’s trim tabs. These are strong flaps of metal on the back of the boat’s transom, one on each side, and they operate independently of each other.

two boat trim tabs

Trim tabs are mounted at the waterline on the transom of the boat, and are controlled by hydraulics or electric. The hinged plate gets pushed against the flow of water to lower the bow.

The boat trim tabs are raised or lowered by either a hydraulic ram or by an electric actuator. Two independent switches on the boat’s console operate the trim tabs and they operate intuitively. At the top of each switch it reads bow down, and the bottom reads bow up. There is a left switch (port side) and a right switch (starboard side).

boat trim tabs switch

The trim tabs are controlled independently with left and right switches, but are often used together.

Put the trim tabs down before you are ready to accelerate up to cruising speed.

When the boat is accelerated from idle speed, the bow naturally rises. The sooner the bow comes down, the sooner the boat gets on a plane and accelerates, and the sooner the captain can see fully in front of the boat.

If both of the trim tabs are down upon acceleration, it forces the stern up, which naturally pushes the bow down. Therefore, the boat gets on a plane much faster, so

It takes less time and effort for the engine to get the boat up to cruising speed. As the boat reaches cruising speed, raise the trim tabs because they’ve done their job and now they create drag. Then trim the motor to give you optimum efficiency. Doing these two practices in tandem will save a considerable amount of fuel.

  • Do Not Over Trim the Boat

An over-trimmed boat, is when the trim tabs are too low and it forces the bow down and the boat plows or bow steers. This can cause the boat to veer suddenly especially at high speeds. Remember, the higher the speed of the boat, the more effect the trim tabs have because the power of the water pushing against them.

  • Use Trim Tabs to Correct Boat Listing or Tilt

If you have a lot of cargo or people on one side of the boat causing it to tilt, the the captain can simply return the boat to a neutral position using a trim tab. Say there are a lot of people on the right or starboard side of the boat, that raises the left or port side of the boat, so in half-second bursts, press the left switch at the top for bow down on the port side. This in fact actuates the trim tab on the starboard side of the boat, and forces the port side of the bow down.

  • Use Trim Tabs to Correct Porpoising

At high speed in performance boats, the bow can rise and fall in a rhythmic motion known as porpoising. To correct this action, use both tabs and press bow down in half-second bursts until the effect subsides.

  • Use Trim Tabs in Choppy Conditions Or in A Head Sea

Seas conditions can vary widely depending on spacing of the waves, if it’s choppy, if the waves are spaced, and of course if the waves are big. Keep in mind, trim tabs only work when the boat is at speed, approximately 20 MPH. Trim tabs do not work at low speed.

Using some amount of trim tab to lower your bow in choppy conditions puts the V-shaped part of the bow into the waves to cleave the waves, and reduce pounding on the boat’s hull. It also makes it more comfortable for the passengers. Using some trim tab when taking waves head-on helps counteract the pendulum effect by keeping the bow down.

  • Use Tabs in a Side Sea

When travelling parallel to the waves, and the waves are hitting the side of the boat, raise the windward side by pushing the bow down the opposite side. This raises the side with the waves, and reduces the amount of spray hitting passengers, and decreases the amount of water coming into the boat.

When not to use trim tabs? 

When going with the waves in trailing seas, trim tabs should be fully retracted for maximum maneuverability and steering control. Same for running an inlet so the tide or current won’t push the stern unnecessarily.

Also, whenever using reverse, the trim tabs should be fully retracted. Lastly, when you put your boat on a trailer, make sure the trim tabs are fully retracted. By following these general rules and recommendations regarding the use of your boat boat power trim and trim tabs, it will give you a good foundational understanding of how and when to use motor trim and trim tabs. If you need more tips, read our blog how to drive a boat.

Practice with your boat and find the sweet spot. This will come naturally over time while experimenting in various conditions. Now you have some tools in your quiver and some understanding to help make your future boating experiences better, safer, and more comfortable than ever. Enjoy!

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