Why Do Boats Porpoise & How To Stop Your Boat From Porpoising

Why is porpoising called porpoising? What does it mean when a boat porpoises?

Just like a porpoise leaping through the water, a boat can bounce up and down out of the water especially when it gains speed. This is called boat porpoising.

In fact, boat porpoising is the effect of a prop trying to lift the bow of your boat out of the water but not having enough thrust to hold it up.

This problem can occur on various boats, including jet boats, aluminum boats, bass boats, jon boats, and flat bottom boats.

Why is my boat porpoising? What is the cause of porpoising?

You need to know the root causes to better address the boat porpoising problem.

#1. Weight Distribution

Porpoising is normally a result of wrong weight distribution.

A boat will begin to porpoise badly if it is too heavy in the stern.

Adding some temporary weight to the bow and doing a test run will quickly reveal if weight distribution is the culprit for your boat porpoising.

#2. Motor Height

If weight distribution is right, then most likely engine height is the problem.

One of the most common causes of boat porpoising is the engine being set too deep.

If the engine is too deep, there will be an unnecessary drag on the leg with a poor angle of thrust to the hull. And all these lead to boat porpoising.

It’s easy to determine whether the incorrect motor height is the cause of your boat porpoising:

Just get the boat on plane at a fast cruise speed and observe.

The best is to see the anti-ventilation plate (the wide one directly above the prop) skimming the surface. If you can’t see it at all, the engine is set too deep and needs to be lifted.

#3. Engine Trim

Porpoising can also be caused by angling the motor too far away from the transom (or trimming too high).

Generally, trimming up means bow up since you tilt the motor upward where the angle of the propeller is facing more downward into the water.

That creates a force that presses downwards into the body of water. This force pushes the stern down and tilts the bow upwards.

Normally, boaters will trim the motor out for more speed (and better fuel mileage) when they get up on plane in nice calm water.

However, if you go too far (trim the motor too high), the bow will start to porpoise.

How to make a boat stop porpoising?

There are a few simple ways to stop your boat bow from bouncing, and keeping the speed down is one of the easiest.

But nobody wants to do that.

Luckily, we have more feasible solutions to correct porpoising for your boat, while keeping the weight, drag, and cost down.

Be sure to check them out.

#1. Add Weight to Bow

Weight balance is one of the major causes of boat porpoising and it’s easy to test.

So do it first before investing in something like trim tabs or adjusting the motor.

You may use friends or woods as test weights to see if it helps to fix porpoising.

If weight distribution is the culprit, putting sandbags or gravel bags in the front (as ballast weight) will help stop porpoising, which shifts your center of gravity forward.

This is especially helpful for smaller boats since the weight of passengers and gear will affect smaller boats more.

If you expect to have passengers sitting on the rear bench, consider weight distribution to eliminate boat porpoising.

#2. Adjust Motor Height

Oftentimes, the boat porpoising is caused by incorrect motor height.

So do a test and ensure you’re running correctly with the motor:

You can simply get the boat up to a good cruise speed and see where the cavitation plate is.

If it’s mounted properly, the cavitation plate should basically flush with the bottom of the hull.

If the cav plate is buried, it explains the porpoising, and you need to raise the engine.

When you get the engine height at the optimum level, you will not only stop boat porpoising, but also see better performance in RPM, speed, and fuel economy.

Tip: To get the motor dialed in with the right mounting height, you’d better raise one set of holes each time and go test the boat to see if it reduces boat porpoising.

#3. Trim the Motor Down

As stated above, boat porpoising can also be a result of trim being too high.

So make sure the motor is trimmed (or angled) properly.

Generally, trimming down (or trimming in) will raise the stern, which in turn pushes the bow of the boat down, and therefore, stops your boat from porpoising.

[Alt: Boat Porpoising Fix with Engine Trim]

So experienced boaters usually trim down to minimize boat porpoising in chop and trim up to maximize speed in flat water.

If you still see boat porpoising with motor trimmed down, consider using some tools to correct it for you.

#3. Trim Tabs

If you’ve searched around about boat porpoising, you will see a lot of people talking about trim tabs and how they changed the boat from a bouncy ride to a smooth operator.

Generally speaking, you will see a huge difference immediately when you drop down the trim tabs all the way.

However, you’ll lose some speed and fuel economy with the trim tabs since they increase drag. You might feel that you’re pushing the water hard.

That’s why some people complain about trim tabs just treating the symptom instead of solving the boat porpoising problem itself.

#4. Hydrofoil

If you own a small boat, consider adding a hydrofoil to the outboard.

We’ve heard a lot of people who have fitted hydrofoil fins to their outboards to cure porpoising with good results.

It can provide some stability to your boat and reduce boat porpoising.

Although not as effective as trim tabs, hydrofoil is a good alternative to treat porpoising symptoms since it’s hard to install trim tabs on small boats.

#5. Change Props

Changing props to one with more stern lift can also help prevent boat porpoising.

Unlike trim tabs and hydrofoil, you’ll gain some speed and fuel economy with more suitable props.

If you’re experiencing boat porpoising on plane, you’d better check the props being used.

Editor’s Note: Boat porpoising is the result of weight imbalance as well as propeller selection, and motor mounting height.

These all work together, so you may not get a boat to stop porpoising completely from just changing one of them.

There is no trim setting or solution that suits all. The best way to stop boat porpoising will vary among different boat’s hull designs, sizes and weights.