7 Reasons My Pontoon Boat Prop Cavitates and How to Fix It 


If you’ve done any amount of boating or pontooning, then you’ve likely experienced the strange phenomenon of cavitation. You might have experienced cavitation without even knowing what it was. It usually features strange vibrations on the bottom of your pontoon that you feel while standing or sitting. There are also loud popping or spinning noises that accompany cavitation. 

There are many reasons that pontoon boats cavitate, but most of them are linked to the propeller. The speed of your propeller and how it’s designed are just a few of the reasons for cavitation. 

Why does a pontoon boat cavitate?

Most of the time a pontoon boat will cavitate because the propeller is too close to the surface of the water causing the propeller to suck in air and spin out. Other reasons may be trim angle, propeller pitch, or even an incorrect propeller on your boat.

In this article, we’re going to look at what cavitation is and what its most common causes are. We’ll also look at why cavitation is bad for your boat and how to prevent it from happening. 

What is Cavitation on a Boat? 

Cavitation is the result of a series of events that lead to the formation of air bubbles on the blades of your pontoons propeller. The result is a series of tiny, popping explosions that can cause tiny knicks and scratches on your propeller. To prevent this from happening, it’s important to know what causes cavitation. 

How Does Cavitation Occur? 

  1. As your propeller is spinning through the water, pressure is reduced on the back of the blades. 
  2. If the pressure gets low enough, it causes the water around the blades to boil at unusually low temperatures. 
  3. If the water boils around the blades, it forms water vapor on the surface of the blades themselves. 
  4. Bubbles from the water vapor on the blades travels to the middle of the propeller after being formed along its edges. 
  5. As the bubbles travel to the center, they stop boiling. 
  6. The result is that the bubbles implode on the propeller, resulting in a tiny burst of energy that causes a tiny explosion. The burst of energy isn’t enough to damage the bulk of the boat, but can cause some damage to the propeller itself. 

What are the Main Reasons for Cavitation and How to Fix Them

While cavitation is fairly common with pontoons and other boats, it isn’t normal and shouldn’t happen regularly. Here are some of the main reasons for pontoon cavitation and what you can do about them. 

1. Your Propeller is Spinning to Fast for the Water. 

Problem 

The whole reason that cavitation is occurring is that your propeller is spinning too fast for the water to handle. The speed of the propeller is what causes the water to boil, form water vapors and bubbles, and eventually explode. However, a healthy and properly placed propeller shouldn’t cavitate under your pontoon top speeds. Therefore, the speed of the propeller is the catalyst that is manifesting another problem that your boat has.  

Fix

To prevent cavitating at high speeds you can simply slow the speed of your engine. As you slow down, you should notice that cavitation slows or comes to a stop. While slowing down is a good way to stop cavitation while it’s occurring, it’s not a permanent fix to the problem. 

You don’t want to be restricted in your pontoon and want to enjoy it at all speeds. In order to completely stop your boat from cavitation, you’ll need to figure out what the underlying condition is that that’s causing it. There are some instances, however, when nothing is wrong and the surface tension of the water forms a perfect storm with your propellers. 

By slowly progressing to higher speeds, you can potentially eliminate your cavitation problem. If, however, you try this and the problem still persists, you likely have another issue that’s causing your pontoon to cavitate. 

2. Nicks or Damage to the Front of the Propeller Blades. 

Problem 

Nicks or dents to the front of your propeller blades will usually result in cavitation at high speeds. The nicks and dents form an ideal place for water vapor to form. These vapors will then travel to the middle of your propeller and cavitation is the result. 

Fix

The fix to nicks and dents in your propeller is to have them repaired. There’s a possibility that you can fix a minor nick yourself but if the problem is too extensive, you’ll need to call in the professionals. 

Using a set of files and a tough brush is enough to get rid of minor damage in propellers. However, if it’s chipped or has excessive damage, you’ll likely need to replace one or all of the blades. 

3. If the Prop is Too Close to the Surface of the Water. 

Problem 

If your propeller is located too high in the water, it’s more likely to cause cavitation. The pressure and surface tension at the top of the water is different than that of deeper waters. The higher your propeller is in the water, the more likely it is that cavitation will result. 

Fix

To remedy the problem of a high propeller, you’ll need to set it lower in the water. Ideally, your propeller should be set around 4 inches lower than the tubes of the pontoon. This will result in your tubes floating in around a foot of water and your propellers being 16 inches under the water’s surface. This can be adjusted by lowering your trim angle if it is too high, or taking the engine off of your boat and lowering it with its adjustment bolts provided you have enough space to move it down. On our Yamaha motor, there is four adjustment bolts on the back trim plate, our dealer mounted our engine in the middle.

4. Redesign Your Propeller or Install a New One. 

Problem 

If you fix all the nicks in your propeller, lower it in the water, and make sure everything is perfect and it still cavitates, you might need to redesign your propeller. It’s possible that you simply have a defective propeller that’s prone to cavitation. For example, your blades might be too big for your boat and for the speeds you typically travel at. 

Fix

Redesigning your propeller is a simple but complicated fix. Usually, the only way to do this is to purchase a propeller with different blades, or have a propeller company adjust the pitch of your blades. Attempting to trim or bend your existing blades will likely only enhance your problem. 

5. Old or Worn Out Propeller Blades 

Problem 

The older your prop blades are, the more likely they are to have wear and tear which can cause cavitation. Pontoon blades are meant to last a long time, but they likely won’t last as long as your boat. 

Fix

Once again, there is only so much that you can do to your existing blades. Attempting to alter or reconfigure them can cause more harm than good. You’ll likely have to purchase a new prop and install it yourself or have them professionally done. 

6. Your Transducer Could be in the Wrong Place 

Problem 

If you have sonar system on your pontoon then you also have a transducer that accompanies it. If the transducer is in the wrong place on your pontoon, it can cause cavitation. 

Fix 

To fix this problem, simply relocate your transducer to an appropriate location on one of the outside pontoons not on the middle. It’s good to catch this problem early so that your transducer doesn’t get too damaged from the cavitation. 

7. There Could be a Hollow in Your Hull

Problem 

If the hull or body of your boat has a hollow or dent in it, it can cause your boat to cavitate. This type of cavitation occurs in the body of the boat and not the propellers which is equally as bad. 

Fix 

Fixing body damage to your boat can be expensive and difficult work. However, it’s important to repair existing problems before they have a chance to worsen. You should contact a boat specialist and enlist their help to diagnose and repair any hull damage to your pontoon. 

Why is Cavitation Dangerous for a Pontoon? 

Cavitation will likely not cause any serious damage to your pontoon, but it can damage your propellers or engine. Every time there is an explosion of energy, which characterizes cavitation, it can cause nicks and dents in your props. It can also reduce the speed and efficiency of your pontoon, which is a major inconvenience. Cavitation can also cause your engine to over rev quickly and do permanent damage.

Eric

I have been an avid boater / jet ski fanatic since I was a kid.

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