You’ve been cruising for hours and are heading for the dock. Therefore, you’re accelerating at a high RPM. You suddenly notice that the boat is moving slowly or appears stuck in the water with no propeller. What exactly is happening in your boat?
Maybe the prop hub is spun. What symptoms of a spun prop hub, however, will confirm your suspicion? The most obvious sign of a spun prop hub is that the boat doesn’t move at high RPM, which you have already experienced.
However, you might still be confused about whether a spun prop hub is the main culprit. So, what should you do to detect the issue? You must stick with us through the end to find out.
What are the Signs of a Spun Prop Hub?
Unlike many other components in your boat, a spun prop hub might not show too many visible symptoms.
Hence, rather than seeking any apparent sign, it’s good to do some diagnosis to discover whether you have a spun prop hub.
A simple diagnosis will inform you about the condition of the prop hub. Anyway, we’ll discuss both symptoms and some simple diagnoses to detect a spun prop hub.
Symptom 1: Your Boat Isn’t Moving At Higher RPM
When you put your boat in gear and throttle, it will start going. However, as the boat reaches a higher RPM, you may notice your boat isn’t moving anymore, even though the motor is running fine.
This mostly happens when the rubber hub inside the prop has become hard. In this case, you’ll notice your boat is running well in the beginning, which means the rubber hub catches at the beginning and then it slips.
If your motor is doing this, you probably got a spun hub. This situation can also be described as losing power while the RPM is high.
Symptom 2: Circular Scratch on the Hub
One of the most apparent indications of a spun propeller hub is that the shaft has uneven circular scratches on the surface that avoids conflict with the thrust washer.
In general, your propeller shaft contains splines. The principal purpose of these splines is to prevent the thrust washer from slipping.
However, when the prop hub is spun, it will start rotating along with the thrust washer that eventually scratches the surface.
Symptom 3: The Prop is Turning in Both Directions
Usually, when the motor is off, you should be able to turn the prop around a respective axis with your hands. However, you won’t be able to turn it in the opposite direction.
So, when the prop turns in only one way, your hub is in good condition. Now try to turn it the other way by inserting your hand further and exerting more force.
If it moves, it may feel like the prop is slipping away, and it indicates your prop hub is spun.
This may not be completely foolproof, though, as you won’t be able to turn the propeller shaft with your bare hands until the prop hub has completely spun. However, it’s an effective indication though.
Symptom 4: Visual Assessment
You can also confirm whether the hub has spun itself into the propeller through a visual assessment.
For this, you have to draw a straight line using a marker. This line should intersect the front side of the hub and propeller. Now, run the propeller for at least two minutes and turn it off.
Once the propeller is turned off, check whether the straight line intersects both the propeller and the hub as you have drawn. If it doesn’t, the propeller hub must be spun.
Possible Causes of Spun Prop Hub on an Outboard Engine?
To understand the cause of a spun prop hub, first, you must understand how it works. Whatever kind of hub your boat has, its primary function is to provide cushioning where the propeller shaft and the propeller come into contact.
This cushioning is essential to minimize the impacts when your propeller strikes against something hard. At the same time, it reduces the amount of shock on the gear case.
However, if the impact is too severe, it can destroy the hub. Now let’s see what can cause a spun prop hub:
Loose Bonding with the Propeller
As you know, a prop hub is firmly bonded to the propeller and rotates along with the propeller.
However, prop hubs, especially those quite old and made of rubber, will dry out or become hard or shrink over time.
Consequently, their bonding with the prop tends to be loosened, and the hub starts spinning freely.
On the other hand, excessive heat released from the exhaust can also deteriorate the prop hubs made of rubber or Polyoxymethylene (POM) materials. The result will also be the same—a loosened and spun prop hub.
Cruising in Large Waves or Windy Conditions
This cause is related to environmental conditions and impacts. When you’re driving in extremely windy conditions, with too many waves or turbulence in the water, your propeller will sometimes come out of the water.
Since the propeller is designed to run in water, it gains abnormally high rpm when it gets out of water due to high turbulence. Even though it may seem something neglectable, it puts much pressure on the propeller.
If your boat goes through this condition at a stretch, it will ultimately wear down the propeller and affect the bonding between the prop and the rubber hub. As a result, you may end up with a spun prop hub.
Sudden RPM Acceleration
RPM upsurge is one of the most common causes of a spun prop hub. But how? This is especially true when your boat is in idle condition, and you suddenly squeeze the pedal down to speed up as much as possible.
But you’re not focusing on the gear position at all. Can you relate to the scenario? Yes, we’re talking about a tournament.
However, this type of situation can arise anywhere, especially if you’re a boater with extreme rage in the head. Sudden acceleration is okay for your propeller unless you do it repeatedly.
When you suddenly push the throttle hard without shifting the gear, an imbalance is created between the speed and gear. Doing this continuously damages the propeller and eventually causes the hub to be spun.
Replacement and Repair Costs of Outboard Spun Prop Hub
In most cases, when the prop hub is spun, you have to replace it. The replacement cost can vary depending on whether the propeller is damaged and the size of the prop.
We have seen different boaters expressing diversified opinions regarding the prop hub replacement cost.
However, the overall cost is limited between $50-$150. Nevertheless, the prop hub itself won’t cost you too much.
Tips for Maintaining the Outboard Prop Hub to Prevent Future Spun
A spun prop hub signifies more severe issues inside the boat, motor, and propeller. So, for a safe journey and to save your cash, try to follow the tips mentioned below. Hopefully, these will help you to prevent a spun prop hub in the future.
Evaluate Your Driving Habit
If you look closely at the causes of a spun prop hub, you can realize that how you cruise your boat can determine the condition of the prop hub and even the whole boat.
So, first of all, don’t push the paddle too hard suddenly. Always try to increase RPM slowly and change the gear as required.
Secondly, don’t accelerate when you’re cruising in high waves. Since you can’t avoid any sudden turbulence, you can minimize the upsurge of RPM.
When the water becomes turbulent, avoid pressing the throttle. This will keep the RPM moderate even when the boat is running airborne.
Ensure Regular Maintenance
In general, the prop hub is designed to withstand the heat generated and released by the exhaust chamber. However, it can become excessively hot due to some other malfunctions.
For instance, malfunctioning in the poppet valve, thermostat, and water pump can lead to excessive heat. This will eventually deteriorate the propeller and the prop hub as well.
Check these components regularly and replace or repair them if any sign of damage or malfunction is discovered.
By now, hopefully, you have a good idea about the symptoms of a spun prop hub. Here are some frequently asked questions that you might want to know.
Should my prop spin freely in neutral?
Yes, you can only rotate the prop when the engine is in neutral condition. The prop won’t rotate if it’s in gear. However, if it does, check the prop hub first.
What happens when you have a spun prop hub?
If your prop hub is spun, your propeller will lose grip at higher RPM. It will feel like your outboard engine is gradually losing power.
How to fix a spun prop?
Fixing a prop hub isn’t a difficult task at all. You can easily get it repaired at a reasonable cost in any marine mechanic shop. However, you can also do this if you have the right tool.
Should I cruise my boat without replacing the spun prop hub?
Absolutely not. Even though you can cruise around with a spun prop hub, you may find yourself stuck in the middle of the water after accelerating high. Moreover, this will damage the propeller as well.
In summary, if you experience a situation where your boat appears stuck in the water or moves slowly with a high RPM, you might have a spun prop hub. The most noticeable symptom is losing power while the RPM is high. Scratches on the propeller shaft and the prop turning in both directions are other indications of a spun prop hub. Loose bonding between the propeller and the hub, cruising in large waves or windy conditions, and sudden RPM acceleration are the main causes of a spun prop hub. If you suspect your boat has a spun prop hub, it’s essential to do some diagnosis to confirm the issue.
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