Fixed vs. Folding vs. Feathering Propellers: What's the Difference?

Choosing a new propeller for your sailboat?

Then you’ve probably come across three types: fixed, feathering and folding.

They all push the boat forward under power. The big differences show up when the engine is off, and in how much maintenance they need.

At Flexofold, we only make folding propellers, so we’re not neutral on the subject. But we’ll explain how each type works, so you can judge for yourself what fits your boat and your sailing.

Who should choose between a folding propeller and a feathering propeller?

Anyone whose sailboat has room for either type. Whether you can choose depends on the space around your shaft or saildrive.

Beyond that, it comes down to how you sail. Do you want to keep sailing in light winds without starting the engine? Do you want to adjust the pitch yourself? Or do you want a propeller you can mostly forget about between seasons? Your answers point toward different propellers.

The different types of propellers for sailboats

There’s a wide range of propellers you can fit on your sailboat.
 In this blog post, we’ll look at the three main types: 

1. Fixed propeller
2. Feathering propeller
3. Folding propeller

Fixed propeller

 A fixed propeller has fixed blades. They can’t fold, so they stay in the same position whether you’re under sail or under power. It’s the least expensive of the three, but the blades create drag when you’re sailing. Furthermore, this model has not undergone the same development over the years as the folding propeller has.

 That drag means you need more wind to get the boat moving and to keep up speed. You’ll also lose more momentum when tacking, so it takes more pressure in the sails to accelerate again afterwards. In light winds, you’ll typically have to start the engine earlier than a boat with a folding propeller. 

 You can reduce the drag by putting the gearbox in neutral, so the water flow makes the propeller rotate. The rotation adds wear on bearings and seals, and you may hear a growling sound from the shaft. That means more parts to keep an eye on and more maintenance over time.  For you as a boat owner, this demands more effort on your part. 

Unfortunately, the sea is filled with debris, including crab pots, fishing nets and fishing lines. Since the blades can't fold, sea debris and dirt can quickly get caught in them, and in the worst case it can wrap so tightly that the propeller stops working. 

On some older boats, the keel and hull design leave very little space around the propeller, and a fixed propeller is the only option that fits. A folding propeller has a longer hub, and the blades need room to open and fold. Many newer hulls are designed with more space, so you can choose between the different types.

Feathering Propeller

A feathering propeller sits somewhere in between. Its blades don’t fold. Instead, when the engine is off, they rotate to line up with the water flow, which creates less drag than a fixed propeller.

Many feathering propellers let you adjust the pitch through the gears in the hub, and some sailors see that as a real advantage. On most models, the adjustment is done out of the water. So to test a change, the boat is hauled out, adjusted and relaunched, and if the result isn’t right, you repeat the process.

The mechanism has more moving parts, and most feathering propellers need to be greased at least once a year.

To feather properly, the blades on most feathering propellers are flat. That keeps drag low under sail, but it also means the blade can’t have the twist that gives the most efficient profile under power. More on that below.

If you don’t have space for a folding propeller, a feathering propeller is the best alternative. And if you’re mainly considering one for the option to adjust the pitch: with the right calculations from the start, a correctly sized folding propeller shouldn’t need adjusting.

Folding Propeller

 A folding propeller uses the forces already at work around the boat. 

Learn more about folding propellers and their benefits on this page

The centrifugal force ensures that the blades unfold when the engine is started. As long as the engine is running, the blades will remain extended thanks to the centrifugal force. As soon as the engine is shut off, the pressure from the water flow forces the blades to fold. In short, the blades open and fold by themselves. 

The folded propeller presents significantly less drag because the water faces less resistance from the blades, thereby not reducing the boat’s speed the way a fixed propeller does. This leads to an increase in speed. The minimal drag also means you can sail in lighter winds without the engine, and it’s quiet onboard. 

The most fundamental difference between a folding propeller and a feathering propeller is that the blade of a folding propeller twists.

When the blade of a folding propeller rotates, it has a specific angle relative to the water at the bottom of the blade, which differs from the angle at the top of the blade. When a propeller rotates in the water, it has a natural circular motion, and the propeller has a given rotational speed (typically measured in revolutions per minute or RPM). The point at the bottom of the blade has only a small circular motion, so it has a relatively lower speed than the point at the top of the blade. The point at the top of the blade has to cover a larger circular motion compared to the point at the bottom. Therefore, the speed is higher at the top of the blade, also referred to as the peripheral speed. This is why the blade of our folding propellers twists, the speed at the bottom of the blade needs to match the speed at the top of the blade. On Flexofold folding propellers, the pitch angle varies from the bottom of the blade to the top, aligning with the peripheral velocity. Once again, this is a matter of the laws of nature. With the twist, a much more efficient blade profile can be achieved.

On a feathering propeller, the angle is the same at the bottom as it is at the top of the blade, which makes the angle low at the bottom and too high at the top.

Given the elimination of many mechanical parts and the simplicity of its design, a folding propeller only needs very little maintenance: mainly cleaning and polishing.  In areas with heavy fouling, you may want to apply an antifouling coating.   There are no gears to grease, because the parts are water-lubricated. The simple construction also means the propeller can be installed underwater. 

With the blades folded, there’s also much less for fishing lines, nets and plastic to catch on under sail. Most Flexofold propellers have closed gearing, which keeps dirt and mussels out of the mechanism, so the blades keep opening and folding as they should. A few of our 2-blade models are the exception. 

You don’t need to be a racer for a folding propeller to make sense. Less drag under sail and reliable thrust under power matter just as much when you’re cruising. 

Thinking about a folding propeller? 

If you think a folding propeller could be right for you, or you’d like to hear more about your options, feel free to contact us.  We are specialists in the field and take pride in helping you make the right decision.

We’ll always recommend the propeller that fits your boat and the way you sail, not the most expensive one.

All we need are a few details about your boat, and then we run the calculations. You’ll need the engine model and the gear ratio. These can vary slightly depending on the year the engine was built, so a quick online search isn’t always reliable. Check your boat’s papers or the information plate on the engine itself.

Boats are getting ready for winter storage, at least here in Denmark and the rest of the northern latitudes. That makes it a good time to look at a new propeller. Request a free, non-binding quote, and if you decide to go ahead, we typically ship within 3-5 business days. That leaves plenty of time to get the boat ready for next season.