Prop Comparison

Propellers for S/V Lynx

Your propellers are an important part of your propulsion system. The right propeller will add speed, save fuel, regenerate more power, and do better in reverse or stopping. That's why we looked at all the options out there and chose a reversing propeller

There are, basically, we had four types of propellers to choose from, (see below).

Standard

Standard propellers have fixed blades, meaning, whether they are in use or not, they blades are still extended.

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Feathering

Feathering props turn the blades. That way, when not in use they can be turned sideways to the flow of water.

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Folding

Folding props, as the name suggests, fold the blades down when not under power.

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Reversing

Reversing props fold down and then reverse the blade so that the leading edge is always used in forward or reverse.

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Standard Props

Pros

Lowest price - These are the price winners, but a long shot! They can be five times less than folding or reversing props, and ten times less than feathering props!
Extremely low maintenance - With no moving parts, these have little maintenance compared to any of the others.

Cons

Fixed Pitch - These props, once setup by the manufacturer, cannot have the blade pitch adjusted later on by the owner.
Poor in Reverse - Because these props do not use the leading edge while in reverse, they are not as efficient as feathering or reversing props when stopping or backing up.
Poor Regeneration - Just like in the reverse situation, the leading edge is not used when regenerating. This affects the efficiency of regeneration if you are using them on a hybrid boat.
Excessive Drag - With the blades always extended, these cost a lot of drag while sailing, up to one knot slower, per prop!

Feathering Props

Pros

Rotating Blades - These props turn the blades so that they are perpendicular to the flow of the water while not in use, reducing drag greatly.
Good thrust Reverse - These open the blades based on the torque of the shaft. Therefore, when in reverse they blades rotate the other way making them also good in reverse. This also adds to the boats maneuverability in close quarters.
Adjustable Pitch - Both forward and reverse pitch may be set to optimize the performance of your engines on your particular boat.

Cons

Expensive - There is no denying it, these props are expensive. They may cost twice as much as folding props.
High Maintenance - They have more moving parts and are more difficult to service, and more expensive in parts and labor, if you have someone else work on them.
Fouling - With the blades still extended, even when feathered, they are more likely to catch on lines, seaweed, ropes, etc. They also cause a little more drag than folding props.

Folding Props

Pros

Reduced drag - Folding props collapse down and offer less drag while sailing compared to feathering props and far more than standard props. This also means they catch on less things, like lines, seaweed, etc.
Reasonably priced - These are half the price of feathering props (though standard props are much less than either).
Lower Maintenance- With fewer moving parts, these are easier and cheaper to service or have serviced.

Cons

Fixed Pitch - These props, once setup by the manufacturer, cannot have the blade pitch adjusted later on by the owner.
Poor in Reverse - Because these props do not use the leading edge while in reverse, they are not as efficient as feathering props when stopping or backing up.
Poor Regeneration - Just like in the reverse situation, the leading edge is not used when regenerating. This affects the efficiency of regeneration if you are using them on a hybrid boat.

Reversing Props

Pros

Good in Reverse and during Regeneration - Because they reverse the blades in forward or reverse, that means they always use the leading edge for efficient maneuvering, or for regeneration capabilities while sailing with hybrid system.
Reasonably priced - Similarly priced to folding props and, also like folding props, these have fewer moving parts, which makes them easier and cheaper to service or have serviced.
Automatic Pitching - Since the blades adjust their pitch based on the RPM of the shaft, these props can adjust to work efficiently at various speeds. This is very useful in a parallel engine/motor situation (like we have on one engine of S/V Lynx)

Cons

Fouling - With the motors are in neutral, the blades are still extended, just like a feathering prop. That means they are more likely to catch on lines, seaweed, ropes, etc.
A little more drag - Also because the blades are still extended and curved, they cause a bit more drag than feathering props while sailing, and slightly more than folding props, but have far less drag than standard props.

Prop Comparison Conclusion

Brunton's Eco*Star Reversing propeller
The Eco*Star is known for its regenerative capabilities. Since we have two electric motors, both using regeneration, this is critical. But that is not the only reason we went with this choice in props. Since we have one Parallel Diesel engine/electric motor, and the diesel engine needs to run at a faster RPM while the electric motor will run at a slower RPM, we needed a prop that would automatically adjust the pitch based on the RPM so that both engine and motor using the same prop are efficient when powering the boat. The Eco*Star is that prop.

Brunton's AutoLock
To feather a Bruntons Eco*Star prop we must stop the shaft or it will spin freely and the blade will not feather to reduce drag. To stop the shafts, we must add a brake. Bruntons also makes a device to do this called the 'Autolock'. Unfortunately for us, it only works with a diesel engine system, working off of oil pressure. This won't work with our starboard parallel engine/motor or our electric motor in the port hull. However, we will purchase just the brake half that attaches to the shaft (the disc and break caliper, left side of image).

Cable Throttles
To activate the brake caliper on the Bruntons Autolock system, we will add a set of dual cable throttle levers. Each lever will activate the brake caliper of the port or starboard shaft, respectively, locking them when needed by just pushing a lever forward or unlocking the shaft by returning a lever to the 'neutral' position.

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