Anecdotally (I'm familiar with the marine industry) they seem to be gaining popularity with the luxury center-console market, half as a fuel-saving metric but mostly because they're a talking point at the marina.
In recreational marine these types of products tend to spread based on word-of-mouth and sell fairly low quantities but at higher price points. Related: Seakeeper (https://www.seakeeper.com/), a fairly crazy gyroscopic stabilization system, wildly popular but fairly quiet in the tech world.
Unsure if this would scale up but as others have mentioned for large ships the operation is very sensitive to cost. Fuel efficiency is weighed against current fuel cost, cost to design a technology into a new ship or retrofit, maintenance, etc. That said, since fuel rates are high and emissions regulation is set to come into effect soon [1] you'll likely see waves of shipbuilders adopt fuel-saving technology.
A few problems that might show up with this type of prop/"screw" on a large ship:
- Ship propulsion uses a fairly large-diameter prop and runs at very low RPM (~100rpm vs 1000-6000rpm) compared to smaller planing vessels. The Sharrow prop advertises decreased cavitation at high speeds but this effect may be diminished at low RPM.
That said, cavitation is a different beast for ships than for recreational boats: In the recreational market few boat owners are concerned about propeller efficiency loss due to cavitation -- Concern is mostly around noise and vibration. In contrast, ships are very concerned with fuel and maintenance cost, so if the Sharrow blade successfully reduces both of these it may be helpful.
- Seems like they're currently machining these on a 5-axis CNC out of blocks of raw material which won't scale to larger sizes. The complicated shape may not lend itself as well to casting, and even if they casted the shape it would need to be finished and this would require expensive equipment.
- Might be more difficult for third-party repair [2] which is done manually or with 3-axis machines.
Generally the commercial maritime market is much slower to adopt new technology than recreational, and also much smaller by volume, so it may make sense for Sharrow to continue serving small outboard boats because margins + sale volume is much higher.
For the most part, very little.
They have recently entered into an agreement with Yamaha outboards[1] to have Yamaha manufacture Sharrow propellers.
So far though there has not been much in terms of real-world validation of the props on common boats. In some cases there are modest gains seen (<10%), but that is not enough to offset the increased upfront price of the Sharrow. If they could get the manufacturing cost down to that of a typical high performance propeller it might have more demand in the market.
They still seem to be around. Not rocking the world yet but I'm surprised that they haven't come out with a cheaper model. Might be harder to cast than expected.
