My professional background is in brass castings AND I served in the US Navy AND I have a 3D printer... but I know nothing about toroidal propellers except watching a video!
The toroidal design is amazing and has MUCH potential; however, other than this being a totally new design, I cannot see why the cost for manufacturing would be 10X the current cost. One of the current methods of producing a regular propeller (for recreational watercraft) is using the ‘lost-wax process’. This works very nicely and some very intricate designs can be made that cannot be produced using a traditional sand cast process. Still, there is a considerable amount of manual work that must be done while preparing the wax components as well as detailed finishing work to the casting itself. This new toroidal propeller would presumably be made using a lost wax or lost foam process AND certainly require some new procedures but NOT at ten times the cost, at least in my opinion. Tooling is expensive but that is offset once the volumes increase. Here is a brief video showing the procedures of how Yamaha makes their propellers using the lost wax casting method -
https://www.youtube.com/watch?v=bnBFm9Xc5DE.
Naval ships are another beast! Their massive propellers are most likely sand cast using a technique of airset casting – airset uses chemically-bonded sand, almost like an amalgamation of sand and super-glue to make some really, really strong molds. A video of this process is here:
https://www.youtube.com/watch?v=Di6fu7F2BxQ. The manufacturing of the controllable reversible pitch propellers are probably made with airset castings as well because the huge size and weight of the individual blades and then machined and assembled. Of course, no one knows how submarine blades are made
… while in the shipyard the sub’s propellers were always cloaked under a HUGE cover. Attempting to make a toroidal propeller the size needed for naval ships and cargo carriers would be nothing short of EXTREMELY challenging… if possible, at all??? I bet some very creative minds are already exploring this avenue.
Off topic but interesting tidbit… in regards to Naval ships and boats, each ship and boat can be identified by their unique propeller noise by the enemy. To aid in hiding this ‘propeller signature’, hundreds of small holes exist on the leading edge of the propeller blade whereby air is ejected that aid in camouflaging this noise. I have no idea of how these holes are cast into the part as machining them in after the casting is produced seems impossible.
Toroidal blades for toy/hobby drones - this is an ideal application for 3D printers. Folks wasted no time creating and sharing designs of this (for example,
https://grabcad.com/library/toroidal-propeller-2). This is great because 3D modelers can be some very inventive folks and will certainly be tweaking and experimenting with designs – this may very well be the same people that help lead a breakthrough for creating a design for toroidal-like blades for large seagoing vessels.
I think we will see a significant reduction in the price of manufacturing toroidal propeller blades because they can provide so many advantages.