Fun thing about the our pumps. They aren't what cause forward movement of the boat. They only generate a pressure differential. The nozzle does the work of generating the moving force. Jet nozzles (either liquid or gas) work under the premise of conservation of mass. If you put 10 units of water in the front, then you must have 10 units of water come out the back. NOW, if the density of the water doesn't change (which at our pressures and temperatures it is considered negligible change) then this assumption holds true.
Now consider that the nozzle has an inlet diameter and an exit diameter that are different. The inlet is larger. So you can move so 10units/minute of water through it. If those same 10 units of water must leave the exit that is a smaller diameter, then it must do so at a faster SPEED. it's the same 10units/min of water throughput, however it must speed up to escape through the smaller diameter. So, what we've done is add kinetic energy to the water.
Energy is equal to one half the quantity of mass times velocity squared. Momentum is described as mass times velocity (found in the kinetic energy equation). So you can see that adding that kinetic energy has essentially allowed us to "throw momentum" out of the back of the nozzle. This set of unequal forces is what drives the boat forward in a jet propulsion system. It's not the "grip" on the water, or the dynamics of how the propellor (impeller in our case) moves through the water.
As a thought experiment, say you're standing in a jon boat floating in a still body of water holding a cinder block. If you throw the block out of the back of the boat, which way does the boat move? opposite direction right?!? What happens if you throw a larger block? What about a smaller one? As you vary the mass you vary the amount of momentum you throw out of the back of the boat. Same premise with a jet boat, we're just throw a LOT of water out of the back instead of cinder blocks.
With that said, there is some additional interaction between the water stream from the nozzle and the surrounding water mass the boat is floating in; however this mostly goes away at high nozzle velocities. As noticed by the nozzle literally being out of the water when on plane. This interaction however, is how reverse and low speed movement works (which is also why it's so sluggish at low speed compared to high speed).
SO, the Sharrow prop really doesn't hold a ton of promise for us. We have an axial flow PUMP that generates a pressure differential for a nozzle. Additional grip or other thoughts are somewhat inconsequential. Those impellers above with long leading edges, and additional blade area are generated from dealing with cavitation and non-laminar flow issues that arise from either high horsepower application through undersized pumps, or poor flow characteristics into the pumps (like from light vessels in less than ideal water conditions and high speeds). The sharrow prop increases traction with the water, and eliminates the tip vortices that shed energy when you spin a fan in a fluid. Ducting an impeller (or propeller) has largely the same affect. Spinning that massive prop to 8k isn't exactly reasonable either. Most outboards and I/O setups have a gear reduction in the lower unit. Sometimes as deep as 2:1. So a Sharrow prop is likely spinning in a max range of ~3k or so. We spin our impellers well into the 8k range on modified boats. The physics of keeping that shape consistent at that rotation rate is likely a significant limiting factor.