It's not my idea, I just stole it. Fairly common on trawlers to increase towing power. The local rescue association used to have an ex navy dive boat here with twin korts nozzles. Excellent vessel but they kept having to replace prop shafts. They seemed to manage to suck up old tyres off the bottom into the props!
The photo is my tenders prop. Normally you would have a square tipped prop with a tight clearance to avoid tip vortex problems bu
t mine has a standard prop with about 5 mm clearance. A few years ago there was talk of making the safety cages on outboards compulsory, that died a natural death.
Seems to wrk really well with that well. He's done a great job restring that boat. She's mint.
Ooooopsy! On this subject l beg to strongly disagree!
We discussed this Alberg 30 earlier and we seemed to agree that this was a butcher job. Big time.
That prop is going to spend half it's life spinning up killing the motor in the process.
It's crazy.
No Steve. While motoring, and the prop coming out of the water, spinning the motor up sans load than re-entering the water at spun-up revs, the prop re-entering the water and loading up the drive train enormously then doing it continuously until somethin !crunch! brakes.
Lucky if it is the cotter pin, less so if it is something inside.
It is no good for the motor, the fuel consumption, the speed, ones ears and not last ones soul.
As you are a rider like me, the analogy of constantly wheeliing a bike, up the back wheel, down, again, up down up down all the time or starting burnouts continuously...something is going to brake rather sooner than later. For sure. 
Well, every time the prop is coming out of the water the engine is not running under load, revs go thorough the roof. Speed boats, yachts all the same.
