Prop. Hub

[rxcomposite]

Daniel,
Before you embark on your duoprop project, read the principles of Naval Architecture. There are three more variants to these.

The freewheeling second prop (like in turbine design).
The fixed nozzle.
The Hull (prop) stabilizer? the correct terms escapes me at the moment.

Boatbuilding may range from simple to highly sophisticated. This forum attracts the best minds in the industry and i myself find that i learn from them. If you are new to boatbuilding you will have a tendency to be confused as the boats and the technology is so overwhelming.

It is a lifelong experience that many shares in this forum. Take things easy, enjoy building the boat, and balance your experiments. Build one boat, use a lot of elbow grease and beer money, and be ready to takle another one as the bug will bite you.
Rx

[cyclops]

The usual purpose of contrarotating props is when you have so much horsepower to be used, that the prop diameter is too large to for the available space provided. The additional geartrains and bearings waste about 25% to 30% of the running horsepower due to frictional gear losses. Double Herring Bone gears can help. Still, it points up a basically poor design that was over powered for some reason. The best example of a need for contra-prop was the British aircraft carrier version of the WW II Spitfire. 2 props of 5 blades each so the props would just clear the deck on landing. Bad extreme design.