Hi Q,

What prop to use depends on the motor, number of cells (voltage) and how you set-up the boat.

The red Kyosho prop is not too bad, it's plastic and will flex under load.

If you have the boat running, you ca experiment with carbon props from the Graupner K-series, 34,5, 36 and 37,5mm.
These props are much stiffer and will be more efficient.

Have you decided on a motor yet?

Please post some pictures of the boat, details would be nice.

Regards, Jan.