Lets see if we can start a thread about boats

[WESTERNAERO]

what would you recommend for my flat ?

Recommend for what, a prop shaft? I recommend you break out your wallet.
I think Bob and I greed that K500 was a wise choice over on PB or it could have been here, I don't remember.
Honestly, I feel the machining of the shaft is more important than the material type, as long as you go with a good material.