Yes I've been reading up on them a lot and they are very quiet with regard to cavitation for listening hydrophoned etc. That's why all the modern ones before turbo props (US atleast) have single fully aft props. If it's close to the hull, the blades go through "dead water" low pressure areas and the pressure change causes micro cavitation which is noisy and even erodes the prop blades apparently! Dave M makes nice white metal props to scale, but they are a bit fragile so the guard will be on it most of the time. Once removed there's only the top hole visible and it's right where the real one has a stern light so I can stick a removable one in the hole if I get all rivet counter happy later on or the club members are too judgemental as they can be at times.
PS Thanks for the much appreciated feedback mate!