Many thanks for the very informative replies I've received. These have been very helpful.
A couple of respondents wanted to know more about the boat I have in mind - but unfortunately I can't be specific since I haven't actually settled on anything in particular at this stage. It's just that quite a lot of the boats I've been looking at are single engine, and that has me worried - given the problems associated with getting into pens in my local yacht club.
I appreciated the comments in relation to the desirability of getting to grips with handling single-engine craft. It's always been my understanding that such skill is the mark of a serious mariner! Sadly, my efforts to date suggest that it might be safer for all concerned at the yacht club if I have the assistance of more than one engine, or of bow/stern thrusters.
I'm also uncertain at this stage whether the boat I end up with will be a displacement, semi-displacement, or planing hull. All seem to be possibilities in the range of boat that I'm looking at. My preference is for a displacement hull craft; most of the interesting destinations in and around the Perth area are fairly easily reached at displacement hull speeds. But, who knows? If the right boat comes up, with a different hull style...
On balance, taking the current comments into account, my inclination at the moment is to look for a twin-engine craft (with or without thrusters).
Jeff