Southerly make quite a good deck saloon
boat. But any mono that leans over is going to be putting its windows at more of a risk than those on a cat, so cannot afford to be as large. Furthermore access across the boat has to be a bit more restricted to try to prevent somebody being thrown from one side to the other during a fast tack. Width of the boat is another factor.
monos also tend to take additional space from the cockpit
in order to maximise the saloon space. Thus the cockpit becomes small and cramped.
Again due to maximising the width of the deck saloon, the deck area either side of the saloon tends to be minimised making transit to the foredeck difficult and in some circumstances dangerous.