A single motor between the two hulls is next to useless in a beam sea. The prop constantly ventilates. On a 60ft boat the trough between the hulls could be 2ft or more below level water. That means going very deep with a single middle mounted prop to avoid ventilation.
There is benefit in having a preferred motoring direction and place the props closer to the trailing end and as the trailing end also sits lower than the leading end when motoring with the boat pitching. 10% to 20% of the length behind the centreline is about the best to avoid ventilation. Set the drives as far apart as reasonably possibly to maximise the turning leverage.
Also no matter how large the rudders are you there is a minimum speed below which the boat will not turn unless there are two drives or a turning thruster. The boats have considerable windage for their displacement and little lateral resistance at low speed so in a cross breeze the time to align to enter a pen or other close manoeuvre can be very short. A high aspect dagger board or deep rudders do not provide much lateral resistance when going sides ways. It is reasonably common to see 2kts sideways in a moderate breeze.
A prop or two dragging in the water kills sailing speed. A folding prop is inconsistent with bi-directional sailing.
On 04/06/2015, at 3:24 AM, "robriley@rocketmail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
not sure but I think the idea is to place engines in the centre of the mass. That would be closer to the WW hull on HP of course, raised and lowered in a box. Perhaps it is only to go forward one way and steer by rudders, never heard it come up so operationally its an important question.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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