DandV

Roof mounted centre lines come into their own in boat handling when "coming alongside" which of course is part of mooring alongside, as distinct to mooring at anchor, or mooring to bouy, or to a pole, or two. But making a "boat fast" that is secured, against drifting away, roof mounted centre lines are inferior to using additional bow and stern lines, or if your boat has provision for it, springs from a gunnel level fastening somewhere near halfway down the length of the boat. We used a soft shackle on a gunnel fender fastening, sometimes taking the roof centreline through it, to provide a spring.

The general rule being, the more water around the prop and rudder, the better they perform. So getting them out into deeper water first makes a lot of sense in most cases. But wind direction, and current from bypasses and lock emptying all play apart. All very much like leaving a berth on a lumpy water boat, where think about how to do it first, and if others are involved, tell them of the plan. I got into difficulty once taking a boat off a pontoon with very little room ahead, so getting the stern out first was really the only option. But the overly enthusiastic crew member told to "let the bowline go" incorrectly assumed this always went with "and push off, the harder the better"

My experience was that prop walk had near negligible effect when reversing. The prime effects seemed to be water depth, the less the bottom clearance the more effect the prop had pumping water away, and wind. As narrowboats normally float bow high, cross winds exert considerable turning moment on the bow downwind. So back and fill it is, and with the help of an able deckhand, perhaps strategic use of lines. In deep water, and with minimal wind, the rudder did have some authority once you had sufficient way on. If you have one, providing steering assistance when going astern, is a legitimate use of a bow thruster.