Originally Posted by Geoff54
.... I was on a canal boat earlier this year and we double-locked with a boat that had a gorgeous open-case engine with direct drive. It used a sliding cone arrangement that engaged/disengage the shaft for forward drive and engaged a set of side gears (probable not the correct terminology) to reverse the shaft direction to go astern.....
One of the places where I used to work had no road access and we commuted to work on a small ferry.. we walked on but it was big enough for a couple of semitrailer trucks.
When it went in for refit and inspection we used an old harbour passenger ferry with diesel direct drive. NO gearbox of any kind.. they reversed engine rotation for reverse. I believe many deep sea freighters still do this...