The one engine- two shafts/props makes absolutely no sense to me. In terms of engine redundancy you have none so no advantage there.
And in terms of maneuverability, you don't have one of the most effective maneuvering tools of a twin which is not only to be able to use differential thrust but to use differential power, too. I am very often adding power to one engine and not the other to speed up a maneuver, counter a wind or current, or improve the accuracy of the maneuver.
While I guess you could split the thrust with a pair of transmissions driven by a single engine, you could not add power to one side while remaining at idle on the other.
So other than having redundancy in the shafts and props I see no advantage to it whatsoever.
A lot of good single-engine boat handlers know how to take advantage of the propwalk from their one propeller. Rather than bemoan it they have learned to take advantage of it and are able to do things that single-engine drivers who don't understand how to make propwalk work for you have no idea how to do. If the two props in the single engine-dual prop setup are counter-rotating, the setup even takes away a good maneuvering tool from the experienced single engine driver.
The cons greatly outweigh the pros in this case, so far as I can see.
And in terms of maneuverability, you don't have one of the most effective maneuvering tools of a twin which is not only to be able to use differential thrust but to use differential power, too. I am very often adding power to one engine and not the other to speed up a maneuver, counter a wind or current, or improve the accuracy of the maneuver.
While I guess you could split the thrust with a pair of transmissions driven by a single engine, you could not add power to one side while remaining at idle on the other.
So other than having redundancy in the shafts and props I see no advantage to it whatsoever.
A lot of good single-engine boat handlers know how to take advantage of the propwalk from their one propeller. Rather than bemoan it they have learned to take advantage of it and are able to do things that single-engine drivers who don't understand how to make propwalk work for you have no idea how to do. If the two props in the single engine-dual prop setup are counter-rotating, the setup even takes away a good maneuvering tool from the experienced single engine driver.
The cons greatly outweigh the pros in this case, so far as I can see.