Twin engine in offset configuration

[GoSlow]

Has anyone had any first hand operational experience or been involved in any research or design where twin engines were installed in a displacement hulled vessel or motorsailer with the intended purpose of running on one engine at a time on long passages for better fuel economy and is this practical? If that requirement were known prior to construction would there be any benefit to installing the engines and shafts at some degree off parallel to the centerline for the purpose of compensating for "pull" to one side and and the required compensation from the rudders? Would a collapsable, adjustable pitch propeller be advantageous or even available? I would also appreciate any thoughts on any other problematic issues that might arise while under way on one engine in a twin engine vessell.

GoSlow

[PAR]

Both twin and single engine installations typically incorporate an element of shaft offset to compensate for prop steer. Yes, using variable pitch, folding and/or feathering props can decrease drag considerably.

All things in yacht design have good and bad issues associated with the decision to employ them in a particular set of design criteria. Eventually the client and designer reach a series of compromises (per issue), that will best fill the design brief.

Do have something specific you're looking for George?

[OFF LINE]

I have personally operated three boats on one engine during long passages. Here is my result:
63' Cheoy Lee Motorsailer....
This boat was equipped with Luke feathering propellers which worked great.
The data that I gathered showed that at or below hull speed the addition of the second engine only increased speed ONE Knot. This held true during several power settings.
78' Cheoy Lee Motorsailer....
I experienced similar results with this boat however it had shaft locks vs feathering propellers. The Shaft locks were activated by lack of transmission oil pressure. I intended to convert to Luke Props to further increase efficiency.
84' Northern Marine Expedition....
My experience with this boat is more limited but at lower speeds i.e. 6 to 8 Knots there was about a 1.5 Knot difference at various power settings. This boat has 50" 5 blade fixed propellers and with a variable pitch/feathering propeller I believe the efficiency would be much better.
NOTE:
All three boats only required about 2.5 to 3 degrees of rudder to compensate for offset thrust.