I've heard conflicting reasoning as to why a locked or a free wheeling prop may be or is more fuel-efficient for twin screw boat while operating on one engine. Common sense tells me that free wheeling is best (as long as the transmission can handle it - such as my boat's Borg Warner Velvet Drive Trany can). I'd like to hear input on this from TF members. Thanks, Art
Fuel efficiency has nor ever been in my case a reason to run a twin as a single. That being said my experience over the years regarding shaft locked vs unlocked in several boats with shaft brakes has been I think a 5 to 10 percent efficiency loss. To put that into perspective hull slime,wind, current, foul props, and waves have had more bearing on nmpg than anything else. 1700 on a single in flat water, shafts locked and no wind is 6 knots at 2.5 g/hr. 1700 on twins 7.5 at 5.5g/hr. Freewheeling 6.1 kits at 2.5 g/hr. Pick your poison. This data is at about 3/4 load. At 1/2 load it's better and at full load it's worse. My conclusion is ...It depends and forget about efficiency.
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