Hi Joe!
A few things jump out at me from your note...
So that leads to two separate options
1. Buy a Nomad frame and have it share the tandems wheels.
If you swap-in the disc-equipped Rohloff wheel from the recumbent, the Nomad has disc mounts on the lower-left seatstay and could be made compatible pretty readily. Lighter wheels will definitely work with a Nomad frame and will render a more lively ride thanks to reduced rotating weight. Of course, the bike will not have the same heavy-duty characteristics it would with more robust wheels, but it would definitely be enjoyable. I occasionally rob the 26x1.5 road slicks from my own tandem and fit them to the Nomad when I want a livelier feel (and slightly different handling due to the change in trail caused by the smaller diameter tires).
Similarly, you could swap-over the Rohloff wheel from the tandem, as you are pondering. Either could work. A third option would be to do a swap initially, then purchase a Rohloff-equipped rear wheel -- perhaps used, from German eBay -- and then sell-on the intact recumbent if it proves to miss the mark over time.
Speaking as someone who has owned a Sherpa and ridden a RavenTour extensively -- and who currently owns a Nomad -- I can say the Nomad would be a "lot" of bike for non-expedition use. It is ideal for my needs and excels at the task, but it is heavier than Thorn's lighter (and lighter-duty) offerings for general use. That said, I did ride my Nomad for a happy 200km yesterday. Neither of us are the worse for wear. If you go with the Nomad frame, then I would suggest considering a suspension seatpost for more comfortable riding while unladen if you pursue rough tracks, cobbles, and logging roads.
If you do later decide a Raven is the bike for you, then take a close look at the Rohloff cabling. Ravens use internal shift cabling, while the Nomad uses external (as does your recumbent, if it is disc-equipped). It is possible to configure a Raven/Raven Tour for use with an EX(ternal) shift-box, but would require fitting Rohloff's own cable stops/guides. At least one of our Forum members (rualexander) converted his Sherpa and did such a nice job of it, the result appears almost OEM.
Joe, will you have Internet access while aboard ship? Will you be checking the Forum from port?
Best,
Dan.
[EDIT: My response is nearly the same as mickeg, who posted just before I hit SEND.
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