My sense is they have selected the catamaran as one with exceptional sailing abilities to minimize dependence on propulsion. Plus they specified diesel-electric which, while having a checkered history in recreational marine applications, just might make sense for their application - of recharge/top-off.
I think success with such a boat is all about how much you can use sail and solar vs how much you need to motor. If you end up motoring, whether to charge batteries or to directly propel the boat, just as much or close to as much as with a conventional drive, then I think you have actually created a less eco boat, not a more eco boat. Assuming this new boat can sail just as much as the last one, being more eco will be all about how much they can realistically apply solar to propulsion. Their solar, assuming 4kw equivalent output for 4hrs per day, and 1/4 for house loads and 3/4 of it available for propulsion, is equivalent to about a 4 hp motor running for 4 hrs per day. I have no idea what the typical hp & hours usage is for sail boats, but just anecdotally I seem to see them motoring as much or more than I see them sailing. My guess is that 4hp for 4 hours is a small percentage of typical propulsion needs, but I don't really know.
I think their power plant is probably as good an approach as any, but if it were me I'd be very concerned about reliability, spares, service, etc., especially given their more remote cruising. There is lots that can be done to mitigate, so that would be my focus.
The OC Tender rigid dinghy is an impressive boat. Had it not been for outrageous shipping costs, I may have gone with it instead of the AB RIB I ended up with. For better or worse, the OC has a flatter bottom and planes easily. That said, if their design requirement is 4 people and 20-kts with 20-nm range, hard to imagine carrying enough batteries. 2-persons with dive gear with 10-nm range at 15-20 kts night be feasible. Time will tell on that one.
Peter
I think that design target will be very hard to meet, though the OC comes the closest. But the closer they come to meeting the boat's operational target, the further way they get from what I expect is an acceptable charging solution. I think an electric tender is a good fit if your use is short, slow runs like taking Fido to shore for a pee a couple of times a day. But for exploring by tender, as the Winns understandably want to do, speed and range are very desirable, hence their requirements. But you also run smack into the realities of the power/energy required to do that.
I'd argue that if you want a tender that will do 40kwh worth of exploring in a day, you need 40kwh per day of solar available for recharging. In other words, 1 day to recharge. Assuming 4hrs of equivalent full sun, that's a 10kw array just for the tender. And that would really end up allowing you to only use the tender every other day, with the off-day for charging. Same for boat propulsion, so add another 40kw or perhaps 80kw array to really be covering your propulsion energy needs. That's 10x what they have if you really want to run off solar. It also suggests that their system will only take a 10% bite out of what would otherwise be all diesel propulsion. That sounds very borderline to me, considering the conversion losses. If that's the case, what the solar is really doing is offsetting the loss of efficiency in the hybrid system. So you made the system less efficiency by 10%, then add solar to bring it back to zero. That's not progress. But once again, I'm just spitballing numbers. What would be really interesting is to see good, hard, objective data from someone operating like this.
