Buy a MacBook Air and run Windows on it. There’s hardly anything out there right now that touches it on battery life, especially in its weight class. The build quality and customer support are top notch and its trackpad is excellent. If you’re taking it on and off the boat its portability is great too. Spec for spec they’re really not any more expensive than a comparable PC anymore either. A DC-DC adapter can be purchased from Marinebeam.
I say this as longtime PC person and as someone who can see the potential of the Windows 8 concept of a unified desktop and mobile OS while others have bashed it undeservedly. I just haven’t been very impressed by hardware coming from PC manufacturers lately as there seems to be, at best, significant inconsistency in build quality, reliability, and customer support. The user serviceability and upgradability advantages of PC laptops are quickly becoming things of the past as well.
The Windows laptop/tablet hybrids are interesting but get mixed reviews largely over hardware and build quality annoyances. I’m not sold on the hybrid concept anyway. Although they’re lighter than most laptops, they’re heavier/bulkier than tablets. I wouldn’t ever use one in tablet mode except in a pinch. It seems like kind of a gimmick to sell an expensive laptop to someone who otherwise would have bought one each of a laptop and tablet.
A pure (non-hybrid) tablet makes a good boat computer if you can either live within its limitations or use it as a supplement to a laptop. For chartplotting and instrumentation, a tablet is great due to its portability and low power consumption. It’s also great for weather, music, movies, light e-mail, and light web surfing. Most tablets will become frustrating if you want to do real word processing, spreadsheets, photo manipulation, web editing, or even surfing the web with multiple tabs open at once.
I highly suggest you do an extended demo on a Microsoft Surface.. The latest Surface has none of the drawbacks you mention above and it truly usable in both laptop and tablet mode. I'm sure you will be impressed with it.. I would not have believed MS could make such a polished device until I played with one.
The latest Surface also has better real world power consumption when compared with a Macbook Air running Windows. Just do a quick google search on power consumption of both devices. Many tests done by users in the real world. Not to mention double the performance when required.