Graham, those are two really interesting articles - thanks. The Sail Magazine one is very revealing, and confirms the 'suspicions' you have expressed about Torqeedo learning about corrosion the hard way.
The low revs plus large prop approach is bang in line with the ideas Jeremy (who I hope will finish his eco-house soon so that he can rejoin us) has expounded on this forum and the HBBR one. I would like to know whether there are insuperable problems to designing electric motors which run comfortably and powerfully at low revs rather than having to whizz, because that would seem to be the way to go. It's a bit of a mug's game, surely, to have to fit an inefficient prop to keep an essentially fast-revving motor happy.
In my shuffle towards an electric outboard I'm trying to get my head round one practical issue. When consulted, the sellers of these things seem to recommend the smallest motor which they reckon will push your boat along reasonably well; so for my boat that might be, say, a 40lb thrust version. Given that the difference in price between that and a 55lb thrust version is there but not huge, would it not make sense to get the bigger one and run it well within itself? I need a few graphs of current consumption, revs, thrust, torque (I'm getting beyond myself here!) etc to work out whether that is logical. Any comments, anyone? My front-runner make at present is the new Mariner: the Minn Kota Riptides look good, but are relatively pricey.
In my little boat I'm going to have nothing to do with lead acid batteries, so I'm VERY interested in Lithium pack progress and prices (especially prices).