Any chance of a link to her FB page?

Here's a link to one of her posts. Its on the fb group "Dinghy Cruising NZ" . You'll just have to scroll back through them to find her other posts, I don't know how to navigate fb - its a dog's breakfast to me.

You lose a bit with that flexible shaft and casing, due to lots of friction.

Instead, I would use the bottom half of a straight shaft line trimmer, and put a drill on that.

And while we are on the subject of marinising gardening tools, I have been following with great interest, on Facebook, the exploits of a most innovative kiwi who designed and built her own boat (including the design and making of the sail) all from cheap locally available materials, including grafting a lawn mower engine onto a clapped outboard motor bottom end. Quick build too,  Its not the first time she's done it.

The lawn mower gives a speed of 5 knots.

Seriously, what about those with disabilities for whom rowing or paddling are difficult? 

In that case I'd take the trouble to make a decent mounting bracket which holds the shaft in place and allows easy one-handed steering. I'll bet you could come up with a way of doing that better than anyone. Steering seems to be a bit of an issue with the longtail configuration, although for a kayak maybe that is still the most practical configuration. For a small dinghy, I think a "L" configuration (like a conventional outboard) would be better, and I'd make one from a broken line trimmer, get rid of the non-functioning motor and apply a cordless drill to the input shaft - there is something rather fun about the idea of re-purposing something as ubiquitous as a cordless drill isn't there? And we are only talking about a bit of fun aren't we? Just bring along a spare battery.

(Robb White Jnr reckoned the best invention of the 20th century was the white plastic bucket. I reckon the cordless drill driver comes a close second).

(That's Robb White the boat builder. "Flotsam and Jetsam" his short stories compiled posthumously by his sister. A great read.)

Turns out the idea has been around for a while.

The mad Brits used to have a "Makita 600 Cordless Challenge" at the Beale Park Boat Show.

A 600m sprint attracting tri hulls, cats as well as monohulls, with multi-engine installations. Inboards, outboards and even paddle wheels - not to mention of course, the inevitable eccentric in a twin-engine cordless drill-powered floating motorbike side car.

You can probably guess the prize

https://www.youtube.com/watch?v=rVrmhoHepmk

(David T I don't know if you are serious, but I can't see the need for any fancy engineering. If there is somewhere on the back of an inflatable to lash to, I would have thought a loose lashing around the rotating shaft would do well enough, of that cheap slippery rope (I forget what its called), you hold the drill in your hand of course. Quick to dismantle should you find you suddenly need to do some home handyman work on your boat. And as for water-proofing - same as for any outboard I suppose - just try not to drop it in the tide.

David Th (very serious) - Ah! But you can't drill a hole in something with a pair of oars can you? Eh? I agree, the last thing we need on a junk is "needless junk", but I reckon in a flat calm one of those little Kohler catamarans should go like a rocket with a couple of 18V Ryobis on the back! (One in reverse of course - counter rotating props LH RH))

H'mm. Interesting. I don't know whether this comes from the same supplier, but clearly someone, somewhere in China, is giving the matter some thought. 

I see that a 21V drill with two 2Ah batteries can be had for less than £40 in the UK. Still needs some engineering to mount it on a kayak, though ... and what about weatherproofing?