DDWFTTW

Ok, this is slightly off the topic of Flying Scots, but it is definitely sailing related.

DDWFTTW = Directly downwind, faster than the wind

Here is the question:

Is it possible to go directly down wind, powered by wind power alone, faster than the wind?

before you snort and dismiss this question, check this out

http://www.fasterthanthewind.org/

this is way cool.

Not a chance of this being real...unless there is a strong wind gradient between the wind meter and the sail/prop. As any pilot can tell you, there can be a big wind change between ground level and 20 feet in the air.

This has been on the Forum some time ago. Look at the video carefully. The mast wind feather shows the wind not from directly aft but from the side and aft.
A completely steady state analysis shows that it is not possible to sail faster than the wind in the directly downwind direction because the craft will have zero relative wind and the propeller will stop turning.
If the craft accelerates through the zero relative wind spot either because of a wind gust or because of it's momentum then it would be encountering a head wind and the propeller pitch would have to reverse to generate some momentary thrust. However the slightest air drag will cause it to slow thus slowing the encountered wind because the craft is generating it's own wind. Propeller thrust will be lost and the craft will slow down eventually to the point where it has no more self generated headwind. Note that this is different than sailing into the wind where the wind speed is constant and as the craft slows the relative wind increases thus generating more thrust.