M_Boats: WATT-As water driven generator/alternator.

Hi All: Gerard Dijkstra , Self-Steering for Sailboats (Sail Books 1979 ISBN: 0-914814-17-6)fig 73 p 104, shows water driven generator/alternator that looks like a electric trolling motor except the prop faces forward. It can supply .25 amps at 1.5kts and 9.5 amps at 5.5 knots for charging a 12v system. Called either WATT-As or WATTas. I have searched and searched for the manufacturer to no avail. Anybody got any leads? TIA! cheers, Shawn Boles (M17: grey mist 1978)