Tony
An excellent review in PBO August 2007, No 488, of 3 electric outboards; one of them the torqueedo http://www.torqeedo.com/en/hn/home.html appears to come out tops in both performance and price (3x 2.2HP Outboards!) but has its own integral battery. Dealers at http://www.cquip.com/Page.php?id=186
HTH
David