As Tom notes, the big issues for gyros is the fact that they need about 3 kw to get started spinning. *The current draw is less once they are going, but most boats will have to think through the supply of electrical energy for them to work. *When designing Delfin's systems, I looked into what is now the most popular design, which at the time was a Mitsubishi product, as I recall. *I declined on the basis of the energy required, plus the fact that they were not going to be as efficient as active fins, which were a proven system. *Still, a self enclosed system without hull penetrations has its appeal, although I must say, I love my Trac system.