There are plenty on the market, but not a lot of praise apart from those who have left glowing testimonials.
http://www.hitekbarnaclean.webs.com/ $2400 for a 25 footer.
http://www.ultrasonic-antifouling.com.au/ No pricing listed, and isn't DIY, must be installed by a pro, so it's going to be expensive. I emailed them to get a price. It's also designed to lengthen the period between antifoul, not completely remove necessity.
http://www.boatsonic.com.au/antifoulinggoldcoast.html This mob have the exact same FAQ as the Ultrasonic people, although do allow DIY, no pricing though.
http://www.globalmarinegroup.com.au/2b-sure.html is more like the HiTek Barnaclean, but $2900.
There are lots more if you search using your favourite search engine, and they seem to be two different types. 1) transducers stuck inside the hull that emit some kind of noise or electronic current or 2) the copper electrodes dropped fore and aft when you park the boat. (adding another thing to do when you arrive or depart the mooring
)
It seems to me that over a longer period, you might save some money by lengthening the time between slip, wash and antifoul, but it also lengthens the time between below waterline inspections.
If you do some numbers and pay $3k for an electronic system, it's going to take 6 years or so to break even at $1k per slip and stretching to 2 years between slips. Of course if you can stretch slips further out, it will pay back much more quickly.
The biggest bug bear for me is that at this stage, we're still paying for the Intellectual Property, not the actual cost of goods or installation.
IF they work, they will get cheaper over time and be worth buying for such a small and inexpensive (comparitively) boat like the Top Hat, but until they do get within the realms of decent pricing, the jury is out for me.
Michael.