If you mean the thing that you tow along and it looks like a square brush sort of thingy I was sure I'd seen it in a Compass24 catalogue but can't find it on their site, either them or Force4.
We used to use a 'subscrub' before regattas.
For best results you need to be moving through the water at about 3-4 knots, but note it was a 3 man task.
(1 steering, 1 controlling the bow line and 1 to lift the up-down line. We felt that it helped a bit and you could certainly feel the bristles pressing on the side of the hull.
Cheers
Steve
Boat Scrubber operated machines in marinas all over, they arent currently trading as far as I know. RS divers do scrubbing, I don't know if they cover your area though.