Well, no-one answered but I went anyway so here's a quick report for furture reference.
I used Aquaticos (
www.aquaticos.com.br). Cost was about US$80 including all the gear for 2 shipwreck dives, the Servemar I and Pirapama (
http://www.brasilmergulho.com/port/naufragios/navios/pe/pirapama.shtml and
http://www.brasilmergulho.com/port/naufragios/navios/pe/servemar1.shtml). All the dives in Recife are wrecks, no reef to see despite the city's name.
The ride out to the Servemar took about an hour as the boat was pretty slow and the sea choppy (2 people were seasick). A dolphin surfaced a few feet from the boat once we got to the start point but by the time everyone was organised to get into the water it was long gone. The group size (about 17 of us including instructors) meant getting in and out of the water was a bit of a chore and involved swallowing a fair amount of sea water while waiting on the line at the start (no snorkels provided in the gear hire which is not good in choppy waters if you want to save on air). Servemar is at about 75ft down (not sure exactly as no depth gage was provided either so had to stick by the divemaster and depend on him for the safety stop), bottom time 25 minutes. Visibility OK. The wreck is a tug boat, almost intact. Big shoals of striped grunts (they called them xiras), glassy sweepers (barrigudinhos) and some kind of soldierfish (mariquitas) around the bridge, a nurse shark sleeping by the hull. A few spanish hogfish, porkfish, big french angelfish and surgeonfish. Only sand round about so you are limited to a fairly small area and just swim around the wreck 3 times.
The second wreck, Pirapama was a much bigger, 100 year old wreck but not in such good shape. Visibility was pretty poor but manageable (sorry, not very good at estimating visibility in feet). Depth about 75ft again. Big highlight was 3 or 4 of the biggest stingrays I have seen, calmly swimming around the wreck, passing a few feet away. They stayed around the whole 20 minutes. 2 huge cobia (local name beijupira) zoomed past at one point. Slightly less fish than on first dive but would have preferred more time at this site than the first one.
In case you're worried, despite Recife having a bad reputation for tiger shark attacks, they tend to eat surfers and the divemaster said he had never seen one in all his time diving.
Overall it was worth it as I was in town anyway. Different kind of diving from what I am used to in the Colombian Caribbean. Bigger boat which had its advantages and disadvantages compared to the little launches I normally go with.
