Hi Mike. I just got back from Coz. I stayed at the Presidente, where the on-site operator is also Scuba Du.
I can't answer your question about the "advanced" sites, since we didn't attempt any of them. However, they seemed to be quite busy in general, so I would expect that they could fill the boat most days. Also, my guess is that they combine divers from El Coz and the Presidente to make sure they have the minimum number of divers more often than not. The Presidente lies between the El Coz and most dive sites.
I doubt that you could request a certain boat for a certain dive. Their schedule seemed to be pretty well fixed. They have several different boats - some big, some small. I was on two of their big boats. Neither was over-crowded in the 3 trips I went on. I saw one of their small boats several times. It wasn't over crowded either. I think they use the small boats primarily for the advanced trips. Sucba Du's boats are *nice*. Everything clean, in order, and "ship shape".
Scuba Du was on time, every time that I saw. The crews running the boats are very, very good.
I dove with 3 different dive masters on 3 different days. They all followed the same script. I would say that their dive profiles are fairly strict, but it isn't babysitting. You are required to descend with and follow the DM. The DMs keep an eye out for strokes, but they don't bother you if your bouyancy is okay and you aren't kicking the crap out of the reef. They will ask if you are okay on air every 10 minutes or so. If one person gets to 750psi, they want that person and his/her buddy to ascend/safety stop/surface while the others continue the dive. I thought that was pretty fair. On the three 2-tank trips I took, max depth on the first dive was about 80 and anywhere from 60-80 on the second. But the DMs weren't being super strict about that. They do want the group to stay with the DM. Since these are all drift dives, I can understand that, given the large number of boats and divers that are in the water in Coz. Having a computer does not buy you any extra time, at least on the regular 2-tank dives. However, my dives were all at least 50 minutes with aluminum 80 tanks.
I had only 2 gripes with Scuba Du. The first was minor. The crew is obviously on orders to set up your gear and swap tanks for you. And they are pretty agressive about it. I like to do it myself. The other gripe is with their business practices. First, they charge 10% extra for credit card. I can understand up to a 5% surcharge. But beyond that, it's unacceptable to me. Forturnately, I had enough cash on me. They are also very agressive about signing you up for multi-day packages. That doesn't work out for my wife and me since one of us often doesn't dive every day for one reason or another. So we are prepared to pay a bit extra to pay as we go. After our first trip, we tried to sign up for the next day, speaking to the same woman that took our money for the first dive (and tried to give us the hard-sell). "Oh the morning dive is sold out and all dives on the following day are sold out." Wife and I thought it over and decided to do an afternoon dive the next day and to just use another operator for the 3rd day. As luck would have it, we talked to a different clerk. I asked him to recommend another operator who would pick us up at the Presidente dock. Suddenly, we could get on the dives we wanted. And they didn't just overfill the boat - everything was normal aboard.
Anyway, a very professional, fairly conservative, operation once you set foot on the boat. Beware of the sales office.
