It's not just numbers of divers on a boat. I tend to think of "cattle boat" experiences more in terms of "herding" than in terms of the capacity of the boat, and I've seen herding done on even small boats with one DM for six divers. But most people only equate the term to the carrying capacity of the boat rather than considering the "herding" factor. I've experienced Caribbean "cattle boat" diving with 10 to 15 divers per guide and a guide whose goal seems to be to reach a pre-determined end-point for the dive in the shortest time possible, and I agree that it's not pleasant to be herded around like that.
I get a lot of emails from North Americans telling me they don't want a "cattle boat" when they come to Thailand, that they want a small boat with few divers like a Mexico six-pack. The thing is that the Andaman Sea doesn't necessarily present the same benign conditions that are typical of the Caribbean. We get monsoon winds, our dive sites are at neighboring islands that we cross open ocean to reach, and we need big boats to make it safely through the sea conditions we sometimes encounter. Small boats may get swamped and cannot go out into the open ocean unless the water is pretty flat. Big boats are comfortable and safe in virtually all but tropical storm conditions. So since we've typically got 20 or 30 dive customers on one of our big boats, does that simple fact mean our boats mirror BoulderJohn's description of a cattle barge? I would argue that most of our boats are not like that at all.
First of all our diver groups tend to be about 4 divers per guide max--usually fewer and occasionally one or two more, but ideally no more than 4:1. It's not infrequent to see 12-15 dive staff on a daytrip boat at capacity with 30 dive customers. Next, we enter the water with our groups, nothing like cattle stampeding off a barge, and each dive leader conducts and manages the dive of his/her group independently of the other leaders and groups. Generally speaking, more experienced divers are dropped on the reef for a drift dive and students/inexperienced divers are dropped in a sheltered bay, so the notion that all divers are massed together regardless of expertise isn't generally the case here. During surface intervals, there's tons of space on our boats (which are typically two or three decks high) to spread out, get some sun, find a quiet corner to take a nap, sit in the shade, get a snack and chat with other divers, etc. I find myself feeling irritated on little boats with the sensation of being squished in a cramped space now that I'm so used to our spacious big boats. We always stay out on the water for two or three dives rather than making for a beach or going back to port between dives. Our big boats have galleys where great food is freshly prepared and served hot, buffet-style, to divers for lunch, fresh-water showers to rinse off under after getting out of gear, heads with standard commodes and sinks in them, compressors on board for filling tanks (we don't usually switch out tanks), under-seat storage to keep the dive deck clear, wetsuit hanging racks, and so on. I can't even imagine doing our two- and three-tank daytrips on one of the six-pack "sardine tins" that are so common in the Caribbean.
