. . . anchor line breaks, boat drifts away . . . .
For a maintained anchor line and little to no current, little to no waves, I'd argue that is a really small risk, small enough for dive ops throughout the world to take it.
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. . . anchor line breaks, boat drifts away . . . .
This is not an uncommon practice from my limited experience in locations outside of the US with no current or waves where the boat captain is the dive op owner and guide. The boat is anchored just off shore, so in the unlikely event of it breaking lose (it would take a while for any wind to make it drift away), you'd just swim 10 to 50 meters or so to shore.
Divers are always accompanied. In one country, it isn't legal for divers to dive solo. That may apply to more countries as well.
Worst case scenario where it breaks just as everyone is far enough away, I'd agree with you. But again, low wind, low waves, low current, low risk. I'm a recreational boater myself. I've never left a boat unattended, other than to a mooring line that is owned/maintained by me. But I've seen it being done. I'd only have an issue if when I surfaced that getting to shore would be an issue.If you are diving 10-50 meters off shore without a current, a boat that drifts away, may be no big deal since you might as well be doing a shore dive. However, I can assure you that during the course of a 50 minute dive in open water, a boat can drift a lot farther in a 10-15 knot wind than you might be able to swim. When I take the family out boating on our lake, I always stay in the boat while they swim and snorkel. If I need to get in the water, another adult gets in the boat before I exit. I am not a boat captain, just a recreational boater, but that is just common sense IMO.
There have been several threads over the years where you have multiple divers with one DM/quide and an issue leads to a diver making a quick ascent with other divers left in the water.
For a maintained anchor line and little to no current, little to no waves, I'd argue that is a really small risk, small enough for dive ops throughout the world to take it.
Worst case scenario where it breaks just as everyone is far enough away, I'd agree with you. But again, low wind, low waves, low current, low risk. I'm a recreational boater myself. I've never left a boat unattended, other than to a mooring line that is owned/maintained by me. But I've seen it being done. I'd only have an issue if when I surfaced that getting to shore would be an issue.
I think it's bad practice to subjectively decide on the spot, based on current conditions, whether it's okay to leave a boat unattended. Sure, the risk may be small, but we as divers take precautions against the small risks all the time. This is a commercial operation, to which safety of their customers should be a prime concern. It's a small risk, but such an easy one to mitigate, simply by not leaving the boat unattended.
You assume that the diver reaching the surface is in good shape. What if they had a medical issue. what if they had cramps. What if they had a marine life injury. Not saying you cannot get away with it 95% of the time but if something happens no boat can be really bad. Seems like you are discarding another layer of safety.