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I was thinking about: maintaining current cpr certification; taking care of and organizing rental equipment; filling and hauling tanks; completing paperwork (especially if there is an incident - any incident); learning enough about the area to answer specific questions; scouting out & planning dives that will be of interest to the divers, and ensuring that those dives are within the experience level of all divers (which involves sizing people up pretty quickly); helping new divers w/ equipment, weighting, procedures, etc.; checking divers off and back on the boat & then following up later to make sure they don't have symptoms of DCS; cleaning/preparing the boat; tying into the U-bolt if necessary and checking out conditions pre-dive; and generally being responsible for the safety of the divers on the boat (the boat captain's duty is to the boat, as I understand it). The boat trips I've been on, the DMs have done all or some of those things. I've even had DMs fix lunch for us...
I personally have had really good service from DMs all over the world, and that's what I was speaking to. Once or twice, what I was most grateful for was that they helped less experienced divers get in the water reasonably quickly and kept them from drowning. And, even if they didn't do much for me, personally, other than give the briefing and answer any questions I had, I was glad they were there "just in case" (that seems to be more true on boats with a large number of divers, which I now avoid like the plague). Also, I was glad they were there - not sure my dives, in a place I didn't know, would be as good if I didn't get a briefing & was just in a group of strangers of varying levels all told to hop off the boat and go explore.
But that's just me. It sounds like your experience was quite different, and I'm hoping, the exception to the rule.
I maintain a current CPR cert. and likely other divers on board do as well. Skills that can equally be given any diver on board in need including the DM. Not sure I or the DM should be tipped for that.
Taking care of and organizing rental equipment; filling and hauling tanks; completing paperwork (especially if there is an incident - any incident) is a service the DM is providing the dive operator, while I am not so sheltered to believe there are not folks doing this for dive operators free, really this is a dive operator responsibility as the customers have already paid for this service.
The other listed items are certainly tip worthy.
It seems that you don't have enough real life dive experience to understand the value of a good DM. The points brought out by Joanna are perfect examples of what DM's do behind the scenes. Maybe you should put the money up to become a DM, maintain your liability insurance, do the job of a DM and then you would realize the reason why gratuities are appreciated.
Not every diver is CPR certified, for that matter most people in general are not current with CPR training. Many of the divers on my boat are not CPR certified, many don't know what a AED is. You are making a broad assumption about the number of CPR trained divers.
Clearly you miss the point that many have tried to express in this thread. I recommend that you stick to shore diving so you don't have to worry about the issue of tipping.
What I have learned is the cost of the dive isn't an indicator of the quality of service, that service quality also varies between DM within each operation, and that I as a diver need to do a little research before making selections. I sure when I do this the tipping part wont be difficult to figure out.
No, my limited real life experiance has produced some real extremes. DMs that have given service above and beyond anything I could ever have expected that got $20 and one experiance that was very McDonolds like.
I don't live in a coastal area and my dives are vacation type events. What I have learned is the cost of the dive isn't an indicator of the quality of service, that service quality also varies between DM within each operation, and that I as a diver need to do a little research before making selections. I sure when I do this the tipping part wont be difficult to figure out.