First of all to work on a boat as a DM your required to have your professional liability insurance which I do have. That costs $350.00 a year.. NOT FREE. I think that if your a boat and you need a DM and frankly unless you can split your self you do need a Divemaster you need to pay them. Divemasters generally work for about $50 a dive trip plus tips. This is the going rate. Good boats that stay busy pay about $100.00 plus tips and generally never loose thier divemasters. A divemaster that has been working for the boat a long time will generally be a much better dm for that boat and know the waters, currents, weather and animals better. Getting cheap labor means you get well trained divers with minimal experience to act as your saftey persons. I think that is fine as long as you have another DM on board to offer additional training. But to pay NOTHING but tips is first of all Illegal in the USA and secondly IS in very poor taste to treat a human being who has worked for months and spent tons of money to become a divemaster. This certification requires, CPR, AED, First Aid, Rescue Training and Certification, Advanced Certification, 60 minimum logged dives, and a plethora of encylopedia of diving knowledge on theory, currents, marine life, physics, equipment and demonstration quality skills. Frankly I know how hard I worked and I am getting paid for my DM time. I think you have little ethics and are breaking the law if you do not do the same. No one should have to work for free.