Salvage
If it goes to trial the factors that a court considers in determining a salvage award are all of the factors described -- how mcuh danger the salvor was in, how much effort they put in, what was the role of others, etc. So, although the starting point is the value of the boat, the percentage applied might be quite small. The good thing for the rest of us to know is that there is a big difference between a tow and a salvage, and if it is a salvage, you should try hard to negotiate an agreement in advance, rather than throw yourself on the mercy of the salvor or the court. And "tying it up in the courts" costs the boat owner lot of money too, so its not necessarily a brilliant strategy.