I am not thrilled about the idea of suspending our robot by a stopper knot, especially with a 1" square retaining opening. There are much more secure ways of fixing a rope to the davit. The blue box 12" rule makes even things less secure, as larger line, with which you could tie larger knots, is more likely to fail the test. I doubt that the line in the field tour videos would pass the test.
Complaints aside, some other knots to consider are those used in soft shackles, such as the diamond knot and the button knot which can be seen
here.