Interesting to see that pilot boarding speeds (or any intership transfer from high speed craft) is around 2 knots.
In practice speeds are closer to 6 knots... in fact I have boarded vessels at 12-15 knots.
You certainly don't want less than 4 knots unless you have an old pilot boat... and I mean old!
Most modern pilot boats have speeds in excess of 20k; older cutters have 13k.
Looking from another prospective dead slow speed on a container ship is around 6 -7 knots minimum, and whilst they can reduce below that (ie stop engines) that is the typical boarding speed.
Maybe the missions need tweaking, but then it maybe much harder to maintain greater speeds, but at least that makes it more realistic.