David's right - we'll never know, without being in the minds of the skippers.
But just for the fun of it, my own guesses on why the Ady Gil skipper
accelerated just prior to collision would be either
1. he wanted to ensure collision;
2. he was panicking, misjudged the rapidity of collision, and thought he might power into a sharp turn away in time;
3. he was panicking, wanted to get reverse thrust, but engaged forward thrust first in error.
1. is certainly plausible, given Sea Shepherd's history
of repeatedly employing deliberate collision tactics between their vessels and the Japanese fleet. But I think it is unlikely, because of the position of the crew members on board Ady Gil. It does not seem to me like they were hunkered down ready for a deliberate collision. So I'm betting 2. or 3.