There is no such thing as trawler hull speed. The computed hull speed is the same for all boats and ships. Full displacement hulled boats are far more dependent on the effects of that speed than other boats but judgement calls can still be made for boats that are not FD.
It is not an exact speed as the number implies but it generally tells where the 1st following wave is relative to boat moving along between the following wave and the bow wave. At hull speed the following wave is at the very aft end of the stern and the bow wave is .. well .. at the bow.
North Western Washington State USA