I’m probably way behind the times here, but I’ve never understood the “technical rehearsals” line. Either the ride functions, or it doesn’t. Testing and sending boats around without opening should be enough to know whether the effects trigger as they should and everything works as planned? Seems like a deliberately ambiguous line to excuse further (and let’s be honest) inevitable delays.
With water rides especially, it can be a bit more complex, as different weights in the boats will travel at different speeds. So I guess one aspect is ensuring all the effects can trigger, reset and then re trigger before the next boat comes, with every possible combination of weights in.
Things like audio, lighting, special fx and mechanical effects will be tested during this period.
Usually a technical rehearsal is when all of the show elements are testing together for the first time, so this is the first set test runs of all the show elements so to speak. Where tweaks will be made, to make sure they all flow, work after each other and reset properly before the next boat comes.
Usually, before a technical rehearsal, all the show elements have not been running in unison and together. This could differ from Pleasure beaches interpretation, but that is usually the case. They may have tested them one by one previously.
If this is the case, it shows they are keen to get the attraction open ASAP, by performing tech rehearsals with guests on, but the boat speed issue is something that is most efficiently carried out with guests.
With all that said and the time it has taken them to get this open, I feel it is somewhat of a cop out. But generally speaking, that is what is involved in a technical rehersal.