Now that the clowns who run this Lunitidal Calculator website have completely ruined it for 2023 with their v2.0 that doesn't work at all, has anyone got another alternative method?
If your following next high tide for your location isn't on the same day, then the lunitidal interval comes out as a negative value and the website chucks a wobbly. In this case I suppose the thing to do is keep counting past 24hrs? So if the website asks for the next high tide after 10pm and that happens to be 6:30 the following morning, then the number you put in will not be 06:30 (which will give a negative result), but 24+06:30 = 30:30?
30:30 isn't a time on any 24hr clock I've ever seen, but the way this LT calculator website has been written, this seems to be the only way of getting a sensible answer out of it. The glaring problem with this approach is that using drop down boxes with limited choices, there's no way you can actually enter a time of 30:30.
So if your next high tide is not on the same day as the one specified, I'm afraid this website is useless.