Pedant's definition of a spring tide?

[Roberto]

also, in the end the precision has to suit the boat and the sailed area

A +-10% mistake in water height at time t in many places of the Atlantic gives a 20-30-40ish cm difference
Getting it +-10% wrong in the Channel islands may mean a couple of metres difference, which in terms of navigation is a completely different matter imho

 

[LadyInBed]

I haven't read all the previous posts, but springs and neaps are more to do with the moon than any particular hight of the tide!

You can get springy springs around the equinox

 

[binch]

tides

There are 31 harmonics to work over in tidal forecasting, some are large amplitude, some can barely be noticed.
When a significant number of rhe largest of them coincide, you get spring tides.
Alternativelyand scientifically, if the tidal stream is against you, it must be springs.