In reply to Cog:
> I've never seen tides as positive and negative values, is this something new?
The website that supplies the data (WorldTides) seems to offer a variety of datums (though UKC has gone for MSL). Tidal heights are normally given relative to lowest astronomical tide as this is convenient for estimating depth of water from charted depths, but if you don't need to do this then it could make sense to use something different. Not sure about MSL though...
Highest astronomical tide might be better as this is the worst case for climbing, just as LAT is the worst case for boats.
Post edited at 21:59
