They also require a 3rd component - Air or more specifically oxygen (hence the term oxidation). Otherwise we'd still be picking at salt with hand tools and getting it to the surface in wooden barrows. Steel and iron ships that were sunk over the decades are still pretty much whole. So yes, your fork-lifts working in seafood environments corroded out quicker than in other environments but that was because the perfect storm of all three components required for oxidisation were present.

As for tidal power, there are a number of sites that at first glance appear to be perfect, the Bristol Channel being a prime one. The strength of tide ripping threough the channel, coupled with the 2nd greatest tidal range in the world also has to be tempered by the amount of silt and other debris (including trees, dead animals and humans) that is also carried by the tide. Tidal barrages also divert the natural water course and could pose other environmental problems, up or downstream, such as unexpected erosion or silt deposits. About five years ago, when the Bristol Channel Tidal Barrage was being considered, another company came up with the idea of anchoring sub-surface turbines to the sea bed, thereby leaving the channel navigable and causing negligible water diversion. As with most things though, no money was thrown at the idea.

There has also been a hell of a lot of environmental opposition to the Bristol Channel barrage as large areas of tidal mud flats may be affected by any alteration in the natural tides - the St Malo barrage in France seems to have worked for 40 or more years though.

There used to be a great ferk-off, working model of the River Humber in an enormous hangar on King George Dock, that was used for prctical modelling of tide flows and effects. Unfortunately once BTDB was disbanded and the docks privatised, no one saw a need for it anymore.

Now that would beat anybody's model railway layout