Mate,
The idea behind trim foils from a moth or a stealth is different to the original idea that inspired the 14's foils.
The International Moth is highly unstable in all directions. Without a trim foil the skipper needs to be somewhere behind and to windward of the hull. ie they are not the easiest to sail normally and downwind almost impossible. A trim foil makes the impossible almost possible (while still being impossible to old fat slow guys like me)

However the I14 while difficult beasty isnt that bad really. What the I14 has, is an issue with is length to power ratio. Biecker came up with the idea to use an assymetrical foil to modify the stern wave. Sort of similar to the bulb one sees on ocean carriers, but in reverse. By flattening out the stern wave, the theory goes the water "thinks" the hull is a much more acceptable 16 foot long. The longer the waterline length the faster the hull.. This is more important uphill than downhill. (Hopefully one doesnt have much hull in the water downhill). To accomplish this the trim foil needs to be the same width as the stern. Also the deeper the foil is below the stern wave the larger the surface area required to modify the surface wave.

Secondary is the anti mining aspect.

hope this makes sense.. I know what I mean anyway.

Stewart