This has been asked before, but the answer that was given is ambiguous.
TNVW asked in this thread whether Silent Spell would enable spellcasting underwater. The answer given was that due to water hindering arm and/or hand movements, "there are still factors resulting in a good chance of spell failure when underwater". This does not really answer the question about whether Silent Spell gives in EfU at least an improved chance of success when casting underwater, though, never mind how much it would help. I think both of those are things that a player would and should know before going ahead and picking the feat with the hope that their intuition is correct -- at least my intuition says that Silent Spell should help considerably.
So: does Silent Spell decrease the underwater spell failure percentage, and if so, by how much? (Assuming the standard spell failure percentage underwater is 100%, which I've always assumed it to be.)