"floundering" vs "foundering"

ベランダに緑のカーテンとして栽培しているゴーヤに２cm程の小さな実がつき始めました。ゴーヤの赤ちゃんはとても小さいので葉の間に隠れて中々見つかりませんが、朝の水遣りの時に探すのが楽しみになっている今日この頃です。　
さて、英語の話題に移ります。英単語のメルマガArcaMaxは普段は１単語についてですが、毎週土曜日は文法や表現についての詳しい説明を特集で配信しています。　先日は紛らわしい単語についての解説でした。
Q. My wife and I are debating whether "floundering" or "foundering" is correct when describing someone who is having a lot of difficulty performing the tasks in a new job. -- Bill, Glastonbury
A. What a coincidence!
Your hapless rookie is floundering if he's struggling, flopping around like a beached flounder. Perhaps he's failing to meet deadlines, flip-flopping in his decisions or constantly misplacing the Flounder File. But enough about me.
But, if he's performing so badly that he's going to be fired, he's foundering, meaning "sinking," as in "the Titanic foundered in the North Atlantic." "Founder" shares the root "fundus" (bottom) with "foundation."
ネイティブの方でも意味・用法で混乱する事があるのですね。　と言うより、ネイティブは単語の意味・用法を辞書で確認しないので、日本人が混乱するのとは異なる単語・表現で混乱するのでしょう。
"floundering" と "foundering" を辞書(OneLook Quick Definitions) で見ます。
"flounder":
1. behave awkwardly; have difficulties ("She is floundering in college")
2. walk with great difficulty
"founder":
1. stumble and nearly fall ("The horses foundered")
2. sink below the surface
3. fail utterly; collapse ("The project foundered")
4. break down, literally or metaphorically