金槌(かなづち)hammer, hopeless swimmer, complete beginner at swimming, someone who sinks like a stone

金槌(かなづち)で釘(くぎ)を板(いた)に打(う)ち込(こ)む。

To drive a nail into the board with a hammer. {hammer, hopeless swimmer, complete beginner at swimming, someone who sinks like a stone}

金槌(かなづち)とトンカチは同(おな)じものである。

A hammer and a mallet are the same thing. {hammer, hopeless swimmer, complete beginner at swimming, someone who sinks like a stone}

君(きみ)は金槌(かなづち)だから、海(うみ)では泳(およ)がない方(ほう)がいいよ。

Because you're a hopeless swimmer, it's better not to swim in the sea. {hammer, hopeless swimmer, complete beginner at swimming, someone who sinks like a stone}

大工(だいく)だけあって、父(ちち)は壁(かべ)に金槌(かなづち)で釘(くぎ)を打(う)つのがとても上手(じょうず)だ。

As expected of a carpenter, my father is very good at hammering nails into the wall. {hammer, hopeless swimmer, complete beginner at swimming, someone who sinks like a stone}

コーチ：「最初(さいしょ)は金槌(かなづち)だったあなたがこんなに泳(およ)げるようになって何(なに)よりです。」

Coach: 'Above all, it's great that you, who initially could barely swim, can now swim so well.' {hammer, hopeless swimmer, complete beginner at swimming, someone who sinks like a stone}