It was amazing to see such a heavy iron ship floating.
It was amazing that such a heavy iron ship could float.
He was amazed by seeing that such a heavy iron ship could float.
例文一:
It was amazing to see such a heavy iron ship floating.
どうしてあんなに重い鉄の船が浮いてるのか不思議だった。
例文二:
It was amazing that such a heavy iron ship could float.
どうしてあんなに重い鉄の船が浮いてるのか不思議だった。
例文三:
He was amazed by seeing that such a heavy iron ship could float.
どうしてあんなに重い鉄の船が浮いてるのか不思議だった。
・「不思議」は様々な英訳がありますが、この場合に"amazing"が相応しいと思います。
・"... see such a heavy iron ship floating ..."と"... that such a heavy iron ship could float ..."はほぼ同じ意味合いですが、"see such"の言い方は何かを自分の目で見ているときに相応しいです。
・例文三の"he"のところに"I"などを入れ替えても良いです。"I was amazed ..."・"They were amazed ..."・"She was amazed ..."も言えます。