"I am a shipwrecked man clinging to a bit of wreckage...."
See in text (Act III)
Krogstad uses this metaphor (a comparison without using the terms ‘like’ or ‘as’) to describe how he felt when Mrs. Linde chose to marry her late husband instead of him. Mrs. Linde replies that she had her mother and younger brothers to look out for and she needed financial stability, which Krogstad could not offer her. When Krogstad says that he is “clinging to a bit of wreckage” he might be suggesting that he is still in love with Mrs. Linde.