A grammatical correct sentence in English.
Actually, it isn’t a grammatically correct sentence. It’s a sentence fragment (which is in fact grammatically correct), containing only the subject: “A ship.” Add as many adjectives to the subject as you wish, but it remains a sentence fragment until a verb is attained.
There are three ways to fix it while maintaining the joke. It’s implied that the caption is describing the image, in which case one would write: “This is a ship shipping ship shipping shipping ships.” In the sentence, is is a verb.
It’s also possible to make it a sentence while extending the joke even further: “A ship shipping ship shipping shipping ships ships,” in which ‘ships’ is a verb; the ship (shipping shipping ships hsips shpis shiphsp hsp shiphishpshphspisihsihs) is shipping the ships.
Finally, one could change only the third word to achieve the following: A ship ships ship shipping shipping ships. This is in essence the above example, but with the verb in a different place. It is, however, a bit more efficient.
Conclusion: this description contains no verb pertaining to the subject, and so is not a sentence. However, it is, in fact, grammatically correct.
(Also, for best results read the above explanation in the voice of a British butler.)