I work in merchant shipping. stowaways are a constant pest - they usually destroy all identification documents that they might have and make up an unknown gibberish language to make it hard to deport them.
Walking the plank has been tried - by a Russian crew on a bulk carrier a few years back -they got coaught - a more humane method also used was to drop them off on the coast of Somalia, until that got too dangerous due to the pirates..
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