On the Stratics siege board today Petra Fyde posted:
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When leaving a boat in the water (with fishing quest - so can't be drydocked). Remove all items from the hold AND re-deed all cannons and remove them.
Congratulations to whoever found my boat, please enjoy the 5 heavy cannon and the box of ammo to fire them that was in my hold.
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Good to know! Oh, and she was a good sport about it. Nightstalker 'hinted' that he might have been the culprit. Czarina offered to make more cannons, but Petra can do that too. But still, it's something that I had not known.