well, there was seaassaultfest.org and before that boatpunk.org (don't click on either one, they are spam now) for the guatamala boat punk gathering, but i dunno if they're even doing that anymore since their terrible and keeping websites updated (or even online).
this blog has some info on previous events:
https://princessofpirates.com/category/boatpunk/
i dunno if it's still active or not, but you could always try
http://blueanarchy.org. they have a mailing list (last link on the page).