Hi Cal, there used to be a yacht that did trips out of Alicante harbour, it had a ticket office near the Tabarca boats.
I'm not aware of trips to other destinations from Santa Pola or Alicante
There are a few boat trips from Benidorm, a regular one to Peacock Island, a daily one to Calpe, should see some great coastline views on that one, there is also a "submarine" operating out of Benidorm, reckon the kids would enjoy that

Hope this helps
Regards all
John
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