He says the wooden vessel with spent bullet casings is 'definitely worth further investigating'.
Steve Ellis said he came across the remains during a dive off Southend Pier last week, when the water was particularly clear.
Mr Ellis often dives to the wreck of 17th Century warship the London, which sank in 1665 with the loss of 300 lives, and was surprised to spot something uncharted. He told BBC Essex: "That's the exciting thing about diving, it's coming across the unknowns. There's spent bullet casings on it. It's definitely worth further investigating."
He believed more of the shipwreck was waiting to be discovered and hoped to return to map the site then look through archives to research what the vessel could be.
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