P&I clubs cover the liabilities hull insurance doesn't. Here's the plain-English version.
A Protection & Indemnity (P&I) club is a mutual association of shipowners that covers third-party liabilities — injury, pollution, cargo, collision damage to others — that sit outside a vessel's hull policy.
Members pool risk and pay "calls" rather than fixed premiums. The largest clubs form the International Group. Specialist clubs (e.g. for fishing and small craft) cover the workboats common in Alaska and the Pacific Northwest.
When a claim lands, the club needs to know where a vessel was and what it was doing. AIS voyage reconstruction, gap analysis, and the 400-day archive turn a fuzzy account into evidence. See AIS for insurers.