The Island Packet 31 is a genuinely well-built cruiser with a short, specific list of things that actually go wrong, one of them buried where you cannot see it. Use this list to know what a survey of a forty-year-old IP31 must not miss.
Every IP31 left the factory with 304 stainless chainplates glassed into the hull where they cannot breathe, setting them up for crevice corrosion and stress-corrosion cracking at the welds with no way to test without destroying them, so hunt for rust weep at the caprail exits and ask in writing for replacement paperwork.
The ballast is encapsulated iron with no keel bolts, but a hard grounding breaches the shell and water reaching the iron corrodes and expands (rust jacking), which can crack the encapsulation from inside, so look hauled for rust streaks, gouges, and cracks along the sole and leading edge, and ask about grounding history.
The rudder is two glass shells over a urethane foam core and water intrusion into that core was the most common rudder complaint across Island Packet models, so meter the whole blade, tap for voids, check the trailing edge and lower bearing for weep, and rock the blade for bearing play.
The most common leak pattern on an un-refit IP31 is original aluminum-framed ports and deck penetrations seeping with age (some ports were self-tapped rather than through-bolted), and that water can reach the deck core or feed a chainplate pocket, so look for tannin staining below every port and hardware base.
The roughly 25-gallon aluminum tank is a flagged wear-out item that pits and corrodes from trapped moisture, and the molded interior liner obstructs access so replacement is more labor than the part suggests, so inspect the low corners and bedding seam for pitting and a fuel smell.
The deck is cored with Island Packet's rot-proof PolyCore rather than balsa and shows no fleet delamination history, but any core can take on water at a long-term leak, so meter and tap the sidedecks and hardware bases to catch a localized wet reading.
The exhaust mixing elbow corrodes and cokes up internally (the most common failure on this engine family) and shows as an inability to reach full RPM, and a failed anti-siphon vented loop can siphon seawater back and hydrolock the engine, so inspect both and run the engine to full RPM on the sea trial.
The IP31 uses 1x19 wire with swaged terminals and a Navtec rod bobstay, and forty-year-old wire past the 10-to-15-year interval should be priced for full replacement alongside the chainplates, especially since most insurers now require a current rig inspection on a boat this old.
Roughly ten percent of the fleet has the shoal-draft keel-centerboard option with a wire lift pendant and a winch under the cockpit, so inspect the cable for broken strands and the winch and pendant, and note the manual's warning never to back up with the board lowered.
The IP31 uses Edson rack-and-pinion steering with no cables, whose free play is taken up at the quadrant cap bolts, so work the wheel lock to lock for play, and treat an original aluminum holding tank and the original Par head as suspect age-out items.
The full Island Packet 31 volume walks every point in depth, with the fix costs, the service data, and the parts sources. Leave your email for the printable checklist and word the moment the doors open.