Island Packet 31

This is a sourced owner's companion to the Island Packet 31, the beamy shoal-draft cutter Bob Johnson drew from scratch and built in Largo, Florida from 1983 to 1989. It is meant to help you understand, maintain, and make good decisions about your boat. It is not a factory service manual, and it is not a substitute for a qualified surveyor, rigger, or mechanic. Read this chapter first, because before any of the advice that follows can help you, you need to know exactly which IP31 you own.

1.1 What this book is, and what it isn't

Welcome aboard. Whether you already own an Island Packet 31 or you are standing on a broker's dock trying to decide, this book is meant to live in the chart table and earn its keep there.

Here is the honest framing. This is an owner's reference, assembled from the public record: the Practical Sailor used-boat review, the SpinSheet and Sailing magazine write-ups, the Good Old Boat and sailboatdata specification cards, the Cruising World profile of designer Bob Johnson, decades of owner discussion on the Sailboat Owners and Cruisers forums, and the Island Packet Yacht Owners Association. Every factual claim in this book traces back to a source like those. Where the sources disagree, you will see both numbers and a note to verify. Where only one source exists, the claim is hedged rather than dressed up as settled fact.

What this book is not:

• It is not a factory manual. Island Packet Yachts, operating as Traditional Watercraft, did not publish the kind of detailed shop documentation you would get from an automaker, and much of the original paperwork has scattered over forty years. Where a factory torque spec or wiring diagram would help, we often simply do not have one, and this book will tell you so rather than invent a number.
• It is not a substitute for a professional. A book cannot put a moisture meter on your side deck, borescope your buried chainplatechainplates, or listen to your Yanmar run under load. When a decision carries real safety or real money, this book points you to a surveyor, a rigger, or a diesel mechanic, and you should go.
• It is not gospel on your specific hull. Two IP31s built a few years apart, kept on opposite coasts, can be genuinely different boats. Use this book to know what to look for. Use your own eyes, and a professional's, to confirm what is actually there.

Think of it as the knowledgeable friend who has read everything, remembers the sources, and will tell you plainly when the honest answer is "it depends, go check."

1.2 How to use this book

The chapters ahead move from identity to systems to problems to upkeep. You do not have to read them in order, but you should read this chapter in full, because almost every later chapter branches on the questions below. The engine access notes, the grounding-repair advice, the rig discussion, all of it depends on which version of the boat you have.

A few conventions to know:

• Measurements are imperial first, metric in parentheses. A draft of 4.0 ft (1.22 m), for example.
• [CONFLICT] means the sources genuinely disagree. You will get both values and a nudge to verify on your own boat.
• [UNVERIFIED] means a claim rests on a single source, often one owner's report. Treat it as a lead, not a law.
• [SAFETY] flags something that can hurt you or sink the boat. These carry an inline source note so you can judge the strength of the evidence yourself.

1.3 Two myths to clear away first

Before we sort out the variants, let us correct two things that "everybody knows" about Island Packets and that are wrong for this boat.

Myth one: the hull is foam-cored. It is not. The IP31 hull is solid, hand-laid fiberglass, knitted or triaxial glass in polyester resin, with no coring below the waterline and no keel bolts (source: Practical Sailor; SpinSheet). The word you have heard, PolyCorePolyCore, is Island Packet's proprietary resin-and-microballoon paste, and on this boat it cores the deck, not the hull. Foam-cored and vinylester hulls are a later, larger-boat development. So when you inspect an IP31, treat it as a solid-glass hull with a cored deck, and read the deck-moisture and blister sections in that light.

Myth two: it has a factory Hoyt jib boom. Almost certainly not. The self-tending Hoyt jib boomHoyt jib boom became an Island Packet signature on later models, and the best IP31-specific source explicitly notes "no Hoyt jib boom" on this one (source: The Sailboat Guide; Forespar on the Hoyt boom as a later-model feature). [UNVERIFIED] in the strict sense, since it rests mainly on that one source plus the boom's known history, but the evidence points one way. On the IP31 the staysailstaysail is a conventional hanked sail on a fixed inner forestay, sheeted the ordinary way. If a boat you are looking at has a self-tending staysail boom, assume it is a retrofit and inspect the deck reinforcement under it accordingly.

1.4 Identify your boat: the axes that matter

The Island Packet 31 was built by Island Packet Yachts of Largo, Florida, designed by Robert K. "Bob" Johnson, and produced from 1983 to 1989. Roughly 260 hulls were built, though the count is genuinely contested. [CONFLICT]: some data cards list about 204, Practical Sailor and The Sailboat Guide say around 262, and SpinSheet reports "265 sold." Use "roughly 260" and do not read too much into the exact figure. This was Johnson's first clean-sheet design, the boat that established the high-volume, beamy, shoal-draft full-keel cruiser template the brand rode for decades, so it matters historically as well as practically.

Within that single model name live a few real forks. Nail these down and the rest of the book snaps into focus.

1. Engine: 22 hp early, 27 hp from about 1985

Every IP31 left the factory with a three-cylinder Yanmar diesel, but not the same one.

• Early boats (1983 through roughly 1984): the Yanmar 3GM, about 22 hp. One owner calls this engine "inadequate" when punching a strong current (source: Practical Sailor).
• From about 1985 on: the Yanmar 3GM30 / 3GM30F, about 27 hp, described as essentially the same engine optimized for a little more power (source: Practical Sailor; SpinSheet).

The later 27 hp boat is the more capable installation, and on a heavy 11,000 lb (4,990 kg) hull that extra power is welcome. The exact suffix stamped on the block varies by hull, so lift the companionway steps and read the plate rather than trusting the listing. Owners report few problems with either Yanmar; this is a long-lived, well-supported engine family.

2. Keel and draft: 4 ft full keel, or the shoal-draft centerboard

The standard IP31 is a full (long) keel drawing 4.0 ft (1.22 m) (source: Good Old Boat; Practical Sailor; SpinSheet). A minority of boats, roughly 10% of the fleet, were built as a shoal-draft centerboardcenterboard variant drawing about 3.0 ft (0.91 m) board up and considerably more with the board down [UNVERIFIED] (source: SpinSheet; The Sailboat Guide; the "~10%" figure is single-source).

This is not a trivial distinction. The centerboard boat opens up thin-water anchorages the deep boat cannot reach, but it adds a board, a pennant, and a trunk to inspect and maintain. Measure your draft, or check the haul-out records, and know which you have, because it drives your cruising grounds, your groundings, and your survey checklist. (You may also see a stray "4'6"" draft figure in one source; treat it as an outlier and trust 4.0 ft for the standard keel.)

3. Ballast material: a genuine open question

Here is one this book cannot settle for you, and it matters. [CONFLICT] on the ballast material. The keel is a full keel with encapsulated internal ballast and no keel bolts, which is a real strength: there is no keel joint to leak and no bolts to corrode (source: The Sailboat Guide; Practical Sailor). The ballast weighs about 4,500 lb (2,041 kg), roughly 41% of displacement, and every source agrees on the weight. What they disagree on is the metal.

• Iron: the two IP31-specific reviews say iron. Practical Sailor describes iron ingots set in concrete in the keel cavity; SpinSheet says "encapsulated iron" (source: Practical Sailor; SpinSheet).
• Lead: the Good Old Boat and sailboatdata data cards list "4,500 lbs encapsulated lead," and general Island Packet brand commentary favors lead (source: Good Old Boat; Practical Sailor keel-care article).

This book leads with iron, because the sources that actually discuss the IP31's construction say iron, and the "lead" statements read like brand-general claims that fit later, larger boats better. But you should verify on your own hull if you can, because the answer changes your grounding-repair math. [SAFETY] Iron ballast is the more serious case: if a hard grounding breaches the fiberglass shell and water reaches iron, it rusts and expands, "rust jacking" that can crack the encapsulation from the inside, and the laminate must be fully dried before it can be re-glassed. Owners have lost most of a season waiting for a grounded encapsulated keel to dry out (source: Practical Sailor, Caring for Encapsulated Ballast Keels; treat the "one season" anecdote as [UNVERIFIED]). An ungrounded, dry IP31 keel is a genuine peace-of-mind feature. A grounded one with wet iron inside is an expensive, slow problem.

4. The one thing to check first: the buried chainplates

If you do nothing else before making an offer, understand the chainplatechainplates. [SAFETY] This is the headline issue on early Island Packets and the first thing a knowledgeable surveyor looks at.

Every IP31 has its stainless-steel chainplates embedded inside the fiberglass structure rather than bolted on externally (source: Practical Sailor; Life of Sailing). On this era the metal is 304 stainless, and stainless needs free oxygen to stay corrosion-resistant. Sealed inside a wet, oxygen-starved glass pocket, it is prone to crevice corrosion and stress-corrosion cracking, usually at the welds, and the damage is impossible to inspect visually without cutting into the structure (source: Island-Packet-Ancestry; Life of Sailing). A failed chainplate can drop the rig. Community guidance puts the service life of embedded 304 at about 20 to 25 years, which means every IP31 is now well past that window [UNVERIFIED] (source: Island-Packet-Ancestry, single detailed source).

Because the plates cannot be seen, a surveyor reads the indirect evidence: rust weeping or staining where the chainplate exits at the caprail, cracked or lifted bedding, any movement under load, and water in the nearby lockers or berths. The upgrade you most want to see is external, through-bolted chainplates on laminated backing pads, a refit attentive owners have done and that surveyors describe as exactly "what you want to see" (source: Practical Sailor). A note on a common shorthand: IP31 chainplates are stainless, not bronze, whatever a listing implies. For a forty-year-old boat, budget for this the way you budget for standing rigging: assume end-of-life unless the paperwork proves otherwise.

1.5 Know your hull: a quick checklist

Before you turn another page, fill in your own answers. Keep them handy; the rest of the book will ask.

• Model and hull: built 1983 to 1989? Confirm it is the Bob Johnson IP31, not an adjacent IP27, IP29, or IP35.
• Engine: early 22 hp Yanmar 3GM, or the later 27 hp 3GM30F? Read the plate under the companionway.
• Keel: standard 4.0 ft (1.22 m) full keel, or the shoal-draft centerboard (~3.0 ft / 0.91 m board up)?
• Ballast: iron assumed for this era; any grounding history, rust streaks, or cracks at the keel?
• Chainplates: original embedded 304 stainless, or refit to external through-bolted plates? Any rust at the caprail exits?
• Hull and rig: solid-glass hull and cored deck confirmed; staysail conventionally sheeted (no factory Hoyt boom)?

If you can answer all six, you are ready for everything that follows.

1.6 A word on liability

This book is a companion, not a command. It gathers what the public record says about a mass-produced boat now four decades old, and it does its honest best to separate what is well established from what is one owner's story. But it has never seen your boat.

Nothing here replaces a qualified marine surveyor, rigger, mechanic, or naval architect. Standing rigging, chainplates, keels, engines, fuel systems, and steering are life-safety items; when this book flags one, that is your cue to bring in a professional and to trust their hands-on inspection over any general statement printed here. Specifications, procedures, and figures may contain errors, may not match your specific hull, and may have been superseded. Verify anything load-bearing before you act on it.

You, and the professionals you hire, are responsible for the safe condition and operation of your vessel. The authors and publisher of Garage, Galley & Hangar accept no liability for any loss, damage, or injury arising from the use of this book. Use it to ask better questions. Go get the real answers on the water.

The Island Packet 31 is the boat where the brand you know today actually began. It was Bob Johnson's first clean-sheet design, shown for the first time at the 1983 Annapolis sailboat show, and it set the template that Island Packet would ride for the next forty years: a beamy, heavily-built, shoal-draft full-keel cruiser with an ivory hull, meant to carry a couple in comfort rather than win a race around the buoys. Roughly 260 of them were built between 1983 and 1989, and the boat's reputation for being overbuilt and worry-free is a big part of why your hull is still sailing.

2.1 The man who drew your boat

Before the IP31 was a boat, it was a philosophy, and that philosophy belonged to one man: Robert K. "Bob" Johnson, the naval architect who founded Island Packet Yachts and drew every early boat by hand.

Johnson's résumé does not read like that of a typical production-boat designer, and it helps explain why your boat feels the way it does. He earned a bachelor's degree in mechanical engineering at the University of Florida, then a master's in naval architecture and marine engineering at MIT. His first career was in aerospace: he worked at McDonnell Douglas designing missiles and rockets, then moved to a California firm, W.A.V.E. Inc., that applied aerospace manufacturing methods to building surfboards. Only after that did he turn to yachts, taking design positions at Irwin Yachts and Endeavour Yachts before striking out on his own. That aerospace-then-boats path shows up in the IP31 as a preoccupation with structure and margin: this is a boat engineered to be stronger than it strictly needs to be.

Johnson founded Island Packet in 1979, and the very first product was not an original design. He bought and reworked the molds of a 26-foot centerboard sloop that had been called the Bombay Express, turned it into the Island Packet 26, and launched it in 1980. In the early days the whole operation ran out of his kitchen: a single brochure, classified ads in Cruising World, and Johnson himself hand-drawing the boats. From the beginning he settled on the detail that would become the brand's calling card, the ivory (cream) gelcoat hull. The company's own line was that "you always know an Island Packet is an Island Packet," and the color is the reason. If you have ever had a stranger on a dock identify your boat's builder from a hundred yards away, you have Johnson's ivory hull to thank.

The design philosophy that runs through everything he built is worth stating plainly, because it is the throughline of this whole book: moderate-to-heavy displacement, full keel, shoal draft, comfort first, built for extended cruising rather than speed. Johnson was not trying to build the fastest 31-footer in the yard. He was trying to build the one you could live aboard, gunkhole into thin water, and take offshore without lying awake worrying about the structure. Whether that trade suits you is a personal question this book will help you answer honestly, but it was never an accident. It was the entire point.

2.2 Why the IP31 matters: the first from-scratch Johnson design

Here is the fact that makes your particular boat historically important. The IP26 that started the company was a reworked purchased hull, someone else's design that Johnson adapted. The IP31 was the first boat Bob Johnson designed from scratch, a genuine clean sheet, and by his own account he had it done by 1983.

That distinction is not trivia. It means the IP31 is where the Island Packet identity stopped being borrowed and became original. The pinched ends and stern counter of older designs were abandoned in favor of a fuller, beamier hull that maximized interior volume, the "much bigger inside than it looks" feeling that became the brand's signature and its selling proposition. Every Island Packet that came after, the whole long run of full-keel cruisers that made the company one of the most recognizable names in American sailing, traces its lineage to the shape Johnson drew for this boat. When you own an IP31, you own the boat where the template was set.

2.3 Where the IP31 sits in the early line

There is a common misconception, one this book's own working notes had to correct, that the IP31 came late in the early lineup. It did not. Ordered by the year each model was introduced, the early Island Packet family looks like this:

So the correct model order by introduction is IP26, then IP29, then IP31, then IP27, then IP35. Note the counterintuitive bit: the IP27 has a smaller number but a later introduction than the 31. Island Packet's model numbers roughly track length, not chronology, so do not read the numbers as a timeline.

[UNVERIFIED] The IP29 is a mild source of confusion because there appear to be two distinct generations of it, an early-1980s run and a restyled 1991-to-1997 version. The dates around that second run vary between sources. None of it changes where the IP31 sits, but if you find yourself comparing an IP29 to your boat, confirm which generation of 29 you are looking at.

How to tell your boat from its siblings

If you are shopping, or just trying to understand what you have, the adjacent models sort out cleanly by weight and volume:

• Versus the IP27 (introduced 1984, roughly 8,000 lb displacement, 10.5 ft beam, 3,000 lb ballast): the 27 is a materially smaller and lighter boat despite both being listed in the "30-ish-foot" range. Your IP31 is about 3,000 lb heavier and carries roughly 50 percent more ballast.
• Versus the IP29 (about 10,900 lb displacement, 10.83 ft beam, 4,800 lb ballast): close in displacement, but the 29 is narrower and shorter on the waterline. The IP31's extra beam (11.5 ft) and longer waterline are what give it noticeably more room down below.
• Versus the IP35 (introduced 1988): simply the next size up, which overlapped the tail end of IP31 production before taking over the slot.

The identity point to hold onto is this: the IP31 is the beamy, high-volume, shoal-draft full-keel cutter that reads much bigger inside than 31 feet. That was exactly the reputation Johnson was chasing when he moved on from the pinched-ended 26, and it is what an IP31 still delivers.

2.4 The 1983 Annapolis debut and the production run

The IP31 was introduced to the public at the 1983 U.S. Sailboat Show in Annapolis, the fall show that has long been the proving ground for new American cruising boats. It stayed in continuous production through 1989. That six-to-seven-year run is respectable for a boat of this type and size, and it did the job that mattered most to a young company: it established Island Packet as a serious, credible builder rather than a one-model kitchen-table startup. The IP31 launched the brand.

How many were built: [CONFLICT]

Here the honest answer is that nobody agrees, and you should know the disagreement rather than trust a single number.

• Some reviews (Practical Sailor, The Sailboat Guide) put the count at 262.
• One magazine review (SpinSheet / Sailing magazine) says 265 boats sold.
• The Good Old Boat / sailboatdata data card lists a notably lower 204.

[CONFLICT] The most defensible thing to say is "roughly 260 boats," while being aware that at least one data card lists closer to 204. The gap between "about 260" and "about 204" is large enough that it is not simply rounding, and the research notes for this book could not resolve it from secondary sources. If the exact production number matters to you (for rarity, for a survey, for insurance), the way to settle it is through Island Packet Ancestry, an independent service run by broker Bill Bolin that has access to the original factory files and can pull the build record for a specific hull. Treat any single published production figure as an estimate, not gospel.

2.5 Construction identity: what your boat is actually made of

This is the section that most often gets described wrong, including in this book's own initial brief, so it is worth getting exactly right. The construction of the IP31 is a genuine part of its identity and a large part of why the boats last. Three features define it.

A solid, hand-laid fiberglass hull

The IP31 hull is solid, hand-laid fiberglass, not cored. Multiple independent reviews describe it as a solid laminate of fiberglass cloth (triaxial cloth in some descriptions) and polyester resin, with no coring below the waterline. Inside, the boat uses extensive molded fiberglass liners and pans to stiffen the structure and finish the interior.

[UNVERIFIED] One data card lists the resin as vinylester rather than polyester. For a boat of this 1983-to-1989 era, polyester is far more credible and is what the construction-focused reviews report, so treat vinylester as a likely outlier. Either way, the load-bearing fact is that the hull is solid glass, which is a meaningful correction to any listing you may see that calls the IP31 a "foam-cored" hull. It is not. That cored-hull construction is a later, larger-boat Island Packet development, not a feature of your 31.

A PolyCore microballoon deck

The place the word PolyCore PolyCore belongs is the deck, not the hull. The IP31 deck is cored with PolyCore, Island Packet's proprietary core material, described by the factory as a mixture of polyester resin and microballoons (sometimes called resin fillers). The company's claim was that it weighed about the same as a half-inch balsa core but resisted the water intrusion and delamination that plague balsa-cored decks. If a listing mentions "PolyCore" or "PolyCel," it is talking about this deck core. The hull underneath is solid.

An encapsulated full keel with no keel bolts

The keel is one of the IP31's strongest identity features and a genuine selling point. It is a full (long) keel with the ballast encapsulated inside the fiberglass, which means there are no external keel bolts and no keel-to-hull joint. On many production boats the keel joint is a lifelong maintenance and worry item: bolts corrode, the joint weeps, the "keel smile" appears. On your IP31 there is nothing there to leak or corrode, because the ballast lives sealed inside the molded keel cavity. That is real peace of mind, and it is one of the reasons owners talk about these boats the way they do.

[CONFLICT] What the ballast is made of is genuinely disputed. The construction-focused reviews (Practical Sailor, SpinSheet) say iron, specifically iron ingots set in concrete inside the keel cavity. The Good Old Boat / sailboatdata data card, by contrast, lists encapsulated lead. This book leads with iron, because the sources that actually discuss how the boat was built say iron, but you should know that some data cards say lead, and neither can be stated as certain fact without the factory's own build record. The weight of the ballast, happily, is not in dispute: 4,500 lb across every source, giving a ballast-to-displacement ratio of about 41 percent, which is a big part of why the boat is stiff and stands up to its sail.

One more construction note for completeness: the rudder is a semi-balanced fiberglass rudder with a foam core, hung in an aperture at the trailing edge of the keel. So the boat does have a cored component; it is the rudder, not the hull. [UNVERIFIED] The finer details (a 1.5-inch stainless rudderstock and a stainless "lobster strap" across the aperture to keep lines from snagging) come from a single source and are credible but unconfirmed.

2.6 Rig and profile at a glance

The chapters ahead cover the rig in full, but the IP31's silhouette is part of its identity, so here is the shape. Most IP31s were built as cutters, carrying a yankee or genoa on the headstay plus an inner staysail on its own stay ahead of the mast, though a simpler sloop rig was also offered. The boat wears a bowsprit forward (which doubles as the anchor platform) and a boomkin boomkin aft, and those two overhangs are why the length overall of 34 ft 4 in is so much greater than the roughly 31-foot length on deck.

[CONFLICT] A word of caution about one common assumption. Later and larger Island Packets became famous for the Hoyt Jib Boom, a self-tacking, self-vanging staysail boom patented by Garry Hoyt and built by Forespar. The evidence indicates the IP31 did not come with one from the factory; its staysail is conventionally sheeted, not self-tending, and The Sailboat Guide's IP31 entry says so explicitly. The Hoyt boom was a later-model signature. So if you are looking at an IP31 that has one, treat it as a retrofit rather than original equipment, and verify against the boat's build record if it matters to you.

2.7 Reputation: why owners are the way they are

Island Packet owners have a reputation for loyalty that borders on the fanatical, and the IP31 is where that loyalty started to build. The boat earned a specific and consistent character in the sailing press over the decades.

On the good side: the IP31 is described again and again as heavily built, stiff, and comfortable, a shoal-draft full-keel cruiser with strong coastal credentials and legitimate light-bluewater ability. The long keel gives it excellent directional stability and self-steering; the encapsulated ballast, absent keel bolts, and solid hull get cited over and over as durability and peace-of-mind features. These are boats people trust, and that trust is largely earned.

On the honest other side, because this book does not sell you a boat it will not also be straight with you: the same full hull and wide bow that make the IP31 roomy and stiff also make it slow in light air and reluctant to tack through the eye of the wind. Its best point of sail is a reach, not a beat. It also has the low-speed reverse-steering quirk common to full-keel boats with the prop in a keel aperture: back down and the stern walks, and the helm feels backward until you learn it. None of this is a defect. It is the direct, predictable consequence of the trade Johnson made on purpose, comfort and strength and volume in exchange for light-air speed and pointing ability.

The fairest one-line characterization, and the one this book stands behind, is that the IP31 is a comfortable coastal and near-offshore cruiser that has done ocean passages, rather than a dedicated bluewater passagemaker or anything resembling a racer. Owned with that expectation, it will not disappoint you. Bought expecting a nimble, close-winded flyer, it will.

2.8 The bottom line

The Island Packet 31 is a boat that matters more than its modest production numbers suggest. It was Bob Johnson's first original design, the boat that turned a kitchen-table startup with one reworked hull into Island Packet Yachts, and the vessel that fixed the brand's identity for the next four decades: ivory hull, full keel, shoal draft, solid glass, encapsulated ballast, built heavy and built to last. Roughly 260 were made between 1983 and 1989 (with some records suggesting closer to 204), and the survivors are still cruising because of exactly the choices Johnson baked into them. When you understand where your boat came from, the rest of this book, the systems, the maintenance, the quirks, all reads as the logical expression of one designer's stubborn, well-engineered idea of what a cruising boat should be.