Design and Construction
The hull of the O'Day 40 represents a notable departure from the production methods O'Day had relied on for years. Rather than solid fibreglass, the hull uses a cored composite of three-quarters of an inch of balsa, polyester resin, and biaxial fibreglass cloth, with decks similarly constructed with balsa and plywood core. Structural integrity is maintained through a combination of fibreglass liners, plywood bulkheads, and longitudinal and athwartship supports. The approach keeps the boat stiff and relatively light for its length — the 33'6" waterline underpins a displacement-to-length ratio firmly in medium territory, striking what one reviewer called "the sweet spot for modern cruising."
The deck layout reflects genuine thought about working conditions. A low cabin trunk slopes gradually to the foredeck, and angled cabin sides create wide sidedecks that remain secure underfoot when the boat heels. Cast aluminium stanchions are set at the rail rather than inboard, so the lifelines do not eat into usable deck space — a detail that matters on passages when crew need to move freely. A large anchor locker sits forward, and the stern features a small sugar-scoop transom swim deck with a folding boarding ladder accessible to someone in the water — a safety refinement that ABYC standards would later formalize, but which O'Day included ahead of the curve.
Rig and Handling
The O'Day 40 is rigged as a masthead sloop, and the numbers confirm a thoughtful approach to sail area. A forestay height of 51'6" and a mainsail luff of 45'5" produce a total sail area of roughly 722 square feet, enough canvas to keep the boat moving in light conditions without creating a handful when the wind builds. The sail area-to-displacement ratio of around 16.3 is deliberately conservative — the boat will not be a pinball in a breeze.
Briand carried the beam well aft, which produces form stability as a complement to ballast weight. The boat resists heeling through its physical shape rather than the keel alone, which flattens the motion and reduces crew fatigue on long passages. The ballast-to-displacement ratio of approximately 40 percent gives the rig good support as conditions deteriorate. A capsize screening factor comfortably below 2.0 provides the credentials for offshore work. Two keel configurations were offered: a deep-draft fin keel at 6'8" for maximising pointing ability, and a wing keel variant at 4'11" that opens shoal anchorages otherwise off limits. The wing keel sacrifices a few degrees of upwind performance but rewards its owners with access to the shallow reaches of the Bahamas and the American East Coast.
Interior and Accommodation
The interior arrangement is fairly standard but executed with care for liveaboard practicality. A V-berth cabin occupies the bow, followed by a port head with shower and a starboard hanging locker. The main saloon features a U-shaped dinette with a drop-leaf table to port and a settee to starboard — an arrangement that provides real table seating for a passage crew. Aft, the galley is U-shaped and positioned to port, tucking the cook into a secure triangle when the boat is heeled. A forward-facing navigation station sits opposite. The aft quarter-berth cabin offers a large athwartship double berth sheltered under the cockpit.
Headroom is generous throughout. The cockpit is deep and protective, comfortable for a couple and workable for a small crew. Fuel and water tankage — approximately 40 gallons of diesel and 100 gallons of water — suits the boat's role as a coastal cruiser with offshore capability. Access to the Westerbeke 46-horsepower marine diesel is reasonable: the companionway steps lift away and panels open along the starboard side. One layout element draws consistent criticism: a second head wedged into the quarter-berth cabin provides no meaningful privacy and would serve the boat better as additional stowage.
Known Issues and Inspection Points
Any survey of an O'Day 40 should begin with a moisture meter and an understanding of where this design is most vulnerable. Osmotic blistering below the waterline is likely on unrepaired hulls, and the balsa core compound the concern — water permeation in a cored composite can migrate well beyond the visible blister, making professional evaluation essential rather than optional. Deck crazing and cracking are also common; some examples show cracking severe enough to affect structural integrity, so questionable areas warrant close attention from a surveyor.
The balsa-cored decks invite water intrusion at stanchion bases and the mast step. Check the compression post below the deck-stepped mast and the surrounding deck area for any sign of sagging. On fin-keel boats, a hairline crack at the forward edge of the keel-to-hull joint — sometimes called the "O'Day smile" — can indicate nothing more than cosmetic gelcoat movement, but can equally signal keel bolts in need of inspection or replacement. Chainplate deck seals have a history of perishing; water stains on interior bulkheads are the tell. Through-hulls on surviving original examples are frequently still the factory plastic fittings and replacing them with bronze or quality composite valves is a standard early task for new owners.
Refits and Upgrades
The O'Day 40's moderate displacement and accessible layout make it a practical refit platform. The osmotic blister treatment, when it proves necessary, follows established protocol: dry the hull, sand back to bare laminate, apply an epoxy barrier coat. It is not glamorous work but it is well-understood and the result is a lasting fix. Deck work — resealing hardware penetrations and addressing any delamination around stanchions or the mast step — is the other common early-ownership investment.
Cockpit lines led to the helm transform the boat's single-handed character substantially, since the sail area is enough to justify an autopilot at nearly all times when shorthanded. Electrical systems on boats of this generation typically benefit from a full audit: replacing corroded wiring runs, upgrading the battery bank, and adding charging redundancy pays dividends well beyond the cost of the work. The Westerbeke diesel, where present, is a serviceable but aging powerplant; parts availability is reasonable, but surveying the raw-water impeller, heat exchanger, and fuel system before purchase is prudent. Some owners have fitted a windvane to complement or replace the autopilot, a sensible addition for any extended offshore work.
The Verdict
The O'Day 40 occupies an honest position: it is not a heavy-displacement bluewater thoroughbred, and it does not pretend to be. What it offers instead is a Briand-penned hull with genuine speed potential, a well-sorted deck, and an interior that can support two couples or a liveaboard couple in real comfort. The construction issues that attend boats of this era — osmotic blistering, deck moisture, ageing through-hulls — are real, but they are knowable and fixable. For a sailor prepared to put in the survey work and budget for the remedial items that will inevitably surface, the fundamental design is sound and the reward is a capable 40-footer that still carries itself well offshore.
Pros
- Briand hull delivers better speed potential and off-wind manners than typical production cruisers of the period
- Generous beam carried aft creates form stability and a flat, manageable motion in a seaway
- Capsize screening figure below 2.0 supports offshore credentials
- Two keel options allow owners to match the boat to their cruising grounds
- Deck layout is practical and thoughtfully detailed, including a period-ahead swim platform
- Interior volume is exceptional for the waterline length, making the boat viable as a full-time liveaboard
Cons
- Balsa-cored hull and deck makes osmotic blistering and moisture intrusion more consequential than on solid-glass contemporaries
- Deck crazing can progress to structural concern if left unaddressed
- Quarter-berth second head is poorly executed and adds little usable privacy
- Fin-keel examples require careful inspection of the keel-to-hull joint for the characteristic forward crack
- Original through-hulls and wiring will need systematic replacement on most surviving boats
