Bostrom B-31 Information, Review, Specs

Sailing Performance & Handling

The Bostrom B-31 is a masthead sloop characterized by a moderate displacement hull, a fin keel, and a skeg-hung rudder. With a displacement-to-length ratio that leans toward the heavier side of the performance-cruiser spectrum, the boat offers a stable and predictable motion in a seaway. Its narrow beam (approximately 2.78 meters) and deep V-shaped sections forward allow it to slice through chop without the pounding typical of modern, flat-bottomed designs.

Under sail, the B-31 is known for its impressive upwind ability. It tracks exceptionally well, a trait often attributed to the well-balanced skeg-rudder configuration. While it may not be a light-air flyer due to its wetted surface area, it comes into its own when the breeze exceeds 12 knots. Owners frequently report that the boat feels stiff and secure, rarely needing to reef before a stiff Force 4 or 5. The cockpit is deep and well-protected, though the narrow beam results in a tighter working space for the crew compared to contemporary 31-footers.

Interior Comfort & Variations

The interior of the B-31 is traditional, utilizing a layout that maximizes the limited beam. Most models feature a classic arrangement: a V-berth in the bow, a small head compartment, and a main salon with facing settees. A compact galley is usually located to port of the companionway, with a navigation station or a quarter-berth to starboard.

Because many B-31s were sold as "half-finished" kits, the interior materials and craftsmanship vary significantly from one hull to another. Factory-finished models typically boast high-quality teak joinery and a professional level of plumbing and electrical installation. In contrast, amateur-finished boats might feature varied wood species or non-standard layouts. There were also two primary iterations of the deck mold: the MK I and the MK II. The MK II version is generally more sought after, as it features a revised cabin trunk that provides slightly more standing headroom (approximately 1.80m) and a more modern window configuration, which brightens the otherwise snug cabin.

Popular Mentions & Media

While the B-31 has not been a frequent star of major cinema, it has a robust "cult" following in the European sailing community. It is frequently featured in Swedish sailing periodicals like Praktiskt Båtägande, which has profiled the boat as a premier choice for budget-conscious sailors looking for a "blue water capable" small yacht. The boat’s reputation for durability is such that several hulls have completed circumnavigations, and it remains a staple in long-distance cruising vlogs and blogs originating from Scandinavia.

Known Issues & Buyer’s Checklist

Prospective buyers should approach the B-31 with a focus on its construction history and age-related wear.

• Kit Quality: Because of the high volume of owner-finished boats, the primary concern is the quality of the original installation of the engine, electrical system, and seacocks. Inconsistent wiring is a common "gotcha" in this model.
• Osmotic Blistering: Like many yachts built in the 1970s, the B-31 is susceptible to hull blisters. A professional moisture meter reading is essential during a survey.
• Keel-to-Hull Joint: The transition between the lead or iron ballast and the fiberglass stub should be inspected for "the smile"—a crack at the leading edge that may indicate the need for re-bedding the keel or tightening keel bolts.
• Rudder Skeg: The skeg-hung rudder is robust, but the bushings can wear over time, leading to play in the steering. Check for any lateral movement in the rudder stock.
• Engine Replacement: Many original B-31s were equipped with Volvo Penta MD7A or similar raw-water cooled engines. Many of these have reached the end of their service life, so buyers should look for vessels that have been repowered with modern freshwater-cooled diesels.

Community & Resources

The most authoritative resource for this model is the B31-klubben, an active owner's association based in Sweden. They maintain a technical archive and a registry of hulls that is invaluable for verifying the history and original specifications of a specific boat.

The Verdict

The Bostrom B-31 is a rugged, aesthetically pleasing cruiser that offers a level of seaworthiness often missing in modern production boats of the same size. While its interior may feel cramped by today’s standards, its performance in heavy weather and its structural pedigree make it an excellent choice for serious coastal or offshore sailors on a budget.

Pros:

• Exceptional upwind performance and tracking.
• Robust construction with a protected skeg-hung rudder.
• Classic, attractive Scandinavian lines.
• High availability and affordable entry price on the European market.

Cons:

• Narrow beam limits interior living space and cockpit comfort.
• Wide variance in interior finish quality due to kit-building.
• Headroom is restrictive for taller sailors, particularly in MK I models.
• Original engines are likely past their prime and require replacement.