Sigma 400 Information, Review, Specs

Sailing Performance & Handling

Under sail, the Sigma 400 is widely regarded as one of David Thomas’s most balanced designs. It features a high-aspect masthead sloop rig and a deep, lead-ballasted fin keel that provides exceptional stiffness. According to an editorial review by Yachting Monthly, the boat is notably more stable than the Sigma 38, allowing it to carry its canvas longer as the wind increases. The rudder is a deep, semi-balanced spade that provides high-fidelity feedback to the helm, making the boat a joy to steer even when pressed hard upwind.

With a displacement-to-length ratio that leans toward performance, the 400 tracks with precision and exhibits very little of the "twitchiness" associated with lighter racing yachts. The cockpit layout is optimized for short-handed sailing, with primary winches situated within reach of the helmsman, though it maintains the space required for a full racing crew to operate efficiently. Owners often report that the boat finds its groove easily at 30 degrees to the apparent wind, maintaining speeds that rival modern "production" cruisers of much greater length.

Interior Comfort & Variations

Unlike the earlier Sigmas, which were often criticized for their utilitarian, "form-follows-function" interiors, the Sigma 400 was finished to a standard intended to compete with Scandinavian builders like Hallberg-Rassy or Najad. The interior is characterized by extensive use of high-quality woodwork, typically finished in American cherry or rich teak, which creates a warm and traditional maritime atmosphere.

The standard layout features three separate cabins: a generous forward V-berth with an en-suite head and two symmetrical aft cabins. A second day-head is usually located to the starboard side of the companionway. The salon is centered around a large U-shaped seating area with a fixed table, providing ample space for six adults. A key variation in the hull’s sibling line is the Sigma 41, which preceded it; however, the 400 utilized a more modern, beamier aft section to improve off-wind stability and increase the volume of the aft cabins. The galley is typically L-shaped and equipped with a deep refrigerator and twin stainless steel sinks, reflecting its design as a serious offshore cruiser.

Known Issues & Buyer’s Checklist

While the Sigma 400 is a robustly built yacht, prospective buyers should pay close attention to several areas common to Marine Projects builds of this era.

• Deck Core Integrity: Like many yachts of its generation, the Sigma 400 uses a balsa-cored deck. Buyers should use a moisture meter or perform a "tap test" around stanchion bases and the windlass, as leaks in these areas can lead to core saturation and delamination.
• Keel-to-Hull Joint: Given its performance pedigree, some 400s have been campaigned heavily. It is essential to inspect the "Sigma smile"—a hairline crack at the leading edge of the keel-hull join—which may indicate the need for re-torquing keel bolts or reinforced glasswork.
• Rod Rigging: Some performance-oriented units were fitted with rod rigging. If the rigging is more than 10-12 years old, it requires a specialized ultrasonic inspection or total replacement, which is significantly more expensive than standard wire rigging.
• Engine Maintenance: Most models were originally fitted with Volvo Penta 2040 engines. Potential buyers should check for evidence of exhaust elbow clogging or heat exchanger leaks, which are common maintenance items for this powerplant.

Community & Resources

The Sigma 400 benefits from one of the most dedicated owner communities in the United Kingdom. The Sigma Owners Association serves as a vital technical repository, offering advice on everything from rig tuning to interior renovations. Because the boats were built in the same yard as Princess Yachts and many early Moodys, technical support for the hull and structural components is relatively accessible through UK-based marine surveyors familiar with Plymouth-built vessels.

The Verdict

The Sigma 400 remains a standout choice for the discerning sailor who refuses to compromise on sailing dynamics for the sake of volume. It is a "sailor’s boat" through and through, offering a level of build quality and sea-kindliness that is often missing in contemporary mass-market yachts.

Pros:

• Exceptional upwind performance and stiffness.
• High-quality interior joinery far superior to earlier Sigma models.
• Proven David Thomas design with a strong pedigree.
• Well-balanced for both club racing and serious offshore cruising.

Cons:

• Balsa-cored decks require diligent maintenance to avoid moisture issues.
• The deep draft may limit access to some shallow cruising grounds or marinas.
• Interior volume is less than modern 40-footers with "wide-beam" stern designs.