Production ran from 1985 to 1993, and 125 boats were completed. The design emerged from a competition between Thomas and Rob Humphreys, initiated by the Royal Thames Yacht Club and the RORC to create a strict one-design offshore fleet. Conceived as a fast cruiser-racer with genuine offshore capability, the Sigma 38 has since established strong fleets in the UK and Ireland. The broader Sigma family also has proven Fastnet experience.
Design and Construction
The Sigma 38 OOD has robust fiberglass construction, with a solid hull and a balsa-cored deck. Below the waterline, an elliptical fin keel with a lead bulb on a cast-iron stub provides a 41% ballast ratio and a draft of just over two metres.
The hull has enough forefoot to avoid slamming, while its aft section is flat enough to surf. A spade rudder controlled through a 42-inch wheel gives a beautifully light helm.
A large stainless steel T-piece laminated into the hull carries the shroud loads. Inboard chainplates and a swept-back, double-spreader rig help keep the decks clear. A cruising version was also offered, but only a handful were built, and the differences from the standard OOD were minimal.
Rig, Handling, and Performance
The 7/8ths fractional rig concentrates much of the sail area in the mainsail. The total sail plan measures 691 square feet, producing a 19% sail-area-to-displacement ratio.
The boat goes about cleanly. Running backstays fitted to the 7/8th rig open the leech of the main and genoa and tension the forestay in conditions above Force 3, sharpening performance when things get fruity. The primary winches sit at the aft end of the coachroof and have a 52:1 ratio more commonly found on a 50-footer. The mainsheet traveller is just ahead of the helm.
Writing in Yachting Monthly, test sailors found the Sigma 38 responsive and stable. Its turning circle to starboard was just over one boat length, while the spade rudder produced a light helm through the 42-inch wheel. In reverse, the shaft drive caused only a small kick to port, which the boat quickly overcame.
Cockpit and Accommodation
The cockpit seats four or five people for cruising. A binnacle-mounted throttle and nearby mainsheet controls help when sailing single-handed, and there’s a deep lazarette beneath the helm seat.
Below, the Sigma 38 OOD has a practical layout for six to eight crew. Two 6ft 8in settees make good sea berths, supplemented by two pilot berths outboard. Forward, the vee-berth bunks flip up to reveal a large storage cage.
Headroom at the foot of the companionway is 6ft 3in, although the steep steps demand some agility from the crew. A proper navigation station sits to port. Opposite it, the longitudinal starboard galley has a top-loading fridge but limited work surface.
Two aft cabins contain equal-length double berths. The port cabin also has a small washbasin above the engine bay.
Machinery and Access
Most boats left the factory with 28hp Volvo engines, though many have since been re-engined. A removable box at the front provides engine access, while panels in the aft cabins give side access to the gearbox and stern gland.
The forehatch measures a substantial 600mm square, which is vast by modern standards.
Known Issues and Upgrades
Surveyor Ben Sutcliffe-Davies notes that the balsa-cored decks commonly soften on these boats and that the alloy toerail can guide the eye to prior impact locations. Hull-to-deck joints should be monitored for collision damage, and the gooseneck fittings wear with use.
Former class chairman Nigel Goodhew says the laminated shroud T-piece has often required reinforcement. This is a manageable job within the class’s established expertise. The structural matrix around the keel can also delaminate after a grounding.
Many owners have upgraded keel security by fitting larger backing plates and adding laminate to the internal matrix frame.
Ownership and Class Support
An active class association and the boat’s one-design discipline give owners straightforward access to shared knowledge and spares. Because the cruising version differed only minimally from the standard OOD, most boats also share the same core platform.
The Verdict
The Sigma 38 OOD is a deceptively quick and powerful offshore one-design that remains manageable for smaller crews—a sheep in wolf’s clothing, as the phrase goes. Its Thomas-designed hull and rig suit both club racing and shorthanded cruising, while the class’s continuity keeps support close at hand. Buyers should, however, budget for careful attention to the deck and structure.
Pros
- Fast cruiser-racer with proven offshore lineage and active fleets in the UK and Ireland
- Light helm, clean tacking, and a tight turning circle from the spade rudder and fractional rig
- Practical six-to-eight-berth layout with sea berths and a proper navigation station
Cons
- Balsa-cored decks are prone to softening, and the keel matrix is vulnerable in groundings
- The shroud T-piece often requires reinforcement, while gooseneck wear is common
- Steep companionway steps and limited galley work surface require agility and compromise
