Jim Brown / Searunner Searunner 31
trimaran · built 1968–present · approved by moderator
Performance & stability indicators
Calculated from the specifications below. Comparative aids only — not a stability assessment.
| SA/D — Sail area / displacement Power-to-weight ratio of the rig — the classic comparison ratio. Imperial: SA ft² ÷ (displacement lb ÷ 64)^⅔. Higher = more powerful for its weight. | 24.14 (16.15 m² per tonne) |
| BN — Bruce number Power-to-weight indicator of speed potential (√SA ft² ÷ displacement lb^⅓). Below ~1.3 is slow in light airs; ~1.6 reefs early offshore. | 1.23 (23.74 metric scale) |
| BSpd — Base speed Distance a boat could average over 24 hours, empirically derived (Richard Boehmer, 1989). Also used to handicap mixed-fleet races. | 8.85 kn (16.4 km/h) |
| KSP — Kelsall speed prediction Derek Kelsall's performance index (PI-C × 10), expressed in knots — an estimate of speed potential on a reach. A value of 8 ≈ 8 knots in a 10-knot wind. | 7.44 kn (13.8 km/h) |
| Texel — Texel rating (Multihull Dynamics) Multihull Dynamics simplified Texel approximation - matches the numbers they published. LOWER = faster. | 123.4 (lower = faster) |
| Texel* — Texel rating (official / global) The authoritative CTC / Watersportverbond Texel formula - the same core used by OMR (Australia) and Multi 2000 (France). Includes crew weight, so it sits on a higher numerical scale than the MD approximation (identical ordering). LOWER = faster. | 154 (lower = faster) |
| SSpd — Stability speed Wind speed (knots) at which the windward hull of a catamaran (or main hull of a trimaran) begins to lift — Shuttleworth, incl. a 40% gust factor. Higher = more stable. | 20.13 kn (37.3 km/h) |
| KSI — Kelsall stability indicator Indicator of resistance to sideways capsize (Derek Kelsall). Higher = more resistant. | 33.86 (37.3 km/h wind equiv.) |
Specifications
| Manufacturer | Jim Brown / Searunner |
| Model | Searunner 31 |
| Variant | — |
| Year from | 1968 |
| Year to | — |
| Hull type | trimaran |
| Boat style | — |
| Construction | — |
| LOA (m) | 9.5 (31.17 ft) |
| Waterline length (m) | 8.56 (28.08 ft) |
| Beam overall (m) | 5.69 (18.67 ft) |
| Beam waterline (m) | — |
| Hull width (m) | — |
| Beam centreline (m) | — |
| Bridge deck clearance (m) | — |
| Draft min (m) | 0.59 (1.94 ft) |
| Draft max (m) | 1.75 (5.74 ft) |
| Board type | Centreboard |
| Displacement light (kg) | 3175 (6999.67 lb) |
| Displacement loaded (kg) | — |
| Sail area upwind (m²) | 51.28 (551.97 ft²) |
| Sail area downwind (m²) | — |
| Total engine power (kW) | — |
| Number of engines | — |
| Fuel (L) | — |
| Water (L) | — |
| Berths | — |
| Headroom (m) | — |
| Notes | — |
| Sources | sailboatdata.com via Wayback (high) - https://web.archive.org/web/20240520174810/https://sailboatdata.com/sailboat/searunner-31/ |
| approved_by | moderator |
| approved_at | 2026-10-30 20:18:48 |
Official Texel* — propeller adjustment
Texel* above uses a propeller factor of 1 (retractable / unknown). Propellers are commonly swapped between otherwise identical boats, so pick a configuration here to compare like-for-like. Board type recorded: Centreboard (already reflected in Texel*).
Texel* with propellers: —