Design and Construction
The hull is solid fiberglass, with a swing keel that pivots to lift clear of the bottom — a pivoting lifting keel that lets the 678 BT sail both coastal waters and shallow inland lakes. With the keel down her draft runs about 1.0 to 1.3 feet depending on load, so she can be beached or dried out alongside a ramp, and with it raised she trails and launches easily. The wing-keel configuration and 770-pound iron ballast on a 3,300-pound displacement give a ballast ratio of 23 percent, which the design data places higher than only 4 percent of similar sailboat designs — she is lightly ballasted for her size. A length-to-beam ratio of 2.92 and a reported interior spaciousness greater than 54 percent of comparable designs mark her as relatively beamy and roomy for a 24-footer, while the solid fiberglass deck and hull keep the structure straightforward.
Rig and Performance
She is built with a fractional sloop rig, and the sheet specifications are practical and uniform: jib and genoa sheets are 7.4 meters long and 10 mm in diameter, the mainsheet runs 18.6 meters at 10 mm, and the spinnaker sheet is 16.3 meters at the same 10 mm diameter. A sail-area-to-displacement ratio of 17.95 and a displacement-length ratio of 196 place her among what the data calls "moderate racers," light and responsive rather than heavy-displacement cruising fare. Her theoretical hull speed is 5.9 knots, with a wetted surface of about 18 square meters and an immersion rate near 568 pounds per inch, so she sits lightly and accelerates readily. The capsize screening value is 2.24 — a number that shows she would not be accepted into ocean races — and her Motion Comfort Ratio of 14.3 is more comfortable than 31 percent of similar designs, so she is a fair-weather coastal boat whose motion is what you would expect from a small, light hull.
Accommodations
The design comparison data shows the 678 BT's hull layout is more spacious than 54 percent of all other similar sailboat designs, a meaningful advantage in a boat this size where every inch counts. That relative roominess, combined with the beamy 8.33-foot width and the lifting keel that frees up interior volume, makes her a practical weekender for sheltered waters rather than a cramped pocket cruiser.
The Verdict
The Tes 678 BT is a purpose-built small sailboat for sailors who want a trailerable, beachable coastal and inland cruiser with surprising room for her length. Siwik's design trades offshore capability for shallow-water freedom and easy handling, and the numbers back that up as a consistent lightweight racer-cruiser profile.
Pros
- Pivoting swing keel allows coastal and inland sailing with beaching capability
- Roomy relative to comparable 24-foot designs
- Light, responsive moderate-racer performance with practical fractional rig
Cons
- Capsize screening value excludes her from ocean racing
- Low ballast ratio relative to peers
- Motion comfort below median for similar boats
