Design and Construction
The 678 BT has a solid fiberglass hull and deck. Her swing keel pivots clear of the bottom, allowing her to sail both coastal waters and shallow inland lakes. Draft with the keel down is about 1.0 to 1.3 feet, depending on load. She can be beached or dried out alongside a ramp, while raising the keel makes launching and trailering easier.
The wing-keel configuration carries 770 pounds of iron ballast on a displacement of 3,300 pounds. That gives a ballast ratio of 23 percent, which the design data places higher than only 4 percent of similar sailboat designs. In other words, she is lightly ballasted for her size.
Her length-to-beam ratio is 2.92, and her beam is 8.33 feet. The design data also reports more interior spaciousness than 54 percent of comparable boats, making the 678 BT relatively beamy and roomy for a 24-footer. The solid fiberglass hull and deck keep the structure straightforward.
Rig and Performance
The 678 BT carries a fractional sloop rig. The specified sheets use practical, uniform sizing: the jib and genoa sheets are 7.4 meters long and 10 mm in diameter, the mainsheet is 18.6 meters long and 10 mm in diameter, and the spinnaker sheet is 16.3 meters long with 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.” She is light and responsive rather than a heavy-displacement cruiser. 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.
Her capsize screening value is 2.24, a figure that means she wouldn’t be accepted into ocean races. The Motion Comfort Ratio is 14.3, making her more comfortable than 31 percent of similar designs. These figures point to a fair-weather coastal boat whose motion is in keeping with a small, light hull.
Accommodations
The design-comparison data shows that the 678 BT’s hull layout is more spacious than 54 percent of similar sailboat designs—a meaningful advantage in a boat this size, where every inch counts.
That relative roominess, together with the 8.33-foot beam and the lifting keel that frees up interior volume, makes her a practical weekender for sheltered waters rather than a cramped pocket cruiser.
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. The numbers support that consistent lightweight racer-cruiser profile.
Pros
- Pivoting swing keel supports coastal and inland sailing, with beaching capability
- Roomy compared with similar 24-foot designs
- Light, responsive “moderate racer” performance
- Practical fractional rig
Cons
- Capsize screening value excludes her from ocean racing
- Low ballast ratio compared with similar boats
- Motion comfort below the median for comparable designs
