This small, early-1960s coastal cruiser favors stability and shallow draft over outright pace. Its twin-keel hull displaces 3,240 pounds and carries 1,450 pounds of ballast. The boat has a 19-foot waterline, an 8-foot beam, a reported sail area of 238 square feet, and a theoretical maximum hull speed of 5.84 knots.
Design and Construction
Thames Marine built the 670 in fiberglass. The era’s heavily laid-up solid hulls give the boat a substantial feel for its length.
The twin-keel arrangement defines the design. Splitting the ballast between two lateral foils keeps draft to 2.67 feet and allows the boat to take the ground upright on a drying mooring—a practical advantage in the tidal estuaries favored by the British market.
A ballast-to-displacement ratio of about 45 percent places the 670 firmly at the stable, forgiving end of the spectrum for a 22-footer. Its 19-foot waterline and 22-foot overall length indicate modest overhangs rather than a stretched, planing hull.
David Feltham, who later developed the builder’s Mirage 28 and 37 lines in the mid-1970s, drew a conservative pocket cruiser here rather than a racer.
Rig and Handling
The masthead sloop rig carries a reported 238 square feet of sail. That’s a moderate sail plan for a boat of this displacement: enough to drive it in a breeze without demanding a large crew, but underwhelming in light air.
The 19-foot waterline imposes a natural hull-speed limit of 5.84 knots. With twin keels and shallow draft, the 670 trades windward pointing ability for the security of standing upright where a fin-keeler would tip. Its 8-foot beam provides enough form stability to carry the rig without nervousness.
Accommodations
The available sources don’t describe the 670’s interior arrangement. The builder context establishes only the broad fact of 1960s solid-GRP construction, not the details of its joinery.
By proportion, at 22 feet overall with an 8-foot beam, the 670 is a two-person coastal camp cruiser rather than a weekender for four. The twin-keel hull leaves a central, dead-flat floor amidships where a fin would intrude, though this is a consequence of the keel arrangement rather than a documented interior plan.
The Verdict
The Snapdragon 670 is an honest early-1960s Thames Marine product: a shallow-draft twin-keeler with a conservative rig and reassuring ballast fraction, designed by David Feltham at the start of his association with the builder.
It asks little of a short-handed crew and can dry out where deeper boats can’t. On the other hand, it’s slow by modern standards and small by any measure of cruising comfort. As a first classic pocket cruiser, it remains a sensible, well-built introduction to the marque.
Pros
- Twin-keel hull draws only 2.67 feet and takes the ground upright
- Ballast fraction of about 45 percent provides high stability for its length
- Solid, hand-laid fiberglass construction from a known British builder
Cons
- Hull speed of 5.84 knots limits passage pace
- 22-foot length restricts accommodation to coastal use
- Masthead rig and modest sail area are underwhelming in light air
