Diamond 27 Information, Review, Specs

Sailing Performance & Handling

The Diamond 27 was designed by Alan Hill, an architect known for his ability to maximize interior volume without sacrificing seaworthiness. With a displacement-to-length ratio that leans toward the "moderate-heavy" category, the vessel is notably stable and provides a sense of security in a seaway. The boat was typically offered with two keel options: a deep fin for better windward performance or twin (bilge) keels for drying out in tidal estuaries.

On the water, the Diamond 27 is a steady, predictable performer. While it lacks the light-air agility of modern racing-derived cruisers, its high ballast ratio makes it a stiff boat that carries its canvas well as the wind increases. Handlers often note that the boat tracks well due to its longish fin, reducing the helm fatigue often found in more skittish contemporary designs. Owners within the Snapdragon Mirage and Invaders Association frequently highlight the boat's "sea-kindliness," noting that it handles heavy weather with far more grace than its 27-foot length would suggest.

Interior Comfort & Variations

For a vessel under 30 feet, the interior of the Diamond 27 is remarkably efficient. The layout generally follows a traditional plan: a V-berth in the forward cabin, a separate heads compartment, and a main saloon with a dinette that converts into a double berth. A generous quarter berth is often located on the port side, tucked behind the navigation station. The use of molded GRP headliners combined with teak or sapele veneers gives the cabin a classic, functional atmosphere that was a hallmark of Thames Marine’s production during this era.

The Diamond 27 shares significant DNA with its sibling, the Mirage 27. While the Mirage line eventually saw greater commercial success and evolution into the Mirage 28, the Diamond served as a premium alternative at the time of its release, often featuring slightly more refined interior joinery. Headroom is generous for a boat of this vintage, allowing most sailors to stand upright in the main cabin—a luxury that was not always guaranteed in 1970s coastal cruisers.

Known Issues & Buyer’s Checklist

Prospective buyers should approach the Diamond 27 with a checklist focused on the longevity of 1970s fiberglass construction. While Thames Marine built robust hulls, the resins of that era are susceptible to osmotic blistering; a professional moisture meter reading of the hull is essential. Another common "gotcha" involves the deck-to-hull joint. Over decades, the sealant can degrade, leading to leaks that manifest as dampness behind the cabin cabinetry or around the chainplates.

The engine is another primary concern. Many Diamond 27s were originally fitted with Yanmar or Bukh diesel engines. While these are legendary for their durability, parts for older models can be expensive or difficult to source. Check for signs of "re-powering," as a boat with a modern Beta or Nanni diesel holds significantly higher value. Finally, inspect the rudder stock and bearings; some owners have reported play in the steering system after decades of use in high-stress coastal conditions.

Community & Resources

Owners of the Diamond 27 are supported by a dedicated and highly active technical community. The Snapdragon Mirage and Invaders Association (SMIA) serves as the primary repository for technical manuals, original brochures, and maintenance advice for all Thames Marine builds. This association is vital for owners seeking to preserve the historical integrity of their vessels or source specific replacement parts that are no longer in commercial production.

The Verdict

The Diamond 27 is a stout, reliable British classic that offers an affordable entry point into coastal cruising. While its aesthetic and sailing speeds are products of a bygone era, its build quality and clever use of space remain relevant for modern sailors on a budget.

Pros:

• Robust GRP construction suitable for offshore coastal passages.
• Available twin-keel versions are ideal for tidal harbors and drying moorings.
• Strong owner support through the SMIA association.
• Excellent headroom and living space for a 27-foot vessel.

Cons:

• Aged 1970s hulls are prone to osmosis if not properly treated.
• Slower upwind performance compared to modern fin-keel cruisers.
• Original engines may require expensive replacement or specialized maintenance.