Bunyip 20 — Information, Review, Specs

Lock Crowther·1962·Plans for home builder
Bunyip 20 drawingBuilder drawing
Hull type
Trimaran · daggerboard
Rig
Masthead Sloop
LOA
20' · 6.1 m
Displ.
700 lbs · 318 kg
First year
1962

The Bunyip 20 is a seminal Australian multihull design that holds a significant place in the history of performance sailing. Designed by the legendary naval architect Lock Crowther in 1959, when he was just a teenager, the vessel was a pioneering open trimaran that helped spark the global interest in multihull racing. Originally built as a day racer, the Bunyip 20 features a 20foot (6.1meter) main hull supported by two outriggers (floats), designed to provide high levels of stability and speed relative to its length. According to historical records preserved by Small Trimaran, the design was a reaction to the emerging Cclass catamaran racing trends of the time, emphasizing simplicity and raw pace. While early models were constructed of plywood, the design’s success eventually led to more sophisticated fiberglass and composite builds as Crowther’s reputation as a worldclass designer grew.

Measurements

Dimensions 01

LOA
20 ft
LWL
18.6 ft
Beam
11 ft
Draft
3 ft
Max headroom
-
Air draft
-

Construction & hull 02

Construction
Fiberglass (Plywood Core)
Hull type
Trimaran
Keel type
Daggerboard
Ballast
-
Displacement
700 lbs
Water
-
Fuel
-

Rig & sails 03

Rig type
Masthead Sloop
P · main luff
-
E · main foot
-
I · fore ht.
-
J · fore base
-
Forestay (est)
-
Sail area
227 sqft

Calculations 04

SA/D ratio
46.07
Ballast/Disp.
D/L ratio
48.56
Comfort ratio
2.33
Capsize screening
4.96
Hull speed
5.78 kn

Sailing Performance & Handling

The Bunyip 20 was designed for aggressive day racing and is known for a "wet" but exhilarating sailing experience. Its performance is rooted in a high power-to-weight ratio, carrying approximately 227 square feet of sail area on a lightweight 20-foot frame. This allows the boat to accelerate rapidly and plane in conditions where monohulls of similar size would struggle to reach hull speed. Historical reports indicate that the original Bunyip was capable of defeating established catamaran designs, such as the Austral 20, due to its superior tracking and efficiency upwind.

Handling the Bunyip 20 requires an active crew. The boat typically utilizes a centerboard for lift and maneuverability, while the narrow main hull provides a fine entry to pierce waves. A notable characteristic of the early designs was the use of flat-bottomed floats. While intended to provide hydrodynamic lift, these often created significant drag in choppy water, a detail noted in technical retrospectives of Crowther’s early work. Later refinements and the subsequent "Kraken" series siblings moved toward fuller, more buoyant floats to improve sea-kindliness. Because the boat is an open trimaran, it sits low to the water; at high speeds, the full bow of the main hull can create significant spray, often saturating the crew.

The Bunyip 20 is most famous for its debut at the 1960 Easter Regatta at Paynesville, Victoria. Sailed by Lock Crowther and his family, the boat won its division against a massive field of 300 competitors, an event widely credited with launching Crowther’s career and establishing the trimaran as a viable racing platform in Australia. This victory is documented in various historical sailing archives and remains a point of pride in the Australian multihull community. While it has not appeared in major cinematic productions, it is a frequent subject of technical discussion in books detailing the evolution of multihull design and the legacy of Crowther Design.

Known Issues & Buyer’s Checklist

Prospective owners of a Bunyip 20, particularly older timber examples, must be diligent during inspection. The primary concern is the structural integrity of the crossbeams (akas) and the attachment points between the hulls.

  • Plywood Rot: Most original Bunyips were built using 3/16" sheet plywood on wooden frames. Buyers should check the "stiches" and joints for soft spots, particularly in the bilges of the floats and around the centerboard trunk.
  • Float Buoyancy: Early flat-bottomed floats are prone to "burying" if the boat is pushed too hard in heavy air. Ensure the floats are airtight and that any subsequent modifications for increased buoyancy were performed professionally.
  • Rigging Tension: As a high-performance boat, the mast step and chainplates undergo significant stress. Inspect the wooden mast (if original) for longitudinal cracks and ensure the deck remains stiff under load.
  • Keel/Centerboard Pivot: Check the centerboard for excessive play or wear in the pivot pin, which can lead to vibration at high speeds and water ingress.

Community & Resources

The primary hub for owners and historians is the legacy documentation of Crowther Design. Technical information is often shared through multihull-specific organizations such as the Multihull Yacht Club of Victoria (MYCV) and the broader Australian Multihull Sailing Association. While no longer in active production, plans and technical specifications are occasionally archived by maritime museums and specialized multihull enthusiasts who maintain "small tri" databases.

The Verdict

The Bunyip 20 is a piece of maritime history that continues to offer high-speed thrills for the minimalist sailor. It is an uncompromising day racer that demands skill and rewards it with a visceral connection to the water.

Pros:

  • Historic design with a pedigree from a master naval architect.
  • Exceptional light-air performance and high speed-potential.
  • Lightweight and relatively easy to trailer for a 20-foot boat.

Cons:

  • Lacks any interior accommodations; purely a day-sailing vessel.
  • "Wet" ride ensures the crew will be exposed to significant spray.
  • Requires frequent maintenance if built from the original plywood specifications.

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