9m Trailerable Catamaran

Mini Coastal Cruiser

Design Update

The new Mk. 2 folding beams have been updated to make the beam to hull joints much stronger. The beam now has a hi-tensile aluminium plate with 6 x 12mm bolts securing it to the hull directly over a structural frame. This means a slight modification to the hull decks, the new study plans will show this change.

Also new is the addition of a screecher, which is a very useful sail. Check study plans for dimensions. The spinnaker also comes with a sock for ease of raising and lowering. Surtees Multihull Designs have a great price on a full set of sails made by professional sail makers here in Australia who have many years of experience in both sail making and racing multihulls.


The 9m (29' 6") trailerable catamaran is my latest design with an estimated build cost of under $30 000. This catamaran is ideal for a weekender or mini coastal cruiser.

This catamaran's turning ability is outstanding due to the addition of a centre-board and the bow/stern of the hulls being clear of the water. Tacking is positive with no need to backwind the headsail. Sea trials to date show a sea kindly motion with heeling of less than 2 degrees. At 10 knots of speed the mast leeward stays remain taught due to no structural flexing. In future sea trials the light air drifter attached to the prodder will be tested along with strong wind sailing under reefed mainsail.


  • The bows of the hulls have a 300mm soft foam crash absorber with a water-tight bulkhead behind.

  • The hulls forward underwater profile has been designed to ride over submerged obstacles, ie. metal shipping containers, tree trunks etc.

  • Kick up centre-board is completely clear of the water when raised in the centre pod. Transom mounted rudders are also kick up elimiating damage to the most important component of the boat.

  • There are no through hull fittings, meaning no possible ingress of water.

  • There are three watertight compartments in each hull.

  • A conservative rig and sail plan mimises possible capsize in sudden strong wind gusts.

  • Due to foam and plywood construction, this gaurantees this catamaran is unsinkable.

  • If boat is moored or berthed at marina it is possible to trailer the boat on land and secure it in the event of a cyclone.

  • 300mm (1ft) draft allows access to more sheltered water.


A cruising mainsail is shown on the study plan but a racing/cruising fully battened mainsail will increase the overall horsepower which will give sparkling sailing performance.

Note – The hulls and mast are easily raised and lowered using the electric trailer winch. The structural aluminium beams have a 34 tonne shear load rating. This cat is over engineered to provide utmost safety in every aspect of the design.

Updated MkII Study Plan

[Click to enlarge]


Building components and materials were chosen with the owner builder in mind. Hulls are PVC structural foam and the centre cabin is ply and epoxy. The design is based around home construction (very little space required) as well as providing safe trailer storage rather than expensive moorings or marina berths which are becoming out of reach to average owners and sailors.

I will make available the complete folding beams for people wishing to buy them.

The study plans show a conservative rig as this boat is designed as a mini cruiser not a racing boat (however a racing version may be offered to those interested).


Due to my wife’s input regarding interior layout, please note that the navigation table has been replaced with a porta-loo (toilet) and stand up shower (when overhead hatch is raised).

Under the galley top is a 60 litre water tank built in. A large ice box which can also be used as a seat between the bunks. Now that this design is nearing completion many small changes have developed and these will be incorporated into the plans.

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