Raku 40 Squareback version
Raku 40 inboard profiles with balanced spade rudder and mini keel.
Raku 40 inboard profiles with dagger boards and transom hung rudders
Displacement Case 1. DWL (max disp)
Volume Displacement = 7066kg
Length to Beam Ratio Hull 11.8:1
Wing clearance: 820mm at lowest point
Displacement Case 2. DWL-50mm
Volume Displacement = 6140kg
Length to Beam Ratio Hull =12:1
Wing clearance 870mm at lowest point
Displacement Case 3. DWL-100mm
Volume Displacement 5276kg
Length to Beam Ratio Hull 12.2:1
Wing clearance 920mm at lowest point
Displacement Case 4. DWL-150mm
Volume Displacement = 4446 kg
Length to beam Ratio Hull 12.54:1
Wing clearance at lowest point 970mm
The images you see on these pages are made with the boat sitting on its designed waterline (DWL) which is where it will sit at a weight of 7066kg and the transom just clear of the water. (45mm).
Typically a boat of this size and style will be launched ready to sail somewhere between 4000kg and 4500 kg fully fitted ready to sail including inboard 35HP diesels and an aluminium rig.
In cruising mode the boat will typically weigh somewhere between Case 2 and Case 3 (column at left) and if fully loaded for longterm cruising the boat might be sitting close to the DWL at around seven tonnes. So the payload is somewhere between 2.5 and 3 tonnes.
As the figures show the WL beam is finer for the lighter boat. For this style of boat we avoid having the waterline any finer than about 1:13 because the higher sinkage rate limits payload and reduces wing clearance. It also increases wetted area which is a hindrance to performance in lighter conditions.
The drawing above shows the internal headroom clearance on the cabin CL. Maximum headroom at the cabin BH is 1869mm or 6'1.5". The wing clearance is measured from the Datum WL at the maximum displacement of 7066kg. At the realistic cruising displacement figure of 5276kg the wing clearance is 920mm -a generous allowance that will allow the boat to safely handle rougher sea conditions.
For the open cabin version with no sill at the companionway there is a transverse beam under the wingdeck and a grate to allow water to disperse quickly before it can enter the saloon. The wingdeck slopes aft to assist drainage.
The cabin top is free standing - supported by fore and aft beams at each side. Not having support poles for the cabin top provides freedom of movement and a minimum of clutter in the cockpit.
The combined Newsletter for Grainger Designs and Rocket Factory Trimarans
Our DuFLEX kit systems streamline the construction process for amateurs and professional yards alike. More details here…