RAKU 40 PERFORMANCE CRUISING CATAMARAN

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About the Raku 40

The motivation to create this design was prompted by the need for a high performance cruiser that incorporated a practical accommodation platform that resisted the urge for a raised coach house with expansive glass windows, an overly long wingdeck, and a mass of internal creature comforts that are better suited to a villa on shore. 

There's nothing wrong with those features if that's what you want, but there are plenty of boats of that genre already out there in the market place, and there are sailors out there who appreciate the agility and more sporty performance of a lightweight cruiser with a streamlined profile, efficient practical hull shapes, and daggerboards or efficient fixed keels for fast tacking and good windward performance.

 

With Raku 40 we like to think we've created the "sailor's cruiser". That is; a boat that can be built one off economically, can be launched ready to sail at a little over 4 tonnes with an aluminium rig and without resorting to exotic materials or construction methods.

The rig is well aft for a cruiser at 47.5% of LOA from the bow and the wingdeck also terminates well aft of the bow to minimise weight and reduce any chance of slamming. At the same time we have been able to provide an accommodation layout comparable to cruising cats that are far heavier, have considerably more windage, and less efficient rig and sail plan design.

An if you're not happy with that Raku 40 is a platform for the deployment of technologies such as rotating carbon wing mast, a taller rig, custom deck layouts for racing and short handed sailing, and custom laminate specification for platform stiffness and light weight.



Raku 40 Specifications and Sail Areas                  Hull and Displacement Data

LOA

BOA

BEAM CL-CL

 

SAIL AREAS

MAINSAIL

JIB

CODE ZERO

ASSYMETRIC A1

M+ FT 

MAST LENGTH

AIR DRAFT

MAST FROM BOW 

 

12m

7.2m

5.6m

 

SAIL AREAS

57.7 sq.m.

22.8 sq.m.

41 sq.m.

112 sq.m.

80.5 sq.m.

16.5 m

18.25 m

45% LOA

BEAM DWL

B:L RATIO DWL

WETTED AREA

SINKAGE RATE*

MAX DISP. 

MAX RIGHTING MOMENT

TYPICAL SAILING WEIGHT

*This means that if you load the boat by an additional 191kg it will sink 10mm in the water.

 

1036 mm

1:11.58

(2 hulls) 31.5 sq.m

(2 hulls) 191 kg/cm*

7500kg

2100 kg/m

4000-4500kg

All details subject to change without notice


Two Rig Options - Cruising (16m Mast) and Racing (18.8m Mast)



Raku 40 Overall Dimensions (plan)


Shaded Cockpit with ample Seating

Creating the Raku 40 wasn't just an exercise in creating a great performing cat and then figuring at how much accommodation we could cram into it. In fact the design has evolved over a number of years taking into account the efficiency of the rig, the hull forms, the helming arrangement, the layout of the sail controls and in particular the layout of the cockpit.

The cockpit provides not just a practical area for the crew sailing the boat, but a convivial socialising space which, with the open layout adds up to a total length of 5.2m and about 4m in width (depending where you take the measurement).

The roof over the cockpit provides 8.4 square metres of shade and covering all of the seating in the cockpit when the sun is overhead.

The cantilevered roof over the cockpit is supported by two beams extending inside the saloon to minimise clutter in the cockpit

On an earlier version of this design we offered the option of bulkhead mounted helm stations but we have left them off this version because of the other design features we have been able to incorporate. You could still incorporate the bulkhead mounted helms but this requires a different cockpit layout with the aft berths moved further aft.

 


Screen Shots from the Drafting Table


Raku 40 Displacement and Trim

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 long term 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.


Raku 40 Design Options

1. Accommodation Layouts

The standard layout includes a central bathroom in the stbd hull and a second bathroom forward in the port hull. A four cabin arrangment is available with central bathrooms in both hulls. Also, berths can be installed on the wingdeck forward of the mast of preferred. In this case there is the option of having forward located bathrooms in both hulls.

 

2. Cockpit.

Two optional layout are available: one with the helm station aft beside the aft aft beam, the other helm station on the saloon bulkhead. For the aft helm option is is preferable to have twin helm stations to ensure good visibility.

For the forward helm station two is preferable but one will work fine.

 

3. Engines

Inboard diesels are preferred for open ocean sailing and security for bar crossings, but outboards can be fitted if the boat is primarily operating in protected waters.

We also have detailed specifications and performance prediction figures for Oceanvolt electrical power systems.

 

4.Rudders and steering.

The standard design is for underhung balanced spade rudders but plans for transom hung rudders are available as an option. Direct link steering is preferred but hydraulic systems are a viable option.

For transom hung rudders tiller steering is an option.

 

 

 

 

5. Daggers and Fixed Keels

The standard design comes with daggerboards and cases with fixed keels available as an optional design feature. For kit construction the price of the materials is the same or both options.

 

6. Longeron and Forebeam

The longeron and forebeam are both built from composite panels with carbon fibre reinforcements. The standard longeron is the same lengyh as the hulls so owners will not be penalised when marina fees are calculated on the overall length. For those who want to carry a large gennaker the option is either a custom made longeron or an extension piece that extends the longeron and is supported by brace lines to the inboard hull sides.

 

7. Rig and Sail Plan

A standard rig and sail plan drawing is provided in the plans and we are happy to recommend experienced rig builders and sail makers. A number of options are availble at the discretion of the owner including a taller rig and choice of carbon or alloy rig, rotating or not rotating.



Raku 40 Deck Plan (details in progress)


Raku 40 classic accommodation layout

We've been using variations on this layout on many of designs over a long period of time and it's still a favorite with a lot of owners, especially those who prefer a sense of security in the saloon when the weather turns adverse.

We've retained a reasonably wide opening in the saloon door (1.5m) and this can be further reduced to provide more bench space in the saloon if preferred.

Port Hull

The standard layout provides for an owner's cabin in the port hull and two berths in the stbd hull. The aft berth is 1.4m wide at the height of the berth panel, but the inboard hull side flares out quickly above the panel so at sleeping height it is 1.5m or more wide depending on the height of the mattress. All of the berths are 2m long.

Stbd Hull

The central bathroom in the stbd hull is part of the standard arrangementbut there is also the option of fitting out the stbd hull the same as the port hull or the same as the stbd hull in the open version.



Raku 40 open accommodation layout

The open layout features a 2.4m wide opening in the bulkhead between the saloon and the cockpit, effectively creating a spacious, airy living space that is ideal for the tropic and temperate climates.

In adverse conditions the saloon can be sealed off from the weather with drop down vinyl clears or with solid infill panels that clip into place and store in the cockit lockers while not in use.

The saloon features a large lounge pad forward to port that can be used as a double bed  for occasional guests or simply serves as a great lounging area.

Forward to starboard is a couch that is also wide enough to serve as a single berth.

Down below you can use the layout we've suggested here or change it to suit your own preferences.

Starboard Hull.

Given the amount of sleeping space in the saloon the forward berth is not essential and that space could be well deployed for storage. If it is used for sleeping the access can be through the stbd bathroom, or you can seal that bulkhead off and use it as a crew cabin with access through the deck hatch.

Port Hull

The owner's cabin allows for a generous bathroom forward with the toilet and washbasin separated from the shower compartment with a bulkhead that can be fitted with a door to prevent shower water splashing into the rest of the bathroom. The area between the bathroom and the sleeping cabin is open for creative deployment of office space or storage of personal items.

The standard plan allows for a sill at the saloon opening to comply with the ISO stands and prevent water washing into the saloon in case of a boarding wave. The sill can be removed to provide a continuous floor between the cockpit and the saloon but in this case there should be provision to close off the passage from the saloon to the hull accommodation, and a drain should be fitted across the bulkhead opening.


Build from a Kit or Order Fully built to Sail Away