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Catamarc
An easy to use comfortable folding catamaran
Marc Van Dessel  marc.vandessel@siemens.atea.be

Specifications

Length overall 7.00 m
Length waterline 6.50 m
Length trailering 8.20 m
Beam sailing 3.50 m
Beam trailering 2.50 m
Draught boards up 0.15 m
Draught boards down 1.00 m
Interior headroom 1.80 m
Displacement empty 500 kg
Trailering weight 500 + 200 kg
Sail area 15 or 25 m
Mast height above WL 7.10 to 8.20 m
Sleeps 3 or 4
Sails 4
Building complexity high
Performance good
Luxury high

Description

Two types of trailerable cruising catamarans are seen today:
  • monoblock type (Jarcat 6, Pocketcat 18, …) :
    • limited to 2.50 m wide
    • this limits the length to +/- 6.00 m
  • demountable type :
    • each hull is maximum 1.20 wide difficult to fit a double berth
    • mounting / demounting takes a lot of time + often a specialized telescoping trailer

So we’re stuck with the choice between rather small or rather difficult.   This new design tries to solve all these problems at once:

  • remove the limit in wide and length by making the boat demountable
  • make the mounting/demounting easy by using hinges
  • make it possible to mount/demount on the water no special trailer needed
  • make the hulls asymmetrical to fit a real double berth in the biggest hull

Exterior

The most important feature is that the two hulls are not the same.

The lower parts of both hulls (the floats) are identical. But the top section of the starboard hull is much wider: 1.60 m. The port hull is 0.80 m wide.

The bows are a sharp V. The middle and aft sections are flat.

The cockpit is L shaped and has two parts At starboard there is a fixed part with two opposing benches. When unfolded, a lot of extra cockpit space comes available at port (1.10 m x 3.00 m). At the aft end there is also a bench. A foldaway bench is attached to the port hull.

There are three hinging parts (see folding). The forward hinging part forms a windshield. The middle part is U-shaped to allow people passing through. The aft part moves under the aft bench, forming no obstruction.

The starboard hull contains the float itself and the fixed part of the bridge deck (cabin, cockpit floor and cockpit bench).

The port hull contains the float and also a cockpit bench attached at the stern. During folding, this bench moves behind the starboard cockpit bench. Unfolded, the bench covers the aft hinging part.

The two rudders can kick-up.

For directional stability, two swing-up boards are mounted at the inside of both hulls. They can be raised high for beaching or trailering. The board cases can be simple because they do not have to be watertight. The cases itself are mounted high enough so they don’t generated drag.

Folding

The folding mechanism is very special.

The port hull moves back or forth while staying connected to the starboard hull. Three hinging parts form this connection. They are attached to both hulls using vertical hinges.

The removable cockpit floor is split in two by the middle hinging part. They are raised for folding.

They are attached to the starboard hull by horizontal hinges. When unfolded they are connected to the port hull by bolts. This locks the hinging parts in places and gives enough structural rigidity.

This system allows the folding/unfolding to be done on the water: the hulls remain connected at all time, and the stability when folded is good.

Interior

 

Starboard hull.
This is the main living area.
At the bow side is a king-size berth (1.40 m x 2.00 m).
During the day the right half of the mattress can be folded away. A table can be folded down.
At the stern side is a galley with double burner and place for a refrigerator.
Plenty of storage room is available. Standing headroom at the entrance (1.80 m).

Port hull.
The entrance is forward of the U-shaped hinging part. At the stern side is an extra berth (0.70m x 2.00 m) and storage room.
At the bow side the builder has the option for a separate toilet room or a fourth berth.
Standing headroom at the entrance and in the toilet room.

Stability

Stability is obtained by the width (3.50 m).   Needing no ballast is good for speed and trailering.

Sail

A symmetrical unstayed una rig is proposed.
This has the following advantages:

  • Easy to raise and lower ( no stays, lighter single rig) important for fast launching
  • The masts are placed on the hulls. Less structural tensions than a single rig in the middle.
  • Easy to depower : just let the sail out, even when downwind (no stays)
  • No boom but wishbones no risk for headache, no vang needed
  • Maximum sail surface when going flat downwind.
  • Little interference when close hauled (a ketch suffers from this)
  • At some sail angle, one sail is in the wind shadow of the other. This happens however at the fastest angle, making it less severe.
  • Reefing possible by lowering one sail.
  • Less physical demanding than one big sail.

The builder has the choice between a cruising rig and a racing rig.
The cruising rig has no battens and can be reefed by rolling the sail around the mast.
The racing rig has a big roach and needs battens.
The distance between the masts is greather than the lenth of the wishbones.

Motor

A standard 6 HP 4 stroke outboard motor. It can be mounted between the hulls, attached to the aft side of the starboard cockpit bench.

Trailer

Because the unfolding can be done on the water, a standard flat trailer can be used.

Building technique

Stitch and glue or plywood over frames.
6 and 8 mm ply is used. Every exposed surface is to be covered with glass and epoxy.
The hinging parts are to made of aluminum.

Time to build

Estimated: 700 hours

Cost

9000$ including motor and trailer

Pro's

  • combines easy trailering and good size
  • good performance
  • level sailing
  • easy to use yet powerful rig
  • no stays to connect reduced launching time
  • easy to fold/unfold
  • standard trailer can be used
  • low trailering weight
  • giant cockpit
  • simple hull shape reduces building time
  • good looking
  • standing headroom
  • king-size double berth
  • real toilet with full standing/sitting headroom
  • sleeps 3 (or 4 when no fixed toilet)
  • lots of storage space

Con’s

  • 1.2 m longer for trailering
  • asymmetrical hulls may influence the handling a bit
  • one sail is in the wind shadow of the other when broad reaching
  • construction of hinges is difficult

Drawings

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catame.gif (5729 bytes) catamf.gif (7895 bytes)

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