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KD 650 Plans

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21' 4" / 6.5m
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The KD 650 is an other approach for an affordable trailer catamaran for amateur construction. The boat is designed for coastal sailing and will have a good turn of speed with its efficient Gunter rig.

The boat is easy to build with plywood/glass/Epoxy construction. The first time DIY boat builder will have no problem building the boat. With the asymmetrical hulls, no dagger boards are necessary to go as well to windward as any very good mono hull.

To avoid the high costs for the rig, i.e. mast and rigging, the boat sports a modified Gunter rig. I "modernized" the rig so that only one halyard is necessary. The yard is fixed to the mast. The mast is free rotating. The result a semi wing sail. The plan shows how to build the mast from an Aluminum tube and some hardware. The gaff is made from clear fir, UD- carbon and glass cloth.

This Gunter rigged boat is a J class boat from Germany. This class is very old but still active. The Gunter rig main sail resembles a wing.

The beams are made from readily available Aluminum tubes. Besides cutting them to length, there is nothing to do. This will shorten the construction time by about 40% compared to boats where wooden beams have to be built.

The set up time, once at your favored sailing ground, is short. To make sure of this, I designed a quick beam fastening system. Only four nuts have to be fastened to fix the beams. The mast is only 4.3 m long and weights a mere 9 kg. Setting up the boat will take 2 people no more than an hour. This will be no different on a beach or in a port.

This picture is from a customer in Poland The boat is almost ready to go.


  • Modern Gunter rig. Easy to build by your self and very efficient.
  • The beams are fastened with a unique quick fastening system and four nuts. Easy to transport on a trailer.
  • Trailing width 2m.
  • The weight of a hull will be under 90 kgs.
  • In each hull is enough space to sleep 2 persons.
  • In one of the hulls there is space for a toilet.
  • Good height for comfortable sitting.
  • A small pantry can be added.
  • The hulls are a-symmetrical to avoid dagger boards.
  • The a-symmetry is 1/3 to 2/3.
  • For easy of construction AL. tubes for the beams are used.
  • Construction is ply wood/glass/Epoxy composite.
  • Construction time will be around 500 hours


Easy set up trailer catamaran.
The rig is a modernized one halyard Gunter rig.
The boat will be relative sea worthy and fast. Offers bunks for 4 persons.
LOA hulls - 6.50 m without rudders
Beam c/c - 3.00 m
Beam Catamaran - 3.50 m
Beam on Trailer - 2.00 m
Draft hull/rudders - 0.33/0.54 m
Weight empty - 340 kg
Weight CWL - 760 kg
Sail area - 18.6 m²
L/B hulls - 1 : 16.6
Prismatic coefficient - 0.568
L/B ratio center line - 50 %
Construction time - about 500 hours
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Additional Information

Designer Name:
Bernd Kohler
Sail area (Imperial / Metric):
200 sq. ft / 18.6 sq. m
Rig Type:
Length (range):
16' - 23'11" / 4.88m - 7.29m
21' 4" / 6.5m
Length at Waterline:
21' 4" / 6.5m
9' 10" / 3m
Hull Weight:
200 - 999 lbs / 90.72 - 453.14kg
Estimated Hull Weight:
750lbs / 340kg
12" - 35" / 30.48 - 91.23cm
Unloaded Draft:
1' 1" / 0.33m
Weight Capacity:
926lbs / 420kg
Primary Material:
Marine Plywood
Method of Construction:
Stitch and Glue
Hull Type:
Hull Shape:
Flat bottom
Power Source:
Built-in Floatation:
Unit of Measure:
Instruction Manual:
General Instructions and Sequence
Lofting Required:
Recommended Experience Level:
Designer's Thoughts on Experience Level:
Chuck Leinweber's suggestion
Boat Type:
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