Mike Coates describes the evolution that has made the International
2.4mR Class keelboat a cheaper DIY home build proposition
area where there are some concave areas
that you cannot avoid. With the use of
foam to build the bustle on the outside of
the plywood hull it proved possible to
achieve a fair hull shape.
For the building process it was decided
to use an external mould system where
the panels are placed inside the moulds
rather than the conventional way of
building a chined hull over a male mould.
In 2010 Hasse, with the help of his
friend Petrus, a kayak builder and
boatbuilding teacher also from Sweden,
set about cutting the inital set of moulds
and ply panels using his CAD router
system. It’s possible to do the same job
with a jigsaw, but the resulting parts will
need more cleaning up.Hasse Malmsten created a chined 2.4m
design using free CAD softwareT
he International 2.4mR class
has been gaining interest
worldwide over the last
few years. However, many
potential sailors are put off joining the
class by the relatively high price of
new professionally built boats.
The designs previously available for
home build featured round bilge
construction utilising the strip plank
method which is time consuming, and
requires quite a high level of skill to obtaina fair hull. So the class proposed a set of
criteria to encourage a design evolution,
demanding a complete set of plans and
documentation to ensure a fair and
symmetric boat could be produced from
sheet material (plywood, foam-core or
anything else) on a small budget without
specialist tools that would still be good
enough for competitive racing.
A chined design would make it easier to
build and the specifi cations should make
use of rigs and sails from older boats to
keep costs at a minimum, or a rig that can
be homemade.
There were plenty of doubters among
the 2.4mR fl eet that it would be possible to
build the complex hull shape with chines
and still meet the rating requirements for it
to be competitive on the race circuit.
But then along came Hasse Malmsten,
an enterprising Swedish designer/builder
known for his round bilge Stradivari 2.4mR
designs. Liking a challenge and determined
not to be beaten by the concept of a chined
hull, using a free CAD software program,
he found it possible with some tweaking of
the design to form a 2.4mR Hc (hard chine)
hull shape out of sheets of 4mm ply.
The main issue was to solve the
problems stemming from the somewhat
awkward shape around the skeg/bustleChined 2.4mR is
simpler to build
than the original
round-bilge versionA design evolution
PRACTICAL
ABOUT THE AUTHORWhitby-based Mike
Coates worked in
the spar and
rigging industry for
many years. A
regular contributor
as PBO’s masts
and rigs expert, he
sailed his Hans
Christian 43T Jolly Swagman on the
East Coast and across the North Sea to
Europe. He has now switched to racing
a single-handed 2.4mR keelboat and
fi nished 25th out of 87 at last year’s
silver fl eet worlds in Sneek, Holland.Photos by Hasse Malmsten