From-South AfricanYachting, May 1990
phrase 'home-built catamaran' conjures up an image of
part-completed, slab-sided hulls festooned in polythene and
plastic sheeting, plumbed into the main drainage system and
providing a weekend hobby on a long term basis for land-based
dreamers who no more want to go near the water than they want
This is unfortunate because the true picture is of seaworthy
boats sailing the seven seas, safe, secure and substantial.
These boats make no headlines because they are built without
fuss and often sail off to far horizons and are
undistinguishable from production boats.
The key to successful homebuilding lies in the choice of
designer and his plans. There is no hope of producing a
professional-looking boat if the design and plans are
amateurish. Surprisingly, success is also unlikely if you work
from plans of a production boat modified for home-building.
The only sensible approach is to buy plans that were
specifically drawn for home-building by a reputable designer.
We have built 10 catamarans for our own use in the last 10
years, ranging in size from 14 to 35 feet and using tortured
ply, foam sandwich and cold-moulded construction methods among
others. Yet we are by no means professional builders.
Currently we are building a 30-foot strip-planked catamaran in
a temporary shed in our backyard. A job we hope will be easier
now that we have a decent jigsaw and power plane.
Partly due to our own lack of facilities we always try to
design boats that anyone can build. As far as we are concerned
this means designing boats that use flat panels as much as
photo shows that this does not mean having a boat that looks
like a box. Admittedly this boat (our 35 foot Banshee) has
round bilge hulls below the waterline (where you cannot see
them). What you can see, however, is a boat made of flat
panels. The term flat panel is mis-leading because it really
refers to single curvature panels. These single curves allow a
huge variety of shapes to be built in almost any material.
THE LOGIC FOR BUILDING IN FLAT PANELS
Although round bilge hulls have the least wetted surface area
for a given displacement and so are considered the optimum
shape, a close approximation to a round bilge hull can be
achieved with a single or double chine hull. On the smaller
boats a dory hull shape works well, simply because the amount
of boat in the water is so small.
Any aspiring home-builder is most concerned about building the
hull. This is understandable since it is usually the first job
to tackle. However, anybody who has built a boat will say that
building the hull is the easy part, it is the fitting out that
is difficult and takes the most time. As an indication the two
hulls of a production Banshee can be built in under 100 hours,
yet it takes 2500 hours to finish the boat. In fact it takes
longer to install the electronics than to build the hulls!
These figures also show how big a commitment boatbuilding is.
The average person works 2000 hours a year at his job,
so 2500 hours is the equivalent of 15 months full time work.
It is a major commitment not only for the builder but also for
his family. The first catamaran I built (a 30-footer) took
less than six months to build single-handed, while working 40
hours a week at my job as designer. The motivation came from
the fact that until the boat was finished I had nowhere to
live, let alone a boat to sail.
Building in a yard where others were doing the same also
helped - problems shared are problems halved. Since a boat
takes such a long time to build, any techniques that can speed
up the building should be seriously considered. Speed in
building should really be given a higher priority than say
ultimate sailing speed or comfort. Many monohull builders
learned about single curvature panels when they built
multi-chine steel hulls. Steel is unsuitable for multihulls
under about 100 foot (aluminium under about 60 foot), so multi
hull builders' materials are wood and fibreglass.
Plywood is usually considered the automatic choice for
home-builders. Fortunately with the advent of epoxy glues many
of its drawbacks have been overcome (although epoxy has some
of its own, mainly because it is highly toxic.) However, more
builders should consider building fibreglass hulls. The two
normal reactions to this comment are "you mean foam
sandwich," or "you need a mould."
In fact, there is a simple way of producing a hull with a
conventional gelcoat finish without using foam or a
The main disadvantage of foam sandwich, apart from its cost,
is that the outside surface is rough. It needs a lot of
filling and sanding to get a smooth hull. Note I said smooth,
not fair, because it also requires a lot of care to get
a fair hull since it is difficult to judge the fairness when
fitting the foam sheets. Changing a shape from a double curve
to single curve helps fairing up considerably. Compound curves
are supposed to add extra stiffness, but multihull topsides
are always fairly flat, so the extra curvature adds little.
The main attractions of foam sandwich are its light weight and
high strength, but this comment has to be qualified. There has
to be a certain thickness of glass on the outer side of the
foam to protect the core from impact damage. Top monohull race
boats now have skins so thin that only the paint keeps them
watertight and they cannot be lifted by slings round the hull
without being crushed. On multihulls under about 35 foot the
use of a foam panel as opposed to one of solid glassfibre
usually results in only a minor weight saving. The saving is
irrelevant on a cruising boat.
we are surprised at the room inside a modern, wide beam
multihull. A boat over 35 feet for family cruising is probably
too large. We would not recommend a boat over this length for
an amateur builder. Thus most home-builders should be able to
use the solide glass flat panel technique. It may sound
difficult and unfamiliar but making the panels is extremely
simple. The photographs of a 27 foot catamaran under
construction show the basic stages involved, while the table
shows the time required to build the boat to a sailaway state.
The mould is a flat worktop made of glossy melamine- or formica-covered
chipboard (the material used for shelves and kitchen worktops).
Resin does not stick to these surfaces so gelcoat can be
applied directly. It is not necessary to make the whole hull
side in one go. Making them, for instance, in eight-foot
sections means it is easier to heat the workshop and less
space is required until they are finally joined together
before final assembly. After laminating the hull panels
stringers are fitted and then they are cut to the exact sizes
given on the plans, offered up to the bulkheads and glassed
along the keel (and chine if necessary) and to the bulkheads.
This procedure only takes a few hours. Although the joints
will need filling and sanding the topsides have a perfect
gelcoat finish, often better than that of a production boat.
As you get more used to the concept of melamine flat panel
moulds the potential uses begin to grow. Simple moulds can be
made for galley worktops, steps, shower compartments or
lockers. Both male and female moulds can be knocked up quickly.
All joints need rounding to allow the moulding to release
easily; inside joints can be made with plasticine, outside
joints of timber battens rounded off. Only the timber needs
coating with a release agent before laminating. I have
suggested using simple melamine moulds to help fit out the
interior because often it is not the external appearance that
gives a home-built boat away but the internal finish. Flat
panel topsides help fit out the interior more quickly, since
making something fit to a straight line is easier than having
to scribe to a curve. Besides being more practical a moulded
gelcoat interior makes the boat look professionally finished.
Most decks have single curvature and need to be foam sandwich
for stiffness. This is particularly true on bridgedeck cabined
catamarans because, although a flexible deck is usually strong
enough, it is disconcerting to walk on. It is seldom worth
making moulds for decks. Normally we cut the foam to size,
glass the inner skin and offer it up to the boat, bend it to
the required camber and then glass the outer skin in situ.
This results in the usual rough finish, but a layer of surface
tissue and a quick skim of filler should be enough since
non-slip deck paint is used over most of it, hiding small
lumps and hollows.
Building a boat yourself in your spare time is a satisfying
and for some even a pleasurable experience. However, for most
people it is the end product - the boat and the sailing that
are important, not the building. You will learn many new
skills and, more important, will know how to maintain and
repair the boat when required. Many beginners have completed
large projects successfully. Often organisational skills are
more important than boatbuilding experience.
One final comment. It may well take years to build your dream
boat. However, once completed she is often a dream for only
three years: year one is spent getting used to it, year two
enjoying it, and year three is spent realising what could be
different. Then one starts looking for another design. So when
building your boat bear in mind that you will probably sell it
again and resale value is important. So remember that spending
10 percent more money and 10 percent more time and effort
while building can increase the resale value by 50 to 100