Short story of catamaran boatbuilding

(Sama Suomeksi)

Or what happen when a monohull (Phillippe Harlé 1/4 ton racer/cruiser, launched 1981) boat owner/builder/sailor fall in love a beautiful catamaran.

Beginning of 1998 the Finnish Sailing Association magazine had a story about cruising catamarans. After couple years hard working without breaks I was missing some interesting hobby. That magazine article really hit the nail on the head. YES!!

In the web I found some links: have books and plans of many kind of boats, multihulls too. I subscribed a Boat Plan CD-Rom (not really good) and "A Multihull Sailboats under 37' (#9)" (OK in proportion of price).

Many boatbuilders, architects and magazines has their own web pages, for example

You can search (, e.g.) more links, they change all the time.

Bookstore has a good selection of multihull and catamaran books and I subscribed some items:

Quite good everyone.

Scale model first

After some cruising in the web I found some plans of Roger Simpson and subscribed few study plans of about 10 meter long cataramarans. Study plans has just few measurements so I draw Simpson 10.2M again myself (some lines are just guessing) and put them to my computer. I made many years ago scale model of my own 1/4 ton boat of scale 1:15 and I do same scale to the catamaran too. In the summer and autumn 1998 I glued 1,5 mm thickness teak stripes on the mould. Surface of model is 60g/m2 chopped mat with epoxy.

Here she is: Simpson 10.2M scale model. Quite realistic except windows that are open entire position (too big).

Making scale model is a really good idea. You can let off steam with that, so it is possibly to think cool about building (or not) a boat yourself. Some phases of building process are really difficult to infer without experience.

When scale model was ready, cruising of the web continued. Really nice models found in url, in the home site of Jeff Schionning. Eleven meter long Cosmos 1100 looks totally beautiful, so I subscribed study plans of it and couple other variants about same size. I just fall in love her (picture below).

Cosmos 1100 I met in February in Helsinki Boat Show -99 (I guess) only professional multihull maker in Finland, Jukka Henttu, and got him many good hints.

In March thinking was over, I ordered Cosmos 1100 plans from Australia.

Building a catamaran

In April my car got deportation out of shed, a separation wall too. Space is 11.2 meter long and 5.5 meter width. Her dimensions are length11 m and width 6.6 m, so the shed is just long enough for one hull. Assembling must do outside, my yard is fortunately big enough.

The Stint start in May. Bundle of 18 mm plywood, sharp nail with wood handle as bodkin and couple big sheet of plans. Patterns are scaled 1:1 in these plans. Frames on the strongback, much measuring, some swearing and mold is set up. Old good plumb-line is still best tool with a line and a spirit level and MUCH of patience.

Materials of hull are simple:

Wood stripes, 12 x 45 mm, about 3300 lineal meter. I use European fir (or spruce, Picea Abies) besides of western red cedar. Weight of fir is about same than W.C.R and much cheaper here in Finland. Fir is traditional spar wood here.

Epoxy that I use is MAS. It is well saturate, non solvent general epoxy. It has no smell at all (a little if you really must put your nose in hardener can). Working time is long (in our temperatures) with slow hardener. Manufacturer inform also that MAS with slow hardener has no flush (amine), like most epoxies do some circumstances. A little more expensive than WEST or SP (in Finland). One hull strip glueing and fairing with one surface layer (painting) got about 17 kg epoxy so far. Now when I know many tricks and approaches, maybe 12 -15 kg is enough for next hull.

Additives with epoxy are cotton fibres (dust) for glueing strips and microballoons for fairing putties. Self made wood dust (from dust bag of sanding machine) is good medium hard filler too, and real cheap.

In June first stripes went to the mould. Instead of dry method I decided use wet method: few full length (pre glued) stripes together glueing and filling holes. I worked alone, so four stripe at once need four hours to glueing and screwing to mold. With slow hardener there was time just enough.

In July hull got some shapes. (My wife call it "A barrel without hoops")

In August - September bridgedeck joint need many hours. End of September it looks quite nice.

In October wood got cover. Glass fibre is 446 g/ m2 Double Bias (or Biax) unidirectional (45 degree both side to planking direction). One layer everywhere, second layer to keel to waterline, third layer on bottom. Temperature outside was so low that I need used a heater a little.

I am ex professional boat builder (glass fibre + polyester) and I was a little worried how can we can saturate (in seams) even three layer dry glass fibre.

Job was easy eventually with dry method: (after smoothing screw holes and cracks) precoating epoxy (one layer), sanding when dry, dust off, glass fibre sheets on place, some staples if necessary. Fibre overlapping min. 5 cm. Epoxy spreading with mohair roller or on flat surfaces a squeegee. Loosen air was not difficult at all, that I was afraid. Mostly little working with mohair roller took air bubbles off, only occassionally need a metal roller. Saturating was good, we had almost 20 centigrade temperature when laminating. Resin:glass ratio is really 1:1, that is difficult with polyester and chopped mat.

Bottom fairing was going through November. Dust everywhere. Hey! A good new training trick: grinding rock-hard epoxy with hand tools with a dust shield on your face. Before that you do not know anything of gasping.

Bottom under waterline got four layers of epoxy. Last couple layers with graphite powder as pigment.

The Great Day of Turning of the Hull was in December, just in our Independent Day.

Bears and boat builders have winter sleep here. Sometimes in March, when temperature climbed over zero, I harnessed my old boring machine (B&D year~76) with grinding disk and started inside grinding. Inside glassing was ready end of May 2000 and almost same work party friends came together in 1st of June 2000.

In the middle of June, the strong back was ready for the port hull.

Port hull strip planking start spring and continued till Autumn 2000.

After sanding dry method let adjust glass fibre quietly without hurrying.

Few days later was saturation of 2nd hull.

Smoothing and coating is few days job, but with my lazy working pace that took over a month.

In February 2001 we had few really frost weather, more than minus 20 centigrade, hrr, but that did not hurt second hull turning upside at all.

During spring inside of 2:nd hull got glass coating.

Framework for a temporary shelter was secondary occupation of spring. Couple of frames was neglect when we kicked out the port hull.

Rest of summer and autumn 2001 has many simultaneous jobs: finishing the shelter ends, bulkheads working and adjusting, making a forward beam.

Couple days sailing with Lagoon 41 give some idea of fixtures.

A winter sleep of a boat builder is really quiet here 61 degrees of North lattitudes, just brisk snow shoveling...

But when spring arrive...began some bulkheads finishing and fixation. Sure all schedules has same quality: always overdue.

Summer holiday 2002 was full of sidedecks strip planking. Not bad job at all, I mean diversion from everyday work.

Sidedecks outside laminating was cool job, literally.

The Spring of 2003 started quite lazy.

In Summer my boatbuilding has more activities.

The last missing big parts got shape in Autumn 2003.

Winter 2003-2004 was just lazy as planned

Summer 2004 brought cabin sides, catwalk, backbench and -back, genakerboom.

Autumn and winter brought some surprises too.. (no big trouble after all...)

The main job of Summer 2005 was carbon fibre mast, but also some other parts was progressing.

Summer 2006 is full of fiting up.

Later of the year 2006 furnishing continued...

Spring 2007 main sail boom and steering pedestal, among other things.

End of Summer 2007 in Finnish. Translate ASAP (hope not full year ;-)

Winter and spring 2008, still in Finnish, sorry.

Summer 2008 is here.

Spring and summer 2009 was full of smoothing and painting.

Spring 2010 is here at last.


Some more pictures

Autumn 2010 assembling continued, but also has some sailing.

First full sailing season was year 2011

In Winter job was building of dinghy

There was brisk winds in Summer 2012

In Season 2013 there was some times even too brisk winds.

Summer 2014 was full of treasure hunting.

Summer 2015 was mostly short trips around. (Sorry for delay and no translate)

Summer 2016 was real quiet, my house preparing took most of my time. New pram anyway.

Summer 2017 was more lively with one longer trip.

Summer 2018 is here (Google translate works usually fine ;-)

I have determine offer for sale Cosmos 1100 and find a trailerable trimaran.
I you are minded whichever, take a contact.

This page has updated: 2019.2.3

Since 11.11.2001 you are guest number

Comments and good advice: (yeah, I know, this is full of spelling and grammar mistakes, but who cares?)