The Lightweight Balsa Canoe Experiment 

Lighter than Carbon Composite.

Origins:
During work experience for my Engineering Course, now a long time ago,  I ended up working for Adhesive Technologies, then in Sydney - the local agents and manufacturers of "West System" Epoxies.

 The proprieter, Arnie Duckworth was at the time involved in building "WILD WEST" a 10 metre derivative of a Jim Young Rocket design - built of Balsa strip plank sheathed in 'glass with small amounts of Carbon Fibre.  I was really impressed by the way a timber that you can crush with your fingers can create a stiff but still light structure.

At the same time Julian Bethwaite was developing his two handed "Prime":18 ft skiffs that radically changed that class by dramatically reducing hull drag with a new type of hull shape (much less volume) and a lightened and simplified rig.  When I saw one of these at a boat show I was amazed not only by the smallness of the boat relative to its peers but just how beautiful the balsa looked.

Inspired by these developments the Australian Moth Association launched a series of very fast and very pretty balsa planked skiff Moths.

A Canoe:
One of the great American canoe builders at the turn of the 19th Century was J Henry Rushton.  One of his best designs is the Wee Lassie, a single person canoe which has beautiful hollow lines in the ends and a straight keel line.

There is no small amount of controversy about what lines are the correct ones - there are several different versions.  I was very pleased with both the paddling characteristics and appearance of the one shown in the book "Rushton and His Times".  

It has a deeper forefoot, a touch more sheer and a greater hollow in the entry than some of the other designs.  The finlike forefoot gives the boat a great grip on the water with the result that for a short boat it has excellent directional stability and is unlikely to be knocked off course as the waves and wind pick up.

The greatest fun for me in boats is to put together a concept that matches construction, materials and design into a unique package.

The idea, in this case was to play with the materials to build something REALLY light.  I was not particularly interested in the durability of the boat.   As far as  I was concerned I was going to be happy if it lasted a couple of years before being chucked into a dumpster somewhere.

So I decided to go as light as I dared with the fibreglass cloth used to sheath the balsa and fairly minimal with all the timberwork.

I had a bit of good luck with materials.  My intention was to do all the trim in Australian timbers.  OK, the hull was  a South American timber, but at least it WAS grown in Australia.  At Duck Flat there was a small piece of now rare Australian Red Cedar the right length for all the sheer reinforcements.  The keelson was a sliver of Jarrah out of a floorboard - an incredibly hard hardwood with a tight curly grain.  For the spreader bar and internal stems I did use some lovely fine grain oregon (Douglas Fir).

In Australia we have a range of timbers that have colour and grain that are almost unbelievable to Americans and Europeans - I have seen visiting woodturners go glassy eyed at some of our timbers.  Every timber makes a statement about colour and grain.  The downside of this Woodie Wonderland is that most of our timber is hardwood of quite high density - not ideal for building lightweight boats.  So thus my slip toward the Fir for the spreader bar.

The Learning Curve 1:
The balsa was only 9ft long so had to be scarfed.  As it was being sheathed in glass I decided the scarfs could be quite short - 2:1 and because of the faint grain of balsa the cut could be in the 24mm face.

There was an incredible piece of luck in joining the balsa.  While I was setting up the strongback we had a fellow drop into Duck Flat who was a model builder.  He told me about "ZAP" a cyanoacrilate glue (ie superglue) formulated specifically for balsa.  There were two types - one for gap filling and the one I was interested in for bonding of tight fitting surfaces.

I got hold of a bottle of ZAP and it was the best fun I have had boatbuilding.
    Overlap the ends of the two balsa planks to be joined
    Cut a scarf with my trusty Japanese backsaw - a perfect fine join results
    Hold two sides of scarf together
    One drop of ZAP along the join - hold 5 seconds - a small puff of vapour
    Turn over planks
    One drop of ZAP on other side of join - ditto.
    Try and break - "HEY ROBERT, LOOK AT THIS!"
A Piece of Cake
(I did try ZAP on other timbers but it didn't work so spectacularly)

Planking was not straightforward.

The Balsa dented badly when I nailed it in place, so I ended up cutting strips of thin plywood to bend down and nail through them.  Generally I tend to use a single nail through each plank at each temporary bulkhead position. - the single hole to me is neater than the cluster of small holes that you get when using staples. - plus I found that the staples had little power to hold the balsa down without tearing the strips.  One nice thing about balsa is after the nail is removed you can brush the area with water - the grain swells virtually hiding the hole.  Also effective if the hull is dented accidently - for small dents anyhow.

As a glue between the planks I used Bote Cote Epoxy with white Q-cels mixed in to provide an easily sanded join.  If the glue ends up a lot harder than the planking it will end up proud of the hull after sanding.

I started planking at the sheer but on such a short boat the strips in the ends of the boat start swinging upwards (boat upside down) as planks are added (it is a shorter distance from sheer to keel at the ends of the boat than in the middle).  So as the angle got more and more crazy I decided to cut the planks parallel with the keel and start a second run of planking.

The hull sanded up very nicely by hand.  Glassing went spectacularly easy - such thin cloth wets out with epoxy very easily.  For second layer of glass in bottom area - no squeegee - just run a gloved hand over second glass layer.  One additional coat of epoxy rolled just as the first coat went tacky filled the weave easily.  Same too for the inside of the boat.

Time to fit the timber trim ...

Well the balsa boat weighed in at 12 lbs.  It has been reported that Rushton's Wee Lassie was 22lbs but there was a special ultralightweight version available at about 18.5lbs.  So it has taken a century to remove 6lbs

Modern materials allow us to eliminate all of Mr Rushton's close spaced ribs, all the copper fastenings that held the plank edges together. 

Conventional clinker (lapstrake) construction overlaps the planks and fits rivets through the two layers.

Rushton used a method of bevelling the two planks so that there is only a total of one layer doubling of the hull in that area carrying the weight penalty of the double thickness.  The fasteners were clenched through the two layers.  Incredibly sophisticated and skilled construction using only the finest materials.

I wish I had the skills and patience to build boats like that - but I won't heartache too much!

What a revelation it is paddling this boat.  After the final coat of varnish had dried I carried (ha) it around to the municipal lake in Mt Barker for a quick paddle.  The lake is quite small, but it was amazing to feel the bow rise and fall over the tiny ripples on the water - the light weight gives a fantastic sense of lightness on the water.

On larger expanses of water the boat was a dream - tracking well in adverse conditions, astoundingly easy to move along briskly.  Speed is limited by the short length, but the feeling of speed from the liveliness more than makes up for it.  Effort to paddle is quite minimal.

The boat has enormous directional stability because of the fineness of the ends - the narrowness of the bows provides a fin at each end of the boat (see the bow-on detail picture above).  For such a small boat she is quite hard to turn, but when the conditions are not so nice and there is still a lot of ground to cover she is perfect.

Balsa Canoe - Coorong Camp.