From: Graeme Cook (email@example.com)
Subject: Re: Ferrocement Boatbuilding
View: Complete Thread (26 articles)
Below is an email that I sent Everett Collier.
I have never owned a stone boat although a couple of friends have, and I
was prevented from buting "Analani" by an uncooperative banker. Thus my
views are second hand.
All the boats I have seen being built have used either galvanised "chicken
wire" or galvanised woven square mesh, plus galvaniseed ties onton
galvanised frames and stringers. A few have used stainless tie wire.
I think all have used some sort of water proofing agent in the cement, but
I do not know the details.
In addition the outsides of my friends boats have been coated below the
waterline with a rubberised or epoxy compound.
All the boats periodically have spots of rust appearing on the topsides,
and they routinely touch up with rust killer and an epoxy waterproofing.
I am not sure if these rust spots are simply common rust at imperfections
in the galvanising in the loom, or if it is the result of electrolysis
action in the metal. Both the zinc in the galvanising and the iron/steel
in the mesh are quite low on the nobility table and thereby prone to
electrolysis attack if moist and there is any stray micro-currents around.
The big danger is that the strength of ferro-cement comes from the
interaction of the loom and the cement and the loom is permanently burried
deep inside the plaster. It is thereby impossible to inspect the loom
directly, and one cannot be sure if insidious corrosion over time has
robbed the hull of its strength.
The second major problem with ferro-cement comes from the effect of severe
repetitious hammering on the hull. I think I can illustrate this effect by
saying that if you belt a piece of concrete with a hammer then the hammer
bounces off, but if you apply a jack hammer then the concrete crumbles
If a stone boat hits a reef hard then it basically bounces off possibly
leaving an "egg-shell" fracture which can be easily repaired. However, if
it remains on the reef, bouncing up and down with the sea, then it very
quickly "jack hammers" itself to pieces. Its initial strength is much
stronger than other materials (except steel) but the dissintegration rate
is frighteningly fast - much faster even than wood.
"Analani" was designed and extremely well built by Wilf O'Kell as a
showboat when he moved his operations from New Zealand to the larger market
of Australia. When I looked at her she was five or six years old and in
as-new condition. She was a 40ft, heavily rigged ketch. About twelve
months later she hit a coral reef near Thursday Island, Northern Australia,
and was a total wreck within 30 minutes. Subsequent diving showed that the
cement plaster had been shaken from the loom over that section of the hull
that was in repeated contact with the coral.
Some concrete boat design books are:
Samson, J and Wellon, G, "How to buils a Ferro-Cement Boat" (Samson Marine
Design Enterprises, BC, Canada, 1968)
Hartley, R, "Ferro-Cement Boat Building" (Broughton HousePrinting, New
Jackson, GW, and Sutherland, WM, "Concrete Boatbuilding" (George Allen &
Unwin, London, 1969)
All these books were published when ferro-cement was regarded as a new
wonder product, and before its shortcomings were becoming obvious.
Also, all the publications emphasised the cheapness of ferro-cement. They
overlook the value of the builders labour (assumed zero value !!), and they
ignore the fact that for a blue water craft the cost of the hull rarely
exceeds 15 - 20% of the cost of the finished vessel. Fit-out, machinery,
rig, sails and electronics cost the same irrespective of the hull, and a
low cost hull does not make a big difference to the cost of the completed
boat. But its resale value can vary very materially. A false economy.
Stick with your research.
"Ferrocement Boats" by Bingham.