Ferro-cement Boatbuilding

Methods Of Construction

Over the last hundred years there have been almost as many

different methods of building ferroboats tried, as the years that have passed.

Almost all have fallen by the wayside because of a lack of

understanding of 5 basic principles.

1/ The transferring of stresses from an impact.

2/ The incompatability of mixed materials.

3/ The effects of Osmosis.

4/ The ability to be repaired.

5/ The ease of fitting out. 

There are 'for's and against's', for every method.

Every method has it's drawbacks.

If the design/method does not include built in floors, it

should not be contemplated under any circumstances.

If the design/method does not include frames, there are serious

drawbacks that should be considered.

There are three basic methods of construction.

a/ Hand lay-up of netting/mesh on a rod matrix.

b/ Hand lay-up over a mould.

c/ Shot blast method. 

IMPORTANT NOTE

The only types of netting/mesh suitable for marine use is either galvanised netting of half inch dia hexagonal known as 'Bird Netting', or half inch square welded mesh. In a concrete/ferro-cement compound 'Bird Netting' is greater in strength, flexibility and impact resistance. Do not use 'Chicken wire/netting' it has 1 inch hexagonal dia spacings and so does not contain enough steel content.

DANGER

Under no circumstances use 'expanded wire', often sold as 'expandamet'. it is manufactured from a flat sheet of steel by cutting small slots and expanding it. In a concrete/ferro-cement compound it has a very poor impact resistance. The layers are not integrated as with netting and so seperate easily under impact. Experience has shown that the very few vessels that have used this method of lay-up have mostly been condemned after very little use, and larger ones found unable to support their own weight on the hardstanding.

 a/ Hand lay-up of netting/mesh on a steel rod matrix, is the only method worth considering for amateur ferro-cement boat construction. Time has proved the method to be the best in almost every aspect. It's only drawback is that it is a more time consuming construction process than methods b/ and c/. However having said that, the latter two methods are only a by-product of attempts to find quicker ways of construction for commercial cost-saving production purposes.

The disasterous effects of grounding on reefs and rocks, of ferro-cement keeled vessels (infact a monocoque constructed hull of almost any material), which have not been constructed with integral floors, has been well in evidence over the last 50 years or so. If you add to the previous analysis the considerably increased difficulties of fitting out a hull without frames. There is logically no practical reason to consider building a frameless or floorless hull. To this end I will only outline the basic two variations of this method of construction ie...'The Hartley Truss Frame method', and 'The Pipe Frame method'.