JIM PRITCHARD ASSOCIATES
YACHT SURVEYORS | YACHT CONSULTANTS | NAVAL ARCHITECTS
CONSTRUCTION MATERIALS
Construction Material
Yachts are built from a number of different materials, as described below all of which Jim Pritchard will survey. Jim pritchard has also built boats from all these materials apart from ferro cement
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Glass Fibre
The vast majority of pleasure vessels have been built in glass fibre since the mid 1960’s. Osmosis tends to be the main concern of purchasers, but it is most unusual for this to develop to a stage where it becomes a structural problem. Osmosis tends to be more of a cost problem as treatment is comparatively expensive. Unfortunately the smaller the boat, the bigger is the cost of osmosis in relation to the value of the boat.
There are of course issues other than osmosis to be considered with glass fibre boats, such as de-lamination, stress cracks, and core material saturation and damage.
Many boatbuilders have changed from the hand lay-up method of laminating, to resin infusion. This is an improved method of laminating when done correctly, particularly when core materials are included in the laminate. If done incorrectly, this may leave dry areas of laminate where there is insufficient penetration of the resin and this usually cannot be satisfactorily rectified.
Steel
Unless the vessel is built from corten steel, the main issue is likely to be corrosion, resulting in wasting of the plating and structure. Water traps and inaccessible areas of the internals of the hull are usually the location of aggressive corrosion. These areas will be sought out before an ultrasound survey is carried out, which will establish the thickness of the steel at the point of measurement.
The preparation and quality of the painting of steel vessels will determine the level of maintenance that is required. Also the internal fit out should allow access to all areas of exposed steel for inspection and maintenance.
High-Tech Composites
High-performance yachts have used light weight composite laminates since the early 1980’s, using epoxy laminating resins, carbon fibre, Kevlar, glass fibre, and high performance core materials such as PVC foam and honeycomb. Often these structures are built over male moulds using vacuum techniques, and have a filled and painted external surface.
These yachts are built to much lower structural factors of safety than production boats, and the condition of the laminates is vital. Surveys in some cases will also require specialised ultrasound measurement investigation, and this can be provided by associated specialists.
Aluminium
Quality built aluminium yachts rarely give any structural or maintenance problems. Special care needs to be taken to avoid galvanic corrosion from dissimilar metals, and electrical discharge.
Aluminium boats of not such high quality can develop weld cracks and work hardening in areas of high stress. Dye testing will usually find such cracks.
Timber
Traditionally built timber yachts depend on jointing and fasteners to hold together the planking and general structure. Modern timber yachts rely on glue, which was formerly resorcinol and is now usually epoxy. There were also double diagonal fastened planked hulls with a calico membrane between the two planking skins, made during the 1940’s and 50’s, usually for single-chined motor launches. Fairey Marine in the 1950’s and 60’s also made hot moulded hulls using Agba timber cut from their own forest in Burma, and glued using resorcinol glue. These hot moulded hulls have proven to be very durable.
The condition of the traditional timber yacht will depend very much on the quality of the timber and fasteners used. Defects relating to rot in the timber, and corrosion in the fasteners are frequently found. If the hull has been stood ashore for too many years, then the planking may have dried out excessively, and will never regain its former structural properties, and the caulking may also require replacement.
Epoxy glued hulls, if well built, are usually extremely durable, as the timber is totally sealed and will therefore not develop rot unless damaged and poorly repaired.
Ferro Cement
The bigger the better, applies to ferro cement boats. Many were home built with very varying degrees of success. Some are excellent durable yachts, and others should never put to sea.
The visual inspection will determine most of the information required in a survey.
