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The Trailer... in Trailerboats - Galvanized Print E-mail

By Barry Tyler

Trailer frames and larger assemblies are all lowered into a huge vat, and ‘hot-dip’ galvanized.

It is fair to suggest most trailerboat owners lack true knowledge and appreciation of the complexity, the rich tapestry of the coating on their trailer, which is known broadly/generically as galvanizing.  And quite frankly why should they, for to most it is seemingly an integral part of the modern-day boat trailer and as such, should last the life of that trailer. 

Wrong, very wrong, for this rudimentary coating is merely a protective coating which very much needs some help along the way.  Steel and salt water do not mix at all well, hence the need for a coating which is still very much durable, price-effective and completely enveloping of the material’s areas of exposure.  The material that is the most effective is zinc in its pure form, and the process used to apply it to the trailer is known simply as ‘galvanizing’. 

In most cases boat-owners totally under-estimate the on-going underlying effects of salt water on steel components.  In fact, Australia’s leading galvanizer, Industrial Galvanizers, class the marine environment as the absolute harshest environment for their product to exist in, far greater than any industrial or similar environments.  For this reason alone then, boat owners must be aware of what is involved in the care and maintenance of their trailer, so as to enhance the longevity aspect of this material.

Many would be unaware that components used on the trailers have a combination of galvanizing methods used, offering differing degrees of protection to the parts used.  In many cases, it is not a choice of the manufacturers to use different methods of galvanizing, it is just that the differing components require different procedures to galvanize those parts.   These methods consist of zinc coating, continuous strip galvanizing, and hot dipped galvanizing. 

Zinc electroplating is a method where the parts are coated in a thin (five to 10 micron) coating of pure zinc, and lack the hard alloy layers of the hot dipped coatings.  Parts you might see on your trailer that may be zinc coated would be the bolts and fasteners and the axle U-bolts.  Many major suppliers aim to use hot dipped galvanized fasteners and U bolts, for although more expensive, the hot-dipped versions do offer superior corrosion protection. 


Coating option one is zinc electroplating, suited to bolts and nuts, and smaller more intricate fittings.

Zinc-coated components are normally not specified for exterior use and may require heavy chromate coatings or similar anti-corrosion products to stop rapid deterioration; so it would be wise to consider these components in any new trailer purchase. 

Continuous strip galvanizing is used in areas such as light guards, mudguard shells and areas where lighter materials are required.  Zinc thicknesses vary between seven and 42 micron depending on the sheet thickness.  These sheet materials are passed through a molten bath of zinc, where the coating is applied.  Hot dip galvanizing on the other hand is the coating that is applied to the main frame and relevant components.  This is the heaviest and most protective coating possible with thicknesses of between 65-300 microns of zinc applied, depending again on the thickness of the material being coated. 

The process involves the parts being dipped in several ‘baths’, firstly a caustic bath is used to get rid of any production lubricants, scale, or foreign matter, that may contaminate the steel.  Then an HCL acid pickle bath removes any impurities that the steel may still hold.  A hot-flux dip then removes any oxides from the pickling process and prepares the steel for the dipping into molten zinc at 450° Centigrade.  After the zinc dip, the components are quenched in a chromate tank prior to cooling off.


Option two is continuous-strip galvanizing, ideally suited to bolt-on componentry such as these light-mounting brackets. Wheels are an often neglected area, here again a coating of ‘galvanising’ offers far greater longevity – and safety!

During the dipping process, the molten zinc becomes part of the steel, NOT a coating on top.  The process sees the molten zinc react with the steel to form a zinc/iron alloy that becomes part of the steel’s surface.  Hence, it is impossible for salt water to get ‘behind’ the zinc coating and cause any type of rusting from behind.  The thickness of the zinc coating is solely attributable to the thickness of the metal being dipped, the frames would have a heavier thickness than for example, the brackets. 

Advice obtained suggests a trailer manufacturer’s claims that their galvanizing is thicker than anyone else’s – simply is just not true!  Once the coating has adhered itself to the frame, the only way corrosion can occur is when the salt water comes in contact with bare unprotected metal. 


Hot-dipping allows an all-over coating, on both the inside and outside of framing. Galvanising, on items such as mud-guards, protects far greater than a layer of paint ever would.

In saying that though, and this must be remembered, like sacrificial anodes on boats/outboard engines, the zinc is sacrificial to the steel and as such its life is solely dependant on the environment it lives in – and the care taken in controlling the action of salt water acting against the zinc, whilst it is being stored.  This is precisely why trailers used in fresh water seem to last twice as long as those on the coast, where salt is a major contributor to the rust equation. 

Similarly, when a trailer starts deteriorating, the lighter components, those with a lighter coating of zinc due to their thinner thickness, are the first to show signs of rust or deterioration.  This in reality is after the sacrificial effects have used up the zinc layer, and the salt water can then begin its ‘job’ on the now bare steel surface.

There are many questions owners have in relation to their galvanized coating, none the least being,  “What are all the holes in my frame?”, and  “Won’t they let too much salt water in?” Simply, when the components are dipped, they are stacked in a way that allows the molten zinc to enter the part in its entirety, without ‘pooling’ molten zinc in one area.  In many cases the venting holes that are in the trailers are in positions where owners think they are drainage holes for their frame, but in actual fact are in the wrong position to do so. 

Hence the venting holes for the dipping process, for the vent holes deliberately are in a position where air cannot be trapped in the steel.  In the 450° heat involved (in the galvanizing process), expanding air can cause the steel to explode, becoming very dangerous to those handling the components. 

Another common inquiry manufacturers and dealers alike receive, is,  “What is the white powder on parts of my trailer?” Fear not, for this is a naturally-occurring process where the zinc exudes a calcium carbonate residue, in the presence of salt water residues being left on the galvanized surface – in an effort to protect itself.  This residue can be cleaned back if required, but in most cases the protective benefits of the carbonate outweigh the aesthetic appearance.  This effect is normally where salt water pools at any area of the trailer invariably whilst in storage.


Protecting springs, hubs, discs and calipers, is a new ‘trailer industry’ innovation.  More expensive, sure, but at least everything functions properly, and lasts longer! A much better look, than the festering mess a large percentage of trailer springs degenerate into.

Many people claim they wash the boat thoroughly before storing but the trailer still has the calcium carbonate residue appearing.  On inspection, when the boat is stored, any residue water from the hull bottom, bait tanks, anchor wells and the like, drip onto the trailer.  The fresh water then evaporates, leaving a very high concentration of salt chlorides to work against the zinc surface, thereby deteriorating its life. 

Care and protection then, of your trailer, will definitely enhance your trailer’s life.  Wash your trailer as well as your boat thoroughly after use, then elevate the trailer slightly and leave to dry.  Once dry, store your rig again slightly elevated, in an area where there is good air flow as well as run-off.  Any areas where bare metal that may appear obviously should be treated as soon as possible with a ‘cold gal’ type of product to seal the steel from the corrosive effects of salt water.   Follow this procedure and you will prolong the life of your galvanized surfaces, five-fold.  

Over the years we all hear of many and varied concoctions as regards corrosion protection, but the stark reality is most quite frankly are useless against the effects of salt water, and wash off in a very short time.  One of the few however that does offer good resistance is the Lanolin-based product, Lanoguard (there are other similar products) giving the best results.  But even then, you still need to re-apply it every three or four months.  The Lanoline-based products seem to work extremely well on the galvanized springs, axles and hubs of the current trailers, but one must accept the fact there is no ‘perfect’ product.


An example of the three coating processes all together.  Forget the TLC and one by one they will deteriorate quickly.  Pay particular attention to these areas especially. Major manufacturers move with the times, bolts, u-bolts, fittings and even the inertia tow hitch, are all now protected from the elements.

The down side of Lanoline for instance, is the colour tint or a sticky appearance of the product, when applied to your trailer.  But if it is obvious that your trailer is deteriorating very quickly, these products certainly offer a first line of defense.

In finishing, please remember that the marine environment we enjoy so much is a traditionally harsh environment particularly for your trailer and their coatings.  Look after your trailer with regular checks and sprays and try to diagnose and understand the causes of any problems that begin to appear.  In short, develop a deliberate maintenance program – to enhance the life of your trailer. 

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