Choosing a Blue Water Yacht – Hull Construction

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Over the last few weeks, Grabau International has taken you through a variety of subjects which encompass choosing the right yacht for blue water adventures. This guide is not written to dictate what to choose, or to supply a comprehensive encyclopedia of every option and variable, but simply a basic explanation of the main options and some guidance on what to look out for. Finding a yacht will always be a battle of your head over your heart, so the purpose of this guide is to give your head some questions to ask in the hope that an amicable compromise can be made with your heart. Part 5 of this guide looks at the question of hull construction.

Hull Construction

With the vast majority of production yachts constructed from GRP laminates, choosing a hull construction type is not usually something a buyer has to consider. However, for those looking to venture into high latitudes, those who have differing requirements in terms of maintenance or even for those lucky enough to be in a position where they can embark upon a project from the drawing board upwards, there are plenty of tried & tested alternatives to the ubiquitous glass fibre.

GRP hull construction

Italia Yachts 13.98 in construction

GRP

Universally adopted by production manufacturers and very much the ‘easy option’ thanks to simple re-use of a female mould allowing multiple identical hulls to be quickly and efficiently produced. Traditionally overbuilt, but with often with questionable material quality, GRP production is now seriously advanced with advanced vinylester or epoxy resins and lamination techniques such as vacuum infusion almost completely removing the risk of osmosis (which in itself is never as bad as tradition made out), dry spots or hull voids. Usually allied with some form of core material such as balsa or closed-cell foam, the structure is both strong in tension, but also stiff and well insulated against heat and noise. Solid laminate hulls are still quite common and are popular amongst those with the ‘keep it simple’ attitude, but even here, core materials are usually added in the deck and superstructure areas.

GRP hull constuction

Traditional GRP hand laminate construction

Carbon/Composite

Very similar to GRP construction but using more advanced fibres such as Carbon or Kevlar to create extremely light, stiff and strong hull shapes. Carbon and Kevlar are usually combined as Carbon on its own has very little impact resistance, whereas Kevlar has plenty. Many GRP yachts are also reinforced with Kevlar in the bow section for this very reason (Kevlar is often referred to as Aramid or Twaron after its manufacturer’s name).

Kevlar glass fibre composite

A composite weave of glass and Aramid (Kevlar) fibres

Steel

Extremely strong but quite heavy. Steel hulls are liable to rust unless well protected from water. Whilst it is relatively easy to monitor the paint system on the outside of the hull, it can be very difficult to see what is happening in the deepest, darkest recesses of the bilge, so most problems with steel hulls manifest themselves from the inside out. Steel is however cheap and very easy and low tech to work with, so for a rugged solution that can be maintained anywhere on the planet, steel certainly has a place.

steel hull construction

Steel hull construction

Alloy

One of the lightest materials for building large yachts, aluminium construction also enjoys a healthy market in smaller craft. For those wanting the security of a metal hull, aluminium will allow the closest match to a GRP hull in terms of weight, stiffness and feel. Traditionally the preserve of specialist manufacturing skills, aluminium welding and construction skills can now be found in most parts of the world, so it is fairly safe to assume that repairs can be made almost anywhere. The downsides are corrosion, both below the waterline and above where imperfections in the paint system can lead to rather unsightly blistering. Many manufacturers side-step this problem by simply not painting their hulls. Electrolysis is also an issue so it is important that the yacht is correctly wired and most well constructed yachts have a double poled system.  When exposed to oxygen in the air, aluminium will develop a very thin layer of oxidization which will then protect the material from further corrosion.

Allures 51 aluminium hull

Allures 51 in construction with an alloy hull and a GRP superstructure (photo courtesy of Allures)

Traditional Wood

The original boat building material and in some eyes, still the best. Naturally buoyant, easy to work with and excellent at cutting out vibration and noise, wooden hulls can be an absolute delight. Rot is always a concern, but this can be mitigated by using woods containing natural preventative chemicals (such as teak, magohany and cedar).  Construction methods vary from traditional clinker construction found in smaller dinghies to the more common carvel construction found on larger yachts.

wooden boat building

Traditional wooden boat building

Wood Epoxy

Worthy of a separate section of conventional wooden construction, wood epoxy or cold-moulded construction allies wood (usually cedar or mahogany) to epoxy resins and fiberglass resulting in a hull with very few downsides yet with all the benefits of GRP and wood rolled into one. As each hull is in effect a one-off rather than simply laminated in a female mould, wood epoxy contraction is more unusual in the production market (although the French builder RM Yachts and English build Spirit Yachts are two notable exceptions).

Sport keelboat / series / ISAF class

A classic Dargon one design in cold moulded (wood epoxy) construction (photo courtesy of Petticrows)

Further Considerations

Hull Colour

Not a construction material, but a process which can have a profound effect on both the aesthetic of your yacht and in some cases the construction material beneath. Very simply put, dark coloured hulls can get hot. A stunning flag blue hull will heat up more in the Caribbean sun than a white hull. This could potentially cause a number of problems for a GRP hull such as post-cure shrinkage of the gelcoat or even delamination, but fortunately these problems are extremely rare and not a reason to avoid dark coloured hulls if you have a hankering for them. The biggest issue with a coloured hull is keeping it looking good. Colours will fade over time and whilst polishing them will bring them back, ultimately, there is only so much polishing you can do before it is time to repaint the hull. If you are happy with this limitation, then there are few things in life as pretty as dark blue yacht, and the manufacturers love dark colours as they create the useful visual illusion of slimming the topsides. Another more modern option is to apply a vinyl wrap to the original topsides. This allows total fleixbility over colour and design and can be removed at any time. The vinyl wrap can also do a good job of preserving the gelcoat or paint finish beneath.

Vinyl_boat_wrap

The faded blue topsides of a motor yacht receiving a new lease of life via a blue vinyl wrap (photo courtesy of MBY)

Teak decks

In many instances there will be little choice as to whether the yacht has teak laid decks or not. High-end Scandinavian or British built yachts will almost always have circa 12mm of teak glued and/or screwed to the sub-deck. Teak has its advantages in terms of aesthetic, grip when wet, and insulation against heat and noise. On the downside, teak is expensive to source sustainably and very labour intensive to restore properly. An 8-12mm teak deck should have decades of serviceable life if looked after and not aggressively scrubbed. Even when the caulking is failing and screw fastenings are showing through, there should generally be enough teak left to re-caulk and refasten the deck. This is in effect, a mid-life refit for the deck. The key with a teak deck is to keep it watertight. Missing caulking or exposed screw fastenings can allow water to penetrate through to the sub-deck which can then cause problems within the deck core. Keeping a small tool kit with caulking and fastening materials aboard the yacht will allow continual maintenance to be carried out and the hopeful avoidance of a big bill – or at least will enable you to put off the evil day.

teak decks

Teak decking on a modern Italia Yacht

Synthetic decks

Increasingly common on cruising yachts where an alternative to teak is desired, a synthetic ‘fake’ teak deck can provide the much of the look and insulation properties of teak without the cost, maintenance and wear implications.  Manufacturers such as Amel and Allures, have made such deck finishes a trademark and there are many products in the market which can be fitted in place of teak very easily.  The finishes available are improving all the time.

synthetic teak

Modern synthetic teak decking
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