Types of material

There are many methods and different materials for building a cruising yacht these days. The four main materials most used for yacht construction are Wood, Steel, Aluminium and Fibre Reinforced Plastic (FRP). Glass Reinforced Plastic (GRP) is the well-known name for fibre glass boats. However, it is only one type of Fibre Reinforced Plastic (FRP) which is used these days. A lot of people have differing opinions of which is the best materials for yacht construction, and which is their favourite. There is no such thing as the perfect material, they all have good and bad points. With the rapid advance in technology, new materials and techniques are helping to alleviate some of the problems experienced in their use. I have written here, some of the good, bad, and ugly points of each material with an unbiased opinion. With the ever-growing concern and need to protect our environment, thought must be given to the recycling of the materials used. See more on Steel or Alloy yachts on my blog Steel and Alloy.

Wood

The beauty, warmth, and pure romance of wood as a boat building material is a virtue, compared with plastic or metal. Wood has good thermal and acoustic properties which other materials cannot match. With boats being mass-produced these days, a wooden boat is as unique as her owner. Wooden boats are the best-known traditional way of building yachts. There are wooden yachts still afloat today which were built over one hundred years ago. Most wooden boats built today are cold moulded using strips of wood and resin. Coating the wood in epoxy resin can reduce maintenance but will not eliminate all problems. Unfortunately, yachts were mostly made of wood, now they are mostly made of fibreglass. This has led to a shortage of skilled wooden boat builders. Ideally, wooden boats need to be built from hardwoods like teak or mahogany which is expensive. With forests shrinking, wood should be from a responsible source. Never from places where they destroy the forests. Responsible sources replant trees to make the supply of wood sustainable. Maintenance is a big thing with wood. All that lovely shining paint and varnish needs looking after to stay nice and shiny. Even if the yacht’s hull is not made of wood. Wood will be used in the interior for the furniture, doors, and hatches. Although adding some weight the beauty of a teak laid deck, will add a touch of class.

Deciding which timber, you are going to use for building your boat will depend on several factors. Not all woods are suitable for boatbuilding like softwoods such as pine. I have owned a 22-meter Greek built wooden motor sailor, with a Caique type hull for over 20 years. These vessels were build using locally sourced wood which is usually pitch pine. This wood is not the best timber for building wooden boats and I am forever cutting out rot. In the past, the timber and labour were cheap, so repairs each time the boat was hauled out were accepted and tolerated. Nowadays wood is not cheap, and labour prices have gone through the roof. I used to keep the boat on the island of Corfu, and I would haul the boat out at the boatyard pictured below, on the left. They started to use Oak to replace any rotten frames and Cedar which was still green for the underwater planking. I now have the boat on the island of Lefkada and the best wood available is Iroko. Iroko is a hardwood that is hard on the tools but has good rot resistance. Every piece of wood which I now replace myself, gets a liberal coating of Epoxy Resin to protect it, should any rain leak into the boat.

Fibre reinforced Plastic (FRP)

Fibre Reinforced Plastic (FRP). Glass Reinforced Plastic (GRP). Most people mistakenly call all fibreglass yachts GRP. However, some composite yachts are now built with other fibres like, Carbon Fibre and aramid fibres such as Kevlar® and Nomex®. Composite construction is basically a binder (usually resin) reinforced with a fibre material (like glass strands, carbon fibres, aramid fibres). The three types of resin used is polyester, vinylester and epoxy. Orthophthalic polyester is a cheap general-purpose resin. In the earlier days there were only Orthophthalic resins and they are still the cheapest. Isophthalic polyesters are more expensive but more water resistant. GRP boats moulded since about 1995 are now being moulded with the more moisture resistant Isophthalic resin. They are used for the gel coat and the outer layers of the hull, as water absorption into the hull, is the main cause of blistering. E-glass is the cheapest fibreglass cloth commonly used. S-glass is the strongest cloth and has the best mechanical performance of the two. It has come from the aircraft industry and is expensive. There are various types of fibreglass mats and cloths used for boat construction. Ordinary mat (Chopped strand) is made up of random fibres held in place by a resin soluble binder. Woven Rovings is a bulky loose fabric and is used to build up bulk quickly and cheaply. Its interlaminar bond is weak so a good practice is to be inter-layered with chopped strand mat. Woven rovings is measured in grams per square metre and the heaviest made weight is 100g. Uni-directional fibre is a mat made up with the fibres running in one direction only. These are held in place with single fibres glued across or sewn in place. Having very high directional strength it is used in areas with higher loads. Then there are others with fibres crossing in different ways, with different thicknesses and weights. Glass mat is measured in grams per square metre usually 300, 450 or 600.

Fibreglass yacht hulls can be built with layers of fibreglass only. However, to achieve the strength and stiffness required, they must be made thick and then end up heavy.

To keep the weight of a yacht hull down and achieve enough strength and stiffness. A lot of fibreglass yacht hulls are built with a material core. This can be end-grain balsa, foam or a honeycomb material. One method of infusing the fibre mat is hand lay-up. This is done by wetting the fibres by hand with a brush or roller. However, along with the advances in materials for composite construction, is the advances in build methods.

Vacuum bagging is a technique where a bag is put over the wet laminate. This squeezes out the excess resin which only adds weight to the laminate. It is the fibreglass which gives the laminate the strength. With resin being oil based, it has risen with the price of oil making fibreglass boats more expensive. So, using less resin also helps to bring the cost down. The vacuum infusion method also uses a plastic film and vacuum to give a good resin-to-glass ratio. The vacuum draws the resin from feed tubes in the plastic film through the cloth. This gives a more precise measurement of materials and an even pressure over a large area.

Of all the materials Fibre Reinforced Plastic (FRP) has the worst green credentials. There are literally millions of boats coming to the end of their lives. What can be done with them all? No one seems to know. The only thing that can be done now is to bury them in landfill sites. The cost of cutting it up and transporting it to a landfill site is going to cost money. This is not ideal as an old abandoned hull is worth nothing.

2.   Keel.

2.1

The vessel’s hulls have fin/skeg long keels and they are separate pieces to the hull mould. The fins are bonded into a socket in the hull and are low enough to give protection to the sail drives. This means that the vessel can dry out at low water in tidal areas.

2.2

The keels were sighted from different positions and looked to be at a fair angle to the hulls.

2.3

Overall, the keels surfaces were found smooth with only a few small areas of damage. The keels were supported on two wooden beams which ran almost the full length of the keels. This prevented access for inspection of the bottom of the keels.

2.4

The port hull at the forward end of the skeg had a small area of damage. The wooden support beam made access difficult to see the full extent of the damage. This beam will need moving aft slightly to enable this area of damage to be repaired. It will need grinding back to good laminate and re-laminating with epoxy resin which has a superior bonding strength.

Recommendation: The wooden block supporting the keel will need moving aft to allow access to the damaged area. The area will need grinding back to good laminate and then re-laminating using epoxy resin. (A)

11. Stern Gear.

11.1

Two Volvo saildrive systems with three blade folding propellers.

11.2

The 18 x 16 (18 = diameter 16 = pitch)  LH propellers with high skew blade tips. A part number was on the boss which was 3584032. The propellers are in good order with no damage or corrosion noted. These were heave tested and no play was noted in the folding mechanism.

11.3

The saildrive legs are in a satisfactory condition with no damage or corrosion. Weight testing confirmed that the legs were secure with no undue movement.

Note: Volvo recommend replacing the saildrive diaphragm seal every seven years. Inquiries should be made to see if the seals have recently been replaced.

5. Deck moulding.

5.1

The GRP deck was moulded using chopped strand mat, woven rovings and white pigmented gelcoat externally. Flat areas of the deck are of sandwich construction with end grain balsa core stiffening. Plywood is usually incorporated into the laminate in way of load bearing fittings and areas of high stress.

5.2

The deck was integral with the Coachroof and Cockpit, no stress crazing was noted around rigging attachment points or load bearing fittings.

5.3

The mast is deck stepped, a load bearing, polished stainless-steel pole is positioned beneath the mast in the main saloon. There was no signs of cracking or damage and no distortion noted in the deck around the mast step.

5.4

The deck had a teak overlay which is badly worn. In certain areas, mainly starboard side forward, the deck had become detached from the deck laminate. In several areas the paying is worn or missing. When originally laid the teak was bonded and screwed to the deck laminate. This can be seen because lots of the wooden screw plugs are missing. When screws are driven through the top of the solid laminate this provides a potential path for moisture to enter the balsa core. Moisture readings cannot be taken on the teak itself and inside the vessel few areas exist where the deck-head can be accessed. Therefore, I cannot say for sure that no underlying problems with the balsa core are present, without destructive testing. Moisture readings were taken around deck fittings where possible and found to be low.

5.5

A small hatch had been retrofitted in the deck on the starboard side forward. The section of deck which was cut out to fit this hatch was found in one of the cabins. I was able to see from this section the thickness of the teak decking and the condition of the balsa core which was good. Unfortunately, this does not mean that the rest of the deck is in the same condition.

5.6

The deck was heavily walked on and found firm underfoot except for one small area. Just aft of the port side mast pulpit, is a small area where the deck is not firm. Pressing down with one foot, I found some flex to the deck, which is not the same on the opposite side. From the section of the deck that I found, altogether the deck is 40 mm thick. The balsa core is 20 mm, the top and bottom laminate is 5 mm each and the teak deck was 10 mm.

Recommendation: The areas where the teak had become detached from the laminate will need lifting and re-bonding to the laminate. All missing paying and missing screw plugs will need replacing. (A)

9. Bulkheads and structural stiffening including internal mouldings.

9.1

Several components contribute to the overall structure of the vessel. A, the internal bulkheads, B, longitudinal stringers and C, furniture and mouldings which have been bonded in.

9.2

Where seen due to restricted access, beneath inspection panels, in the engine compartment, under the bunks and in any other compartments. All the reinforcements appear to be firmly fibre glassed in with no signs of cracking or movement.

9.3

However, a problem exists with the bonding of the transverse bulkhead on the starboard side between the saloon and forward head. In the bilge area the plywood on this bulkhead had rotted and the laminate had parted from the plywood. The cause of this is a leak from the shower tray in the head, which had not been made watertight when fibre glassed in.

9.4

A problem exists with the bonding of the longitudinal bulkhead of the aft head. The shower tray of the aft head had also been leaking and this had caused the plywood around the shower tray to rot. The same recommendation is given for the repair of the forward head. Figure 11

Recommendation: The rotten plywood must be replaced, and the bulkheads must be re-bonded to the hull. The shower trays will need re-fibre glassing to make them watertight.(A)

33.3

Water maker fitted but not used or serviced for some years (brokers details)

Note: If Water makers are not treated with a storage biocide when not in use for long periods. Nasty stuff can grow on the membrane causing damage and an expensive replacement.

Steel

Steel is a material formed of Iron Ore and Carbon plus other elements. The elements used give the steel producers the mechanical and chemical properties they want to achieve. Steel has been used to build ships for over 200 years now. Modern steels for shipbuilding have a higher tensile strength to the steel used for earlier ships built. They now contain Carbon 0.21% max, and small amounts of Manganese, Silicon, Phosphorus, Sulphur, and Aluminium. This gives them an ultimate tensile strength of 400 – 520 (N/mm2). The production of Steel has now become a very precise science. In Europe, the International Organization for Standardization (ISO) specifies standards for ship building materials (ISO, 2011).

A yacht made from steel will be very strong but it is the heaviest out of all the boat building materials. Corrosion on steel can be a continuing problem and a maintenance headache. Some very good marine coatings are available on the market these days to help protect steel. However, if the yacht knocks or scrapes into something this can get damaged. Wood, Aluminium and FRP all burn, this makes steel the only fireproof material for yacht construction. It also has good green credentials as steel can be recycled.

Aluminium

Good strength to weight ratio, Aluminium is lighter than steel for the same strength. For example, very roughly speaking, and neglecting corrosion allowance in steel, aluminium plate should be between 1.25 and 1.5 times thicker than steel for the same strength. Aluminium, though, weighs 168 lb./cu. ft. vs steels 490 lb./cu. ft. only 34 percent of steels weight. A lightweight boat means a lower centre of gravity for better stability and sea worthiness. More speed for less power or sail area which means improved performance. Which is the main reason aluminium was used for racing yachts for many years. Which is the main reason aluminium was used for racing yachts for many years.

Aluminium being a softer metal, it is easier to work into any shape required for a hull. Aluminium does not rust as the surface forms an oxide coating which protects it. It can suffer corrosion if dissimilar metals are in contact with it, or stray currents, but so can steel. It does not require added plate thickness to allow for corrosion. Aluminium is expensive but if you compare it with the weight of steel needed to build the same size yacht. With metal being bought in £’s per lb in weight, it will be nearly half the weight of the steel needed. Aluminium has good green credentials as a boat building material which can be recycled. Aluminium has a higher scrap value compared with Steel.

Design and Construction

A steel vessel is made watertight with the hull and deck plating. The steel used should be ductile enough to be shaped, but still stiff enough to withstand the forces of the sea. However, the vessel gets its strength from its structure which is made up of transverse frames, internal bulkheads, and longitudinal framing. The structure is designed to allow a certain amount of flexibility. But must be strong enough to withstand the forces imposed upon it by water pressure. Therefore, the framework is tack welded to the hull plating. This makes the hull plating into small panels which do not bend so easily.

For example: A 4.75mm thick aluminium plate 250mm by 750mm will deflect by almost 1 x it’s thickness (4mm) when a pressure loading of 12PSI is applied. However, a larger panel, 400mm x 1000mm, would deflect by approximately 20mm with the same pressure applied.

The vessel’s structure will have the weight and torque of the engine, fuel, freshwater and other equipment creating an opposite force to the water pressure. The rig of a sailing yacht also causes loads on the structure, with the tension of the mast’s stays and sails. The careful design of the vessel must spread the various loads over the internal structure. This must also support the hull and deck plating to prevent collapse under various loads, as above.

Surveyors Test Methods

A surveyor must try to find defects on a steel or aluminium vessel without doing any destructive testing. A surveyor looks for defects by looking into every space onboard a steel or aluminium constructed craft. Getting down into the bilges and engine compartments with his torch and magnifying glass. Looking for cracks, dents, rust, broken parts, or bad construction practices, which could affect the structural integrity of the vessel. To do this difficult job he has certain test methods available to help him come to his conclusions. First is his sight and good lighting for visual inspection. A mirror with a light on a long handle is handy for reaching difficult to get at spots. I have a snake camera/video scope for this which is a camera on a bendable probe. The picture comes up on my phone through a Bluetooth connection and photographs can be taken with it. A camera is useful for taking photographs of defects which will be added to the report.

A 1kg or 2-pound ball-peen hammer is an especially important piece of test equipment for steel vessels. Along with trained hearing, which becomes used to the percussion when hammering plates, frames, and other parts to check for hidden rust, on steel vessel. The sound from steel when struck with a hammer has a good ring to it. This sound gets duller on thinner plate, through rust or light scantlings. Sometimes, on frames bits of rust will fall off and the remainder of the frame/plate can be measured with a Vernier. When pitting is seen a pit gauge can be used to measure its depth into the surface of the metal.

Testing Welds

When a surveyor is looking for defects in a weld, the first thing will be a good visual inspection of the welds. Is there enough penetration, is there any undercut, porosity, or cracks? Also, is there enough weld and is the size of the weld big enough for the thickness of the metal. The surveyor can use a dye penetrant to help him with his visual inspection. First the weld is cleaned with a wire brush, preferably a stainless-steel brush if on an aluminium hull. A dye penetrant is simply just sprayed on, then after a few minutes the excess is wiped off and a developer is sprayed on. The developer draws the dye out of the surface defects and shows up any cracks or porosity.

Ultrasonic Thickness Gauge

A steel vessel can loose some plate thickness each year. The equipment used for finding the vessels plate thickness without destructive testing these days is called an Ultra-sonic thickness (UST) gauging equipment. The traditional way was to drill small holes in the hull. However, with the new ultra-sonic testers which have probes which use a multiple echo. This allows measurements to be taken through surface coatings, which means not even the paint is damaged.

I have an ultra-sonic thickness meter to determine the remaining plate thickness of the hull structure. I have a Cygnus 4+ Ultrasonic thickness gauge which is compact and portable. It is a handheld instrument with a digital display and is designed for the marine environment. It can be used with a choice of ultrasonic probes to suit the material and thickness. The gauge measures material thickness using three methods; Single Echo, Echo-Echo or Multiple Echo. Echo-Echo and Multiple Echo allow measurements through surface coatings. Ultrasonic thickness surveying (UTS) is a non-destructive measurement of the local thickness of a solid object like metal. An ultrasound wave travels through the metal and reflects off the other side at a constant speed. Using the measured speed, called the celerity, and the distance travelled by the wave. The object’s thickness is then calculated by the meter.

They say that buying a boat can be the best day of your life. However, they also say that the second best day is when you sell your boat. Owning a boat can be a joy and pleasure, full of adventure.

The first decision to make when buying a boat is the type of boat you will need to suit what you intend to do, Sailing, Fishing, Speed, Inland Waterways, etc. The amount of money you have available could also be a big factor. Some bargains can be found if you are the type of person who would like and be able to do some work yourself.

The type of material a boat is made of should also be taken into consideration. Boats do take a lot of looking after and if you have never owned a boat before their is a lot to learn. If you can afford to put your boat in a boat yard every year and have them do all the work, then great. If not then you must be prepared to roll your sleeves up and get stuck in. All boats need some maintenance, some more than others.

Wooden boats are beautiful and romantic with glossy painted topsides, shining varnish, and polished stainless-steel. However, this all takes a lot of work to keep it that way. Wooden boats don’t like rain and they don’t like the sun. The sun’s UV rays damage the varnish and rain causes rot. If you buy a wooden boat you could be spending more time working on it than sailing on it.

Many production boats are built these days with Glass Reinforced Plastic (GRP). They are not maintenance free but they easier to look after than other materials.

Surveyor

A surveyor is like a detective and he spends his working day looking for clues. These clues are often hard to find, and sometimes they are deliberately hidden by the present owner or repairer of the boat. This means that he has to observe accurately and continuously and report what he finds in clear understandable English. He requires good knowledge and must keep track of advances in technology. Above all he must be honest and behave in a professional manner.

Yacht Surveying

There are different types of survey requirements which boat owners will require. With a lot of second-hand boats on the market the pre-purchase survey is the one that is asked for the most. People purchasing a second hand boat want to know the condition of the vessel they are about to purchase. They want peace of mind so that they do not later find that the boat they have just bought is going to cost them lots more money. We can take care of your surveying needs as we perform all of the following vessel surveys.

Pre-Purchase survey

If you are about to buy a boat it is strongly advised that you have it surveyed first. A pre-purchase survey is the most comprehensive type of survey. The surveyor will check the condition of the vessel and this will in include. The integrity of the hull and deck, all on-board systems and safety equipment. This will include an out of the water survey and sea trials.

Insurance survey

This type of inspection is not as comprehensive as a pre-purchase survey. However, older boats are required every 5 to 7 years by insurance companies to have a survey report on the condition of a vessel. The surveyor will check the condition of the vessel to ensure that it is in a condition to be an acceptable risk. the insurance company will also want to know that the vessel is in a safe condition for its intended use. They may also want to know its currents market value.

Appraisal inspection

This type of inspection is performed to collect enough information to work out a current valuation for the vessel. This is normally needed for financing, estate settlements, donations and legal cases.

Damage inspections

The surveyor can sometimes be retained by an insurance company to investigate the cause of a loss. He will need to report on the extent of the damage and advise on possible repairs and costs.

MCA coding

Any British registered vessel which is used for commercial use. Will require coding to the MCA code of practice. This will possibly require the surveyor to visit the vessel several times. At the first inspection the surveyor can give the owner a list of requirements which he will need to be in compliance with the code. He can then revisit the vessel when the requirements have been completed for the final inspection.