Which hull material should you choose when buying a yacht? There is no ideal boat building material, they all have advantages and disadvantages. In this article we’ll show the advantages and drawbacks of GRP, steel and aluminium as hull materials in yacht building.
Boats made from GRP
Advantages of GRP yachts
Readily available
Let’s start with the most common of all boat types: GRP boat (glass fiber reinforced plastics). And that brings us to the first major advantage: availability. GRP yachts are the most common on both the new and used boat market. The choice of GRP yachts, whether new or used, whether for the Mediterranean or for sailing around the world, is huge.
GRP yachts make up the majority of yachts
Easy to clean
GRP stands for glass fiber reinforced plastic – simply put, plastic. GRP as a hull material means easy maintenance! GRP boats are the easiest of all boats to maintain. Their gelcoat needs to be cleaned with soap and water, occasionally a little wax and even less frequently a polish. After around 20 to 40 years, depending on the thickness of the gelcoat and the owner’s keenness to polish, the gelcoat is polished through and the hull and deck need to be painted.
20 year old GRP yacht
The gelcoat is easy to care for and has hardly aged at all
Easy to repair
Repairs to yachts made of GRP are very easy to carry out yourself. No welding equipment required, just some resin, mats and sanding equipment.
Disadvantages of GRP yachts
Osmosis
Acute osmosis
This boat is in the middle of a refurbishment
Most yachts were and are made of polyester laminate, which is not water-resistant but is cheap. The gelcoat, which is supposed to form a protective barrier between the water and the laminate, is more water-resistant because it is denser, but it is not completely impermeable to water. Over time, moisture therefore diffuses into the laminate and leads to destruction over the years – which can be seen in the form of blisters on the hull in the acute stage. If the blisters give way when pressed with a screwdriver and a liquid smelling of vinegar escapes, then you are dealing with osmosis. In this case, depending on the severity, a full refit of the hull should be carried out in order to maintain or restore the stability of the hull. A professional restoration costs around 1000 Euros per meter of boat. This is not cheap, but after treatment you can assume that the problem has been solved and will not return very soon. Nowadays, some yachts are built from vinyl ester resin; this can significantly slow down the osmosis process. The majority of yachts also have epoxy resin osmosis protection between the gelcoat and antifouling. This means that osmosis should not pose a risk.
Comparatively unstable
GRP is less robust than aluminium and steel. Specifically, GRP can break/rip in the event of collision and grounding, while aluminium and steel get dented. However, the story for GRP isn’t quite as dire as it may appear: For yachts built before the 2000s, it was not yet possible to calculate the minimum material thickness required. In keeping with the motto “better to be safe than sorry”, very robust GRP yachts were built back then. These yachts are hardly affected by “normal” grounding and even collisions with growlers (see also: keel bolts). Accordingly, there are numerous examples of sailors who have sailed the North-West Passage in GRP yachts. Newer GRP yachts with thin laminate are no longer suitable for such trips, but are perfectly adequate for a “normal” circumnavigation.
Unlike steel and aluminium, GRP can rip and crack
Steel boats
Advantages of steel yachts
Very stable
Those who place particular importance on safety or are planning trips to extreme areas may opt for a steel yacht. Boats made of steel are extremely robust and forgive the odd grounding. Instead of breaking like GRP, steel is more likely to dent if it hits the ground. Due to their high dead weight, steel yachts sail very smoothly and, like heavy old GRP boats, are forgiving if they are reefed too late.
Dented steel after ground contact
This ship took on water despite its steel hull
Inexpensive
Compared to similar yachts made of GRP or aluminium, steel yachts are less expensive. So if you are on a budget, a steel yacht can be the sensible choice, if only because you can afford it. For the same money, you often get a few feet more on a steel yacht.
Disadvantages of steel yachts
Galvanic currents
Not as pronounced as with aluminium yachts, but steel ships are also at risk of galvanic corrosion. Installation errors in the electrical system can quickly lead to problems, as salt water in particular is a fantastic conductor.
Slow
As mentioned above, steel yachts tend to sail good-naturedly. You will certainly be pleased if you sail a boat that can cope with a lot in heavy weather. But if you want to sail fast even in light winds, a steel yacht is probably the wrong choice for you. Due to the high weight, it takes more wind for a steel yacht to get moving.
A steel yacht like this takes you everywhere
Very robust, but probably also slow
Intensive care
Steel boats require a lot of maintenance. Even boats that are galvanized (although this is rare) suffer from rust. Steel boat owners will jokingly say: “I’m painting my way around the world”. One serious problem is the formation of rust inside the boat, between incorrectly fitted insulation and the hull. If condensation forms there, the boat rusts from the inside out.
Spot rust treatment of the bilge of a steel yacht
A steel yacht requires a lot of maintenance
Conditionally DIY-friendly
GRP boats can be easily repaired with epoxy and mats that fit in any locker. Welding steel is not difficult in itself, but you need to carry a welding machine if you want to weld it yourself. However, the advantage of steel over aluminium is that there will be someone on every island, no matter how small, who can weld and has a welding machine as long as there are cars on the island. So the actual welding process is not necessarily a problem, but the preparatory work is. If you want to weld a spot in the hull above the water line, you first have to remove the insulation around the welding point, which is often located behind furniture in the interior. It is quite possible that you will have to dismantle the boat for two days to weld for 10 minutes.
Boats made of aluminium
Advantages of aluminium yachts
Robust
Aluminium yachts are considered to be very robust and safe. Similar to steel, aluminium dents in a collision and only tears in extreme situations. Unlike steel yachts, however, aluminum yachts are not particularly heavy and therefore sail faster in light winds.
Relatively easy maintenance
Aluminium yachts therefore have desirable characteristics in terms of safety similar to steel yachts, but do not have the same disadvantages. They are generally easier to maintain because rust is not a problem. Boats made of aluminium can be used unpainted.
An aluminium yacht
Here the aluminium was left raw and not painted
Disadvantages of aluminium yachts
Electrolysis & Corrosion
Although aluminium does not rust, corrosion is a massive problem with aluminum boats. Aluminium is much more reactive than steel and much more reactive than stainless steel. This means pitting between, for example, a stainless steel cleat and the aluminum deck if the metals are not well isolated. A properly installed electrical system is particularly important on aluminum boats! All electrical devices, including the engine, must not be grounded and the battery minus must only be connected to the hull at a single point to prevent currents flowing. The shore power installation must also be meticulously installed and a polarity warning device must be fitted to prevent damage to the boat. Copper-containing antifoulings such as Coppercoat must also not be used on aluminum (or at least not directly), as this would corrode the aluminium.
Aluminium yacht with severe corrosion
The entire hull is damaged due to an electrical wiring problem
Expensive
Aluminium as a hull material has another drawback, namely the price. Aluminium yachts are comparatively expensive to buy. With the same equipment and the same boat size, the steel yacht will probably be the cheapest, followed by GRP and finally aluminium.
Rare
Aluminium boats are quite rare on the used boat market. Once you have settled on aluminium as a boat building material, you will have to be patient, simply because aluminium boats are less common than plastic and steel boats.
Not DIY-friendly
Welding steel is fairly easy, even without much experience. Welding aluminum is more difficult and requires experience. You also need a special welding system, which you may not find on every atoll in the Pacific. As with steel boats, you may need to carry out lengthy preparatory work, including removing the insulation, before starting a welding project.
Difficult to paint
If you don’t like the look of raw aluminium, you will have a hard time in the long run. Paint does not adhere well to aluminium and often blooms after a short time, even with professional paintwork.
GRP, steel or aluminium?
Just as an aside: Yachts made of wood, ferro-cement and stainless steel are not covered in this article, as we generally advise against these materials, especially for a blue water cruising trip, but also in general, as the disadvantages outweigh the advantages.
