Perhaps you have already read our article about the best reasons to live on a boat and we managed to convince you? And now you are looking for a proper cruiser sailboat to turn your dream of living as a liveaboard into reality? Sooner or later, you will definitely ask yourself which hull material is most suitable for a cruiser and this is exactly the question we want to discuss in the following.
What Materials Are Considered?
The materials used for hull construction of sailboats are GRP (glass fiber reinforced plastic), carbon, Kevlar, wood, aluminum, steel, ferrocement and also various hybrids of these. Some of these materials are not suitable for use in cruisers due to their specific characteristics. Carbon and Kevlar usually only play a role in extremely lightweight high-performance boats typically found in racing, not to mention that they are astronomically expensive.
Wood disqualifies itself due to the extremely costly maintenance and thus it is not practical for use in cruisers. Ferrocement never really caught on as a hull material and primarily played a role as an easy-to-handle material in DIY sailboat construction. This leaves GRP, aluminum, and steel as materials that come into question for us.
GRP vs. Aluminum vs. Steel
In the following, we will take a closer look at these three materials and compare them with each other under various aspects that are important for a cruiser.
Strength
GRP is the weakest of the three materials, especially when it comes to impact and abrasion resistance. However, the strength of GRP is highly dependent on its processing quality, as GRP can be laminated in very different ways, which can make for large differences in stability. For example, the first GRP boats built in the 1960s and 1970s often featured much thicker material thicknesses because people were not yet familiar with the material and this resulted in nearly indestructible hulls. There are also some manufacturers who additionally reinforce their GRP hulls with Kevlar or metal inserts. So, there are a lot of differences in terms of stability, but in general a GRP hull is clearly inferior to metal hulls in terms of stability.
In the video below you can see a few crash tests of a Dehler 31, which is made of GRP and takes the collisions impressively well.
Aluminum and steel hulls, on the other hand, have extremely high impact and abrasion resistance, with steel being even slightly superior to aluminum here, as steel is more elastic and has a higher tensile strength. Thus, a metal boat is much more robust and therefore safer than a GRP boat, especially in collisions.
Weight
GRP is far superior to steel in terms of weight. For boats up to about 40 feet, it is also superior to aluminum, since aluminum has a minimum thickness of about 5mm making smaller boats heavier than their GRP competitors. Above the 40-foot mark, the tide can turn, and aluminum may be lighter than GRP, but it depends on the exact construction.
Aluminum as a material itself weighs only about a third as much as steel, but the typical weight saving of a hull is typically 20-25% (but up to 50% savings are possible in some cases). This can be attributed to the fact that aluminum requires thicker material thicknesses than steel.
As should already be clear, steel boats are by far the heaviest of the materials we are considering here.
Sailing Characteristics
The sailing characteristics are of course not primarily dependent on the hull material, but rather on other characteristics such as the hull shape, the rig, etc. Nevertheless, certain characteristics are attributable to the hull material.
GRP boats sail very fast because of their low weight, but the residual flexibility that is unavoidable in the material can cause annoying creaking noises inside the boat.
Aluminum boats, on the other hand, also sail very fast, but much more stiffly and you are not plagued by creaking noises.
Steel also makes for stiff sailing and there are no creaking noises, but due to the enormous weight, a steel boat sails rather sluggishly. However, the high weight also gives steel boats good-natured sailing behavior, which is more likely to forgive too much sail area.
Interior Space
Unlike metal hulls, a GRP hull does not need an internal reinforcement structure that reduces the space inside the boat. Thus, GRP boats offer a lot of interior space relative to their dimensions.
The stability of aluminum hulls, on the other hand, depends on an internal reinforcement structure (consisting of frames and stringers), which takes up some of the valuable space inside the boat. Especially for smaller boats this can be more important than you might think. In the image below you can see the construction of an aluminum hull built by Dutch shipyard KM Yachtbuilders.
Steel boats also need such a reinforcement structure, but it is much more compact than that of aluminum boats, thus offering more interior space.
Insulation Properties
Due to its sandwich construction, GRP is inherently a poor conductor of thermal energy and therefore requires little insulation and, under certain conditions, none at all. Along with the good insulating properties, GRP boats also have less condensation to contend with than their metal competitors. In addition, it also has good sound insulation.
Aluminum and steel boats have very similar properties in terms of insulation. Both materials are very good thermal conductors, which makes good insulation essential. Due to the cold bridges found in metal boats, a lot of condensation occurs inside the boat. The sound insulation of metal hulls is also poor.
Visual Design Options
GRP hulls offer a lot of room for styling, since gelcoats are available in all possible colors and applying them is easy. Another big advantage of GRP is that round shapes can be realized very easily with this material, which makes ergonomics and design very appealing.
In contrast to GRP boats, round shapes in metal boats can only be achieved with significantly more cost as this requires a lot of effort and special skill in welding. The many welds on metal boats can in some cases look rather rustic, which may bother some people.
Aluminum hulls usually leave the shipyard unpainted, as painting them is very time-consuming and expensive and therefore rather unusual. The raw aluminum look does not appeal to everyone.
Steel boats can be painted as desired, but they almost always have minor visual rust spots somewhere, which are hardly avoidable.
Safety During Thunderstorms
Unlike metal boats, a GRP boat offers no protection to the boat, equipment, and crew against lightning strikes, and you are dependent on a proper lightning conductor system.
In contrast, boats made of aluminum and steel provide excellent protection against lightning strikes purely due to their construction, because they act as a Faraday cage – the inside of the electric field created by a lightning strike is reliably shielded.
Risk of Material Decomposition
A known risk of material degradation of GRP is osmosis, which occurs when the hull is not properly protected, and moisture can penetrate through the gelcoat where the moisture collects in the hull cavities. The resin in the laminate is decomposed by the penetrated moisture and an acid is produced. Due to its chemical properties, it draws further moisture into the cavities. The pressure in these then increases and pushes the gelcoat outward forming blisters. The brittle gelcoat cracks open and the laminate is progressively decomposed as osmosis continues.
However, we want to emphasize that osmosis is often overdramatized, and we are not yet aware of any case where a boat has actually sunk because of osmosis. Nevertheless, you should not underestimate this danger and prevent it from happening in the first place through proper care. Unfortunately, structural defects in the hull of used boats caused by osmosis are difficult to see as a non-expert.
In the case of aluminum, there is a risk of galvanic corrosion, in which the base metal aluminum decomposes under the influence of electric current when it comes into contact with a more noble metal. Although such galvanic corrosion can cause considerable damage to the boat within a very short time, this risk can be virtually eliminated if the boat is professionally constructed and regularly maintained. However, this means that any electrical leakage currents must be eliminated, and the many sacrificial anodes must be maintained. Besides, when it comes to electrical installations, you need to know what you’re doing.
Steel is generally known to be very susceptible to corrosion. Once steel comes into contact with oxygen in the presence of water, rust forms as a result of oxidation. As owner of a steel boat, there is not much you can do against the constant danger of corrosion, except to always make sure that the steel is protected from external elements, which requires a lot of maintenance. In addition, it should be emphasized that the greatest danger of corrosion is the rusting through of the hull from the inside to the outside and not the other way around. Often it is difficult to see all the areas inside the hull and this harbors some undetected dangers.
Repairability
Even fairly extensive damages in the GRP can be repaired quickly and easily because all you need are fiberglass mats, resin, and hardener. Minor blemishes in the gelcoat such as scratches or small chipping can be repaired with ease.
Repairing aluminum, on the other hand, is much more difficult, because you first need aluminum plates with the right alloy, and then you also need the right welding equipment. In addition, not everyone has the necessary know-how to weld aluminum properly. Minor blemishes such as scratches can be polished, and dents can be attempted to bulge from the inside. However, if you can’t get to the dent from the inside, you’ll have to live with it willy-nilly.
Steel must be welded as well, but suitable steel plates can be found in most workshops around the world and welding is also much easier than welding aluminum. In addition, the required welding equipment is cheaper and more widely available. The repair of scratches can be easily done yourself, but this is often much more time-consuming than repairing the gelcoat on GRP boats. Dents can be attempted to be removed in the same way as with aluminum boats.
Maintenance Effort
The maintenance effort is kept within limits with GRP. You should just sand, fill and seal the underwater hull regularly. The great thing about GRP is that such maintenance can be postponed once in a while without having to fear immediately serious consequences (but don’t let it become a habit!).
Aluminum boats also require little maintenance, as you only need to regularly renew the antifouling coating and maintain the numerous sacrificial anodes, as well as ensure that there is no potential for galvanic corrosion. However, unlike GRP, the maintenance of aluminum boats allows significantly less time leeway, because if galvanic corrosion does occur, it can cause significant damage in a very short period of time.
Steel boats, unlike GRP and aluminum, require constant maintenance, as there are virtually always some rust spots that should be treated early to prevent worse. At regular intervals, the entire hull should also be sand stripped followed by priming with an epoxy system and then sealing with a paint (polyurethane based). Although a steel hull does not rust as quickly as aluminum does with galvanic corrosion, you should avoid postponing maintenance for anything, otherwise nasty surprises can await you.
Costs
The cost of GRP boats, from serial and semi-custom production is the lowest compared to those for metal boats. This is mainly due to the fact that a mold only needs to be designed once, which can then be used for all builds of the model. Custom builds, on the other hand, cost significantly more because a mold must be made individually, which involves high costs.
Metal boats are more expensive in serial production as they require a lot of manual welding, with aluminum being even more expensive than steel due to the more complex processing and higher material prices. However, metal boats can be more attractive than GRP for custom builds, but it depends on the individual project.
In addition, it can be said that aluminum boats have a very good value retention compared to GRP and steel boats, which is also reflected in the second-hand market. On the second-hand market, aluminum boats are usually traded at very high prices, whereas GRP boats depreciate significantly and there is a large supply at low prices. The supply of steel boats is rather limited, but the prices for them are nevertheless rather low.
Besides these initial costs, you should also always consider the follow-up costs, because these can make a lot of difference in the long run, especially when you look at the differences in maintenance requirements. Consider how much time and money you will have to put into the boat and even if you want to do most of it yourself, keep your individual opportunity costs in mind.
A Summarizing Overview
In the table below, we have briefly summarized the various characteristics of the respective materials.
| GRP | Aluminum | Steel | |
|---|---|---|---|
| Strength | + | ++ | +++ |
| Weight | +++ | ++ | + |
| Sailing Characteristics | +++ | +++ | + |
| Interior Space | +++ | + | ++ |
| Insulation Properties | +++ | + | + |
| Visual Design Options | +++ | + | ++ |
| Safety During Thunderstorms | + | +++ | +++ |
| Risk of Material Decomposition | ++ | ++ | + |
| Repairability | +++ | + | ++ |
| Maintenance Effort | +++ | +++ | + |
| Costs | +++ | + | ++ |
An Important Note
Finally, we want to note that there is no such thing as the perfect hull material, because as we have pointed out, each has its strengths and weaknesses. Keep in mind that the properties of the various materials we have discussed are the general ones that apply to most boats. However, the properties of a hull also depend on the specific boat because construction and quality of workmanship are at least as important as the material itself. When comparing different hull materials, you should always keep these differences in terms of construction and workmanship in mind and not compare apples with oranges. It would not make sense to compare a production GRP boat produced under cost pressure with a custom aluminum boat and then conclude that the GRP boat is inferior to the aluminum boat.
Our Recommendation
In general, we claim that for the majority of people a GRP boat makes the most sense. It is very user-friendly in both use and maintenance and is also relatively affordable. We see no reasons against the use in bluewater or for a circumnavigation, although this scene is strongly influenced by advocates of metal boats. We can certainly understand the aspect of increased safety of metal boats, especially in collisions, but we doubt that this justifies the disadvantages of steel or the additional costs of aluminum. Severe collisions are of course a high risk, but always keep in mind how low the probability of such a collision actually is. Nevertheless, we can understand that the increased sense of safety is a very high priority for some.
When using the boat under extreme conditions, such as in Antarctica or Patagonia, we would also want to use a metal boat due to its increased robustness. So, it’s best to ask yourself honestly which areas you actually want to sail.
In addition, you should also let your own skills and experiences that you have made with the respective material flow into the decision-making process. For example, if you have had a lot of professional experience with steel processing, then you will see the work involved in a steel boat from a completely different perspective… In this sense, listen a little to your gut feeling.
And last but not least, as already mentioned above, it always depends on the specific boat and especially if you are on the second-hand market, you can certainly be a little more flexible with regard to the choice of material and look at the overall package. But we hope that we could help you understand what to expect from the different materials and assist you in making your decision.
If you have any other questions, need advice on your upcoming boat purchase, or want to give us feedback, feel free to post it in the comments, we’ll try to answer everyone!
Happy sailing!
