Hull Construction Materials

When searching for your perfect boat, the question of hull material will inevitably come up. The most common categories are fiberglass, wood, and metals; lesser seen categories are carbon, kevlar, and cement. 

Exotic Hull Materials

High Tech Materials

Kevlar and Carbon Fiber hulls are typically found in the ultralight and high performance yachts. These materials have incredibly high strength to weight ratios, creating hulls of mammoth proportions and negligible weight. The price tag of these yachts keeps pace with the astronomical properties of these construction materials, and the cost of repairing any damages that might occur to these hulls is pricey. Even more difficult than the yard bill to fix an issue is the struggle to find qualified skilled technicians who know how to work with these materials. Large cities will usually have one yard that is capable of handling these repairs, but a small yard on a tiny island may not be able to help with these repairs.

Cement

Cement hulls were popular for amateur boat builders. It was advertised as an easy way to make a cruising boat, you could buy the molds and get a bunch of friends over to mix and pour the cement. After the cement cured, you could pop it out and sail it (after you finish the rest of the construction, it is funny how kit boat companies make it sound like building the hull is the hard part)! The problem with cement boats is the integrity of the hull greatly depended on the skill of the builder. If the cement was not mixed properly, the hull could develop cracks and leak. The other problem with cement boats is insurance companies do not like them, so finding insurance for a cement hull can prove difficult.

All this aside, there is a cement boat in my marina that has been abandoned for years.  The owner died and the heirs have not come to collect it. This boat has been rotting away for the past 4 years with no maintenance, and it still floats! The paint is peeling and her topsides look like hell, but the boat doesn't leak, doesn't fill with water, and doesn't sink. This is probably an example of a well made cement hull, which shows that any well made boat will last a long time.


Popular Hull Materials

Looking at the more common hull construction materials, we see wood, fiberglass and metals dominating the scene. Each has their strengths and weaknesses, proving that none is better than the other. It really is a personal choice about which hull material you prefer. If the cons outweigh the pros from your perspective, then that is the wrong hull material for you. On the contrary, if you don't mind the drawbacks and love the strengths, that is certainly the perfect material for you!

Metals

Metal hulls fall into two main categories: Aluminum and Steel. Metal hulls in general are favored for their high strength and durability. People who are comfortable working with metal tend to love metal hulls. To them, it is a known material that they feel confident in their ability to repair. Steel hulls are preferred by people who plan to sail in high latitudes and will run into ice. Steel hulls offer excellent durability and repairability, if you were to collide with a reef, sandbar, or ice sheet, the steel will simply rub on it without much damage. Thicker steel hulls will offer more puncture resistance and added durability to the wear and tear of uncharted cruising where groundings and collisions are inevitable.

Aluminum hulls are very light weight and incredibly strong, making them a favorite material for boats over 80 feet in length. High performance luxury yachts are made of aluminum because the hulls are lightweight, strong, and sturdy without taking up much interior space in the form of bulkheads and frames. This allows the interior to be finished in utmost luxury and spaciousness. 

While metal hulls may sound like a dream come true, they have one major pitfall: corrosion. Steel hulls rust wherever water accumulates on bare metal. If you rub into a pilling, you need to cover the bare metal in fresh paint quickly to avoid rust from starting. The inside of the boat is at risk of rusting in unseen areas where the paint has chipped and moister has accumulated. Rust can propagate at alarming rates if left unchecked, and it can be difficult to repair when the time comes to recondition the yacht. Steel hulls are repaired via welding new metal onto them. The problem is the act of welding produces incredible heat which will ignite interior joinery and insulation. This makes a simple patch become a arduous project of dismantling and reassembling the interior.

Aluminum hulls won't rust with the epic red bleeding that spews from beneath the paint of a steel hull, instead they corrode in a much quieter way. Aluminum will turn to aluminum oxide, a white dust that will blow away when exposed to moist air, or via galvanic corrosion when immersed in an electrolyte such as sea water. Aluminum hulls must also be very careful about what bottom paint they use, as copper bottom paint will destroy the entire bottom of the hull in a short amount of time due to the dissimilar metals reacting in the solution. If you use the correct type of bottom paint and maintain the hull clean and dry, you still need to worry about stray current in the water. Galvanic corrosion caused by this stray current will eat holes into your hull if insufficient sacrificial anodes are not available. Aluminum hulls will typically have anodes attached all over the hull, hoping that if something will be eaten away by electrolysis, let it be the sacrificial anode. While these holes are easy to fill with a welder, they still require the same amount of disassembly and reassembly to protect the interior from the heat of the welder.

Welders are available worldwide, so your chances of finding a repairman on a remote island are quite high. It would be a good idea to carry some welding wire with you, that way you don't risk the welder accidentally welding on the wrong kind of metal and causing greater problems to your hull. People who have had metal sailboats love them! They feel very safe and secure in their vessel, knowing that they won't sink if they run aground or brush against some rocks.

Wood

Wood is another known material which has been used to build boats for over a millennium, and there is a reason it has been so popular, wood floats! A properly built and cared for wooden boat will provide a very safe and sturdy vessel which can take you across oceans! If you run into problems in a foreign port, you are probably going to be able to find the needed materials and the skilled labor to repair the problem. If you are capable and willing to do the work yourself, you can do all the maintenance yourself which will keep costs down.

While wood may sound amazing, it does have it's draw backs which have given it a bad name. If left in the water, marine borers (worms) will eat away at your timbers. Termites will attack the dry wood inside the boat, and on land the wood will dry out and the seams may pop open. It may seem that wood is in danger no matter where it is kept, but it can be easily repaired with only a few tools. 

Wood boats do need a lot of care. If neglected, they will begin to rot away in their slip, slowly becoming a major undertaking to revive. 

Insurance companies and marinas seem to have an aversion to wooden boats as well. Some marinas won't allow them into their slips or yards. It seems that they feel that stems will open up and draw in the seas, taking them to the bottom and are too much of a liability for them. 

Wood hulls are susceptible to electrolysis damage. Electrolytic damage will cause acidic damage to the wood planks, eating them away and turning them into mulch and mush. Electric connections must be properly installed and maintained to prevent serious damage to the hulls planking.

A well built wooden boat is not a disaster as most will make you believe. Poorly built wooden boats which were not properly maintained simply ruined the name for all wooden boats. It is not uncommon to come across a properly built wooden boat with original frames and planking that is approaching 100 years old. These boats were well built and maintained throughout their lives, letting them be strong cruisers for nearly a century!

The most common issues on a wooden boat are leaky garboards and open seams. If the keels rabbet line is not wide enough, the garboard seam will wear out and open up. This will start a leak that can only be remedied by manufacturing new garboards. Most people will try to over caulk the seam to avoid the task of fitting new garboards, leading to the continued leaks. A leaky wooden boat will have a musty smell, which is what most people think of when they picture a wooden boat.

The truth is, if the rabbet seam is cut properly and the garboard is well attached, the joint will be strong and not leak. When it does finally wear out (as this seam resists the forces of the shrouds pulling up and the keel pulling down), replacing the garboard with a new strake will fix the problem so that the boat can continue sailing along with a dry bilge.

Fiberglass

Fiberglass has been around for a long time now, and has dominated the boating scene as the standard hull material for most boats. When fiberglass was first used in boat building, the builders didn't know how strong fiberglass actually was, so they greatly overbuilt these hulls. Hulls from the 1960s will typically be very thick and not cored. 

The benefit to a very thick, non-cored fiberglass hull, is they will last forever! The draw back to these hulls is they are insanely heavy. Fiberglass hulls from these years were the pioneers, testing the waters with these plastics. It turns out that these hulls did hold up over the years, as is evidenced by the number of boats from these years that are still floating.

As time progressed, they soon realized that the hulls could be much thinner and still be strong enough to provide a safe boat. Core materials were also incorporated into the hull construction to produce a very strong and light weight hull. 

Thinner hulls do tend to flex more, and some brands of sailboats are famous for this flexing; at the same time, the weight savings greatly adds to their performance. Everything on a boat is a trade-off, you just have to find the kind of boat that you are happy with.

Cored hulls are a double edge sword, similar to sail battens, they are great when they work and will be the root of all your problems. Cored hulls add thickness to the hull without adding much weight. A thicker hull will be much stiffer and stronger than a thin hull. Adding a core adds thickness without adding much weight to the hull, resulting in a much stronger hull without the added weight. If a solid fiberglass hull were made to be as thick as a cored hull, it would have a similar strength but it would also be insanely heavy. This sounds great, but cores tend to rot when they are exposed to moisture, leading to delamination issues and costly repairs. 

Cores are supposed to be applied to the hull as the fiberglass layers are being laid up. Layers of roving and chop strand mat will hold copious amounts of wet resin which will adhere blocks of wood or foam to the hull. This wood or foam is the core. After the core is added, more layers of resin and fiberglass will be added and allowed to cure. The core needs to be fully saturated with resin before it is applied to the underlying mat, but it rarely is done this way. What usually happens is the core is a bit dry and acts as a sponge, drawing the resin out of the mat and into the core. This dry pocket that develops is the beginning of the end for a cored hull. This dry space will slowly collect moisture and begin to rot the core. 

Sadly, no brand of boat is exempt from this problem. I have seen quality boats like Hatteras and Kadey Krogen suffer from dry cores delaminating. These boats underwent the long and costly process of re-coring the entire hull, which left the owners with a very strong and sturdy yacht after the expensive yard bill was paid.

You might be wondering why boat manufacturers don't use a bit more resin and avoid these problems? It is once again due to a trade off. Hull strength comes from the fiberglass and not from the resin that binds it together, the more resin used, the heavier and weaker the hull will be. In order to minimize weight and maximize strength, hull manufacturers use various techniques to mass produce a strong hull with as little resin as necessary. The result is a very strong hull with the risk of core failure. 

Another issue that plagues fiberglass hulls is blisters. Blisters are caused by water getting into the layers of the fiberglass and causing little bumps on the hull. They don't know exactly why some hulls develop blisters and others don't, but some boats will have blisters develop everywhere while other boats will hardly develop any. Blister repairs are costly and time consuming, and their necessity is debated. Some claim that they can lead to larger delamination issues, others disagree. While small blisters are more of an eyesore than a structural problem, large blisters (larger than a few inches) should be repaired as they can cause costly repairs later on. Wooden boat owners often tout that their hulls will never develop a blister, but a blister won't sink a fiberglass boat.

One major advantage of fiberglass hulls is they are more resistant to neglect. While I don't condone neglecting your boat, it won't kill your fiberglass boat to sit in the water for months on end. Growth will form and dirt will collect, but the boat will continue to float until you return. Fiberglass offers a more flexible maintenance schedule over other materials. Wood hulls need to be hauled every year for maintenance and inspection of the strakes; metal hulls need to be hauled to check for electrolytic damage and corrosion below the waterline. Fiberglass hulls don't need this rigorous schedule. Two year maintenance rotations are commonplace, where the boat is hauled for a few days every two years to apply new anti-fouling paint. Bottom cleaning and anode replacement can be completed by way of diver or short haul in between the maintenance hauls. I know of a couple who has had their boat in the water for the past four years without a single haul out. They have a diver clean their bottom every two months to knock off any growth that has started up and to change their prop shaft anode.


When considering the hull material for your next boat, take into consideration the amount time you have to devote to maintenance and the resources you have to pay for repairs. Doing the repairs yourself will save a lot of money, but you still need to pay for materials, making any repair "not free".

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