Did you know that there are 44 shipyards and ship repair facilities in the US spread in 15 states that build and repair with aluminum?
This evidently indicates that aluminum is increasingly replacing steel as the favored hull material in naval applications as it offers diverse capabilities aside from reduced operating costs.
Weight Advantage Over Steel Or FRP
A hull structure made of aluminum built to the same standards has a weight that is between 35% and 45% less than a steel hull structure. This means that a well-designed aluminum boat can be lighter in weight but stronger than other counterparts such as fiber-reinforced plastic (FRP) or stainless steel. The hull weighs two-thirds the weight of an FRP boat and less than ½ the weight of a steel hull of similar size.
Large Displacement Needed By Smaller Vessels
The issue of the weight of the hull structure has more impact on smaller vessels as larger vessels are able to carry the needed displacement regardless of the materials used in the structure. This does not hold true for smaller vessels. A small cruising vessel, for example, that is under 35 feet would require a large water plane and large displacement to carry the hull structure’s weight, making steel or FRP less optimum.
Steel Vs Aluminum Weight
Steel weight is 7850 kg per cubic meter while aluminum weighs 2660 kg per cubic meter which is roughly one-third the weight of steel. This amounts to a dramatic reduction in fuel costs and at the same time allowing for additional mission capability including sensors and weapons.
The significant difference in structural weight more than offsets the additional weight from structural fire protection material and active fire suppression systems including fire mains and hydrants installed on an aluminum platform with appropriate vibration spring isolators to prevent unnecessary movement.
Benefits Of Aluminum Hull Structure
Some of the known benefits of an aluminum hull structure include:
- Better fuel economy – resulting in as much as 21% savings or about 150,000 liters of fuel per year
- Reduced susceptibility to mines (as aluminum is non-magnetic) and eliminating the need for a costly and heavy degaussing system
- Retained watertight integrity against significant underwater blast loads
- Significant tolerance of plastic deformation before structural failure due to aluminum structure’s ductile nature
- Significant savings on maintenance costs as the protective aluminum oxide layer that forms on the material surface does not necessitate annual maintenance and coating on tanks, voids, bilges, and other interior spaces.
- The corrosion resistance of marine-grade aluminum alloy eliminates the need for protective coatings on all hull surfaces.
Several naval platforms such as the Littoral Combat Ships have been built and manufactured sans any topside paint, thereby reducing the weight and maintenance cost of the ship.
The key reason why the use of aluminum has become widespread aside from its lightweight and high-strength properties is its unrivaled corrosion resistance. Aluminum possesses a strong and adherent layer of aluminum oxide that forms on the surface when the bare metal is exposed to the atmosphere. Steel on the other hand has oxide or hydroxide corrosion properties that are loose and powdery, thus affording no protection to the metal surface.
Other Aluminum Issued Addressed And Overcome
Additionally, past concerns with aluminum in terms of sensitization, repair, and corrosion have been addressed and overcome by advancements in the design, analysis, and manufacturing methods of the ship.
Westpac Express: Best Example Of Aluminum Reliability
The advantages of an aluminum vessel are best exemplified and exhibited in the longest-serving high-speed vessel (HSV) for the US Defense Department – the “WestPac Express”. It has been in continuous service for eight years providing support to the US Marine Corps 3rd Marine Expeditionary Force in Okinawa. Westpac Express is a 101 catamaran built from aluminum that operates for up to 3500 hours yearly and with the capability to transport up to 19,000 personnel and 15,000 tons of cargo yearly at 35 knots. In its eight years of service, WestPac Express had no technical reliability issue related to or associated with the primary aluminum hull structure.
Are there other benefits of aluminum that you know of?