How to Make Vessels More Sustainable: Small Tweaks to Make a Difference
With the growing need for more sustainability, processes and the way things are done need to change. This also affects the shipping industry. Apart from alternative propulsions that are more sustainable, it also makes quite a different to change the way vessels are built. In this article we will guide you through (small) changes that make a huge difference in terms of sustainability and reduce the overall fuel consumption.
Table of Contents
- Why Vessels Need to be Modified
- Propeller Modifications
- Changing the Bulbuos Bow
- Modifying the Bridge
- Keeping it Clean: Hull and Propeller Cleaning
- Conclusion
Why vessels need to be changed in terms of sustainability
Before we take a closer look at the sustainability aspect, let’s start with some physics: When a vessel is in the water it is similar to when you drop a stone into a pond. Both – the stone and the vessel – displace the water. In terms of the vessel this leads to a resistance as it is moving forward and continuously displacing and pushing away the water. In terms of the resistance, two different ways can be observed:
- Frictional Resistance: This type of resistance is formed by the water “sticking” to the surface of the vessel. This leads to a drag, slowing the vessel down which leads to an increased need of energy and thus, fuel to keep the ship moving. By the way: The dirtier the hull, the more friction and drag is created. But more on that later.
- Wave Resistance: By moving forward, the vessel also creates waves. These are building up against the vessel and also make it harder and more energy consuming to keep the ship moving forward.
Both resistance factors are affected and influenced mainly by the way a vessel is built and how certain parts of it are shaped and make the water flow around them. This is called hydrodynamics. By improving hydrodynamics, ships can move faster, consume less fuel, and thus decrease their environmental impact.
What possibilities are there to make ships more sustainable?
First up, we have to take a look at the two main types of vessels used in container shipping. While there are more vessel types such as Feeders, ULCVs and Panamax, in terms of sustainable design we are only covering the superstructure layout of large container vesselsin this article. These superstructures being One-Island Vessels and Two-Island Vessels.
A One-Island Vessel has only one superstructure (the so-called island). Both – the bridge and the engine room – are located in this structure which maximizes the space for containers on deck. A Two-Island Vessel has two separate superstructures – one at the rear for the engine room and one at the bow for the bridge.
Regardless of the ship’s superstructure, there are mainly four modifications that can be done to improve the aero- and hydrodynamics.
Propeller modifications to save fuel
The propeller is the main propulsion for the vessel and pushes the water away to make the ship move forward. By doing so it also creates friction. So, what can be done to reduce the friction caused by the propeller?
The propeller efficiency mainly depends on three factors: the blade shape, size and rotation speed, and the number of blades on the propeller.
To make them more efficient, it helps to reduce the surface that can cause friction and also make the overall shape narrower to glide through the water smoother. Added Propeller caps can also help to streamline the waterflow around it. Improved propeller design can account for roughly 5% of fuel savings.
Modification of the bulbous bow
At the other end of the vessel, we also encounter potential for friction – and even more potential to make vessels more sustainable: The bulbous bow. This is a protruding structure in the front of the vessel, just below the waterline and very important for the fuel efficiency and drag reduction.
While the propeller pushes the ship forward, the bulbous bow disrupts the waves and reduces the energy needed to pass through them. It also simultaneously creates a second wave that cancels some of the drag caused by the friction on the hull. The shape can be modified and for older ships it can also be retrofitted to be more efficient. Similarly to the propeller design, the bulbous bow should be sleeker and more pointed instead of rounded to basically cut through the waves. If done right, an efficiently shaped bulbous bow can save up to 7% of the used fuel.
Elevating or re-fitting the bridge and making space for more containers
While it is possible to refit Two-Island Vessels into One-Island Vessels it is rarely economical. But nonetheless there are possible improvements to make space for more containers aboard without having to retrofit the entire vessel.
One solution is a refit with bridge elevation. For this, the bridge is boosted upwards and reinforced. This leads to a higher set navigation room and increases the field of view which makes it possible to stack the container rows a bit higher. But: This is also a quite cost-intensive solution and might not always be economical – especially when it comes to older vessels.
Alternative solutions can be container stacking adjustments. By improving the stacking system on the vessel, higher and heavier stacks can be placed behind the bridge, making more room for containers in the front.
Hull cleaning and paint
The last speedway modification makes quite a difference, even though it’s quite mundane: Keeping the hull and propeller clean. By being under water at all times, the hull is exposed to algae, barnacles and water pollution that can build up over time. By cleaning the hull (and propeller) on a regular basis, up to 53% of fuel can be saved after cleaning by significantly reducing the friction area.
Did you ever wonder why a lot of hulls are painted red? This is because most marine organisms don’t like reddish tints and will stick less to red surfaces. In the past this was mainly because of used copper oxide-paints. Modern paints are formulated differently and nowadays it also possible to use a repellent paint that has other colours. But for the sake of tradition most vessels still use red paint.
A small change on the vessel a giant leap for sustainability
As you can see, despite their sheer size it is possible to make small adjustments to increase sustainability and overall reduce friction. Next to more sustainable fuel options such as biodiesel, methanol or LNG, adjustments directly made on the vessel have the most impact on sustainability.
© Hapag-Lloyd AG