Air Lubrication, Whale Tails and Vertical Bows

HMS Dreadnaught

A collection of interesting stories from around the civilian maritime sector…

Air Lubrication

The first is about air lubrication, I looked briefly at this some time ago, 2013 in fact.

The cost of fuel is a significant contributor to naval vessel running costs. Last year the Japanese carrier NYK Line announced it had successfully completed trials of the Mitsubishi Air Lubrication System (MALS) which put quite simply, uses air bubbles to reduce drag. They have reported a not insignificant fuel reduction of 6%. With continuing pressure on Royal Navy operating costs is this something that could be retrofitted to existing ships and designed in to new ones?

Click here to read the post.

The Japanese are not alone in looking at this technology, DK Group in Denmark are also developing a similar system.

The Finnish marine design and engineering company Foreship has recently introduced what it claims is a commercially viable air lubrication system that does not add to drag whilst the system is turned off. It claims trials on a Royal Caribbean Cruise Lines ship have yielded fuel savings of between 6% and 8% whilst sailing at 20 knots which is a significant saving. What seems clear from Foreship and the other studies is that careful design and placement of the air nozzles is needed to avoid reducing propeller efficiency. It has also been shown to reduce propeller excitation that reduces noise and vibration at the stern of the ship which is another considerable advantage in the cruise sector.

Following the trials, the Foreship system is now fitted to the Quantum of the Seas, in service and being used regularly.

Predictable cruising speeds on predictable routes is not something that springs to mind when thinking about frigates or amphibious vessels so no doubt there are many technical and operational barriers to overcome before this type of technology is even considered for naval vessels but at least, the basic technology and engineering are proven for vessel speeds between 12 knots and 18 knots.

Vertical Bows

The second story is about what seems like the resurgence of vertical bows.

The first dreadnoughts, like HMS Dreadnought, had a vertical bow (or something approaching vertical)

HMS Dreadnaught

As designs evolved and a greater understanding of fluid dynamics was realised the raked bow become common. Bulbous bows started to become more widespread in the twenties and thirties and are now common on large vessels. There have been various development in hull forms such as transom flaps and the well know X Bow but Damen resurrected the vertical bow with their Twin/Sea Axe design, mostly for smaller vessels such as crew transfer boats, workboats, yacht tenders, platform supply and small patrol vessels. The higher speed Sea Axe vessels appear to have multiple horizontal strakes to reduce over deck spray but Damen customers seem to agree that the design has benefits.

A recent story from GCaptain highlighted Foreship again, specifically their trials with vertical bow designs for larger ships than most of the Damen vessels. Using improvements in computational fluid dynamic software and computing hardware they have shown a couple of percentage points reduction in hull resistance when comparing bulbous and vertical bows, read the paper from Foreship here.

Whale Tails

A team from the Norwegian University of Science and Technology (NTNU), Rolls Royce, Seaspeed Marine Consulting and MOST have developed and trialled a system that uses fins placed at the bow of the ship to harness wave energy.

Whale Tail

From Seaspeed

Wave foils are essentially streamlined hydrofoil shaped fins connected to the hull of a vessel, that generate lift and drag by nature of the varying flow into them from orbital wave motion and vessel pitch, roll and/or heave motions. This technology has in the past been trialled to aid the propulsion of a number of ships and boats and, more recently, for the propulsion of small unmanned vessels.

There is also a video from NTNU, but it is in Norwegian.

The foils were shown to reduce hull resistance between 9 and 17 percent in wave heights of less than 3 metres. Heaving and pitching were also reduced by the same amount.

Will any of these developments make it into naval vessels, who knows, but innovation driven by the commercial needs to reduce fuel consumption and emissions may prove a valuable source of savings for military vessels.

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