And now for something completely different. Well, a little different, at any rate. Boat designers and naval architects are always looking for ways to increase speed and fuel efficiency. There’s a fairly simple equation that says the more boat there is in the water, the bigger the engine you need to push it along at a given speed. And big engines drink lots of fuel.
So take the boat out of the water on hydrofoils, or turn it into a hovercraft – or at least make it go fast enough get out of the water and into planing mode – and you’re going to save effort, and fuel. The question is always, how much grunt do need to get the thing up and going – in the case of a hovercraft, quite a lot!
So how about an aluminium catamaran that is projected to hit 45 kts when fully loaded with full fuel and 13 passengers, powered only by two 250hp outboards? The HAWC 11m is under construction right now at Wang Tak Shipyard in Hong Kong.
‘HAWC’ stands for Hydrofoil Assisted Water Craft, and the crux of the design is a lifting foil on or near the centre of balance of the boat, and smaller ‘pitch stability’ foils towards the stern. The hull is referred to as a ‘split deep vee’ – meaning in design terms that it is a monohull that’s been split in two and the two parts separated. The central tunnel has a curved ‘M’ cross-section, the curved part of which is designed to dissipate slamming when running through rough water. The boat is being built as a ‘demo’ for potential customers such as the Hong Kong Police, HK Marine Dept and HK Agriculture, Fisheries & Country Parks.
The design is specifically suited to Hong Kong’s choppy waters. The builders confidently believe that 'she will ride smoothly and at high speeds, and with a fuel economy that surpasses all vessels of a similar size and displacement weight currently in operation.'
The technology and the design has been available since the mid-80s, but is still relatively unknown. ‘The numbers’ suggest that a hydrofoil-hybrid boat that doesn’t attempt to get out of the water completely will achieve very similar efficiencies to a ‘full’ hydrofoil design where reduction of drag is concerned, but will less initial power needed to get out of the water.
This is not all supposition: it has been done before, tried and tested. In 2006 and 2007 a similar boat, called the ‘Kodiak Project’, achieved a top speed of 44 kts and cruised at 31 kts, using only 64 litres/hr between the two 300hp outboards. Calculated comparisons with 13 boats of similar size, displacement, weight and power indicated a 38% improvement in efficiency. In 2008 the HAWC system was retro-fitted to a Zeta Cat design, in Vancouver. The 440hp diesels and the gearbox were unchanged, and the boat’s top speed increased from 26 kts to 37 kts.
The HAWC 11 in Hong Kong will be ready for sea trials very shortly. Her backers assure us that 'this boat is guaranteed to out-perform
all existing vessels of the same size and weight.' We are also reassured to hear that the boat is built to DNV and HSC IMO standards, and is intended to be operational in up to sea state 6 – 15’ to 18’ waves – and will be able to run at full speed in 4’-5’ waves.
I hope I don’t spill my gin and tonic at the sea trial…