High end propulsion installation
Irish commercial marine boatbuilder Safehaven Marine has completed the engine and propulsion installation for its new XSV20 ‘Thunder Child II’.
While the XSV20 is intended for a Transatlantic record attempt, like the round Ireland record breaking XSV17 before it, it has also been designed as a prototype for a new Safehaven fast interceptor vessel.
The installation is a quad engine and propulsion arrangement using France Helices surface drives driven with a total installed power output of 2600hp from four Caterpillar C8.7 650hp engines. Being both supercharged and turbo charged they had the best power to weight ratio in this class.
Safehaven carefully considered the optimum solution for the vessel and determined, at least in this instance, that a quad arrangement provided slightly better efficiency than a twin engine solution. There was also a significant weight saving by using four smaller capacity engines, instead of two larger more powerful, but heavier engines. This in turn enabled the use of a smaller and lighter surface drive model.
Other factors also came into play in the decision, factors that were unique to Thunder Child II and her Transatlantic capability such as redundancy: if one engine is lost, it should still be possible to achieve planing speeds and stay underway, which wouldn't be the case with a twin engine set up. Also with a quad arrangement there is the option of running on just two engines by lifting the inner drives, this will be beneficial in very rough seas when high speed just isn't an option. And by using the lower gear ratio of the twin speed ZF 325ATS gearboxes, it will be possible to greatly unload the propellers when they inevitably become deeply submerged in large waves. A full Humphree Interceptor trim control system with automatic stabilization is being fitted, as such her rough weather manoeuvrability and operation should be excellent.
The surface drives are manufactured by France Helices, the chosen SD3L model of drive weighing just 270kg and, according to Safehaven, is superbly engineered, with all hydraulics and cables contained within the transom inside the hull. The units being almost like ‘engineering works of art’ and look very impressive mounted on the transom.
Surface drives are designed to run with only the lower half of the propeller submerged, and as such there is very low appendage drag. The drives are articulated, able to be raised or lowered to both trim the hull and adjust the props’ submergence, as well as steer with vectored thrust. According to Frank Kowalski, Managing Director at Safehaven Marine: “Like all types of propulsion, surface drives have their pros and cons, but for this application demanding both high speeds of 50kts and economy, especially in rough seas at transitional speeds, they were the best choice.”
XSV20 has a unique and innovative hull design with a patent applied for by Safehaven and seamlessly fuses an asymmetrical catamaran hull form with a wavepiercing monohull, designed to provide high operational speeds combined with very high levels of seakeeping in rough conditions.
By Jake Frith
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