Safehaven Marine in 2018-19 developed a new model to add to their extensive range of commercial, naval and recreational craft: ‘XSV20’. The design is a high speed offshore patrol / S.A.R interceptor and cruiser with a moulded length of 21.5m and a LOA of 23m (75ft). The hull design is extremely innovative (Patent applied for) and seamlessly fuses a twin stepped asymmetrical catamaran hull form with a wave piercing monohull, to create a hybrid design that delivers the rough weather and high speed dynamic transverse stability of a catamaran, with the steep head sea capabilities of a deep V monohull. During the designs initial development 6mth R&D programme was undertaken, during which Safehaven built 12 scale model variants which were extensively tank tested to optimise the designs performance characteristics and hydrodynamics.
The first of class 'Thunder Child II' was launched early 2019 and underwent extensive sea trials during the last two months during which she proved to have excellent seakeeping and performance during a range of trials in varying sea states right up to Force 10 and in 5m seas off the Atlantic coast of Ireland, she proved to be very sea kindly and soft riding with excellent stability. Safehaven plan upon attempting a 4,500km UIM approved Transatlantic record attempt from Canada to Ireland via Iceland and Greenland in Thunder Child II in July 2010, an extremely challenging voyage where she will face hazards of sea ice and the inevitable North Atlantic storms, ‘Thunder Child II’ is fitted with quad Caterpillar C8.7 650hp engines coupled to quad France Helices SD3L surface drives in a staggered arrangement, the quad engine decision providing the desirable redundancy for such an epic voyage, as should one engine fail she will still be able to maintain planning speed. She is fitted with an 8,000 litre fuel capacity allowing an 800nm+ range at her cruise speed of 40kts, and is capable of altering her LCG for prevailing sea conditions via a fuel transfer arrangement to a 2,000L f/wd ballast tank. A second XSV20 fitted with Waterjets and Caterpillar C18 1,150hp engines achieving 45kts was delivered in 2019.
XSV20’s unique hull design was developed to solve the head sea limitations inherent in traditional catamarans design whereby when a sea state exceeds a given size, steepness and frequency, waves, especially in head seas, will inevitably impact on the flat surface of the bridge deck causing slamming. On XSV20 the forward mono hull section comprising a wavepiercing bow and very deep V midship section that seamlessly transitions into the catamaran sections, very effectively pushes through and splits waves, dampening motions and preventing the flat surface of the bridge deck from ever directly impacting the water surface. The hull of course will be design fully wave pierce, the level to which is speed dependent, but in general wave height needs to exceed 2m before this begins to occasionally occur and to this end the superstructure is especially strengthened and incorporates 25mm ballistic glass for the front windows, with above deck fit out, arrangement’s and air intakes especially designed for this.
Integral to the design is the incorporation of a hydrofoil system, designed by Hyuscraft installed between the asymmetrical catamaran hull, (the asymmetrical form particularly advantageous in this respect) and as such lifts the hull 400mm at higher speeds allowing the forward monohull section to run mostly dry and clear of the water with very little wetted area, the monohull sections only coming into significant effect in larger sized wave encounter effect allowing the hull to cut through waves.The hydrofoil also significantly improves seakeeping as it very effectively damps pitching as well as overall hull motions in waves. The hydrofoil comes into effect for speeds of 30kts and over and provides excellent efficiency at these higher cruising speeds, with range and fuel economy actually increasing the faster you go., the complete opposite of typical planning hulls.
The design also allows for wider load variations as the monohull section supports a significant percentage of the vessels overall displacement, and by virtue of its steep deadrise, buoyancy rises exponentially supporting increases in displacement, thereby preventing excessive hull sinkage, which on a pure catamaran hull design results in a significantly reduced bridge deck clearance when heavily loaded. As such seakeeping in large waves at displacement speed when inevitably forced to slow down is excellent with negative impact on seakeeping, slamming never occurring on the bridge deck.
XSV20 can be powered by either surface drives or waterjets, the design has a maximum speed well over 50kts, a 40kts+ cruise speed and a range of 500nm. The design incorporates all the features of Safehaven’s smaller 11-17m Barracuda range of naval craft, with greater endurance, payload and crew capacity.
XSV 20 Principle dimensions / characteristics
L.O.A. 23m / 75ft
Hull length 21.4m / 67ft
Beam overall 5.4m / 17ft 7"
Draft .85m / 2ft 9"
Displacement lightship 24,000kg
Fully loaded 29,000kg
Fuel capacity 4,000L
Crew capacity 12
Seating SHOXS Shock mitigation seats
Engines 2 x 1,500hp MAN
Surface Drive France Helices SDS5L
Waterjets Marine Jet Power / Hamilton
Trim control/stabilization Humphree
Air-Conditioning Dometic 2X 2,7000BTU
Speed Maximum 50kts+
Cruise speed 40+kts
Survivability 8x watertight compartments
Construction FRP Composite