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Specifications Max Beam: 35m Displacement (loaded): 2000T Interior surface area: 3000 sq.m Propulsion machinery: 2 X 42MW (gas turbines), 2 X 4MW (diesel) Max speed: 100 knots Cruising speed: 50 knots Economical displacement cruising: 12.5 knots Range (100kts): 2000 n.miles Range (50kts): 2800 n.miles Range (12.5kts): 4000 n.miles The Merits of the “Reverse Tricycle” Geometry Present day fast off-shore powerboats fall into two main categories, mono hulls and multi hulls. Multi hulls can be further subdivided into catamarans (conventional twin hull lay-out), and trimarans. The first of these two categories of multi hulls are by far the most popular, but there have been some interesting examples in the recent past of variations on the trimaran concept. In simple terms these variations can be sub-divided into two types, namely “the tricycle” (central hull forward and twin hulls aft), and ‘the reverse tricycle’. It is now generally accepted, that for fast offshore work in rough conditions, a mono hull is superior to a conventional twin hull ‘catamaran’. On the other hand, there is no argument about the greater speed potential of the ‘cat’ over the mono hull due to the aerodynamic lift created in the cat’s tunnel which in turn reduces the wetted area resistance of the hulls. This lift, generated by the flat underside of the wing, also produces pounding and slamming in rough water, which apart from causing acute discomfort can also result in severe structural damage to the craft and injury to the crew. The pounding usually occurs in the aft portion of the tunnel, near where the vital organs of the vessel are located, namely engines and crew. ‘The Reverse Tricycle’, or ‘Y-Tunnel Craft’ mitigates this grave inconvenience since a well veed hull is located where the pounding and slamming occurs in the tunnel of the conventional twin hull catamaran. At high speed, in rough weather when the craft ‘takes off’, the re-entry is as smooth as a mono hull’s, since the first contact with the water takes place aft where the central hull is situated. Although the aerodynamic lift will not be of the same magnitude as a catamaran of comparable size, owing to the reduced area of the tunnel and aero drag of the central hull, nevertheless, an appreciable amount of lift will be generated. This in turn, will permit higher speeds than a conventional mono hull owing to a reduction in wetted area. One might ask why the tricycle geometry favoured for world speed record breakers is not considered here? The reason is that conditions are completely different and the one aim in a record breaker, apart from achieving high speeds, is to avoid the dreaded involuntary ‘take off’. |
