A high performance escort tug Velox, developed by Robert Allan Ltd. of Vancouver (BC, Canada), was recently delivered from Astilleros Gondan (Spain) to Østensjø Rederi (Haugesund, Norway). Velox is the first of two tugs being built at Gondan to this new design, designated as the AVT 37/65-E Class. The new design incorporates a number of refinements in hull form, deck gear and skeg design to maximize indirect towing performance. This combination marks the Velox as one of, if not the most effective escort tug afloat, in terms of performance per unit power or performance per size.
The hull form of Velox is based largely on the successful form of Ajax, with a number of subtle refinements to increase underwater lateral area with minimum increase in displacement or wetted surface. The distinctive sponson form introduced in Ajax has been retained, with minor refinements to increase restoring moment when heeled over at maximum escort towing condition. The bow incorporates a "quasi-bulb" form, intended to increase underwater lateral area rather than reducing wave forming pressures. The skeg geometry is the result of an extensive series of investigations into shapes and appendages which would enable a significant increase in indirect steering force. A wide variety of options were explored, and their merits in terms of lifting force and complexity were evaluated. The final skeg configuration incorporates a refined profile offering better lift generation than typical NACA profiles and, most critically, incorporates the first application of the Voith "Turbo-Fin" rotating cylinder at the leading edge to maximize lift in the skeg when operating in indirect mode.
The towing staple on Velox is very unusual. Designed to accommodate both steel wire and synthetic line, it was clearly necessary to have two distinct apertures which would function effectively in both escort and towing functions. The result is a very wide-based channel slot for the escort hawser operations, with a central fairlead above for towing wire operations. The hawser slot permits the line to migrate far outboard towards the pressure side in an indirect operation, thus reducing the heeling moment on the tug and increasing the line tension capacity.This combination of features gives Velox an indirect steering force capability of 150 tonnes at 10 knots and 130 tonnes at 10 knots within the special requirements of the DnV escort class notation.