Stepping out with the Carson Interceptor

Ship & Boat International: eNews July/August 2017

If RIB design typically tends to be a simple affair, a new family of RIBs, conceived by designer Barry Carson and manufactured by Probond Marine, is set to shake this perception to its foundations with a unique hull form. Primarily aimed at coast guard, law enforcement agency and naval clients, the Carson Interceptor range of RIBs comes in three custom sizes (see Technical Particulars, below), their common bond being a commitment to combining excellent sea-keeping with capability for breakneck speed. 

A demonstrator version of the 950 model – the largest in the series, so far – occupied Probond Marine’s jetty slot during Seawork 2017 in June. Although the 950 was not providing waterborne demonstrations, a glance at her outboard motor arrangement, comprising three 224kW Mercury Verado units, gave a good indication of her power and potential pace.

Colin MacAndrew, Probond Marine MD, told Ship & Boat International that this configuration is sufficient to grant the RIB a top speed in excess of 70knots without sacrificing stability in harsh weather. In fact, in mid-June, the 950 was put through her paces in a sea trial, during which, MacAndrew recounted, the RIB comfortably coasted through a 1m swell whilst retaining a cruise speed of 45knots. “The 950 is also capable of taking three 298kW outboards,” he added.

What especially makes the Interceptor range unique, though, is that it can be configured with three inboard engines, two aft and one midships forward, with the centre engine feeding a waterjet. This is a highly unusual arrangement, given that all RIBS in the Interceptor series are built upon a stepped hull form. Stepped hull forms are usually highly effective in reducing vessel drag, but the steps do lead to a significant amount of aeration which can interfere with waterjet efficiency. As such, stepped hulls and waterjets seldom, if ever, feature on the same craft.

However, the Interceptor’s deep-vee, stepped hull form is in itself unique. The hull features what Carson has christened “delta steps”: these are U-shaped steps, pointing aft, which have been situated centre-forward. As these steps progress aft, towards the vessel centreline, they “fade”, or recede into the hull before they get to the keel line. Thus, the keel line is straight, continuous and unbroken, unlike other stepped hulls.

This design has two key benefits, Carson said. Firstly, these produce less aeration in the after sections along the centreline right where the jet intake would be positioned, so the craft can take advantage of the ‘best of both worlds’ – namely reduced drag from the steps and extra kick from the waterjets – to achieve high speeds and manoeuvrability. Carson said: “When the crew are in loitering mode, they can solely utilise the waterjet. This not only provides them with a quiet means of propulsion when they are undertaking covert coastal surveillance missions, but means they can take the vessel into very shallow waters, where there may be more debris present.”

Secondly, the receding nature of the steps makes it easier to launch the Interceptor from trailers, shallow-water environments and/or for the vessel to experience beaching and grounding, “where otherwise the steps may sink into and become embedded in the sand or soil, or dig into the ground and impede movement,” Carson said.

From the mid-section of the hull forward, the Interceptor also incorporates a “vertical stem”-style design, perhaps more common as a staple of yacht design than as a standard RIB feature. A fine semi-wave-piercing  bow enables the RIB to slice through moderately sized waves – “and not bounce off them”, Carson explained – thus adding another layer of stability to the boat.

In terms of range, meanwhile, the Interceptor has a fuel capacity of 1,000litres, although up to 2,000litres could be stored in total below deck, granting the vessel a range in excess of 1,000nm at cruising speeds.  

Beyond the basics, the Interceptor range is fully customisable and can be tailored to each client’s individual needs. For example, the demonstrator version of the 950, as displayed at Seawork, was fitted with Ullman Dynamics’ Echelon shock mitigation seats, which have been developed specifically for small, high-speed boats and provide lateral support for personnel’s legs, hips and torsos.However, buyers have the opportunity to specify a cabin version, complete with beds and toilet/cooking facilities, making the RIB suitable for extended missions.

TECHNICAL PARTICULARS

Carson Interceptor RIB