NEW INTERCEPTOR 42

We are currently expanding our existing model range of 33 and 38ft fast offshore craft with a new 41 ft vessel. Called the Interceptor 41, this vessel has been designed to be our new flagship, with a length overall of 42ft, and a beam of 13ft 10” she will meet the demands of owners requiring the maximum deck area and stability.

In designing the new vessel the following criteria were considered the main requirements:

1/  Sea keeping. With the main emphasis on overall rough weather capabilities. In order of importance these capabilities were:

·          Course keeping and dynamic stability in following seas.

·          Static stability when stationary in rough conditions.

·          Attitude of vessel to wind when static and speed of drift.

·          Adequate head sea abilities set as the ability to maintain 15 kts into a head sea generated by a force 5-6 open sea wind.

·          High freeboard to prevent green water been shipped on deck or over the bow.

2/ Performance. The hull to be easily driven and economical.

3/ Large load carrying capabilities with impressive GZ curve and GM figures.

Hull form development.

In order to meet the above requirements careful consideration was made to the hull form chosen. A deep V, hard chine hull form was considered to most easily meet these requirements. Used in our other vessels the deep V hull form is generally accepted as having superior seakeeping abilities to other designs most notably in course keeping abilities in large following seas. A point of interest is that in designing the R.N.L.I.’s new fleet of  ‘fast afloat boats’ the Severn and Trent class, a comparison test of the seakeeping of traditional round bilge craft and Deep V hulls was made in order to determine which hull form would eventually be used in the new class of Lifeboat. These tests indicated that whilst vertical acceleration motions measured at the bow at speed in head seas were similar on both types the deep V hull showed a dramatic advantage in been able to maintain a course in following seas with much less recourse to the helm, heel and yaw were also much less in the Deep V hull as were rolling in static tests.

                Bearing in mind the intended operational envelope of the craft which is to be able to run at a speed of 15kts regardless of direction in a sea state generated by a force 5-6 open water wind, with the potential ability to run at greater speeds in beam, quartering and following seas, the hulls deadrise angles were set at 22 degrees amidships, 17 at the transom and a fine waterline entry of 49 degrees. The relatively fine waterline entry is achieved through a high main chine at the bow which will reduce the likelihood of slamming occurring in head seas.

To provide good course keeping abilities the vessels beam to length ration was optimized with a beam overall of 13ft 10” giving a high GM, which will reduce heel and subsequent yaw in large quartering seas.

A full length keel was considered for amongst other reasons good directional stability at slower speeds.

Hard chines and spray rails with a 10 degree down angle fwd are used to provide lift to the hull, stability, and aid in spray deflection as well as general boat dryness. To further aid stability, the secondary spray defection rail used successfully on the existing 38 has been modified to become a second chine, which is designed to run dry at speed but become immersed at rest when heavily loaded aiding in stability. As a secondary feature general seakeeping and boat dryness is improved, as any spray running past the main chine is deflected by the second chine, the second chine also helps to provide additional lift and resistance to rolling at large angles of heel encountered in heavy seas.

Special consideration was given to the vessels bow. In order to prevent the likelihood of green water been shipped over the bow adequate sheer was provided with plenty of flare and reserve buoyancy above the chine. Furthermore to prevent any likely hood of broaching in large following seas the hull has a cutaway forefoot and well raked stem, designed to prevent the bow burying deeply into the back of waves, and acting as a fulcrum causing the stern to swing round in a classic broaching action.

As commercial charter and static gear work is envisaged as a part of the vessels intended use special attention was paid to the vessels likely attitude of drift to the wind, speed of drift and stability whilst static. To this end a full length keel is used providing good grip and roll dampening . Also as it is envisaged that most owners will require a large single engine configuration the keel has sufficient depth to allow propeller sizes of up to 28” (5-600hp) to run in a specially developed, large propeller tunnel, fully protected by the keel. To this end the likelihood of damage and fouling of the propeller is reduced and allows the vessel to beach safely.               

Extensive computer resistance and propulsion analysis has been carried out to optimize the hulls performance. Deadrise angles beyond the slamming area are reduced to increase lift. The angle of rise in the hulls run is reduced to 1 degree to optimize trim angles. The hulls bottom has near parallel buttock lines in the aft sections, and warp in the bottom kept to a minimum. A slight degree of convexity is present in the very f/wd sections to soften motions. Maximum WL beam is at midships in order to provide a LCB of 58%, needed in order to provide level longditudal static trim with the relatively f/wd LCG of this type of craft.

As the first of class is to be a class 6 passenger vessel, the hull has to provide an exceptionally high degree of stability, especially in passenger crowding heel angles and maximum GZ. The hulls ample beam will provide a safe, stable platform in this respect.

Finally, the overall looks of the vessel have not been overlooked. The same attractive, graceful sheer line, styling knuckle and two tone colour scheme (a main dark colour above the knuckle and white below) as used on our 38 is retained.

Superstructure.

A sleek, modern superstructure has been designed, very similar to that used in our existing 38. Similar window styling is retained as this has proved very popular and has become a distinctive feature of our Interceptor range. An optional flybridge moulding is to be available which will extend some way over the aft cockpit to provide shelter for passengers. The mould for the superstructure will be able to be altered to provide either short wheelhouse versions for commercial vessels. Std wheelhouse length used for charter work to extended versions for recreational and cruising vessels.

The first vessel ordered is to be a class 6 passenger vessel for 34 passengers operating on the west coast of Ireland. Conforming to the very strict intact and damage regulations that apply to passenger vessels. Her general arrangement can bee seen below. Fitted with a st/d length superstructure to provide comfortable accommodation and seating inside for 8 persons. A full galley and separate heads compartment are provided. Powered by twin Caterpillar 3126 engines at 300hp each. On a light ship displacement of 10,000kg she is expected to have a maximum speed of 25kts and cruise speed of 18-20kts.

The commercial short wheelhouse version being developed simultaneously will provide a 26 sq m flush aft cockpit whilst still retain comfortable accommodation for the crew. The commercial version will use as st/d Caterpillars 3208 10.4 litre V8 rated at 375hp, which will give a sustainable, loaded, economical cruise of 16kts.

Recreational versions will have increased accommodation yet still retain a good sized aft cockpit.

Propulsion.

As standard the vessel is fitted with a single Caterpillar 3208 10.4 litre V8 rated at 375hp/450hp. Running conventional stern gear through a twin disc gearbox, 1 ¾ T/met shaft and 25” dia 4 blade propeller. On an anticipated lightship displacement of approx 9,000kg she will have a maximum speed of 21/ 23kts and a cruising speed of 16/ 18kts.

As an option Caterpillars 3196 electronic 12 litre straight 6 rated at 570hp will provide a maximum speed of 26kts and a cruise speed of 21kts. For twin engine installations, two Caterpillar 3126 8 litre straight 6 engines are used at 300-420hp (600-840hp total) which will provide a maximum speed of  25-30kts and a cruise of 20-24kts. Flush deck installations are available on twin and single engine craft.

Construction

                Shell laminate and scantlings on commercial craft have been determined in general from Lloyds special service craft rules and regulations.

GRP composite construction  using CSM. Woven rovings and uni-directional fibres. (All materials Lloyds approved)

Hull main shell laminates: Bottom- 6800gm2. Sides- 3900gm2. Keel 8400gm2. Chine- 8400gm2.

Scantlings: Transverse frames @ .600mm centres. 2x 200x50mm main longditudals. 2x secondary longditudals. Additional panel breakers positioned to provide a max unsupported panel width of  280mm over the bottom structure.

The above scantling and hull thickness will provide a very strong, durable structure capable of operating safely in rough offshore conditions.

As we progress with the development of the Interceptor 41 we will keep adding information and pictures to keep you informed, so watch this space!!!

The final drawings for the first boat have been completed, shown below: