DISCOVER Magazine #7

Damen Interceptors – much more than just a fast boat

Published in category: Defence & Security

The need for more than speed

Interceptors. It’s all about speed, right? Well maybe not. Speed is certainly a crucial factor – after all, how else are you supposed to intercept? But it’s not just about speed on flat water, it’s also about maintaining the pace in waves. And for that, you need good seakeeping.

This is the reason that Damen’s Interceptors 1102 and 1503 are based on a very simple single chine deep V-shape. This goes a long way towards reducing impact acceleration in higher sea states as well of providing improved manoeuvrability and reduced resistance at high speeds.

The 1503 has a second chine high in the side – to reduce the wetted area and provide increased stability. Damen has achieved a further reduction in wetted area by adding spray rails at the bottom, improving the dynamic stability of the vessel.

Fast & forgiving

Safety too is of great importance. And a safe boat requires the sacrifice of some of the speed. Steps in the bottom of the craft, for example, would offer an additional 3 knots.  At the same time, though they would raise the risk of broading. The air under the hull, in addition to reducing resistance, reduces the grip of the vessel in the water, which can result in a spin-out during hard turns. In turn, this runs the risk of lowering crew confidence in the vessel, rendering them less able to utilise its full potential and get the job done.

Wim Boerma, High Speed craft, Damen Shipyards GroupFor the same reason, a good interceptor has to be forgiving. “Damen’s designs deliver excellent stability for safe, steep turns in waves – and also in case the helmsman makes a mistake,” says Wim Boerma, Damen Product Manager High Speed Craft. We’ve designed these boats to take into account the possibility of human error so that users can feel fully confident in using them to the fullness of their potential. For example, in a typical loading condition, with a trial load of 4.66 tonnes, the 1102 is stable to a lean angle of 108 degrees.

Simple, ergonomic efficiency

An interceptor may seem like the simplest of boats and to some extent this is indeed the case. This simplicity though, is well thought out and almost always serves a purpose. The ergonomics of Damen interceptors played a major role in design, prototype testing and full-scale testing. And the related-features cover all aspects of the vessel.

“As standard, for example, the seats are shock-mitigating. The thinking incorporated into these goes way beyond comfort and security, however. The seats provide ample space for belt equipment without negating freedom of movement,” explains Wim.

The controls have been laid out in a logical manner. As an example, switches are positioned so that the operator’s hand can be braced against a part of the console for activation underway in waves. And close attention has been paid to comfort in the wheel and throttle – as these will be used constantly.

Damen interceptors have been designed to be stronger than their crew

Maximum impact

The position of the helmsman is far from random, too; his location is deliberately placed not only for the best possible view, but also where he will most feel the impact of the waves. This ensures the protection of the rest of the crew – if the helmsman experiences discomfort it will be greater than that felt by the crew.

Not only does this afford the helmsman the opportunity to reduce the pace as soon is necessary, it also offers a degree of protection to the crew – who need to be in optimal condition in order to perform their duties once they reach their target.

The cockpit is deep with high coamings, putting the crew into a sheltered enough position that they feel sufficiently secure to operate the interceptor to its full potential. Consideration has also been invested into communications. An interceptor underway represents a noisy environment, so an intercom system has been integrated into crew helmets, which can interface with the vessel’s radio. Grab rails have been incorporated into the most logical places around the vessel.

Fast, strong & effective

An interceptor must be both strong and light to be effective. Light to go fast and strong enough to be put through its paces. Damen Interceptors are constructed from composite. In comparison to aluminium this makes them stronger, lighter and simpler.

Damen interceptors have been designed to be stronger than their crew.

What this means is that the helmsman is guaranteed to throttle back before there is any danger of damage occurring to the hull structure – or to those onboard.

Round the bend

Global bending is important for interceptors – especially with so much of the deck cut away for a cockpit or flexibly-mounted wheelhouse. As slamming causes high bending moments, Damen has applied a large amount of uni-directional carbon fibre to the cockpit cannings.

Of course, aside from added strength and reduced weight, composite also carries additional benefits; building from a mold gives extreme flexibility in shaping the vessel and, unlike with metals, there is no corrosion.


Choosing propulsion

Propulsion options on an interceptor are somewhat limited, realistically including just stern drives, surface props, waterjets and outboards.

Wim says, “Outboards, though light and offering manoeuvrability and propulsion efficiency, deliver, petrol only, poor fuel economy and are insufficiently reliable for professional operations. Waterjets – also manouevrable – offer better efficiency and good stopping characteristics, though are limited in speed performance characteristics. Really, they are only suited to smaller vessels operating in the speed range 30-45 knots.

“Surface props offer a good combination of high speed and efficiency. However, they also give high torque at low speed and, whilst manoevrability at speed is good, this is certainly not the case at lower speeds. Surface props are really only for high powered, high speed craft. This leaves stern drives. These are light, with good trim control, manoeuvrability and efficiency as well as being able to absorb considerable impact.

Stern drives combine inboard diesel reliability and excellent propulsion efficiency. The counter rotting propellers deliver great manoeuvrability, trim control and reliability. They really are the logical choice for an interceptor.

For this reason Damen has opted to use stern drives for its own interceptor range –Volvo for the Interceptor 1102 and the 1503.

Diesel comes of age

For interceptors, the days of petrol engines are over. In the past, when diesel engines could not provide a sufficient power-weight ratio, petrol engines were necessary to reach the required speeds – but the speed came at the considerable cost of fuel consumption as well as high maintenance and safety.

Damen’s Interceptor 1102 is fitted with a twin engine Volvo D6 arrangement. “As commercial off the shelf equipment, this matches Damen’s philosophy of standardisation. As such it can be fit straight into the vessel. It represents a lightweight solution offering extreme reliability and fuel economy. Added to this, its capability for loitering for extended periods of time make this the perfect choice for a light, high speed boat.”

The 1503 can also be fitted out with a D6 arrangement – triple instead of double, the boat can operate up to 55 knots.

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