Inside The Grand G980 Design: The Hull

What is a twin stepped hull?

Most RIBs are built on a deep V hull. That design, characterised by a continuous V-shaped cross-section running from bow to stern, is reliable, handles chop well and tracks predictably. A deep V hull maintains full contact with the water across its entire running surface as it planes. At higher speeds, that wetted area creates drag, the hull has to work harder to maintain pace, fuel consumption rises and the boat becomes more susceptible to rolling in beam seas and chop.

A stepped hull solves this differently. Rather than running the hull surface continuously, one or more transverse steps are built into the hull. As the boat planes, each step draws air underneath the hull behind it. The boat runs on a combination of water and air rather than water alone, which reduces the wetted surface area and cuts drag at the source.

The practical outcome of that difference is measurable across all speeds. The G980 planes earlier with less throttle input and minimal bow rise. At cruising speed, the running angle flattens, engine load drops and fuel efficiency improves. At higher speeds, the air cushion between the steps keeps the hull planted and resistant to rolling, rather than allowing it to work against the water it is sitting on. The stepped hull is not fighting drag; it is designed around avoiding it.

Stepped hulls have always been used in race boat designs, but is becoming the direction of the wider. Brands like Axopar and Saxdor, two of the most respected names in European performance boating, have both shifted to stepped hull designs over the last decade. The reasoning is straightforward: a well-engineered stepped hull is a more capable, efficient platform.

Why Does The Grand G980 Have A Twin Stepped Hull?

At the crux of Grand’s design philosophy for the G980 is a goal to deliver genuine offshore range, extended family cruising and real-world performance, and so the boat’s hull needed to handle everything that comes with that kind of use without compromising on efficiency or composure.

A conventional deep V hull at this size and power level would deliver performance, but would also mean more fuel consumed per nautical mile, more load on the engines and a hull that is working harder than it needs to.

For a boat expected to carry families across open water in comfort and arrive with fuel to spare, the G980’s twin stepped hull negates that trade off. By lifting sections of the hull clear of the water on an air cushion, it cuts drag at the source. The G980 reaches higher speeds with less power, cruises more efficiently and remains more stable and planted at pace than a conventional hull of equivalent size.

To engineer that correctly at 10 metres, Grand partnered with Mannerfelt Design Team, Swedish naval architects whose background spans some of the fastest offshore race boats ever built. Stepped hull geometry is sensitive: the position, depth and angle of each step has a measurable effect on how the hull behaves at different speeds and in different sea states. Getting it right requires specialist knowledge and rigorous testing. After using computational fluid dynamics simulations, Grand and Mannerfelt produced a hull with a 30-degree deadrise at the midsection and 22 degrees at the aft, paired with long chines that manage water release and spray efficiently.

Is a twin stepped hull harder to drive?

This concern comes up and is an assumption that tends to come from racing, where extreme stepped hull designs are tuned to the absolute edge of performance.

In real-world use, a well-designed stepped hull is more predictable than a conventional deep V, not less. The air cushion between the steps keeps the hull more settled and means it resists the tendency to roll in turns. It tracks more cleanly through wash and does not hunt or pitch at higher speeds in the way a conventional hull can when pushed hard.

Under hard cornering at speed, a properly designed stepped hull maintains grip rather than breaking away and sliding. The geometry holds the hull to its line. This is precisely the characteristic that makes stepped hull design appealing in a performance context, and it is as relevant at 30 knots on a family day out as it is in competition.

The adaptation for drivers coming from a standard deep V RIB hull is minimal, and the benefit at the helm is immediate.

What does the G980 hull feel like at the helm?

Early independent sea trial data is consistent across conditions. In hard, committed turns at speed, the hull holds its arc without cavitation and without any loss of composure. The hull does not feel like something working at its limits. It feels like something with significant capability still in reserve. Even when facing significant wash from passing vessel traffic, the boat remains completely dry from bow to stern.

That character carries across the full range of use. Whether the G980 is running hard on open water or sitting at anchor with a full complement of passengers, the hull’s behaviour is settled and consistent. It is a boat that handles with composure and comfort across conditions.

What about slow-speed handling?

The Grand G980 is fitted with an integrated Sleipner bow thruster, working in conjunction with the Yamaha HelmMaster EX Joystick system. Together, these allow the boat to be crabbed sideways, held against wind or current and positioned with precision in tight spaces.

For owners, the Grand G980 allows owners to push hard offshore, then arrive somewhere busy without stress.

How fast is the G980?

In testing with twin Yamaha 350HP engines, a full tank of fuel, passengers on board and a fibreglass hard-top fitted, the G980 exceeds 58 knots.

For a 10 metre family RIB, the twin stepped hull is what makes it achievable: less drag means less fuel consumed to reach speed, and more stability once the boat is there. The efficiency gain is not just about performance. It means longer range, lower running costs and a hull that is working with less effort across the entire rev range, not only at wide-open throttle.

The foundation that everything else is built on

For Grand’s design team, the goal was a 10 metre RIB that performs at pace, handles offshore conditions, and – crucially – creates a real home on the water for the families onboard. The twin stepped hull is the crucial foundation that makes the performance, capability and efficiency possible, whilst also ensuring stability and comfort for everyone onboard.

But the hull is where the Grand G980’s design story starts; the modular space and cabin design give the Grand G980 its refined character above the waterline.