When choosing a hull shape, finding the right balance of speed and stability can seem like an impossible task. While stepped hulls are often painted as unpredictable and difficult to handle, there are in fact many advantages to this hull shape, as we explain in this blog.
Hull Shapes and their Performance
When in water, the underside of a planing hull develops both lift and drag. The ultimate goal of boatbuilding is to find the perfect hull lift/drag ratio for speed and efficiency, ensuring that there is enough friction for the vessel to remain stable, but not to the point where it causes the boat to be slow.
What is a Stepped Hull?
A stepped hull has breaks which are intended to reduce the amount of surface area in contact with the water. These ‘steps’ can either run straight across the hull, or in a ‘v’ shape with apertures on the outboard side of the hull which allow air to be drawn into the step.
What are the Advantages of a Stepped Hull?
As the aspect ratio of the hull lifting surface increases, so does the efficiency. With a single hull surface displaying a 1:3 aspect ratio (where the length is three times that of the width of the hull), a stepped hull creates instead three short, wide, high-aspect surfaces which are in turn far more efficient.
By creating a higher lift, this modified hull reduces its frictional drag on water, making boats with a stepped hull up to 15% faster than those with a standard hull. A stepped hull also distributes this lift more evenly, making your vessel more level at higher speeds with a consistent trim angle.
Lighter, faster boats benefit hugely from a stepped hull throughout the entire speed range, resulting in lower fuel bills and generally more efficient vessels.
Comfort vs Efficiency
Boats with stepped hulls can benefit from both higher levels of comfort, and better fuel efficiency. Their consistent plane improves visibility making handling easier at any speed, and the reduced friction results in softer landing when travelling at high speeds, with less pitching, slamming and spray.
Offering a smoother ride for smaller, lighter boats, a stepped hull can also make it easier to maintain a faster average top speed.
Disadvantages of a Stepped Hull
Although there are significant benefits to a stepped hull, there are also a few drawbacks to this design:
- Boats with stepped hulls can be known to be slightly noisier
- Stepped hull boats are more costly to build
- Some vessels which incorporate stepped hulls into their design can be harder to drive safety at high speeds or in choppy water. If in doubt, always test-drive your vessel before purchasing!
After many years of boating experience, the team at Ocean Sports believe that the advantages of a stepped hull more than offset the drawbacks, with the fuel efficiency and comfort of this design outweighing the functionality of a regular hull.
About Ocean Sports Tuition
Ocean Sports Tuition is a Southampton-based company offering RYA-recognised practical and theory courses and boat charters. We have successfully delivered training on the South Coast and the Solent since 2004, and pride ourselves on providing excellent tuition and service to beginner, intermediate, and advanced sailors alike. Find out more about Ocean Sports and our friendly team here.