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Posted by on May 9, 2012 in High-performance, Powerboating, UK, US |

Stepped Hulls vs. Traditional V Bottom: Everything you Need to Know

What exactly is a stepped bottom? Is it better or worse than a regular V hull? What do you need to know, to decide if having a step in the hull is right for you?

Stepped hull bottoms are popular, though traditional V bottom boats still account for most of the hulls on the water today. Should you be seeking out a ride that has a step or two? Or, would that be a bad move for you? Understanding just what that step is and what it does holds the answers.

Caption: Some boat manufacturers, including Intrepid Powerboats (shown here), have researched, tested, and perfected unique stepped hull designs that unquestionably boost speed and efficiency.

Some boat manufacturers, including Intrepid Powerboats (shown here), have researched, tested, and perfected unique stepped hull designs that unquestionably boost speed and efficiency.

A step in the hull is a longitudinal notch that runs from chine to chine, and comes high enough on the side of the boat to reach above the waterline when the boat is on plane. Low pressure is generated just aft of the step as the boat moves forward, creating suction that draws in air in from the sides. As speed increases and the boat generates more and more lift, the section of the hull just aft of the step becomes completely free of the water. Drag and friction are reduced, and as a result, the boat can go faster without burning more fuel or adding more horsepower.

Introduce air under a boat’s bottom, however, and there can be some unintended consequences. The severity of each (as well as the amount of efficiency gained) depends to some degree on the particular hull and step design, but generally speaking, boats with steps feel lighter and easier to turn.

This may be a good thing, but there’s a down-side: since certain sections of the hull are unsupported by the water, at high speeds some boats can have reduced stability, especially when placed into fast turns. Many stepped hulls also tend to run with more of a bow-down attitude, since the boat is balanced on a forward area (the step) and an aft area (where the hull again meets water) instead of in the middle. In a few cases, steps have also been known to aerate the lower drive unit of outboards, causing them to gulp air as they draw in cooling water, which can lead to overheating.

The traditional V-hull, meanwhile, has a far more predictable center of resistance to ride on. At the helm, the boat’s grip on the water feels more secure, and trim is more bow-up in nature.

So, which is better? Neither, and both— to make this call, you have to understand your priorities. If you’re most interested in gaining efficiency and speed, a stepped hull is probably going to serve you well. If predictability and the ability to change trim through a wider range has more value to you, the traditional deep V is often a better choice.

What about safety and stability? You can have confidence in a time-tested stepped hull design, but an unproven design could have issues—make sure one you’re considering has been thoroughly vetted, and comes from a builder which has plenty of experience in designing and building boats with stepped hulls.

Got a preference between stepped hulls and V hulls? Tell us about it in the comments below.

-Lenny Rudow