Nov 10

Nov 10 Hull Design: Pad vs Steps

Even though many people like to argue about catamarans vs V hulls, a different debate has always been about different V hull configurations; Pad vs. Stepped hulls. The problem is that there are many configurations of each. For the sake of the article, let’s look at the benefits of a pad V hull and a stepped V hull and why it is not a zero sum game, there is a winner but it depends on what you’re using it for. Each design has a distinct purpose and advantages over the other.

If you are into top speed and you’re running a boat that is 30’ and under, there is no contest, the pad V hull will be the fastest, if we assume several things. The design has to be good the boat has to have the right weight distribution. Some of the fastest pad hulls ever made typically are really light, where weight is as far aft as possible and the center of gravity is really close to the dynamic center of gravity. The dynamic being the the point of stability that changes throughout operation, due to drag, trim, weight and design.

The Allison XS 2003 hull design, is incredibly fast and features a wide pad, major setback, a deep deadrise and a slight lip to help it fly level among other things. Allison hulls are among the most sophisticated hull designs on the water.

Many fast V hulls have notches to increase setback, pushing the CG further back, while the boat lifts up on to the pad, drag is reduced, pushing the dynamic CG further back, the gearcase and prop also have an effect on this. That’s why and how you can balance a boat on a such a small running surface with minimal trim. A really well setup boat will balance right on the pad and if you’re setback and engine height are optimal, you need only a minimal amount of trim.

Although the fastest pad hulls get big numbers, the issue then is rough water. Many can still run in big water but you wont’ be able to “air” it out while running fast and you will most likely have to run more of the hull in the water. This isn’t a problem, just simply the nature of the hull design. And this is where the idea of steps can be a benefit and why you see steps on almost all larger modern hulls.

Even the smaller Chaudron boats, 22 and 25, use twin steps, set far aft in the hull, they allow the boat to run fast and flat in rough water. A different driving experience than a pad hull, with benefits that help the narrow design.

With stepped hulls, there are many variations of steps themselves, from multiple steps, single steps and aerated steps; effectively, the design is trying to reduce drag without the extreme lift the pad accomplishes. If you’re running a heavier hull, a longer hull or simply the style of boat is designed to run flat, steps aerate the hull surface, reduce drag and are faster if you were comparing a similar straight V hull design. A V without a pad just won’t get the lift of a pad so inevitably the stepped hull is faster in that comparison; assuming a similar boat in design, weight and configuration.

The Phantom 32 SV utilizes two steps far aft in the hull. Fast and light yet races offshore at high speed.

The driving experience is distinctly different. For one, pad bottom boats that are fast tend to be drivers boats and need to be “driven” when running fast in order to balance the hull as the surface area is reduces. With a stepped hull, less trim and often less balancing is often the case. Both design take active driving, especially at higher speeds but in general I would say a pad V is more of a drivers boat. Just put someone in the driver seat of a light pad bottom boat that hasn’t driven one before and you will see immediately how driver input is critical.

A nice sketch from Jim Russell at Aeromarine Research shows the surface contact area of a conventional hull vs a stepped hull.

Turning is another major difference between how different hulls perform. Since there are so many different designs, it’s hard to generalize but pad hulls and non stepped hulls steer very well when under control, you are using as much of the running surface as you want, via trim and speed. Whereas with a stepped hull, particularly multi stepped hulls, you want to avoid aggressive turns and digging the bow in, where the varying running surfaces of the steps will cause the hull to slide on you, potentially spinning out. To me, the key is to not trim down too much and keep the hull flat, let it set in. That said, you can hook and spin a non stepped hull, it’s just not as common. A jagged turn with the bow down could test the tracking ability of the hull. Like any boat, seat time and knowing the boat you’re driving helps prevent any accidents like that.

In a deep heavy boat like this Cigarette 30’ Vice, steps benefit efficiency over a non stepped similar hull. Although many fast offshore boats in the old days were straight V hulls, they were left behind by stepped hulls in pure speed.

When it comes to the debate about what is better, I would say: It depends. I love a really light pad V hull design for the fun of driving and potential speed. That said, in rough water, even on smaller boats a stepped design can let you run faster with more of the hull in the water. There is no doubt, the fastest V hulls utilize a wide pad bottom, some have pads as wide as 10”. It’s worth mentioning that Fountain, Scarab and others experimented with pads, notches and different configurations borrowed from small boats to find the fastest design for offshore racing.

With all hull designs there is always a compromise with benefits and drawbacks. If you know the type of boating you do and the water conditions that you often run in, it can help you decide. Under 30’ I really like a hull with a pad unless you are looking for pure rough water performance, a deep V with steps can be a great ride. In the end it’s not really a debate and more about deciding what boat will work best for you.