Not That Simple
When we got back to shore and compared the data for the six runs (two speeds in three directions), what was immediately obvious was how low the numbers were. Both these boats rode extremely well.
But the differences between them, no matter how small, told a story. The deep-V was the better of the two going down sea and across the waves. Going into the waves-the touted head-sea ride by which many of us judge a boat-the deep-V rode softer at 30 mph but was surpassed by the RIB as speeds increased.
Running into waves is the toughest course and produces the roughest ride. One reason is wave shape. Driving into an oncoming wave forces the boat to meet the wave's steep face rather than its more rounded back. Speed and time also come into play. A wave moving at you adds its speed to yours, increasing the impact. Plus the boat has less time to react. It comes off one wave and sinks into the next wave. Before the boat can become buoyant enough to lift itself so it can present its keel and stem to the next wave, that oncoming wave is already there. These are situations you won't experience when running down sea or when the waves are on your beam.
Any deep-V should do well punching into a wave. Its high deadrise doesn't just affect bottom shape, the stem and forefoot (the boat's "entry") are also finer than the blunter bow of a modified-V. This sharp bow penetrates the water easily and then slows the impact. Why? The widening flare of the bow makes the boat more buoyant the farther it sinks.
A RIB hits an oncoming wave slightly differently, in a way that noticeably softens its ride at high speeds. As its bow digs in, the air collar makes contact, absorbing some of the impact by lifting and deforming slightly to further slow the deceleration. A RIB's hull is also narrower(the collar isn't in the water when underway), and a skinny hull rides softer than wide one because it presents less area for the water to hit.
On the other hand, RIBs tend to be lighter than conventional fiberglass boats, which may not help their ride. The Regulator 29 displaces about 6,800 pounds whereas the Zodiac Pro 20 comes in at less than half- around 2,976 pounds. In general, the object with more mass accelerates (and decelerates) slower. The result: You feel less impact.
Regulator's designer, Lou Codega, simplifies the concept by asking us to consider two identical balls that can float: one light, the other heavy. If you drop them into a tank of water both will hit at the same speed. But the lighter ball won't sink in as far, and it begins its upward motion sooner than the heavier one. It has faster (greater) negative accelerations.
And Another Thing...
Our tests focused on ride quality as measured in vertical accelerations, what is typically called "slamming" or "pounding." By necessity, our procedures and parameters were limited.
For example, accelerometer testing conducted by the U.S. Navy uses trial times measured in hours rather than minutes. They measure wave speed and period and can wait for a day of perfectly snotty weather when the sea state is high and well defined. Sure, our gentle swell test is a good indication of how a boat will ride, but it might not pass muster with an MIT-trained naval architect.
Also, anyone buying a boat should consider the other aspects important to ride. Stability, heave, roll period, and pitching are just some of the characteristics that also determine how comfortable and secure you will feel.
But based on our singular concern for this test, that of pounding, we can definitely conclude that our deep- V produced a softer ride running down sea, in a beam sea, and in a head sea at moderate speed. But at higher speeds in a head sea, the RIB pounded less.