On Step design...
Steps in planing surfaces is a controversial subject. It's history goes back a long way, but the difficulty of designing a proper step makes it a very 'design-dependent' feature, and not one that all boats will benefit from.
The concept of steps in the hull running surface was originally proposed by Reverend Ramus in 1872. He proposed both a single step with tandem planing surfaces, and a combination of 3 pontoons with one forward and 2 aft. There were published drawings for small stepped hulls with hard chines as early as 1906, and W. Fauber obtained the first US patent for hulls with multiple steps in 1908. There is quite a history of step design... the Solair set a record of 46 mph with 70 hp with a 12 stepped hull in 1910... and the record was upped each year to 1929, when the Estelle IV set the record at 105 mph with 2000 hp on a 35 ft. hull. It was an interesting era, more outlined in the
History of Powerboat Design book.
Stepped hulls dominated race boat design until about 1938 when Adolph Apel patented the 3-point hydroplane configuration. Even though 3point hulls were very successful in small limited class racing, stepped hulls were still running competitively in Unlimited class racing until 1949. In 1950, Slo-Mo-Shun demonstrated 'prop riding' and boosted the world speed record significantlly.
There are a number of reasons why stepped hulls did not continue their popularity for pleasure boats...complexity of design, cost of development, they were banned from Gold Cup racing from 1920 through 1931, and there were many, many huge war-surplus aircraft engines available after WW1 at low prices, so it was easier to buy a big engine for a standard mono-hull, than to develop an efficient stepped hull. Quite a
history...
The most significant issue with step design was, and still is, the very difficult engineering challenge of properly locating an efficient step on the hull. The length of planing surface behind the step (ie: the location of the step) and depth of the step have a huge impact on the performance of the setup. To design the step improperly can actually decrease performance. The issue of multiple steps makes the challenge even more tricky.
During the early development of stepped hulls, the reason that performance varied so drastically, was just exactly this issue...the designers didn't always achieve the best engineering solution to the placement and depth of the step.
This is still the case today...performance of stepped hulls can widely vary. So it's difficult to assume that any boat with steps, will necessarily be any better than one without.
I recently wrote a series of articles on Factors that influence performance in high performance powerboats and tunnel boats. You can download it for free in ....
TBPNews, my newsletter for high-performance and tunnel boat enthusiasts....check out "Rocket Science! (Part 2, Planing surfaces)" (Series of articles on high performance powerboat design, and technical opportunities for performance improvements by design).
i think i understand the point of it now...but i wont test it on my 21" electric tunnel as i dont think it would make much of a difference at the speeds i will be going at.
