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Passing the stepped-hull test

Michael Peters Yacht Design in Sarasota, Fla., is well-known — and well-regarded by me — for its high-performance conventional and stepped-bottom hulls. Peters has been on my radar for a number of years, and I had a chance to ride on one of the firm’s stepped military designs last June at the Navy’s Multi-Agency Craft Conference in Little Creek, Va. The weather was favorable and seas calm, but this 70-mph 40-footer went through its paces, including hard high-speed turns, without surprises.

MPYD's stepped hull uses a tunnel with vertical side walls that act as mini keels.

Michael Peters Yacht Design has done a lot of experimentation through the years to make its stepped hulls run as reliably as its conventional bottoms. The formula it has settled on calls for a sort of tunnel aft along the centerline, with the tunnel bounded by vertical walls that act as mini keels. A keel may seem like exactly what you want back here, but the recessed section works well in preventing spinouts without tripping the hull in a turn as a keel might.

To address the hull’s tendency to trim down at the bow in a turn, and also to help it run a little more bow-up in general, Michael Peters Yacht Design puts a little rocker in the hull just forward of the transom. This reduces lift at the stern, and since the hull surface — stepped or otherwise — acts as a fulcrum, the bow comes up when the stern sinks. This has the positive effect of creating a naturally higher trim angle while allowing the drives to be raised to get the bow up higher still. If the bow is drier in a hard turn, the center of resistance is farther aft, reducing the potential for a spinout.
Offshore, where Mother Nature rules, there are no performance or survival guarantees, so we should always be on our guard. That said, Peters, who has a refreshing humility for his accomplishments, believes his firm’s hull concept is no longer just a good idea theoretically. “Zodiac builds an 11-meter RIB to our design, and they took one of them on a 10-day, 1,700-mile excursion through the Northwest Passage last year,” says Peters. “They averaged 30 knots threading though icebergs, often in very rough water, while crossing the north shore of Canada, and never spun the boat out.”
The Zodiac expedition confirmed “that the boat can take a lot of weight, since it was loaded down with fuel initially. It can also take a wide range of longitudinal CG locations — up to 2 feet, which is very forgiving for a boat like this,” he adds.
Zodiac’s creative marketing people came up with the term Military Air Channeled Hull, or MACH, to describe MPYD’s bottom, which is a real wordsmithing tour de force, as it forms an apropos acronym while revealing that military air channels more compliantly than civilian air. MPYD just a tad less inventively calls its stepped hull a Stepped “V” Ventilated Tunnel. Samuel Johnson reminds us that “Promise, large promise, is the soul of an advertisement.” In this case the promise is well-kept by MPYD (

Michael Peters

See related article:

- The stepped hull has come of age

This article originally appeared in the December 2011 issue.


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