The decisions that go into the design of a stepped hull are similar to the tradeoffs designers face with any other boat-design—every time you make one thing better, you compromise something else. But with a stepped hull the unintended consequences can be less predictable and more dramatic.
For example, while placing steps farther aft reduces drag, these deeper steps can destabilize the boat’s handling.
“You can get away with this for a light boat with an aft LCG [longitudinal center of gravity]—but with forward LCGs you need rear steps moved forward,” said naval architect Lorne Campbell. “Otherwise the forward steps do all the work while the rear steps are shielded. You need the lateral contact to hold you straight.”
Campbell, a longtime designer of high-speed powerboats, presented his notes on stepped hulls at the 2010 edition of the High Speed Boat Operations Forum in Gothenburg, Sweden. You can watch video of the full 25-minute presentation below:
We’re sharing this video as part of our extensive coverage of the 7th edition of HSBO, attended by Professional BoatBuilder senior editor Paul Lazarus. (Read the online story “Crash Course” for a brief preview of the 2016 show.)
The forum connects boat designers and builders with the professional drivers of high-speed craft.
These drivers often work for militaries or law enforcement agencies. Their jobs require the latest in fast, powerful boats. But they also need to be protected from the cumulative physical toll from riding around in high-speed boats for a living.
To read more of our HSBO-related coverage, also see “RIB on the Göta älv” (Professional BoatBuilder No. 166), about the powering of Norsafe’s Marathon 900 (9m/30’) with a pair of Mercury OptiMax diesel outboards; and “Team Mannerfelt,” an interview with the Swedish father and son designers of fast, safe boats at their studio outside Stockholm (PBB No. 163).
You can also look forward to a story on Swedish naval architect Petter Håkanson, who specializes in high-performance combatant craft (upcoming, in PBB No. 167), and our coverage of Lorne Campbell’s technical presentation on Crouch’s formula at the 2016 conference (upcoming, TBD).
Also note Campbell’s expansive letter in PBB No. 166 in response to Michael Morabito’s analysis of end-swapping in small planing craft published in PBB No. 163. And visit Campbell’s website.