The magazine for those working in design, construction, and repair NUMBER 149 SLAMMING STANDARDS JUNE/JULY CAPSIZE: LESSONS LEARNED 2014 DAVID JONES & ASSOCIATES

Slamming Standards As awareness of impact injuries on high-speed boats grows, research and debate thrive in the quest for strategies to accurately measure slamming and for practical rules that will keep boaters safe. Text by Johan Ullman Graphics courtesy HSBO (except where noted) Above—It’s not enough to engineer high-speed boat hulls, superstructures, and systems to endure the impacts of extreme slamming while under way; crew and passenger well-being must be considered as well. Impact injuries— fractured vertebrae, ruptured disks, sprains, and tearing of soft tissue—are increasingly the subject...

A fast boat in motion even on a relatively calm sea is bafflingly dynamic, making it difficult to accurately predict the slamming loads passengers in a particular boat in particular conditions will be exposed to. It’s safe to say that risk of acute injury is proportional to the level of energy absorbed from a particular slam, but accurately predicting the magnitude of any slam is practically impossible. structure, mechanical failure results. A single impact can cause such struc­ tural failure and injury in the body but might not register as potentially harmful under specific standards. The total...

Some of the most extreme slamming must be endured by military, rescue, and other government employees engaged in hazardous duties. This jet-powered 50' (14.9m) Combat Boat 90 (CB90), built for the Swedish special forces by Docksta Shipyard (Docksta, Sweden), can deliver to beach landings as many as 18 fully equipped soldiers at speeds up to 50 knots. Seats claimed to comply with this standard are known to have failed, contributing to operator injury. This standard has no bearing on the shock-mitigating function or perfor­ mance of suspension seats. Maritime and U.K. Coastguard Agency Marine Guidance...

Free fall Steady state Platform filtered Seat filtered Platform raw Seat raw Platform 10 Hz LPF Seat 10 Hz LPF Time (ms) Graphing filtered and raw impact data of seat testing shows how even a good filter can somewhat skew specifics. The difference in magnitude of accelerations is as much as 10%, but there is also a slight displacement in time of the impacts, measured here in milliseconds. As commonly applied by some researchers, a low-pass filter (LPF) at 10 Hz reduces the 11.7 g raw platform impact (dark blue line) to just 5.9 g (purple line). This is why it’s useful to retain original (raw)...

The difference between impact and vibration is easy to understand: watch a boxer jumping rope (vibration), and the same boxer being knocked out (impact). It is not possible to predict the risk of injury caused by that impact by analyzing and quantifying mean values of the preceding vibration. Indeed, it is the limitations of many of the existing standards based on wholebody vibrations that drive discussion and research efforts to better quantify injury risks on high-speed boats. Linking Exposure Levels to Injury Risk Pain remains the best indicator of impending injury. If the slamming is really...

The test boat employed to gather the data on page 53 illustrates that even a welldesigned V-hull can present a flat surface to the surface of the water and deliver a hard slam and an oblique impact, which is potentially more damaging to the crew’s spines than a vertical impact would be. Limiting Impact Exposure Regardless of whether or how you want to quantify your exposure, here are some fundamentals that boat designers and builders can consider in their efforts to reduce slamming, and damage to passengers. • Hull shape is important. Deeper-V shapes reduce slamming by displacing water more gradually....

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