Eliminating Hull Slap at Anchor: Precision Engineering Through Experience

If you’ve ever tried to relax at anchor only to hear that relentless thump-thump from under the stern, you know hull slap can turn a bluewater dream into a reverberating headache. On Maximus II, a new 106-foot custom build now in sea trials in Taiwan, our team confronted a persistent problem with a precision fix—engineering a quiet, comfortable stern without compromising performance. For owners planning 2026 projects, this is a case study in why design vigilance and smart retrofit thinking matter from concept to cruising.

During early trials, even small wakes in the marina produced loud thumping as water was trapped beneath the swim step. The step was deliberately set 10 inches above the waterline to improve clearance—more than a prior 92-foot sistership with a 3-inch overhang that had suffered the same issue. The takeaway: clearance alone wasn’t the cure. Flow behavior under the stern needed to be managed, not just avoided.

We hauled out and developed a “box” structure under the swim step—essentially a shallow, hull-width cap that is watertight, glassed directly to the hull, and carried from the swim step edge down past the waterline by roughly a foot before fairing back to the original bottom and stern thruster geometry. Three contour profiles were proposed to cope with varied sea states and a following sea. A naval architect validated the concept, modeled the additional buoyancy—about 4,500 pounds—and the shipyard refined the design in CAD. The result maintained access, preserved hydrodynamic fairness, and controlled the under-step pressure zone where slap was born.

Targeted stern flow control eliminates pressure pulse and slap beneath the swim step.

Shallow, hull-width cap adds ~4,500 lb buoyancy without compromising underway performance.

Validated by naval architecture, built in-yard, and proven quiet at the dock and at speed.

On the second sea trial, the difference was immediate—quiet at rest, poised under way, and zero drama from harbor wakes. For owners shaping a custom brief, this is precisely where a build’s value is either locked in or lost: in those subtle interface decisions between comfort, hydrodynamics, and maintainability. When we guide a project, we look for these system-level refinements early, long before they become costly yard-time fixes.

Thinking about a 2026 new build or major refit? Let’s engineer the silence—and the confidence—into your design from day one. Contact David at david@baranofyachts.com to start your concept-to-cruising plan.