Seaplane Hydrodynamics

Hydrodynamic Analysis with SILAS

SILAS (Stability Investigation and Load Analysis for Seaplanes) is a proprietary analytical framework that Aufwind developed to address seaplane hull hydrodynamics from first principles. The code base implements a hierarchy of water-impact and planing theories that cover the full speed range from displacement through impact and transition to planing, and has been validated against flight test data to within 3 to 10 per cent accuracy. It has been applied to amphibious aircraft ranging from light sport aircraft to large utility amphibians.

SILAS Capabilities

Water impact load prediction

covers the full transient impact event from initial contact through chine immersion, producing pressure distributions, sectional forces, and design load cases suitable for hull structural substantiation under CS-23 and CS-25.

Planing performance

prediction determines resistance across speed regimes, evaluates step effectiveness, and assesses spray patterns. Takeoff and landing performance can be predicted for specified water conditions and wave states described by Pierson-Moskowitz or JONSWAP spectra.

Porpoising stability

analysis maps the stability boundaries for coupled heave-pitch motion as a function of speed, trim, and longitudinal centre of gravity position. The analysis identifies critical speed ranges and quantifies the sensitivity of the stability margin to hull geometry parameters such as step depth and afterbody angle.

Hull geometry evaluation

provides parametric assessment of deadrise distribution, beam-loading ratio, step geometry, and afterbody configuration against established hydrodynamic performance criteria from the systematic hull series programmes.

Parametric design studies

are possible because the analytical approach does not require mesh generation or test model fabrication, which allows hull geometry parameter sweeps within the scope of a single engineering task.

SILAS Wagner validation against flight test data — Wagner impact load validation against flight test data

SILAS porpoising stability map — Porpoising stability boundary mapping

SILAS wave severity analysis — Wave severity and operational envelope analysis

The methods implemented in SILAS are drawn from the analytical seaplane hydrodynamics literature spanning the 1920s to the present, and each method is benchmarked against published experimental or numerical reference data before it enters production use. For design questions that require higher fidelity than the analytical methods provide, Aufwind coordinates CFD validation and water basin test programmes with specialist partners.

Water Loads and Structural Design

Hull impact load determination and design load case definition form the basis for structural substantiation. The analysis produces bottom panel pressure distributions that feed directly into structural sizing, and extends to corrosion assessment and repair scheme development for hulls exposed to marine environments. Float installations, hull reinforcements, and sponson structures are covered where the scope requires modifications to the original hull geometry.

Certification Support

Compliance substantiation for CS-23 and CS-25 water operation requirements addresses both the prescribed semi-empirical methods and rational analysis alternatives that the standards explicitly permit. The scope includes regulatory pathway development for seaplane modifications and new designs, coordination with EASA and FAA certification authorities, and STC application support.

Technical Programme Leadership

Seaplane development and certification programmes require coordination across hydrodynamics, structures, flight test, and certification, because a change in hull geometry affects the load cases, which in turn affects the structural substantiation and the flight test programme. Aufwind takes lead engineer roles in these programmes, managing the integration across disciplines from preliminary design through certification.