1. Dynamic Stability & Righting Moment in a Small-Waterplane Trimaranesque Platform
Why this is critical and very different from a yacht
- Your platform has extremely small waterplane area (only three slender NACA foils). This gives very low hydrostatic restoring force and low metacentric height (GM).
- Because the three legs are 19 ft long and only 50 % submerged, the center of buoyancy can shift dramatically with even modest heel or wave slope.
- The large 80 ft × 40 ft triangle truss 7 ft above the water creates a very high center of gravity (especially with people, solar, roof, and dinghy on top).
- The three small “airplane” stabilizers may help at speed but provide almost no restoring moment at zero speed or in following seas.
Immediate next steps you should model:
- Calculate static stability curve (GZ curve) for heel angles 0–40° in both calm water and with one leg partially emerged.
- Run seakeeping analysis (RAOs) for heave, pitch, and roll in typical ocean spectra (especially 8–15 s waves).
- Determine whether you need active ballast transfer between the three legs or additional submerged sponsons.
2. Structural Loads on the Truss-to-Leg Connection (The “Knee”)
Why this is a major departure from normal boat design
- The 7 ft tall triangular truss is essentially a rigid platform sitting on three slender, widely spaced cantilevers. Every wave impact or gust creates enormous bending moments and torsion at the leg–truss interface.
- Unlike a normal trimaran, your legs are not deeply integrated into the structure; they are “hanging” 19 ft foils with only the upper half attached.
- The NACA foil shape is excellent for drag but poor for resisting side loads and fatigue at the root.
Immediate next steps:
- Finite-element analysis (FEA) of the leg-to-truss joint under worst-case slam, green-water, and torsional loads.
- Check fatigue life — ocean cycles will be in the millions.
- Decide on material (aluminum vs composites vs steel) and whether the legs need internal bulkheads or active strain monitoring.
3. Station-Keeping & Propulsion in Real Ocean Conditions
Key differences from a yacht
- Six rim-drive thrusters mounted on the legs 3 ft from the bottom are very low and will be subject to enormous side loads and ventilation in waves.
- Because waterplane area is tiny, the vessel will react quickly to any thrust imbalance — it may be twitchy in surge/sway/yaw.
- The design relies on the legs acting as passive foils for forward efficiency, but thrusters are aimed to “push water past the wing.” This creates complex interaction ( Coandă + induced drag ).
Immediate next steps you should study:
- Thrust vectoring logic and DP (dynamic positioning) control algorithm — especially how to counteract yaw when one leg is in a wave trough.
- Power budget: solar + battery vs hotel + propulsion load in trade-wind conditions.
- Backup propulsion or sails — total loss of thrusters would leave you unable to maintain heading in heavy weather.
4. Safety, Evacuation & Damage Stability
This is the area most overlooked in novel seastead concepts
- Only three buoyancy elements. Flooding or major damage to any single leg is likely to be catastrophic.
- The 14 ft RIB dinghy is the only lifeboat. Launching it in 3 m seas while the platform is rolling heavily will be extremely difficult.
- High freeboard on the legs but very low freeboard on the truss edges (only ~4 ft railing) means green water will regularly sweep the deck.
- Human factors: motion sickness will be worse than a normal boat because of the small waterplane and high CG.
Immediate next steps:
- Perform probabilistic damage stability analysis (treat each leg as a separate compartment).
- Design an emergency “abandon ship” procedure that does not rely on the dinghy being usable in every sea state.
- Consider adding foam buoyancy or inflatable collars near the top of each leg as a failsafe.
Recommended Immediate Action List
- Build a 1:20 or 1:12 scale model and test it in a wave tank (or at least in ocean swell) before committing to final leg length and truss stiffness.
- Hire a naval architect experienced in SWATH or semi-submersible platforms — your design sits between a SWATH and a surface trimaran.
- Run OrcaFlex / ANSYS AQWA / MOSES seakeeping + stability simulations with realistic mass distribution (include solar, batteries, water, people, dinghy).
- Revisit leg length — 19 ft with only 9.5 ft draft may be too short for ocean stability; many SWATH designs use deeper struts.
These four topics are the ones that differ most dramatically from conventional yacht design and carry the highest risk of catastrophic failure if ignored. Once you have preliminary answers here, we can move on to secondary issues such as vortex-induced vibration on the legs, biofouling of the NACA foils, solar shading by the stabilizers, and crew motion comfort.