| Item | Estimated value |
|---|---|
| Triangle enclosed floor area | ~607 ft² |
| Equivalent interior area in m² | ~56.4 m² |
| Total displacement at 50% immersion of 3 legs | ~32,800 lb |
| Total displacement in metric tons | ~14.9 t |
| Solar parameter | Estimate |
|---|---|
| Usable panel area | ~85 m² |
| Installed panel density | ~200 W/m² |
| Total installed solar | ~17,000 W (17 kW) |
| Average Caribbean equivalent sun hours | ~5.5 h/day |
| System derate | 80% |
| Average daily energy | ~74.8 kWh/day |
| 24 h average if spread evenly | ~3,117 W |
So for planning:
Installed solar ≈ 17 kW
Average Caribbean production ≈ 75 kWh/day
Equivalent continuous average power ≈ 3.1 kW
| Battery item | Estimate |
|---|---|
| Total storage | 500 kWh |
| Assumed system-level specific energy | 110 Wh/kg |
| Battery mass | ~4,545 kg |
| Battery mass in lb | ~10,020 lb |
| Cost at $90/kWh | $45,000 |
Split among 3 floats, that is about:
Yes, placing this low and spread apart would help roll inertia and overall motion response.
Your idea of 3 separate solar/controller/battery/inverter systems is good from a resilience standpoint. A practical split might be:
This is a strong architecture for redundancy, but it does add some cost and complexity.
I estimated frontal projected area when pointed into wind as roughly:
Total effective frontal area ≈ 370 ft² = 34.4 m².
Assumed drag coefficient for bluff/mixed body: Cd ≈ 0.9.
Using F = 0.5 ρ Cd A V² with air density 1.225 kg/m³:
| Wind speed | Wind speed | Drag force | Mechanical power at zero boat speed to hold position in still water | Estimated electrical power incl. losses |
|---|---|---|---|---|
| 30 mph | 13.4 m/s | ~3,400 N = 760 lbf | Not strictly zero at zero speed; thrust must match force | ~5-8 kW practical |
| 40 mph | 17.9 m/s | ~6,050 N = 1,360 lbf | — | ~10-16 kW practical |
| 50 mph | 22.4 m/s | ~9,450 N = 2,125 lbf | — | ~18-28 kW practical |
Why practical power instead of a neat formula? Because true station keeping in wind requires some water flow over the propulsors and depends strongly on current, waves, heading control, and thrust efficiency at low speed. In real sea state, the required average electrical power may be 1.5x to 3x the calm-water ideal.
With 6 rim drives, holding in 30 mph wind should be feasible. 40 mph is plausible but power-hungry. 50 mph starts to become doubtful for long duration unless there is substantial battery reserve and excellent control software.
Yes, if you sail slightly off the wind instead of pointing directly into it, much of the wind load can be reacted as lateral hydrodynamic lift in the submerged foil sections. That is usually much more efficient than brute-force station keeping. This is conceptually similar to making leeway like a sailboat, except with powered heading control.
The amount of control in strong winds depends on:
Conceptually, this should improve survivability/control a lot. My rough view:
| Condition | Likely control outlook |
|---|---|
| 20-30 mph wind | Good control likely |
| 30-40 mph wind | Likely controllable with careful heading and active thrust |
| 40-50 mph wind | Possibly controllable in moderate seas, but very dependent on real foil performance and yaw control |
| 50+ mph wind | Not something I would assume safe without model testing / CFD / sea trials |
My rough answer: with active control and enough battery reserve, perhaps control into the low-40-mph range with confidence, and maybe upper-40s in favorable sea states. Beyond that, not enough certainty from first principles alone.
| Load item | Average power | Daily energy |
|---|---|---|
| 1 AC unit running part-time average | 900 W | 21.6 kWh |
| Refrigerator/freezer | 120 W | 2.9 kWh |
| 2 watermakers average duty | 250 W | 6.0 kWh |
| Starlink x2 average combined | 140 W | 3.4 kWh |
| Lighting | 80 W | 1.9 kWh |
| Electronics, pumps, controls, sensors | 180 W | 4.3 kWh |
| Cooking/small appliances averaged over day | 250 W | 6.0 kWh |
| Waste, freshwater, misc hotel loads | 120 W | 2.9 kWh |
| Battery/inverter/controller losses | 180 W | 4.3 kWh |
| Total average non-propulsion draw | ~2,220 W | ~53.3 kWh/day |
Compared with solar production of ~74.8 kWh/day, this leaves:
So your normal-day solar surplus is useful, but not huge. It is enough for slow propulsion, not fast propulsion.
For a low-displacement foil-column craft, a rough electric propulsion estimate is:
| Speed | Approx required electric power |
|---|---|
| 2 knots | ~0.6-1.0 kW |
| 3 knots | ~1.5-2.5 kW |
| 4 knots | ~3-5 kW |
| 5 knots | ~6-10 kW |
| 6 knots | ~10-16 kW |
| 7 knots | ~16-26 kW |
| 8 knots | ~24-40 kW |
With only the ~0.9 kW average excess solar, I would expect:
24/7 solar-only cruise speed ≈ 2 knots, maybe 2.5 knots in calm conditions.
Below I assume 500 kWh usable battery and two drag cases:
| Speed (knots) | Power OFF stabilizers | Hours OFF | Statute miles OFF | Power ON stabilizers | Hours ON | Statute miles ON |
|---|---|---|---|---|---|---|
| 4 | 4 kW | 125 h | 575 mi | 3.7 kW | 135 h | 622 mi |
| 5 | 7 kW | 71 h | 410 mi | 6.4 kW | 78 h | 449 mi |
| 6 | 12 kW | 41.7 h | 288 mi | 11 kW | 45.5 h | 314 mi |
| 7 | 20 kW | 25 h | 201 mi | 18.4 kW | 27.2 h | 219 mi |
| 8 | 32 kW | 15.6 h | 144 mi | 29.4 kW | 17.0 h | 156 mi |
1 knot = 1.1508 statute mph. These are broad estimates only. Real drag could differ materially.
Assuming fabrication in China for the hull/legs and mixed China/global sourcing for equipment:
| # | Item | Estimated weight (lb) | Estimated cost first unit (USD) | Notes |
|---|---|---|---|---|
| 1 | 3 legs / foil floats | 5,500 | $140,000 | Marine aluminum, internal framing, watertight compartments |
| 2 | Body / triangle truss enclosure | 8,500 | $220,000 | Aluminum primary structure, roof, walls before glazing/interior |
| 4 | 6 rim drive thrusters | 1,200 | $90,000 | Assuming custom/specialty electric thrusters |
| 6 | Solar panels | 2,300 | $17,000 | 17 kW installed |
| 7 | Solar charge controllers | 180 | $8,000 | 3 redundant systems |
| 8 | Batteries 500 kWh | 10,020 | $45,000 | At your stated $90/kWh |
| 9 | Inverters | 300 | $12,000 | 3 systems, marine-grade |
| 10 | 2 watermakers and water storage | 900 | $14,000 | Includes tanks and plumbing, not full stores |
| 11 | Air conditioning | 300 | $6,000 | 3 units, one generally used at a time |
| 12 | Insulation | 400 | $6,000 | Marine foam/panels |
| 13 | Flooring, cabinets, kitchen, furniture, bathrooms, bedroom | 3,500 | $70,000 | Moderate quality, marine fitout |
| 14 | Waste tanks | 250 | $3,000 | Excluding contents |
| 15 | Glass and glass doors at ends | 2,000 | $35,000 | Laminated marine glazing, likely expensive |
| 16 | Refrigerator | 180 | $2,000 | Marine/efficient household type |
| 17 | Davit/crane/winch for dinghy | 500 | $8,000 | |
| 18 | Safety equipment | 300 | $7,000 | EPIRB, rafts, fire suppression, PFDs, flares, etc. |
| 19 | 14 ft RIB dinghy | 900 | $18,000 | With outboard |
| 20 | 2 sea anchors | 150 | $2,000 | |
| 21 | Kite propulsion system | 350 | $8,000 | Experimental |
| 22 | 8 airbags in each leg | 250 | $4,000 | 24 total inflatable buoyancy bags |
| 23 | 2 Starlink systems | 40 | $1,500 | Hardware only |
| 24 | Trash compactor | 120 | $1,000 | |
| 25 | 3 aluminum airplane stabilizers + actuators | 600 | $18,000 | Custom fabricated |
| 26 | Other to finish out | 1,600 | $40,000 | Wiring, plumbing, paint/coatings, controls, fasteners, electronics |
| Estimated subtotal | 40,340 lb | $775,500 | ||
| Scenario | Estimated cost |
|---|---|
| Parts/fabrication subtotal | $775,500 |
| Engineering, tooling, shipping, import, yard assembly, commissioning, contingency (35%) | $271,000 |
| Estimated first unit total | ~$1.05 million |
| Estimated cost each at 20-unit run | ~$720k-$820k each |
This concept has:
That generally gives a longer natural period and often a gentler ride than a conventional beamy box barge. My rough estimates:
| Motion mode | Estimated natural period | Comment |
|---|---|---|
| Roll, side-to-side | ~8 to 11 s | Depends strongly on actual mass distribution and submerged geometry |
| Pitch, front-to-back | ~7 to 10 s | Likely somewhat similar to roll due to triangular spacing |
Estimated damping ratio:
| Condition | Roll damping ratio | Pitch damping ratio |
|---|---|---|
| Without stabilizers | ~8-12% | ~7-10% |
| With stabilizers active | ~15-25% | ~14-22% |
That means the shape alone likely gives moderate damping, and the small airplane-like active surfaces could materially improve it, especially near resonance or while underway.
Body tip is interpreted as difference in elevation front-to-back or side-to-side across the living area. Gs are vertical acceleration at the center of the triangle.
| Speed | Wave | Direction | Stabilizers | Body tip difference | Gs felt at center |
|---|---|---|---|---|---|
| 6 kn | 3 ft / 3 s | From front | Off | ~0.5-0.8 ft | ~0.05-0.09 g |
| 6 kn | 3 ft / 3 s | From front | On | ~0.4-0.6 ft | ~0.04-0.07 g |
| 6 kn | 3 ft / 3 s | From side | Off | ~0.4-0.7 ft | ~0.05-0.08 g |
| 6 kn | 3 ft / 3 s | From side | On | ~0.3-0.5 ft | ~0.04-0.06 g |
| 6 kn | 5 ft / 5 s | From front | Off | ~1.0-1.6 ft | ~0.10-0.18 g |
| 6 kn | 5 ft / 5 s | From front | On | ~0.7-1.2 ft | ~0.08-0.14 g |
| 6 kn | 5 ft / 5 s | From side | Off | ~0.9-1.4 ft | ~0.09-0.17 g |
| 6 kn | 5 ft / 5 s | From side | On | ~0.6-1.0 ft | ~0.07-0.13 g |
| 6 kn | 7 ft / 7 s | From front | Off | ~1.8-2.8 ft | ~0.16-0.28 g |
| 6 kn | 7 ft / 7 s | From front | On | ~1.2-2.0 ft | ~0.12-0.22 g |
| 6 kn | 7 ft / 7 s | From side | Off | ~1.5-2.5 ft | ~0.15-0.26 g |
| 6 kn | 7 ft / 7 s | From side | On | ~1.0-1.8 ft | ~0.11-0.20 g |
| 7 kn | 3 ft / 3 s | From front | Off | ~0.6-0.9 ft | ~0.06-0.10 g |
| 7 kn | 3 ft / 3 s | From front | On | ~0.4-0.7 ft | ~0.05-0.08 g |
| 7 kn | 3 ft / 3 s | From side | Off | ~0.5-0.8 ft | ~0.05-0.09 g |
| 7 kn | 3 ft / 3 s | From side | On | ~0.3-0.6 ft | ~0.04-0.07 g |
| 7 kn | 5 ft / 5 s | From front | Off | ~1.2-1.8 ft | ~0.12-0.20 g |
| 7 kn | 5 ft / 5 s | From front | On | ~0.8-1.3 ft | ~0.09-0.16 g |
| 7 kn | 5 ft / 5 s | From side | Off | ~1.0-1.6 ft | ~0.10-0.19 g |
| 7 kn | 5 ft / 5 s | From side | On | ~0.7-1.1 ft | ~0.08-0.15 g |
| 7 kn | 7 ft / 7 s | From front | Off | ~2.0-3.1 ft | ~0.18-0.32 g |
| 7 kn | 7 ft / 7 s | From front | On | ~1.4-2.2 ft | ~0.14-0.25 g |
| 7 kn | 7 ft / 7 s | From side | Off | ~1.7-2.7 ft | ~0.16-0.29 g |
| 7 kn | 7 ft / 7 s | From side | On | ~1.1-1.9 ft | ~0.12-0.23 g |
Overall this suggests a potentially soft ride, especially compared with a conventional surface-piercing multihull of similar length, but only if the structural and hydrostatic balance issues are solved.
Your enclosed area is about 607 ft². A conventional cruising catamaran with roughly similar usable interior area would typically be around:
Cost comparison:
So a comparable catamaran might cost about: 1.3x to 2.5x as much, depending on finish level and brand.
Would this seastead pitch and roll less than a 100 ft catamaran in 7 ft waves?
Not automatically. A good 100 ft catamaran has enormous waterplane, long length, and can be very stable in many conditions. But compared to a more ordinary catamaran of much shorter length, your small-waterplane concept could indeed have less sharp motion in some sea states. I would not confidently say it will beat a well-designed 100 ft catamaran overall. I would say it may have a gentler motion than a conventional 50-60 ft catamaran in certain wave periods.
In a flag-of-convenience jurisdiction like Panama or Liberia, it may be possible to register this under a yacht category, but classification is not just about number of hulls. Issues that may arise:
So: Possibly yes, but probably not as simple as “just a trimaran yacht.” A flag/surveyor may ask for custom stability booklets, structural calculations, electrical system review, and safety compliance documentation.
Potentially interesting, but the concept is not yet investment-ready. The biggest issue is weight versus buoyancy. If that is solved, then the design has a compelling story:
As a business, it probably works better first as:
Not mass market. But there may be a real niche for a few dozen to a few hundred units if the product is reliable and safe. The niche is likely “high-income adventurous waterfront living,” not mainstream boating.
If operating near the southern Caribbean and using modern forecasts, routing, and conservative seamanship, a platform capable of 6-7 knots continuous can improve weather avoidance. But I would not call it storm-proof or assume speed alone makes it safe from tropical systems. Forecasting helps a lot, but storms can develop, shift, or expand faster than expected. This platform should still be designed to survive rough conditions, not just avoid them.
Your 3-way electrical redundancy is good. The added airbags in the legs are also good as backup safety. I would still recommend:
| Summary item | Estimate |
|---|---|
| Estimated total cost, first unit | ~$1.05 million |
| Estimated cost each if ordering 20 | ~$720k-$820k each |
| Installed solar | ~17 kW |
| Average solar produced | ~74.8 kWh/day |
| Average solar used, non-propulsion | ~53.3 kWh/day |
| Average solar left for propulsion | ~21.5 kWh/day |
| Equivalent continuous power from total solar | ~3,117 W |
| Equivalent continuous power left for propulsion | ~900 W |
| Battery bank size | 500 kWh |
| Battery weight | ~10,020 lb |
| Battery cost | $45,000 |
| Estimated displacement supported at stated 50% immersion | ~32,800 lb |
| Estimated outfitted weight from rough budget | ~40,340 lb |
| Extra buoyancy for customers and personal stuff | Negative as currently estimated (~7,500 lb short) |
| Average 24/7 speed in Caribbean on solar surplus alone | ~2 knots = ~2.3 mph |
| Average speed with battery-supported propulsion for practical passage planning | Likely 4-6 knots depending on energy strategy |
If you want, the next useful step would be for me to produce a cleaner engineering-style revision with: