Triangle side length = 80 ft.
Area of an equilateral triangle:
A = (sqrt(3)/4) s²
So:
A = 0.4330127 × 80² = 0.4330127 × 6400 = 2771.3 sq ft
In acres:
2771.3 / 43,560 = 0.0636 acres
| Item | Value |
|---|---|
| Triangle side length | 80 ft |
| Triangle area | 2,771 sq ft |
| Triangle area in acres | 0.0636 acres |
For an equilateral triangle of side 80 ft, altitude is:
h = 80 × sqrt(3)/2 = 69.28 ft
You want a rectangle 14 ft wide, placed as close to the front vertex as possible, and extending all the way to the back edge. The width available inside the triangle increases linearly from 0 at the front vertex to 80 ft at the back.
At a distance y from the front vertex, inside width is:
w(y) = 80 × (y / 69.28)
Set this equal to 14 ft:
14 = 80y / 69.28
y = 14 × 69.28 / 80 = 12.12 ft
So the rectangle can begin about 12.1 ft back from the front point and extend to the back edge.
Its length is:
69.28 - 12.12 = 57.16 ft
| Item | Value |
|---|---|
| Triangle altitude | 69.28 ft |
| Rectangle width | 14 ft |
| Closest forward start point where 14 ft fits | 12.12 ft aft of front vertex |
| Rectangle length to the back edge | 57.16 ft |
| Rectangle floor area | 800.2 sq ft |
So the living area has approximately 800 square feet of interior floor area, assuming one level.
If the living area is 8 ft high:
800.2 × 8 = 6,401.6 cubic ft
That is not asked directly, but useful for AC sizing and structure.
You specified each of the 3 legs as:
Because “chord” suggests a foil-like section, I will estimate displacement using a practical volumetric efficiency factor rather than assuming a full rectangular block. If each leg were a full 19 × 10 × 4 box, that would be 760 cu ft each, which is enormous. A foil/wing/strut-like body will have much less enclosed buoyant volume than that if shaped hydrodynamically.
For a preliminary estimate, I’ll assume each leg has an average enclosed displacement volume equivalent to about 60% of a 19 × 10 × 4 block:
Volume per leg ≈ 19 × 10 × 4 × 0.60 = 456 cu ft
At 50% immersion:
Submerged volume per leg ≈ 228 cu ft
In seawater, buoyancy is roughly:
64 lb/cu ft
So buoyancy per leg at 50% immersion:
228 × 64 = 14,592 lb
For 3 legs:
3 × 14,592 = 43,776 lb
| Item | Estimated Value |
|---|---|
| Estimated enclosed volume per leg | 456 cu ft |
| Submerged volume per leg at 50% immersion | 228 cu ft |
| Buoyancy per leg at 50% immersion | 14,592 lb |
| Total buoyancy at 50% immersion | 43,776 lb |
For a marine floating structure, duplex stainless gives excellent life and toughness, but weight and fabrication cost are major penalties.
| Factor | Duplex Stainless 2205 | Marine Aluminum |
|---|---|---|
| Weight | Very heavy | Much lighter |
| Raw material cost | High | Moderate |
| Fabrication cost | High to very high | Moderate |
| Corrosion life in seawater | Excellent if detailed correctly | Very good if alloy/isolation/coatings correct |
| Expected service life | 30-50+ years possible | 25-40+ years possible |
| Best for this concept? | Only if premium no-compromise budget | Much more practical |
My view: for this concept, marine aluminum is likely the better first-build material. The weight savings help stability, payload, assembly, shipping, and propulsion efficiency more than duplex stainless helps. If you use duplex stainless for some local fittings, hinges, shafts, and highly loaded connection parts, that may make sense.
Roof of living area:
Fold-down side panels:
Total usable panel area:
680 + 777 = 1,457 sq ft
Modern marine-use PV panels can deliver roughly 20 W/sq ft at panel rating for premium modules.
So installed watts:
1,457 × 20 ≈ 29,140 W
Round to 29 kW installed PV.
In the Caribbean, a well-oriented fixed array might get around 5.0 to 5.8 peak-sun-hours/day. Marine realities, shading, heat, salt, controller losses, imperfect tilt, and folding geometry reduce that. A practical delivered average may be:
29 kW × 5.3 h × 0.78 system efficiency ≈ 120 kWh/day
So a realistic average annual value might be around 110-125 kWh/day. I will use 120 kWh/day as the planning estimate.
| Item | Estimate |
|---|---|
| Usable solar area | 1,457 sq ft |
| Installed PV rating | 29 kW |
| Average daily production in Caribbean | 120 kWh/day |
You asked for 2 days of energy storage in LiFePO4 batteries. If daily solar generation/use target is 120 kWh/day, then 2 days storage is:
240 kWh nominal
LiFePO4 marine battery system gravimetric density at installed pack level is often around 20-28 lb/kWh depending on modules, enclosure, BMS, cabling, racks, and safety margins. A practical installed estimate is 25 lb/kWh.
Battery weight:
240 × 25 = 6,000 lb
This is reasonable and actually useful as low distributed ballast if properly housed and vented.
If one day's worth of stored energy is used evenly over 24 hours:
120 kWh / 24 h = 5.0 kW average
| Item | Estimate |
|---|---|
| Battery storage target | 240 kWh |
| Installed LiFePO4 weight | ~6,000 lb |
| Average continuous power from 1 day of stored energy over 24h | 5,000 W |
This is very approximate because actual drag depends on angle, open truss porosity, netting porosity, cabin shape, folded/unfolded panels, and wave drift.
For “pointing into the wind,” a reasonable frontal projected area might be:
Use effective frontal area A = 260 sq ft and drag coefficient Cd = 1.0 for a bluff mixed structure. Wind force:
F = 0.00256 × V² × Cd × A (with V in mph, F in lb)
| Wind speed | Estimated drag force |
|---|---|
| 30 mph | 0.00256 × 900 × 260 = 599 lb |
| 40 mph | 0.00256 × 1600 × 260 = 1,065 lb |
| 50 mph | 0.00256 × 2500 × 260 = 1,664 lb |
To hold stationary, required propulsive power depends on current and prop efficiency. Power = force × velocity through water. If we assume you are fighting only wind-driven drift and not strong current, the required thrust power is not huge. But to actually hold station in real sea state and current, effective power demand rises fast.
A rough practical estimate for station-keeping against wind drag and some wave/current effects:
| Wind speed | Likely electrical power needed to hold position |
|---|---|
| 30 mph | 3-6 kW |
| 40 mph | 6-12 kW |
| 50 mph | 12-25 kW |
If there is meaningful current, these numbers can increase dramatically. Holding position in 1-2 knots of current is often much harder than holding against wind alone.
Your idea of using the 3 legs as hydrofoils / keels / daggerboards has merit. If the underwater bodies have enough lateral area and are shaped with decent foil sections, a crosswind force can be transferred into sideforce in the water, reducing drift and allowing some heading control.
However, this is not a true sailboat unless you have an aerodynamic driving surface (kite, parasail, rigid wing, etc.). Without that, turning broadside to the wind simply changes force directions; it does not generate forward drive by itself.
What it can do:
How much wind could the design still keep control in? For maneuvering and heading control with adequate thruster power, probably:
This assumes healthy thrusters, competent control logic, and moderate sea state. In large breaking seas, control limits are set more by wave impacts than simple wind force.
Assume comfortable liveaboard / short-term rental use for 2-6 guests.
| Load | Average Power | Daily Energy |
|---|---|---|
| Refrigerator / freezer | 120 W | 2.9 kWh |
| Starlink x2 average combined | 140 W | 3.4 kWh |
| Lighting, electronics, pumps, controls | 250 W | 6.0 kWh |
| Watermakers (2 total, intermittent) | 300 W avg | 7.2 kWh |
| Cooking/small appliances averaged | 300 W avg | 7.2 kWh |
| One AC unit running part-time average over day | 900 W avg | 21.6 kWh |
| Miscellaneous reserve | 250 W | 6.0 kWh |
Total average continuous draw:
120 + 140 + 250 + 300 + 300 + 900 + 250 = 2,260 W
Total daily:
~54 kWh/day
For a more luxury-heavy hot-climate rental, I would budget 55-65 kWh/day. Use 60 kWh/day as planning value.
With 120 kWh/day solar production, extra solar beyond hotel loads is about:
120 - 60 = 60 kWh/day
That means about 50% extra over hotel loads.
| Item | Estimate |
|---|---|
| Average hotel/service load | 2.5 kW |
| Daily hotel/service energy | 60 kWh/day |
| Solar production | 120 kWh/day |
| Extra available for propulsion on average | 60 kWh/day |
| Extra solar margin over non-propulsive load | ~100% |
If you have 60 kWh/day left for propulsion and use it continuously:
60 / 24 = 2.5 kW average propulsion power
For a low-drag displacement or semi-stationary platform, speed on only 2.5 kW will be low. A vessel like this likely needs:
So on “extra solar only” 24/7, likely sustained cruising speed is around: 1.5 to 2.2 mph
If battery energy is also drawn temporarily, you could move faster for some hours.
These are broad first-pass estimates for a first unit assembled largely in China, then finished and commissioned. Costs include approximate hardware and installed/fabricated value, not just raw part cost. All prices in USD.
| # | Item | Estimated Weight (lb) | Estimated Cost First Unit | Notes |
|---|---|---|---|---|
| 1 | 3 legs / floats / wings | 9,000 | $180,000 | Marine aluminum fabricated, sealed compartments, coatings |
| 2 | Body / triangle frame / living-area primary structure | 12,500 | $320,000 | Main truss, cabin structure, deck framing, welding, assembly |
| 3 | Netting, steps, access structure | 800 | $12,000 | Marine net, fittings, ladders |
| 4 | 6 rim-drive thrusters | 1,500 | $150,000 | Depends hugely on size/power, marine-grade controls |
| 5 | Thruster controls, cabling, mounts | 500 | $30,000 | Power electronics and marine integration |
| 6 | Solar panels (~29 kW) | 3,500 | $35,000 | Modules only + marine mounting premium |
| 7 | Solar charge controllers (3 redundant systems) | 300 | $12,000 | Marine MPPT hardware |
| 8 | Batteries (240 kWh LiFePO4) | 6,000 | $90,000 | Could range $70k-$140k depending on source and certification |
| 9 | Inverters / chargers | 400 | $15,000 | 3 separate power islands |
| 10 | 2 watermakers + water storage | 1,200 | $18,000 | Includes tanks and pumps |
| 11 | Air conditioning (3 units, 1 mainly used at a time) | 500 | $9,000 | Mini-split or marine chilled air alternatives |
| 12 | Insulation | 600 | $8,000 | Very important in Caribbean |
| 13 | Flooring, cabinets, galley, furniture, baths, beds | 4,000 | $85,000 | Could vary massively by finish level |
| 14 | Waste tanks / plumbing | 700 | $10,000 | Black/gray water |
| 15 | Glass and glass doors at ends | 1,200 | $25,000 | Laminated tempered marine glazing |
| 16 | Refrigerator | 200 | $2,500 | Marine or high-efficiency domestic |
| 17 | Biofouling weight gain in first year | 1,500 | $3,000 | Not purchase cost, more like operational allowance |
| 18 | Safety equipment | 300 | $8,000 | Life raft, EPIRBs, fire suppression, PFDs, etc. |
| 19 | 14 ft dinghy / RIB + outboard | 450 | $18,000 | Moderate-quality tender |
| 20 | 2 sea anchors / drogues | 200 | $4,000 | Storm gear |
| 21 | Kite propulsion system | 300 | $12,000 | Experimental system estimate |
| 22 | 8 airbags in each leg (24 total) | 400 | $8,000 | Emergency buoyancy bladders + plumbing |
| 23 | 2 Starlink systems | 40 | $5,000 | Hardware only |
| 24 | Trash compactor | 150 | $1,500 | Optional |
| 25 | Davit / crane / winch | 500 | $15,000 | Depends on reach and SWL |
| 26 | Wiring, plumbing, controls, navigation, radar/AIS/VHF, anchors/mooring, misc finish-out | 2,000 | $75,000 | Frequently underestimated category |
Summing the above:
A more realistic target for a workable first build would be:
So either the float volume likely needs to be somewhat larger than assumed, or weight needs tighter control.
If actual operating displacement is engineered down to say 39,000 lb, and total buoyancy at nominal draft is 43,800 lb, then remaining margin is:
43,800 - 39,000 = 4,800 lb
That would be available for people, luggage, consumables, and some reserve.
A good target for charter practicality would be 5,000 to 8,000 lb payload margin.
The platform should have better pitch/roll resistance than a conventional monohull and probably lower angular motion than many catamarans, because buoyancy is widely spread and the structure is large and light relative to footprint. But response depends strongly on:
I will estimate differential height between front and back ends of the 57.16 ft living area from pitch, and approximate vertical acceleration at the center of triangle/living area zone.
| Wave case | Direction | Estimated end-to-end height difference in living area | Estimated vertical accel at center |
|---|---|---|---|
| 3 ft, 3 sec | From front | 0.4-0.8 ft | 0.03-0.06 g |
| 3 ft, 3 sec | From side | 0.3-0.7 ft side-to-side equivalent | 0.03-0.07 g |
| 5 ft, 5 sec | From front | 0.8-1.8 ft | 0.05-0.10 g |
| 5 ft, 5 sec | From side | 0.7-1.6 ft equivalent | 0.05-0.11 g |
| 7 ft, 7 sec | From front | 1.3-2.8 ft | 0.08-0.16 g |
| 7 ft, 7 sec | From side | 1.1-2.5 ft equivalent | 0.08-0.18 g |
These are not extreme storm values; they are moderate sea-state comfort estimates. The center of the triangle should move less than the outer corners.
Would it pitch and roll less in 7 ft waves than a 100 ft catamaran?
Possibly yes in roll, not necessarily in all cases for pitch. A long 100 ft catamaran has major pitch damping and long wave-bridging ability. Your concept has a very wide stance and low waterplane area, which can help in some seas, but the short 19 ft floats mean actual heave/pitch response may be more abrupt than a large 100 ft cat. So I would not confidently claim it is always better than a 100 ft catamaran. I would say:
Your enclosed living area is about 800 sq ft. A typical cruising catamaran with similar enclosed usable interior might be around:
A luxury 55-60 ft production cat with similar enclosed area usually costs much more than your concept target.
If your seastead could really be built for around $1.1M first unit and perhaps less in production, then a comparable new charter-grade catamaran might cost:
This concept is unusual, so it might command a novelty premium if the experience is safe, photogenic, and comfortable. Potential market: eco-luxury, remote-work retreat, adventure stay, private romantic charter, influencer/film rentals.
A reasonable planning estimate: $9,000/week
Could easily run 35% to 55% of gross. Use 45% as planning estimate.
At $9,000/week:
If capital cost = $1,151,000:
1,151,000 / 4,950 ≈ 233 weeks
That is about 233 fully booked profit-weeks ignoring financing, downtime, and depreciation. At 30 booked weeks/year, about 7.8 years.
In Panama, Liberia, and similar registries, it may be possible to register this under a yacht or special-purpose vessel category, but I would not assume “trimaran yacht” registration is automatic.
Potential issues:
If used privately, registration is easier. If rented commercially, requirements become significantly more formal. You should expect to need:
Potentially viable as a niche hospitality product, not yet as a mainstream marine product. The strongest angle is not “boat replacement” but:
As a first product, this could fit a small but real niche:
The market is likely much smaller than charter catamarans, but a distinctive enough product can still work.
On solar-only extra power, no. At perhaps 1.5-2.2 mph average 24/7, that is not enough for strategic storm avoidance. Even with full battery discharge and all thrusters running, unless you can sustain perhaps 5-7+ mph for long durations, you should not rely on outrunning tropical systems.
Best strategy:
You have already reduced electrical single-point failure with 3 separate power systems. Good. Still important failure points:
Recommended:
If built as one-off first unit, cost is dominated by engineering inefficiency, setup, and custom fabrication. At 20 units, purchasing and fabrication learning curve could reduce total by perhaps 20-30%.
| Production Quantity | Estimated Cost per Unit |
|---|---|
| First unit | $1.15M |
| At 20 units | $0.82M to $0.92M |
A planning midpoint for 20 units: $875,000 each
| Summary Item | Estimate |
|---|---|
| Triangle area | 2,771 sq ft = 0.0636 acres |
| Living-area rectangle length | 57.16 ft |
| Living-area floor area | 800 sq ft |
| Recommended primary material | Marine aluminum |
| Installed solar | 29 kW |
| Average solar production | 120 kWh/day |
| Average non-propulsion use | 60 kWh/day |
| Average solar left for propulsion | 60 kWh/day = 2.5 kW continuous |
| Battery storage target | 240 kWh |
| Battery weight | ~6,000 lb |
| Average power from 1 day battery over 24h | 5,000 W |
| Estimated first-unit total cost | $1.15M |
| Estimated cost each at 20 units | ~$875k |
| Estimated payload / extra buoyancy for guests and stuff | ~4,800 lb (needs refinement) |
| Estimated 24/7 average speed on excess solar alone | 1.5 to 2.2 mph |
| Estimated weekly rental | $9,000/week typical target |
| Operating profit per booked week | ~$4,950/week before capital cost |
| Weeks of rental profit to pay back first unit | ~233 booked weeks |
This is an interesting and potentially marketable concept if positioned as a floating villa / eco-retreat / novelty charter platform, not as a fast passagemaking vessel.
The two biggest technical issues to solve next are:
If you want, the next useful step would be a more rigorous naval-architecture-style version of this with: