Here's a complete, website-ready HTML page with recommendations, specs, costs, weights, speeds, and links for all three craft:
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Seastead Watercraft Package — Dinghy · Tender · Liferaft
Seastead Watercraft Package Dinghy · Tender · Liferaft — sized for a 4–6 person Caribbean operation
Design logic: The three craft deliberately overlap so no single failure strands you:
Dinghy (electric) — daily ship-to-shore taxi, charged free from your own solar. Zero fuel logistics.
Tender (gasoline, twin engines) — fast runs ahead to islands, medevac, storm evacuation. Independent energy source (gasoline), so a battery/system failure on the seastead can't disable your escape craft.
Liferaft (canister) — last resort if the tender can't be launched or is lost.
Bonus synergy: the Yamaha Harmo is a rim-driven electric outboard — the same propulsion concept as your six RIM thrusters. No exposed propeller (safer for swimmers and boarding), and mechanical familiarity for maintenance.
1) Dinghy — 14 ft RIB + Yamaha Harmo
RECOMMENDED Hull: Highfield Classic 420 (CL420)
Attribute
Spec
Type
Aluminum-hull RIB, PVC or Hypalon tubes
LOA / Beam
13′9″ (4.20 m) / 6′6″ (1.98 m)
Weight
~450 lb (205 kg) — hangable from your stern rope bridle
Capacity
Certified for ~7 persons; realistically 4 adults + gear
⚠ Availability caveat: the Harmo launched in Japan first; export availability outside Japan is still limited. Confirm with a Yamaha marine dealer before committing. If unavailable, the drop-in alternative below is excellent and in stock worldwide.
ALTERNATIVE MOTOR ePropulsion Navy 6.0 Evo + E60 battery
6 kW continuous / 9.9 kW peak, ~137 lb total system, ~$9,000–10,500 kit. Slightly more power and range than the Harmo, widely available, established dealer network. epropulsion.com
BUDGET HULL Chinese 4.2–4.3 m aluminum RIB (e.g., Liya)
Equivalent size and construction, ~$4,500–6,500 FOB China plus ~$1,500–2,500 freight to a Caribbean hub. Inspect weld quality and tube material on arrival; buy spare valve kits. Search “aluminum RIB 4.3m” on alibaba.com; Liya: liyaboat.com
2) Tender — Fast Utility / Lifeboat (twin engines)
Your requirements map cleanly onto a 5.2 m (17 ft) deep-V aluminum RIB with twin 15–20 hp four-stroke outboards: redundant propulsion (the Anguilla norm), light enough for davits, fast enough for a 10 nm medevac in 30 minutes, and cheap to run.
RECOMMENDED 5.2 m aluminum deep-V RIB + twin 20 hp
Why twins instead of one big engine: true redundancy (one engine failure = limp home at 8–10 kt, not a drift), cheaper than a single 40 hp, better weight distribution, and differential-throttle maneuvering that matches how your seastead itself steers. If one dies during a medevac, you still arrive — slower.
Shipping / stowage notes
Container fit: most 5.2 m RIBs have ~2.05–2.20 m beam — fits upright through a 45′ HC door (~2.34 m opening). Verify the exact model’s beam before ordering. Wider boats (e.g., Highfield Patrol 600 at 2.36 m) must ship on their side (fits under the 8.9 ft door height) or in a second container.
On the seastead: options are (a) electric-winch stern davits on a reinforced cross-beam, (b) roof stowage with a small crane, or (c) towed only in calm conditions. Rigged weight ~1,400 lb with a significant moment arm if davit-mounted — this needs a structural check against your walkway/railing loads. When parked on tension legs, leaving the tender on a mooring ball is simplest.
Lifeboat role: keep a grab bag aboard (water, flares, handheld VHF, first aid, EPIRB), rotate fuel monthly, and run the engines under load at least monthly.
ULTRA-BUDGET ALTERNATIVE Whaly 500 + twin 15 hp ≈ $13,000 rigged
Rotomolded polyethylene double-hull boat — virtually indestructible, zero gelcoat maintenance, ~700 lb, ~$6,500–8,000. Twin Tohatsu MFS15 (~$3,200 each) gives ~16–18 kt top. Flatter hull = a wetter ride in chop than a deep-V RIB, but for fair-weather Caribbean work it’s remarkable value and nearly unsinkable. whaly.com (confirm transom layout suits twin mounting).
3) Liferaft — 6-Person Canister
Go with 6-person even if you’re 4 — the weight penalty is small and the extra volume, supplies, and boarding margin matter in real evacuations. A canister (not valise) survives years of outdoor tropical UV on deck. Choose ISO 9650-1 “Pack II” (offshore-lite: 24h+ survival equipment) — appropriate since you operate beyond easy swimming distance but not mid-ocean, and outside hurricane season.
Lash the canister in a cradle on the aft railing or walkway — quick-release lashings if always attended; add a Hammar H20 hydrostatic release (~$140) if it must float free unattended.
Servicing every 3 years, ~$450–700 (amortized ~$200/yr). Caribbean service stations exist in St. Martin, Puerto Rico, and Trinidad — buying a major brand (Revere/Viking) guarantees a nearby station will touch it. Insurers and flag registries favor serviced, branded rafts.
The raft has no beacon of its own — pair it with the EPIRB below.
All figures are approximate 2024–2025 USD street/FOB prices, excluding tax, duty, and freight. Freight for the tender hull from Asia adds ~$1,500–2,500 to a Caribbean hub.
6) Key Caveats
Verify Harmo export availability with Yamaha before finalizing the dinghy plan — it is the one item on this list with genuine supply risk. ePropulsion is the safe fallback.
Check tender beam against the container door (~2.34 m clear) for your chosen model, or plan side-loading / second-container shipping.
Davit loads: a 1,400 lb tender on stern davits is a real structural load case for your aft framing — involve your naval architect early.
Fuel strategy: the gasoline tender is intentionally your independent-energy escape craft. Store 100+ L in rotating jerry cans low in the legs, away from batteries.
Drill it: launch the liferaft at its 3-year service, run man-overboard and abandon-ship drills quarterly, and test the remote-control seastead handoff before storm season approaches.
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A few key points worth highlighting outside the document:
- **The Harmo is the risk item, not the boats.** It's still primarily a Japan-market product — confirm export availability with Yamaha *first*, and treat the ePropulsion Navy 6.0 Evo as your pre-approved fallback so the dinghy plan never blocks the build schedule.
- **Twin 20s beat one 40 hp** for your stated use cases: Anguilla-style redundancy, lighter transom loading for davits, and differential-throttle handling that mirrors your seastead's own steering logic.
- **The tender is your de facto lifeboat**, so I weighted the recommendation toward deep-V RIBs over cheaper flat-bottom options, with the Whaly 500 called out as the honest budget alternative with its ride-quality tradeoff stated plainly.
- **Watch the tender's beam vs. your container door** (~2.34 m clear) — most 5.2 m RIBs fit, but verify the specific model before ordering, since a few popular ones (e.g., Highfield Patrol 600) are a hair too wide to roll in upright.