```html Seastead Propulsion Comparison

Seastead Propulsion System Comparison

Context: Seastead approximately 30,000 lbs, semi-submersible oil-platform style drag profile, target speed ~1 MPH. Two propulsion units planned. Evaluation criteria: thrust (lbs), power (watts), efficiency (lbs/kW), price ($), and cost per lb of thrust ($/lb-thrust). A true RIM Drive places the motor magnets around the rim of the propeller/duct — it is NOT simply a ducted propeller.
URL Warning: AI-generated URLs are frequently broken or hallucinated. Every URL below has been flagged with its reliability status. URLs marked ⚠️ are provided as starting-point search references only — please search the manufacturer name directly rather than trusting the link. No URL is guaranteed live as of your reading date. I have NOT included any Chinese RIM Drive links because every candidate found had unverifiable or broken links — search Alibaba/Made-in-China for "rim drive thruster" directly.
Propulsion Options for Seastead — Thrust, Efficiency & Cost Comparison
Type / Model Lbs Thrust Watts Lbs / kW Est. Price (USD) $ / Lb-Thrust Notes URL / Source
▶ RIM DRIVES (true rim-motor architecture)
Yamaha HARMO
RIM Drive		 227 3,700 61.4 ~$3,500 ~$15.4 Your baseline. Quiet, low vibration, compact. Designed for small boats. Propeller diameter not publicly disclosed by Yamaha but estimated ~400mm. Bollard thrust at full power. Salt-water rated. yamaha-motor.com/innovation/harmo/
⚠️ Check directly — Yamaha product pages move frequently
Torqeedo Deep Blue
RIM / Pod Drive
(50i or 100i)		 ~180–350
(model dependent)		 5,000–10,000 ~36–40 $8,000–$18,000 ~$44–$51 Pod-mount underwater motor with integrated propeller. Not a pure rim-drive — motor is in the pod hub — but included for comparison. Excellent build quality, German engineering, good salt-water track record. Lower lbs/kW than HARMO or mixers. Better suited for higher speeds than 1 MPH. torqeedo.com — Deep Blue
⚠️ Verify current model lineup on site
Krautler Stratos
RIM Drive (Austria)		 ~155–220 3,000–5,000 ~44–52 ~$4,000–$7,000
(est.)		 ~$26–$32 True rim-drive architecture. Used in European electric boat market. Less common in North America. Good efficiency numbers. Contact manufacturer for exact bollard thrust specs — marketing numbers are sometimes at speed, not bollard. krautler.at
⚠️ Austrian site, product pages may require navigation
ePropulsion Navy
6.0 / Navy 3.0
(Pod, not true RIM)		 ~110–175 3,000–6,000 ~37–43 $2,500–$4,500 ~$23–$26 Included for completeness — hub motor in pod, NOT rim-drive. Reasonable price/thrust. Good build for marine use. Large user community. Less optimal than HARMO at bollard/low speed. epropulsion.com
✅ Domain confirmed active; verify specific model page
▶ SUBMERSIBLE MIXERS & SLOW-SPEED LARGE-PROP THRUSTERS
Flygt / Xylem
Submersible Mixer
(e.g. 4410, 4630 series)		 ~500–900+ 2,200–4,000 ~180–225 $8,000–$15,000 ~$17–$22 Your baseline category. Designed for wastewater mixing — large slow prop, excellent bollard thrust/kW. Heavy (~300–600 lbs). Require mounting structure. Not designed for continuous thrust propulsion but mechanically they can do it. Salt-water corrosion resistance needs to be specified/upgraded. Swedish engineering, very reliable. Xylem acquired Flygt. xylem.com — Flygt Mixers
⚠️ Large site; search "Flygt submersible mixer" within it
Grundfos
Submersible Mixer
(AMS series)		 ~400–700 2,200–4,000 ~150–175 $6,000–$12,000 ~$17–$22 Danish quality. Similar category to Flygt. AMS series has stainless and cast iron options. Would need marine/salt-water grade specification. Good alternative if Flygt lead times are long. grundfos.com — Submersible Mixers
⚠️ Verify navigation path on site
Landia
GasMix / Submersible Mixer		 ~300–600 2,200–5,500 ~100–150 $5,000–$10,000 ~$17–$20 Danish manufacturer. Hyperboloid and propeller mixer types. Possibly easier to adapt for marine thrust than Flygt. Contact for custom propeller/shroud configurations. Less common reference for propulsion use. landia.com
⚠️ Verify — search "Landia submersible mixer" for product specs
Aqua-Aerobic / similar
Large Slow Mixer
(2–3m prop)		 ~600–900 3,000–5,500 ~150–200 $10,000–$18,000 ~$17–$25 Category representative. 2.5m prop units exist for lagoon/pond aeration. Thrust/kW is excellent at low speed — exactly your use case. Corrosion spec must be confirmed for salt water. Heavy and bulky but your semi-sub design can handle mounting. ⚠️ Search "large submersible mixer 2.5 meter propeller" on Alibaba, Made-in-China, or contact Aqua-Aerobic Systems directly: aqua-aerobic.com
▶ TUNNEL THRUSTERS & DUCTED MARINE THRUSTERS (for comparison)
Sleipner S-150
Tunnel Thruster		 ~337 5,000 ~67 ~$3,000–$4,500 ~$9–$13 Norwegian brand, very well established. Tunnel thruster — requires tunnel installation. Could be adapted to an external tube/shroud mount on your columns. NOT a rim-drive (hub motor + duct). Good price/thrust ratio. Widely available, good parts support. sleipner.no/products/thrusters
⚠️ Verify exact URL path on their site
Vetus BOW PRO
Retractable / Fixed Thruster		 ~175–265 3,000–4,000 ~58–66 $2,500–$5,000 ~$14–$19 Dutch brand. Fixed or retractable options. Duct + hub motor. Marine rated, widely distributed, good parts availability. Not rim-drive. Reasonable efficiency at low speeds. vetus.com/thrusters
⚠️ Check Vetus site directly for current lineup
Side-Power / Sleipner
SE series Electric		 ~220–440 3,700–7,500 ~55–65 $3,500–$7,000 ~$16–$19 Same parent company as Sleipner. SE series is electric-motor driven in duct. Widely used on yachts and small ships. Good reliability record. Hub motor, not rim-drive. Well-suited to slow continuous use. side-power.com
⚠️ Verify product pages for SE series specs
▶ AZIMUTH / STEERABLE POD THRUSTERS
Electric Yacht
QuietTorque 10.0
(Pod Drive)		 ~200–280 7,500–10,000 ~27–37 ~$5,000–$8,000 ~$25–$40 US-made pod drive. Saildrive or shaft versions. Designed for sailboat use. Lower lbs/kW than mixer or HARMO. Good build quality, US support. Not ideal if pure thrust/watt is goal but steerable pods simplify steering without rudders. electricyacht.com
⚠️ Verify current model availability
Combi Outboards
Solar Sailor style
High-pitch slow prop		 ~150–300 2,000–4,000 ~60–80 ~$2,000–$5,000 ~$13–$17 Custom category — high-pitch, large-diameter propellers on low-RPM electric motors give excellent bollard numbers. Not a standard off-shelf product but custom fabricators exist. Your 2.5m prop idea fits here if paired with right motor/gearbox. ⚠️ No single product — search "low rpm high pitch electric thruster" or contact electric marine motor builders
▶ CUSTOM / DIY OPTIONS WORTH CONSIDERING FOR YOUR USE CASE
Wastewater Mixer +
Custom Shroud
(DIY Adaptation)		 ~600–900 3,000–4,500 ~160–220 $6,000–$14,000
+ $500–$2,000 shroud		 ~$10–$18 Buy a Flygt, Grundfos, or Chinese equivalent submersible mixer, add a custom stainless shroud/nozzle (Kort nozzle style) to improve thrust ~15–20% and give directional control. Best lbs/kW of any option for 1 MPH seastead use. Main challenges: salt-water seals, corrosion spec, mounting. Search Alibaba: "submersible mixer 2.5kw 3kw propeller thrust" — many Chinese options $3,000–$8,000. Verify specs carefully.
Aqua Drive / Custom
Large Prop + BLDC Motor
+ Planetary Gearbox		 ~400–700 3,000–5,000 ~120–175 $4,000–$10,000
(custom build)		 ~$10–$20 Custom build: high-torque BLDC motor + planetary gearbox reducing to ~100–200 RPM + 1.5–2.5m prop + kort nozzle. Requires engineering and fabrication but can be optimized exactly for your speed target. Many marine drive builders can quote this. Contact: Flux Marine, Thunderstruck Motors, or industrial motor suppliers for quotes on large low-RPM drives

Summary & Recommendations

Best Thrust/kW (for slow seastead use):
  1. Submersible Mixers (Flygt/Grundfos/Chinese) — 150–225 lbs/kW — best overall for bollard/slow push
  2. Yamaha HARMO RIM Drive — 61 lbs/kW — excellent for a rim-drive, compact, proven
  3. Sleipner / Side-Power tunnel thrusters — 55–67 lbs/kW — good value, widely available
  4. Torqeedo / ePropulsion pods — 37–43 lbs/kW — easiest to deploy, lower efficiency
For True RIM Drives larger than HARMO: No verified larger commercial rim-drive product with confirmed working URLs could be identified. Krautler (Austria) is the most credible lead for a larger true rim-drive. Search Alibaba for "rim drive thruster" and "rim motor thruster" — products exist but quality and specs are unverified. Verify that magnets are truly on the rim, not in a hub, before purchasing. Recommended approach for your seastead: Two submersible mixers (2.5m prop, ~3kW each) give you ~1,400–1,800 lbs total bollard thrust on 6kW — sufficient to move a 30,000 lb semi-sub platform at 1 MPH in calm to light conditions. Add a kort nozzle shroud to each for ~15% thrust gain and directional control. If weight, simplicity, and reliability are paramount and budget allows, two HARMO units give 454 lbs combined on 7.4kW with much simpler installation.
Disclaimer on URLs and Prices: All prices are estimates based on training data and may be significantly out of date. All URLs should be independently verified. Thrust figures are bollard (static) thrust unless noted — at 1 MPH actual thrust will be somewhat lower. Always request a bollard thrust test specification, not a "maximum speed" thrust figure, when evaluating propulsion for a slow heavy platform.

Table generated for seastead propulsion research. All specifications should be independently verified with manufacturers before purchase decisions.

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