Seastead Propulsion: Submersible Mixer Analysis

Seastead Low-Speed Propulsion: Submersible Mixer Feasibility Analysis

Your Requirements Summary

Vessel: 30,000 lbs (13,600 kg) displacement, 4× 45° columns, small waterplane area, high pitch/roll damping
Power budget: 22 kW solar installed, targeting 2 kW continuous for propulsion (0.5 mph), up to 5 kW for 1 mph
Configuration: 2× thrusters wide-spaced for differential steering
Propeller target: ≥ 2500 mm diameter, "banana"/hydrofoil blade, low RPM (30–50), high thrust per kW
Environment: Seawater (requires 316L/duplex SS, marine-grade seals, cathodic protection)
Control: Variable speed (VFD or integrated), 220V 3-phase 60 Hz preferred
Budget priority: Low cost, but must survive seawater

⚠ Critical Feasibility Concerns

Mismatched duty cycle: Submersible mixers are designed for continuous stationary mixing in tanks/lagoons. Propulsion imposes: (a) thrust bearing axial loads 5–10× higher, (b) dynamic side loads from vessel motion, (c) seal pressure cycling from depth changes, (d) cavitation risk at forward speed. Most mixers lack a dedicated thrust bearing.
Seawater compatibility: "Cast iron" units will corrode catastrophically in months. 304 SS is marginal. You need 316L or duplex (2205/2507) stainless for all wetted parts, plus marine-grade mechanical seals (SiC/SiC or SiC/Carbon), and ideally impressed current cathodic protection.
No integrated thrust bearing = short life. Mixer gearboxes handle radial load from propeller weight + hydraulic side force. They do not handle 500–1000 lbf continuous axial thrust. Expect gearbox failure in 100–500 hours.
Seal failure = flooded motor. Mixer seals see static head pressure. Underway, dynamic pressure fluctuations + shaft runout from thrust load will leak standard mixer seals.

1. Engineering Reality Check: Thrust & Power

Vessel: 30,000 lbf displacement ≈ 133,400 N Target speed: 0.5 mph = 0.224 m/s | 1 mph = 0.447 m/s Column drag estimate (4× cylinders @ 45°, ~1m dia, 10m submerged length each): Re ~ 4.5e5 at 0.45 m/s → Cd ~ 1.0–1.2 (subcritical) Wetted area ~ 4 × π × 1m × 10m / cos(45°) ≈ 178 m² Drag ≈ 0.5 × 1025 × 0.45² × 178 × 1.1 ≈ 18,600 N (4,200 lbf) at 1 mph Drag at 0.5 mph ≈ 4,650 N (1,050 lbf) (quadratic scaling) Required thrust per thruster (2 units): At 0.5 mph: ~2,300 N (520 lbf) each At 1 mph: ~9,300 N (2,100 lbf) each Propulsive efficiency (large slow prop, open water): η ~ 0.6–0.7 Shaft power needed: 0.5 mph: 2,300 N × 0.224 m/s / 0.65 ≈ 790 W per thruster (1.6 kW total) 1 mph: 9,300 N × 0.447 m/s / 0.65 ≈ 6.4 kW per thruster (12.8 kW total) Your 2 kW budget for 0.5 mph is **plausible but tight**. Your 5 kW hope for 1 mph is **unrealistic** — you need ~13 kW shaft power.

📌 Key Insight

At 0.5 mph, the mixer thrust ratings you found (2000–3800 N) are in the right ballpark for your 2,300 N/unit requirement. At 1 mph, you need ~4× the thrust — mixers won't deliver without 4× the power (12+ kW per unit).

2. Product Comparison Table

Model / Source	Prop Dia (mm)	Power (kW)	RPM	Thrust (N / lbf)	Material (wetted)	Seawater Ready?	VFD / Control	Est. Price (USD)	Notes
PTM Phantom 2500 ptm-mixer.com	2500	~3–4	~35–45	~2500–3000 N (est)	316L SS option	✅ Yes (marine line)	External VFD needed	$13,000–18,000	European build quality, marine division exists. Thrust not published — request datasheet.
Flygt / Xylem 4410 / 4320 xylem.com	2500	2.2–4.0	30–50	Best thrust/kW in class (~3200 N @ 3.5 kW)	316L / Duplex avail.	✅ Yes (marine/offshore use)	4320: Integrated VFD ("Adaptive") 4410: External VFD	$22,000–35,000	Gold standard. 4320 has integrated VFD + condition monitoring. Expensive but reliable. Thrust bearing upgraded in "HP" versions.
Landia POPL-I 2300 landia.co.uk	2300	1.5 / 2.0 / 4.0	38–48	Not published ⚠	316L option	⚠ Possible (inquire)	External VFD	$10,000–16,000	No thrust data = red flag. Landia makes good mixers but propulsion use unproven. Ask for "thrust curve vs RPM".
Wilo EMU TR 216/326 wilo.com	Up to 2600	1.5–5.5	30–60	~2000–3500 N (est)	316L / Duplex	✅ Marine versions exist	External VFD	$12,000–20,000	German engineering. TR series = low-speed propeller. Good dealer network in US.
Sulzer ABS XSB 2750 sulzer.com	2750	Up to 7.5	25–40	~4000–5000 N (est)	316L / Duplex	✅ Yes	External VFD	$18,000–28,000	Largest prop in class. Heavy. Good for higher power if you upgrade solar.
ShinMaywa SM-VRTN shinmaywa.co.jp	2500	2.0–3.2	35–45	3200 N (720 lbf) ✅	316L SS standard	✅ Designed for seawater	External VFD (3-phase)	$14,000–20,000	Best documented thrust. Japanese marine/aquaculture heritage. 316L standard. Ask for "marine propulsion" duty rating.
VIVAMIX VML2500/3kW vivamixer.com	2500	3.0	~29–35	2090 N (470 lbf)	Cast iron (std) / 316L (opt)	⚠ Only if 316L + seal upgrade	External VFD	$2,000 (CI) / $4,500–6,000 (316L)	Chinese. Cast iron unacceptable for seawater. 316L quote required. Verify gearbox thrust bearing. No UL/CE marine certs.
Henan Eco / Lanling / Lanshen / Qiankun (various QJB/QDT models)	2500	3–5.5	29–47	1960–3840 N	Mostly cast iron / 304 SS	❌ No (standard) ⚠ Maybe custom 316L	External VFD	$1,800–4,500 (CI) $4,000–8,000 (316L est.)	Lowest cost. High risk: no thrust bearing, seals not for dynamic pressure, 304 SS crevice corrodes, no third-party certs. QDT 5.5 kW = 3840 N best thrust/$ but 5.5 kW exceeds your budget.

Model / Source

Prop Dia (mm)

Power (kW)

RPM

Thrust (N / lbf)

Material (wetted)

Seawater Ready?

VFD / Control

Est. Price (USD)

Notes

PTM Phantom 2500
ptm-mixer.com

2500

~3–4

~35–45

~2500–3000 N (est)

316L SS option

✅ Yes (marine line)

External VFD needed

$13,000–18,000

European build quality, marine division exists. Thrust not published — request datasheet.

Flygt / Xylem 4410 / 4320
xylem.com

2500

2.2–4.0

30–50

Best thrust/kW in class (~3200 N @ 3.5 kW)

316L / Duplex avail.

✅ Yes (marine/offshore use)

4320: Integrated VFD ("Adaptive")
4410: External VFD

$22,000–35,000

Gold standard. 4320 has integrated VFD + condition monitoring. Expensive but reliable. Thrust bearing upgraded in "HP" versions.

Landia POPL-I 2300
landia.co.uk

2300

1.5 / 2.0 / 4.0

38–48

Not published ⚠

316L option

⚠ Possible (inquire)

External VFD

$10,000–16,000

No thrust data = red flag. Landia makes good mixers but propulsion use unproven. Ask for "thrust curve vs RPM".

Wilo EMU TR 216/326
wilo.com

Up to 2600

1.5–5.5

30–60

~2000–3500 N (est)

316L / Duplex

✅ Marine versions exist

External VFD

$12,000–20,000

German engineering. TR series = low-speed propeller. Good dealer network in US.

Sulzer ABS XSB 2750
sulzer.com

2750

Up to 7.5

25–40

~4000–5000 N (est)

316L / Duplex

✅ Yes

External VFD

$18,000–28,000

Largest prop in class. Heavy. Good for higher power if you upgrade solar.

ShinMaywa SM-VRTN
shinmaywa.co.jp

2500

2.0–3.2

35–45

3200 N (720 lbf) ✅

316L SS standard

✅ Designed for seawater

External VFD (3-phase)

$14,000–20,000

Best documented thrust. Japanese marine/aquaculture heritage. 316L standard. Ask for "marine propulsion" duty rating.

VIVAMIX VML2500/3kW
vivamixer.com

2500

3.0

~29–35

2090 N (470 lbf)

Cast iron (std) / 316L (opt)

⚠ Only if 316L + seal upgrade

External VFD

$2,000 (CI) / $4,500–6,000 (316L)

Chinese. Cast iron unacceptable for seawater. 316L quote required. Verify gearbox thrust bearing. No UL/CE marine certs.

Henan Eco / Lanling / Lanshen / Qiankun (various QJB/QDT models)

2500

3–5.5

29–47

1960–3840 N

Mostly cast iron / 304 SS

❌ No (standard)
⚠ Maybe custom 316L

External VFD

$1,800–4,500 (CI)
$4,000–8,000 (316L est.)

Lowest cost. High risk: no thrust bearing, seals not for dynamic pressure, 304 SS crevice corrodes, no third-party certs. QDT 5.5 kW = 3840 N best thrust/$ but 5.5 kW exceeds your budget.

3. VFD / Variable Speed Control

How Variable Speed Works for These Units

All 3-phase AC induction motors (except Flygt 4320) require an external VFD (Variable Frequency Drive) for speed control.
VFD input: Your 220V 3-phase 60 Hz (or 480V 3-phase if you step up). Solar → inverter → VFD → motor.
VFD output: 0–60 Hz (or higher for overspeed), torque-limited, ramped accel/decel.
Flygt 4320 "Adaptive": Has integrated VFD in the top housing. Power in = 380–480V 3-phase. Comm = Modbus/Profibus. Most expensive but simplest install.
Control signal: 4–20 mA, 0–10V, or Modbus/TCP from your vessel control system.

VFD Class	Power Range	Example Models	Price (USD)	Notes
Budget (Chineses)	2.2–5.5 kW	VFD-E, Huanyang, STEPPERONLINE	$120–300	No marine certs, limited protection, noisy PWM. OK for testing, not for permanent salt-air install.
Industrial Standard	2.2–7.5 kW	ABB ACS380, Schneider ATV320, Delta MS300, Lenze i550	$450–1,200	UL/CE, STO (Safe Torque Off), conformal-coated PCBs, 50°C rating. Recommended minimum.
Marine / Harsh Duty	2.2–7.5 kW	ABB ACS580-01 (marine), Danfoss VACON 100 X, Yaskawa GA700	$1,200–2,500	IP54/66, salt-fog tested, DNV/ABS type approval, harmonic mitigation. Overkill unless classed vessel.
Flygt 4320 Integrated	2.2–4.0 kW	Built-in	Included in $22k+	No separate box, no cable run, condition monitoring (vibration, temp, leak). Best reliability.

VFD Class

Power Range

Example Models

Price (USD)

Notes

Budget (Chineses)

2.2–5.5 kW

VFD-E, Huanyang, STEPPERONLINE

$120–300

No marine certs, limited protection, noisy PWM. OK for testing, not for permanent salt-air install.

Industrial Standard

2.2–7.5 kW

ABB ACS380, Schneider ATV320, Delta MS300, Lenze i550

$450–1,200

UL/CE, STO (Safe Torque Off), conformal-coated PCBs, 50°C rating. Recommended minimum.

Marine / Harsh Duty

2.2–7.5 kW

ABB ACS580-01 (marine), Danfoss VACON 100 X, Yaskawa GA700

$1,200–2,500

IP54/66, salt-fog tested, DNV/ABS type approval, harmonic mitigation. Overkill unless classed vessel.

Flygt 4320 Integrated

2.2–4.0 kW

Built-in

Included in $22k+

No separate box, no cable run, condition monitoring (vibration, temp, leak). Best reliability.

💡 VFD Sizing Rule

Size VFD for motor FLA (Full Load Amps) × 1.1–1.25. For 3 kW @ 220V 3φ → ~9–11 A → buy 15 A (5.5 kW) frame. For 5.5 kW @ 220V → ~18 A → buy 25 A (7.5 kW) frame. Oversizing reduces thermal stress.

4. Realistic Total Installed Cost (Per Thruster)

Cost Item	Chinese 316L (VIVAMIX et al.)	European Mid (PTM / Wilo)	Premium (Flygt 4320 / ShinMaywa)
Mixer unit (316L, 2.5–3.5 kW)	$13,000–18,000	$18,000–25,000
VFD (industrial grade)	$600–1,000	$600–1,000	Integrated
Subsea cable (10m, 4C+ground, 316L armor)	$400–700	$400–700	$400–700
Cable penetrator / gland (hull, 316L)	$300–600	$300–600	$300–600
Mounting bracket / strut (316L, engineered)	$800–1,500	$800–1,500	$800–1,500
Cathodic protection (anode + reference)	$200–400	$200–400	$200–400
Engineering / integration / test	$1

Cost Item

Chinese 316L (VIVAMIX et al.)

European Mid (PTM / Wilo)

Premium (Flygt 4320 / ShinMaywa)

Mixer unit (316L, 2.5–3.5 kW)

$13,000–18,000

$18,000–25,000

VFD (industrial grade)

$600–1,000

Integrated

Subsea cable (10m, 4C+ground, 316L armor)

$400–700

Cable penetrator / gland (hull, 316L)

$300–600

Mounting bracket / strut (316L, engineered)

$800–1,500

Cathodic protection (anode + reference)

$200–400

Engineering / integration / test