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Lewmar · tunnel thruster · bow or stern
Lewmar 125TT Tunnel Thruster: specs, price and the boats it fits
It gives 77 lb (35 kgf) of push. It runs on 12 V.
- Haul-out to install
- DIY 2 of 5: wiring prep only
- 3-year warranty
Quick stats
- Thrust 77 lb 35 kgf, Lewmar's rating
- Boat length Not published See our sizing below
- Price per lb of thrust $23.97 Unit only. $119 to $193 installed
- Voltage 12 V As sold
- Battery Not published Ask the maker before wiring
- Run limit Not published Ask the maker before long use
- To install it Haul-out The boat comes out of the water
- Mounts Tunnel Fixed mount, bow or stern
About the Lewmar 125TT
The 125TT Gen 2 fills the gap between Lewmar’s 110 and 140 mm tunnels: a 2.0 kW motor on 12 V turning one five-blade composite propeller in a 125 mm tube. Lewmar’s 2020 catalog rates it at 77 lb of push and 12 kg, a light unit for a small cruiser or sailboat that needs help at the dock.
Defender lists it at $1,846. Its Gen 2 installation manual covers the 110, 140, 185, 250 and 300 mm units and leaves this one out, so we hold no current draw, fuse or cable figure from Lewmar for it. Ask the dealer for the fuse before you order. The tube, a control and the battery switch come to about $465 to $1,013 more. See the parts.
Read more
It shares the Gen 2 controls and rules of the other TT units: push one way for more than three minutes and the system goes into fault mode, so use short bursts. The warranty is three years on paper, with one year on the motor and the electronic controls.
The full spec sheet for a yard sits lower down, and the Lewmar thruster review covers Lewmar’s whole range.
Where this summary comes from (4 sources, read 15 October 2026)
- Defender, Lewmar TT125 2 kW 12 V Gen 2 (590101) listing
- Lewmar Gen 2 TT installation manual 559231 Iss.3 (three minutes one way, then fault mode; warranty one year on motors and controls)
- Lewmar, About (making boat hardware in Havant, England, since 1946)
- Lippert Components acquires Lewmar Marine Limited, 1 August 2019
Will the Lewmar 125TT Tunnel Thruster steer your boat?
34 FT TRAWLER · BOW · 15 KT WIND
Every knot figure here is wind speed, not boat speed or current.
On a 34 ft trawler the Lewmar 125TT Tunnel Thruster (77 lb) steers her in a 15 knot breeze. Her bow needs about 78 lb from a tunnel to steer her in a 15 knot breeze. Its 77 lb lands within 15 percent of that figure, which this site counts as enough.
The finder lists it for her.
The Lewmar 125TT Tunnel Thruster on a trawler, by length
- 25 ft20 kt
- 30 ft17 kt
- 35 ft14 kt
- 40 ft13 kt
- 45 ft11 kt
- 50 ft10 kt
- 55 ft9 kt
- 60 ft8 kt
- 65 ft8 kt
- 70 ft7 kt
- 75 ft7 kt
- 80 ft6 kt
Outlined: the finder does not list it at that length (under 13 kt, far more than she needs, or outside Lewmar’s own length range).
- Under 10 kt
- 10 to 15 kt
- 15 to 20 kt: the sweet spot
- Over 20 kt: more than she needs
Prices are the low end of the installed total, from our estimate. For your own boat, drive and installer, the finder prices each unit.
Is it right for your boat?
Every kind of boat it fits, by length
| Boat | Full thrust at 15 knots | Still a fit, in lighter wind |
|---|---|---|
| Pontoon & tritoon | Not listed. A pontoon has no hull body between the logs to bore a tunnel through, and nobody sells one for these boats. | |
| Sailboat | 25 to 35 ft | 36 to 40 ftfull thrust to about 13 knots at 40 ft |
| Houseboat | None | 30 ft onlyfull thrust to about 13 knots at 30 ft |
| Catamaran | 30 to 39 ft | 40 to 45 ftfull thrust to about 13 knots at 45 ft |
| Trawler | 25 to 34 ft | 35 to 40 ftfull thrust to about 13 knots at 40 ft |
| Motor yacht | None | 35 to 40 ftfull thrust to about 13 knots at 40 ft |
| Bass & flats | Not listed. Nobody sells a tunnel kit for these hulls, and a bass boat’s shallow planing bow has almost no depth to hold one. | |
| Wake & ski boats | Not listed. Nobody sells a tunnel kit for these hulls. | |
| Express cruiser | 32 to 44 ft | 45 to 51 ftfull thrust to about 13 knots at 51 ft |
| Center console | 35 to 40 ft | None |
The Lewmar 125TT Tunnel Thruster against each kind of boat, in a 15 knot wind. Our sizing, from the finder’s own rules.
The first column is where one unit gives all the thrust the boat needs in 15 knots. The second is where the finder still lists it: the unit steers her in a 13 or 14 knot wind, within 15 percent of the 15 knot breeze this site sizes for. On a boat shorter than the first column’s shortest length, the unit is more than the boat needs.
How we size it
Our figure is the longest boat one unit can steer in a 15 knot wind. It is a range because each kind of boat catches the wind differently. Here a trawler gets full thrust to 34 ft, and an express cruiser to 44 ft.
The table tries the Lewmar 125TT Tunnel Thruster on each kind of boat, at every length that kind of boat is built in. The wind is 15 knots and the rules are the finder’s own. A length counts as a fit when the unit gives the thrust that boat needs at the bow. Lewmar publishes no boat length, so thrust alone decides.
It is sized for seven kinds of boat here. For your own boat, the finder gives an answer that also counts your drive and who does the installing. The compare page sets this unit beside others.
What it costs installed
A yard job, everything in. Our estimate.
| Boat | Total installed |
|---|---|
| 25 ft | $8,881 to $11,229$115 to $146 a lb of thrust |
| 40 ft | $9,141 to $14,829$119 to $193 a lb of thrust |
| 51 ft | $9,441 to $19,319$123 to $251 a lb of thrust |
From the shortest to the longest boat it is sized for.
What is in each total
These totals are our estimate of a yard job: the unit’s price, plus a yard’s hours at $160 to $180 an hour, plus the batteries, cable and charger, plus the other parts the box does not hold. A Lifting the boat out of the water on a travel lift or a trailer so work can be done below the waterline. It is billed separately from the job itself. adds $450 to $2,460 at these lengths, with 5 to 7 days out of the water, worked from eight yards’ own rate cards. The hours come from what owners and yards report. The cost page builds the same figures line by line.
| Boat length | The unit | Yard labor | Haul-out | Batteries, cable, charger | Other parts |
|---|---|---|---|---|---|
| 25 ft | $1,846 | $5,120 to $5,760about 32 hours | $450 to $1,210 | $1,000 to $1,400 | $465 to $1,013 |
| 40 ft | $1,846 | $5,120 to $8,64032 to 48 hours | $710 to $1,930 | $1,000 to $1,400 | $465 to $1,013 |
| 51 ft | $1,846 | $5,120 to $12,60032 to 70 hours | $1,010 to $2,460 | $1,000 to $1,400 | $465 to $1,013 |
For every length in the table above.
The sizing and the costs on this page are estimates, for guidance only and without warranty. They are no quote, and nobody has inspected your boat. Check them against the maker’s manual and your yard before you rely on them. Terms of use.
DIY breakdown
DIY levels
- Level 5: Owner install. No yard, no electrician.
- Level 4: You install it, electrician connects. You mount and wire it; a marine electrician makes the final connections.
- Level 3: Split with the yard. The yard does the below-waterline part; you do the wiring.
- Level 2: Wiring prep only. The yard installs the unit and does the hull work; you do the wiring prep.
- Level 1: Yard job. A qualified professional does all of it.
You Yard Electrician. The bar is labor hours; a haul-out is a note.
How we rate DIYYou: 4 to 16 hours Yard: 32 to 70 hours Electrician: 2 to 4 hours Plus a haul-out.
Your part needs:Heavy battery cableCrimping big lugs
Every step, and who does it
- Cut, bond and fair the tunnel; fit the gear leg, motor and propeller Yard 32 to 70 hours The low end is two crew over two days, the job as owners describe it on the forums. The high end rises with boat length between two real billed figures: 32 hours at 35 ft, and the largest invoice we hold, 70 hours at 47 ft.
- Mount the battery box, switch and fuse holder; run and secure the cables You 4 to 16 hours Our estimate. No maker times this step, and a first-time owner is slower than a yard, so the range is wide.
- Final connections at the battery and the motor, load test Electrician 2 to 4 hours Our estimate. Nobody publishes a time for the final connections and test on their own.
A qualified marine electrician should make the final connections and test them before first use. Hours are labor only.
Related videos
One from Lewmar’s own channel and one from other channels. Each one is labeled. They play from YouTube only when you tap. Take any claim in a video back to the figures on this page, which are the ones we checked.
Know before you buy
What sets this model apart, what it costs to keep, and what to weigh.
Price per pound of thrust
$23.97 a lb The unit’s price over its published thrust. The bars are Lewmar’s next sizes and the nearest other makers.Controls
The solenoid, the ICU control box and a 2 m motor loom are in the box. The panel, its loom, the fuse and holder are bought.
- Lewmar Gen 2 single joystick control (589268), $373.53 at Fisheries Supply.
- Lewmar Gen 2 AUX control loom, 7 m (589802), $69.10 at Fisheries Supply.
Service and warranty
Lewmar gives 3 years, but 1 on electric motors and their electrical equipment and on electronic controls. Service by anyone but an authorized Lewmar representative can void it. Removal, transport and installation costs are not covered.
See Lewmar’s warranty Lewmar's Gen 2 installation manual.Special mentions
Lewmar sells it for either end, so it can go at the bow or the stern.
Dealer prices at Fisheries Supply, read 26 October 2026.What to weigh
The boat comes out of the water to install it: it needs a tunnel bore below the waterline.
Lewmar publishes no boat length for it. The boat table is our sizing alone.
Parts for the Lewmar 125TT Tunnel Thruster
Search for the number as printed here, with no spaces. Prices are each dealer’s on the day shown, before shipping and tax. Check the plate on your motor before you order: some parts change with the tunnel size, the voltage or the year.
For the install what the box leaves you to buy
From Lewmar’s Gen 2 TT installation manual 559231 and the RT manual 55110070, Iss.3 and Iss.4, read 30 September 2026.
- In the box
- The motor, the solenoid and its loom, the ICU control box, a 2 m motor loom, the saddle, gasket, hub, propeller, anode kit and fixings. The RT ships with its own housing and actuator.
- Bought separately
- Under Accessories: the control panels, the panel looms, the fuse holders and ANL fuses, the automatic battery switch. "The installation MUST have a battery switch". The tunnel fits a Lewmar saddle.
- Charging
- The manual sizes the battery by cranking amps and says to "ensure batteries are fully charged before switching on the main power". It gives no rule on a charger, a feed or a bank of its own.
The manual’s words, page 12: “Battery crank capacity should be at least equal to the thruster current.”
The “other parts” line in the estimate above covers these parts as a range, $465 to $1,013 at Fisheries Supply’s prices on 30 September 2026 and 26 October 2026, because the exact items depend on your boat. The batteries, cable and charger have a line of their own. The cost page has what every maker says about each part.
Tunnel tube
Fisheries Supply lists it as “Sleipner fiberglass tunnel tube, 125 mm bore, 600 mm”.
Sold in lengths from about 24 to 35 in. This is the shortest: the yard cuts the tube to the width of your hull at the thruster. No Lewmar tube is listed at this bore. This one is another maker's.
Control panel
Fisheries Supply lists it as “Lewmar Gen 2 single joystick control”.
Check the listing or the box before you buy: the maker does not say whether one is included.
Control cable, panel to thruster
Fisheries Supply lists it as “Lewmar Gen 2 AUX control loom, 7 m”.
Sold in lengths from 7 to 18 m. This is the shortest: measure the run from the helm to the thruster and buy the length that reaches.
Main fuse
Ask for The size and type the maker names for this model.
We could not find this model's fuse in a manual we hold. Ask the dealer or the maker for it before you buy.
Fuse holder
Ask for The holder for the fuse type your manual names.
Match it to the fuse.
Battery switch
Ask for A manual battery switch rated for this circuit.
Rate it at or above the main fuse your manual names. If your manual names its own switch, use that one.
Control-circuit fuse holder
Fisheries Supply lists it as “Waterproof in-line ATO/ATC fuse holder”.
Lewmar's control unit (ICU) draws 8 A and has a slow-blow fuse inside; fuse its own supply to suit the wire, and use cable rated for 8 A.
Batteries and cable
Ask for From the battery and wiring calculators.
We do not hold this maker's battery and cable figures for this model.
Outside the hull replacement parts in the water
Propeller
The propeller on the drive. Lewmar calls it “PROPELLER AND WASHER”.
The manual lists the 125TT as 591251; Defender sells it as 590101. Both are the 2.0 kW 12 V 125TT.
Drive pin (breaks to protect the drive)
The pin that locks the propeller to its shaft. Lewmar calls it “DRIVE PIN”.
The 125TT and 140TT use the same pin. The manual lists the 125TT as 591251; Defender sells it as 590101. Both are the 2.0 kW 12 V 125TT.
Tunnel gasket
It keeps water out of the joint it sits in. Lewmar calls it “TUNNEL GASKET”.
The manual lists the 125TT as 591251; Defender sells it as 590101. Both are the 2.0 kW 12 V 125TT.
Inside the boat replacement parts on board
Solenoid (the motor switch)
The heavy switch that sends battery power to the motor. Lewmar calls it “SOLENOID 2.0”. This one is for the 1.5 kW and 2.0 kW version.
The 140TT 2.2 kW takes B11126 instead. The 110TT list prints it as SOLENIOD.
Controller box (the ICU)
The electronics that run the motor when you press the panel. Lewmar calls it “GEN2 TT ICU”.
The 250TT parts list prints its ICU as 589834, the same number as its solenoid loom, so we list no ICU number for the 250TT.
Main fuse, 200 A
The main fuse at the battery, in the rating the maker gives. Lewmar calls it “200 A ANL TYPE FUSE”.
The rating the manual gives for each model it fits. Lewmar sells it as an ANL fuse.
Control panel, dual joystick (bow and stern)
The control at the helm. Lewmar calls it “Controller, Dual Joystick”.
Control panel, dual pad (bow and stern)
The control at the helm. Lewmar calls it “Controller, Dual Pad”.
Control panel, single joystick
The control at the helm. Lewmar calls it “Controller, Single Joystick”.
Control panel, single pad
The control at the helm. Lewmar calls it “Controller, Single Pad”.
Replacement motor
The electric motor that turns the propeller. Lewmar calls it “MOTOR ASSY 2.0KW 12v”. This one is for the 2.0 kW version.
The standard motor. The manual lists a separate IP (ignition protected) motor. The manual lists the 125TT as 591251; Defender sells it as 590101. Both are the 2.0 kW 12 V 125TT.
No part matches. Try the number without spaces, or the part’s name.
The install parts are matched to Lewmar’s own figures and priced at Fisheries Supply, with the battery cable at Defender, cut to length.
Spare part numbers come from Lewmar’s parts pages and manuals. A dealer may sell a part we have not priced. Search for the number.
Other sizes and close alternatives
- Size down Lewmar 110TT Kit 62 lb · $936
- Size up Lewmar 140TT 82 lb · $1,486
- Other maker Max Power CT35 77 lb · $1,276
- Other maker VETUS Bow 35 77 lb · $1,607
- Other maker Sleipner SE25/110S 66 lb · $1,485
The other makers listed are the nearest match each makes, of the same style and for the same end, within a quarter of its thrust. The compare page lists every model, and the thruster index lists every model with a page here.
For the yard and the installer
Every published figure, with its source.
Full spec sheet
| Thrust and motor | |
|---|---|
| Thrust | 77 lb (35 kgf) As printed: "590101 TT 125 2.0KW 12v 125 2.0 2.7 12V Composite Single 5 Blade 35 77 12 26" - Lewmar catalogue 2020, GEN 2 TT Electric Thruster specifications (the Gen 2 manual 559231 Iss.3 does not list the 125TT) |
| Motor | 2 kW |
| Voltage | 12 V |
| Run limit | Not published |
| Installation | |
| Type | Tunnel, fixed mount |
| End of the boat | Bow or stern |
| Tunnel diameter | 125 mm |
| What it does to the hull | Tunnel bore below the waterline |
| Haul-out to install it | Yes |
| Maker’s boat length | Not published |
| Price and ordering | |
| Price | $1,846 equipment only, a dealer's price, defender.com, 26 October 2026 |
| Part number | 59010112 V, 12 V DC |
| Documents | |
| Manual | None found |
| The site’s review | Lewmar thruster review |
Every published figure the site holds for the Lewmar 125TT Tunnel Thruster, with where each came from.
The tunnel: length and depth rules
Tunnel length. A minimum suggested tunnel length of twice the diameter. Lewmar’s installation manual.
Depth below the waterline. One tunnel diameter below the waterline to keep air out of the tunnel, with 0.75 of a diameter the minimum. Gen 2 TT installation manual, 559231 Iss.3 (2018).
Our notes from the manual and listings
In the box: The solenoid, the ICU control box and a 2 m motor loom are in the box. The panel, its loom, the fuse and holder are bought.
Our note
The 2.0 kW 125TT Gen 2: a single five-blade propeller in a 125 mm tunnel, between the 110TT and the 140TT. Lewmar's 2020 catalog rates it 35 kgf (77 lb) and 12 kg, and prints no fuse or current for it.
Where each point above comes from
- Lewmar sells it for either end, so it can go at the bow or the stern.The maker's listing
- The boat comes out of the water to install it: it needs a tunnel bore below the waterline.The mounting: a bore through the hull, or a housing recessed into it
- Lewmar publishes no boat length for it. The boat table is our sizing alone.The maker's documents, as the database records them
Not sure this is the one? The thruster finder asks about your boat and prices every unit that fits.