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Thruster specs
Lewmar 125TT Tunnel Thruster: specs, price and the boats it fits
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.
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
Key facts
- DIY level 2 of 5 Wiring prep only
- Thrust 77 lb 35 kgf, Lewmar's rating
- Boat length Not published See our sizing below
- Price $1,846 equipment only, defender.com, 14 October 2026
- Fitted by a yard $9,141 to $14,829 Our estimate at 40 ft, unit and job
- Voltage 12 V As sold
- Mounts Tunnel Fixed mount, bow or stern
- To fit it Haul-out The boat comes out of the water
- Run limit Not published Ask the maker before long use
Every figure here is the maker’s or a dealer’s, except the fitted cost, which is our estimate. The full spec sheet is further down.
How much of the install is yours
DIY levels
- Level 5: Owner install. No yard, no electrician.
- Level 4: You fit 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 fits 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 h Yard: 32 to 70 h Electrician: 2 to 4 h Plus a haul-out.
- Cut, bond and fair the tunnel; fit the gear leg, motor and propeller Yard 32 to 70 h 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 h 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 h Our estimate. Nobody publishes a time for the final connections and test on their own.
Your part needs:Heavy battery cableCrimping big lugs
A qualified marine electrician should make the final connections and test them before first use. Hours are labor only.
Is it right for your boat?
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 sailboat gets full thrust to 29 ft, and a center console to 40 ft.
The table below 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.
| 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 29 ft | 30 to 44 ftfull thrust to about 10 knots at 44 ft |
| Houseboat | None | 30 to 33 ftfull thrust to about 10 knots at 33 ft |
| Catamaran | 30 to 33 ft | 34 to 50 ftfull thrust to about 10 knots at 50 ft |
| Trawler | 25 to 29 ft | 30 to 44 ftfull thrust to about 10 knots at 44 ft |
| Motor yacht | None | 35 to 44 ftfull thrust to about 10 knots at 44 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 37 ft | 38 to 56 ftfull thrust to about 10 knots at 56 ft |
| Center console | 35 to 40 ft | None |
Reading the two length columns. 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 falls short of what the boat needs by no more than 10 percent, and gives the whole figure only in the lighter wind named. On a boat shorter than the first column’s shortest length, the unit is more than the boat needs.
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 fitting. The compare page sets this unit beside others.
What it costs fitted
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 $2,700 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. Your own yard will have its own opinion. The cost page builds the same figures line by line.
| Boat length | The unit | Yard labor | Haul-out | Batteries, cable, charger | Other parts | Total |
|---|---|---|---|---|---|---|
| 25 ft | $1,846 | $5,120 to $5,760about 32 hours | $450 to $1,210 | $1,000 to $1,400 | $465 to $1,013 | $8,881 to $11,229 |
| 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 | $9,141 to $14,829 |
| 56 ft | $1,846 | $5,120 to $12,60032 to 70 hours | $1,090 to $2,700 | $1,000 to $1,400 | $465 to $1,013 | $9,521 to $19,559 |
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.
What else you buy
What follows comes 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 is the priced parts below, $465 to $1,013 at Fisheries Supply’s prices on 30 September 2026. The batteries, cable and charger have a line of their own.
| Part | What it is | What to ask for | Dealer price |
|---|---|---|---|
| Tunnel tube | The fiberglass, aluminum or steel pipe the thruster sits in, bonded through the bow. | Lewmar names none | $136–$209125 mm fiberglass tunnel tubes up to 60 in (1.5 m) long (Sleipner Side-Power), at Fisheries Supply, read 16 October 2026. |
| Control panel | The buttons or joystick at the helm. One helm, one panel: a second steering station needs a panel of its own. | 589268 single joystick, 589267 dual joystick, 589222 and 589223 pads | $219–$374Side-Power touch panel and single joystick, VETUS push-button panel, Lewmar single joystick, at Fisheries Supply. |
| Control cable, panel to motor | The thin cable from the helm to the motor. Sold by length. | Gen 2 AUX loom, 2 to 22 m | $29–$173Side-Power control cables, VETUS panel cables, Lewmar Gen 2 connecting cables, at Fisheries Supply. |
| Main fuse | A slow-blow fuse of the ANL type at the battery, in the size the maker prints for the model. | Lewmar ANL fuse, the rating in the yard table below | $18–$57Side-Power ANL fuses, Blue Sea ANL fuses, at Fisheries Supply, read 16 October 2026. |
| Fuse holder | The block the ANL fuse bolts into, with a cover. | 589006 (589010 for the T2 fuse) | $27–$93Egis and Blue Sea ANL fuse blocks, Side-Power ANL fuse holders, at Fisheries Supply, read 16 October 2026. |
| Main battery switch | The switch that cuts the thruster off from its battery when you leave the boat. | Gen 2 ABS 589810 (12 V) or 589830 (24 V), or any manual battery switch | $35–$107Egis m-Series 300 A, Blue Sea e-Series 350 A and HD-Series 600 A on/off switches, at Fisheries Supply, read 16 October 2026. |
| Battery cable and lugs | The two heavy cables from the battery to the motor, sized to the length of the run. The wiring calculator sizes them. | Lewmar names none | In the electrical line |
| Battery bank | A cranking-type bank near the motor, sized by the maker's cold cranking amps. The battery calculator checks it. | Lewmar names none | In the electrical line |
| Charger or charge feed | How the thruster bank gets charged: a shore charger of its own, a DC-to-DC charger or charging relay from the boat's system, or a charger built into the unit. | Lewmar names none | $146–$305NOCO GEN5X2 shore charger, Victron Orion-Tr Smart DC-DC charger, Blue Sea ML-ACR charging relay, at Fisheries Supply. |
| Glass, resin, filler and sealant | What bonds the tube or housing into the hull and seals the gear leg. | Lewmar names none | Not priced |
The cost page has the whole list with what every maker says about each part.
For the yard and the installer
The full spec sheet, grouped the way a yard reads it. Every figure is the maker’s or a dealer’s, with its source.
| 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 |
| Fitting | |
| 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 fit it | Yes |
| Maker’s boat length | Not published |
| The tunnel | |
| 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) |
| Price and ordering | |
| Price | $1,846 equipment only, a dealer's price, defender.com, 14 October 2026 |
| Part number | 59010112 V, 12 V DC |
| Documents | |
| Manual | None found |
| 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. Lewmar's Gen 2 installation manual |
| The site’s review | Lewmar thruster review |
What holds up and what to weigh
Each point names the fact it rests on.
What holds up
- Lewmar sells it for either end, so it can go at the bow or the stern.The maker's listing
What to weigh
- The boat comes out of the water to fit 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
What the manual and listings say
This is the note we keep on the Lewmar 125TT Tunnel Thruster, written from the maker’s manual, its product pages and the dealer’s listing.
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.
Videos
One of Lewmar’s own videos, from its YouTube channel: what changed in the Gen 2 tunnel units. It is the maker’s pitch. Watch it for what the unit looks like and how it goes in, and take any claim back to the figures above.
Other sizes and close alternatives
These are Lewmar’s next sizes in the same line, by thrust.
- One size down: Lewmar 110TT Thruster Kit, 62 lb, $936.
- One size up: Lewmar 140TT Tunnel Thruster, 82 lb, $1,486.
These are other makers’ units of the same style, for the same end, within a quarter of its published thrust. Each is that maker’s nearest match.
- Max Power CT35, 77 lb, $1,276.
- VETUS Bow 35, 77 lb, $1,786.
- Sleipner SE25/110S, 66 lb, $1,485.
Every model with a page here is listed, maker by maker, on the thruster index.