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Thruster specs
Sleipner SEP40/125S: specs, price and the boats it fits
The SEP40 is a bow thruster you can feather. Its joystick sets how hard it pushes, from a gentle nudge up to 106 lb, so a boat of about 23 to 34 ft can be eased onto the dock instead of shoved. PRO is Sleipner’s name for this variable speed, and the speed controller comes in the box.
Defender’s price is $4,545; the on/off SE40 is $1,845, so the difference is what the speed control costs. Plan on about $473 to $1,024 more for the tube, the helm panel, a main switch and a fuse, and pick one of Sleipner’s joysticks made for variable-speed thrusters. A strong starting battery close to the bow, with its cable and charging, adds about $601 to $677. See every part.
At full power the motor is rated for 2 to 3 minutes, like any brushed thruster. Hold back to half power or less and it will run close to continuously, because the controller trims power to keep the motor cool. That is the real gain for anyone docking alone. Warranty: two years, and it transfers when you sell.
The full spec sheet for a yard sits lower down, and the Sleipner (Side-Power) review covers Sleipner’s whole range.
Where this summary comes from (5 sources, read 12 October 2026)
- Sleipner product page
- Sleipner SEP80 to SEP150 installation manual, document 2728 rev 23 ("the included PPC unit", S2 rating 2 to 3 min)
- Defender, Side-Power SEP80/185T listing (close to continuous use below half power; two-year warranty)
- Sleipner PJC421 joystick panel, "for variable speed thrusters"
- Sleipner warranty statement, effective 1 April 2022
Key facts
- DIY level 2 of 5 Wiring prep only
- Thrust 106 lb 48 kgf, Sleipner's rating
- Boat length 23 to 34 ft Sleipner's own range
- Price $4,545 equipment only, defender.com, 28 August 2026
- Fitted by a yard $11,359 to $13,696 Our estimate at 35 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 2 to 3 min Duty cycle at 20 C ambient
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 trawler gets full thrust to 34 ft, and a catamaran to 37 ft. The maker gives one range for every boat.
The table below tries the Sleipner SEP40/125S 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 and the maker lists it for that length.
A boat up to 10 percent past the maker’s range still counts here, as it does in the finder. So the table runs up to 37 ft, just past Sleipner’s own range (23 to 34 ft).
| 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 | 29 to 35 ft | 36 to 37 ftfull thrust to about 14 knots at 37 ft |
| Houseboat | None | 30 to 37 ftfull thrust to about 11 knots at 37 ft |
| Catamaran | 33 to 37 ft | None |
| Trawler | 29 to 34 ft | 35 to 37 ftfull thrust to about 14 knots at 37 ft |
| Motor yacht | None | 35 to 37 ftfull thrust to about 14 knots at 37 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 | 37 ft only | None |
| Center console | No length. More thrust than the boat needs. | |
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 six 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 $520 to $1,790 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 |
|---|---|---|---|---|---|---|
| 29 ft | $4,545 | $5,120 to $5,760about 32 hours | $520 to $1,400 | $601 to $677 | $473 to $1,024 | $11,259 to $13,406 |
| 35 ft | $4,545 | $5,120 to $5,760about 32 hours | $620 to $1,690 | $601 to $677 | $473 to $1,024 | $11,359 to $13,696 |
| 37 ft | $4,545 | $5,120 to $6,84032 to 38 hours | $660 to $1,790 | $601 to $677 | $473 to $1,024 | $11,399 to $14,876 |
How the batteries, cable and charger add up. We price a battery bank close to the thruster, as the makers recommend, with 10 to 20 ft of cable out and back: red for the positive, black for the negative, cut to length. The low end is the cheapest battery that meets the figure and the shorter run; the high end is a sealed (AGM) battery and the longer run. The charger is a NOCO GEN5X2 two-bank shore charger.
Batteries and lugs are priced at Fisheries Supply and the cable and charger at Defender, read 12 October 2026.
- At 12 V: one 12 V battery, at least 570 CCA (Sleipner’s minimum), $360 for the battery; Sleipner’s cable table gives 1/0 AWG: $95 to $171 for the red and black cable and the lugs; a GEN5X2 charger, $146.
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 Sleipner’s SE80 to SE150 installation guide, document 2687 rev 30, 2025, read 30 September 2026.
- In the box
- The gasket, bolts and anode come with the unit. The SEP guides call the power controller "the included PPC unit".
- Bought separately
- The ANL fuse and a main switch ("must include"), the control panel with its own guide, the panel cable, the tunnel and the cable.
- Charging
- The word "charging" is not in any of the Sleipner guides we read. The battery is sized by cold cranking amps, and a battery near the thruster is suggested. How it gets charged is left to you and your installer.
The manual’s words, page 19: “For installations on large vessels with bow and stern thrusters or catamarans a dedicated battery for each thruster should be considered.”
The “other parts” line in the estimate above is the priced parts below, $473 to $1,024 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. | SM5001, SM5002 (24 in, 35 in) | $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. | SM8960G single joystick, SM8950G touch panel | $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. | Side-Power 4-wire control cable, by length | $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. | Side-Power 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. | SMANLHOLD (SMANLHOLD-C with a cover) | $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. | Side-Power manual main switch, 350 or 600 A, or the automatic AMS | $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. |
| Control-circuit fuse and switch | A small fuse, and often a switch, on the thin wire that powers the panel or control box. | Sleipner names none | $8–$12Blue Sea in-line ATO fuse holders, 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. | Sleipner 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. | Sleipner 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. | Sleipner 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. | Sleipner 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 | 106 lb (48 kgf) As printed: Thrust @ 12 VDC: 105 lbs (48 kg) |
| Thrust under load | 88 lb at 10.5 V |
| Motor | 2.2 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 | 23 to 34 ft |
| The tunnel | |
| Tunnel length | Avoid a tunnel longer than four times its diameter. Friction inside a long tube slows the water and cuts thrust. Too short, and the flow reaches the propeller before it has straightened, which the manual says causes cavitation and noise. The propeller must sit entirely inside the tube. Sleipner’s installation manual |
| Depth below the waterline | As deep as possible under the waterline, and as far forward as possible. The depth for a given model is in that model’s own measurements. Deeper prevents air being sucked in from the surface and raises the water pressure at the propeller. SE20 to SE40 installation guide, 5611 rev 25 (2025) |
| Price and ordering | |
| Price | $4,545 equipment only, a dealer's price, defender.com, 28 August 2026 |
| Part number | 88339712 V |
| Documents | |
| Manual | Installation manualon the maker's product page |
| Warranty | Sleipner gives 2 years for leisure use and 1 for commercial use. It transfers to the next owner, and it starts no later than 18 months after the boat's first launch. Sleipner's warranty statement, effective 1 April 2022 |
| The site’s review | Sleipner (Side-Power) review |
Draw, cable, fuse and battery, at each voltage
These are the maker’s own figures, at each voltage it is sold at. The cable is the size for the shortest run in the maker’s table. A longer run may need heavier cable, and the wiring calculator works that out for your own boat.
| Voltage | Draw | Maker’s cable | Fuse | Battery | Run limit |
|---|---|---|---|---|---|
| 12 V | 315 Anominal draw | 1/0 AWG for up to 22 ft of cable counted out and back. Longer runs take heavier cableinstallation guide | ANL 250installation guide | 300 CCA DIN minimumSleipner installation guide, SEP20 to SEP40, document 5090 rev 19 (2025) | 2 to 3 min duty cycle at 20 C ambientproduct page, "Motor cycle duty" |
- At 12 V: size the cable for your run, or check the battery you have.
What holds up and what to weigh
Each point names the fact it rests on.
What holds up
- Sleipner sells it for either end, so it can go at the bow or the stern.The maker's listing
- Sleipner also prints a second, lower thrust figure for when the battery sags under load: 88 lb at 10.5 V.The maker's published rating
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
What the manual and listings say
This is the note we keep on the Sleipner SEP40/125S, written from the maker’s manual, its product pages and the dealer’s listing.
In the box: Proportional: the joystick sets how hard it pushes. The power controller (PPC) is included.
Our note
PRO means proportional: the joystick sets how hard it pushes. The 2026 catalog says to expect close to continuous run time at half power or less. A 125 mm tunnel for boats of 23 to 34 ft. The manual gives 280 A and a minimum battery of 300 cold cranking amps DIN (570 SAE).
The manual gives 1 AWG cable to 7 m of total run, 2/0 to 14 m and 3/0 to 21 m. The manual has no fuse table. The page rates the brushed motor for two to three minutes' running at 20 C. The control panel switches itself off after about six minutes unused. Sleipner's FAQ wants the tunnel at least three quarters of its diameter below the surface, never less than half.
Videos
Two of Sleipner’s own videos, from its YouTube channel: how the tunnel mouth changes the thrust you get, and the current E-series tunnel units. They are the maker’s pitch. Watch them 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
Sleipner also sells this thrust built another way. Each has its own page:
- On/off (SE): Sleipner SE40/125S, $1,845.
- On/off (SE), ignition-protected: Sleipner SE40/125S-IP, $3,195.
- Ignition-protected: Sleipner SEP40/125S-1IP, $5,760.
These are Sleipner’s nearest sizes by thrust, in any of its lines.
- One size down: Sleipner SE30/125S DC, 88 lb, $1,755.
- One size up: Sleipner SEP50/140S, 137 lb, $5,350.
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 CT45, 99 lb, $1,473.
- VETUS Bow 45, 99 lb, $1,927.
- Lewmar 140TT Gen 2 Thruster Package with Joystick and Tunnel, 92 lb, $2,754.
Every model with a page here is listed, maker by maker, on the thruster index.