We may earn a referral commission from some links on this page. It doesn't change your price or our recommendations.
Finding one
Hydraulic bow thrusters: who needs the pump
A A thruster whose propeller is turned by oil under pressure instead of an electric motor. A pump on the engine or a power pack supplies the oil. The thruster needs no battery bank at the bow and can run as long as the pump does. is the same tunnel and the same propeller as an electric one. What turns it is oil from a pump, instead of an electric motor wired to a battery bank at the bow. This page shows where the electric range runs out and what the rest of a hydraulic system is made of. It also covers why nobody publishes a price for one, and which boats it suits.
Where this comes from. Max Power’s CT HYD 125 installation manual, and Sleipner’s SRHP240 and SRHP650 retract manuals and its 2026 catalog, all read 20 September 2026. Lewmar’s Gen 2 manual, which covers its hydraulic units in the same pages as the electric ones. ABT-TRAC’s and HydraNautics’ sites. The one price on the page is an owner’s, labeled.
The short answer
A hydraulic motor on the The underwater part of a thruster: the housing in the tunnel that holds the gears and the propeller. The motor sits above it, inside the boat. turns the propeller, fed by a pump on the engine. An electric unit has a motor wired to a battery bank at the bow.
The first is too big for an electric thruster. The biggest battery-powered unit this site lists makes 2425 lb, and Sleipner’s hydraulic range runs to about 3,086 lb. Where electric stops has the detail.
, for stabilizers, a The electric winch at the bow that raises the anchor. It has its own heavy cable and often its own battery. That is why a bow thruster is sometimes wired alongside it. or a crane. On that boat the thruster is one more thing for a pump that is already there and already paid for.
You are paying for a whole system sized to your boat. The one owner figure this site holds is $20,000 installed on a 54 ft boat.
Going hydraulic would mean buying a pump, a reservoir, a cooler, a valve and hoses to run one thing. The thruster finder, our free tool that matches a thruster to your boat, will show you which electric units fit her.
What a hydraulic thruster is
Below the waterline, nothing changes. The tunnel, the gear leg and the propeller are the ones on the types page. Max Power’s manual installs the hydraulic CT HYD 125 in the same eight-layer laminate as its electric units. It adds that the unit can be fitted “vertically, horizontally or tilting.”
What changes is above the leg. The manual lists what a typical installation needs in place of a motor and a cable to a battery: oil reservoir/tank, hydraulic pump, directional control valve, hydraulic motor, circuit piping and an oil cooler (depending on type of installation).
The pump itself can come off the engine or off a motor of its own. The manual puts it this way: “The pump can be driven by either an internal combustion engine (crankshaft pulley or gearbox PTO) or an electric motor.”
The makers sell the thruster and leave the rest of the system to the boat. Sleipner says so plainly: “Hydraulic thrusters are supplied with hydraulic motors only.” And it puts the system in the fitter’s hands: “The installed hydraulic system is the responsibility of the fitter/ installer and must be within the limitations outlined in this manual to ensure no damage is caused to the thruster.”
Lewmar has one line for the whole of it on its hydraulic checklist: “Hydraulic system has been checked and adjusted to correct pressures and flows.” Its operation section sends the owner elsewhere: “Refer to system suppliers instructions.”
The figures are flow and pressure instead of amps and volts. The CT HYD 125 wants 30 to 35 liters a minute at 130 to 140 bar.
Sleipner’s SRHP240 retract can be ordered with any of six motors, and the table shows the trade. The smallest needs 21.4 liters a minute at 275 bar for full thrust. The largest needs 58.3 at 153: about 2.7 times the flow at a little over half the pressure.
So the motor is chosen to suit the pump the boat already has. The SRHP650 wants 110 liters a minute at 274 bar.
The oil is the working part. Max Power asks for “synthetic, mineral or vegetable hydraulic oil, to ISO standard 32 to 48.” The hoses have to be of the “thermo-plastic non-conductive type”. Lewmar says why the hose must not conduct electricity: “It is advisable to fit insulated pipe sections to prevent thruster corrosion.”
Sleipner wants the oil under 75 degrees C, and 40 to 60 in normal running. Keeping it there is the cooler’s job.
A shock valve stands in for the shear pin. Sleipner wants one set 10 to 15 percent above the working pressure. That valve does the job the shear pin does on an electric unit: “This will prevent the system from being damaged if the propellers are blocked for any reason.”
Where electric stops and hydraulic starts
Start with where electric runs out. The biggest battery-powered tunnel thruster this site lists with a published price is the Sleipner Side-Power SAC1100: 2425 lb, at $48,000.
The biggest at any price is the Sleipner Side-Power SAC1100, at 2425 lb, and nobody publishes what it costs. Max Power’s CT550 (three-phase) makes 992 lb. It runs on three-phase power, so it is no battery unit either.
Hydraulic goes a long way past that. Sleipner prints two thrust ratings for each hydraulic unit, one for light duty and one for heavy duty. On the heavy-duty rating its catalog runs from 80 to 1,400 kg, which is 176 to 3,086 lb. On the light-duty rating it runs from 100 to 1,100 kg, 220 to 2,425 lb. The tunnels run from 185 to 610 mm, for boats of 30 to 175 ft.
The catalog’s own headline, “100 kg to 1,400 kg”, takes its bottom from the light-duty scale and its top from the heavy-duty one. That is why the smallest unit is named the SH100/185T and rated 80 kg heavy duty.
That range holds 11 models. The smallest is the SH100/185T, 6.9 kW, for boats of 30 to 34 ft. The largest is the SH 1400/610TC, 80.1 kW in a 610 mm tunnel, for boats up to 175 ft. The top of it pushes about 1.3 times as hard as the biggest battery-powered unit.
The two overlap over most of the electric range. Past the top of it, only hydraulic is left. Max Power’s CT HYD 125 starts at 90 kg (198 lb) in a 185 mm tunnel, which is the size of a mid-range electric unit.
Max Power builds six hydraulic models in all, up to the CT1000. That one makes 1,000 kgf (2,205 lb) heavy duty in a 500 mm tunnel, on 200 liters a minute at 210 to 250 bar.
Lewmar’s Gen 2 manual carries three hydraulic rows beside its electric ladder. They are the TT 185 Hyd (7 kW, 100 kgf), TT 250 Hyd (15 kW, 200 kgf) and TT 300 Hyd (22.5 kW, 300 kgf). (The manual prints the 250 mm unit’s 200 kgf as 240 lb. It converts to 441, a misprint the Lewmar review reports.)
So thrust alone rarely decides it. A boat that needs less than about 2425 lb has an electric unit available to her, whatever her length. What moves a boat to hydraulic is the next two sections: how long she has to push, and what else is already aboard.
Run time
Run time is the catalog’s main selling point. Sleipner opens its hydraulic pages with it: “Power from 100 kg to 1400 kg and continuous operation make a hydraulic thruster system ideal for yachts, super yachts and professional vessels. It is the natural choice when extensive thruster usage or long run cycles are required.” The first benefit in its list is “Continuous use”.
The manuals are more particular. The SRHP650 retract is rated “Continuous”. The SRHP240 and SRHP320 carry “2-3min at 20°C ambient temperature”, which is the same rating as the electric retracts. A hydraulic motor does not by itself lift the limit on a small unit.
Max Power’s CT HYD 125 manual prints no run limit at all. Its pump table marks most pump types “require oil cooler when time of operation exceeds 15 minutes”. A fixed-flow pump driven straight off the engine needs a cooler whatever the run time. The rule is written for runs longer than any brushed electric unit is rated for.
Lewmar prints its three-minute limit in the fault table for its electric units. For the hydraulic ones it says only: “Refer to hydraulic system supplier for service requirements.”
Two things still stop a hydraulic thruster.
The oil getting hot. That is what the cooler is there to prevent.
The engine. A pump driven off it only turns while it is running.
The run-time page has every electric maker’s figure beside these, from two minutes to continuous.
What it costs, and why nobody prints it
No maker this site has read publishes a price for a hydraulic thruster. That is why the 22 hydraulic units held here are kept out of the thruster finder. They are commercial gear sold on a dealer’s quote, with no published price. ABT-TRAC publishes no price and no thrust figure per size, and nor does HydraNautics.
Sleipner’s own argument for the system explains the missing price: “Once the primary system is in place, including the pump, reservoir, and cooler, adding a function is simply a matter of adding a relatively inexpensive hydraulic valve.”
What you are buying is the whole system. The pump, the reservoir, the cooler, the valve, the hoses and the fitting are all sized to your boat, so there is no list price to print.
Two figures give the scale. The first is Max Power’s electro pump pack, which is what a boat with no engine-driven pump has to buy. It is a 24 V, 8 kW electric motor driving the pump, with a relay and a fuse. The reservoir comes in one of four sizes: 8, 12, 18 or 40 liters.
Buy that pack and you are back to batteries. The motor driving the pump needs the same bank and the same cable an electric thruster would. Hydraulic only saves you the battery bank where the pump runs off the engine or, on a houseboat, off the generator.
The second figure is an owner’s. Arthurc reported $20,000 installed on a 54 ft boat, “full tube, integrated hydraulic controls” (Trawler Forum, Feb 2018). That is one boat and one thread.
The quote-check page reads an electric quote line by line. A hydraulic one needs the yard’s own breakdown of the pack.
The warranty follows the same split. Lewmar’s three-year warranty gives “Hydraulic pumps, valves and actuators” one year, the same as it gives its electric motors.
Maintenance is the electric list plus the oil. Max Power’s yearly jobs for the hydraulic unit: change the anode (if necessary); change drive leg oil, if classic (bronze) leg; check the oil and the hydraulic filtration circuit (only if necessary). Every five years: “drain hydraulic oil system and change the filter and refill.” The maintenance page has the electric schedules beside it.
Who sells them
| Maker | What | Range | Run limit |
|---|---|---|---|
| Sleipner | SH tunnel series, 11 models, and the SRHP retractables | 80 to 1,400 kg on the heavy-duty rating (100 to 1,100 kg light duty), boats of 30 to 175 ft | “Continuous use” on the tunnel range. The SRHP650 retractable runs continuously. The SRHP240 and 320 run 2-3min at 20°C |
| Max Power | CT HYD tunnel series, 6 models, and hydraulic retractables | 90 kg (CT HYD 125, 6 cc motor) to 1,000 kgf (CT1000, heavy duty) | None printed. Most pump types need an oil cooler past 15 minutes |
| Lewmar | TT Hyd Gen 2, three sizes, in the electric units’ manual | 100 to 300 kgf, 185 to 300 mm | “Refer to system suppliers instructions.” |
| ABT-TRAC | Hydraulic bow and stern thrusters for yachts on an integrated hydraulic system that also runs capstans, windlasses, cranes, generators, and bilge pumps, plus AC and DC electric versions | Tunnels from 8 to 28 in, 7 sizes in all. Control is single-speed or proportional. No thrust figure is published per size | Not published |
| HydraNautics | Bolt-on hydraulic bow and stern systems for houseboats, fitted afloat by the maker | “Powered by Existing Generator - No Batteries or Chargers”. No thrust figure published | Not published |
ABT-TRAC’s home page makes a claim for its twin counter-rotating propellers. It says they “deliver more thrust per horsepower than any other thruster on the market”. Those are the maker’s words, and no figure on its site lets anyone check them.
HydraNautics sells no kit. It installs its systems itself, which is why no price and no thrust rating are published for any of them. The houseboat guide covers it in full, with the one itemized houseboat bill this site holds.
Who it is for
Hydraulic suits four kinds of boat.
A boat that needs more thrust than a battery can give it. Among the units listed here, that means more than about 2425 lb.
A boat that already carries hydraulics, for stabilizers, a windlass, a capstan or a crane. On that boat, in Sleipner’s words, the thruster is one more valve.
A boat that needs the push for long spells: a workboat, or a yacht holding her position, where an electric motor’s few minutes run out. Sleipner’s catalog calls it “extensive thruster usage or long run cycles”.
A houseboat on a generator.
The makers add one more case themselves. In Sleipner’s words: “Hydraulic valves and motors are better choices in harsh environments such as the forepeak, bilge, and transom areas and areas requiring ignition protection.”
It is not for a thirty to fifty foot boat with no hydraulics aboard. On that boat the pump, the reservoir, the cooler, the valve and the hoses are all bought to run one thing, and an electric unit will do the job.
The thruster finder lists every one that fits. The size calculator works out how much thrust your boat needs.
If a yard proposes hydraulic on a boat like that, ask for the pack itemized. Then ask what else aboard the pump will run.
Sources, by maker. Max Power: its CT HYD 125 manual. Sleipner: its SRHP240 and SRHP320 manual, SRHP650 manual and 2026 catalog. Lewmar: its Gen 2 manual. ABT-TRAC (the row read 28 August 2026, the home page 20 September 2026) and HydraNautics (read 30 August 2026). The owner’s figure is from the Trawler Forum thread the stern thruster cost page cites.