We may earn a referral commission from some links on this page. It doesn't change your price or our recommendations.
Finding one
How long can you run a bow thruster? Every maker’s limit
Most thrusters run for a few minutes and then need to cool. That sounds short, but a docking uses seconds. This page sets every maker’s run limit side by side, explains the rating behind it, and shows you the difference between a hot motor and a flat battery.
The limit is a rating on the motor, so it is the same at either end of the boat. Max Power, Sideshift, Yacht Thruster and ezDrive also make units only for the stern, and each of those makers has a row in the table.
Where this comes from. Every figure is the maker’s own. Each one was read from an installation manual, a control-panel manual, an FAQ or a product page for the brand reviews on this site, and is held there with its source. Where a maker prints two figures in two documents, you get both.
The short answer
Sleipner rates its Small carbon blocks inside a motor that press on the spinning part and carry the current into it. They wear down, they shed dust, and they are the usual reason an old thruster motor stops. SE series at 2 to 3 minutes. VETUS rates its standard units at 2 to 4 minutes at 12 V. Lewmar allows 3 minutes in one direction, and Quick about 5. Then the motor needs to cool.
A 5-second burst is a normal push at a dock. By our arithmetic, VETUS’s shortest rating holds 24 of them.
A hot motor resets once it cools, which Lewmar puts at 20 minutes. A battery unit such as DockStar runs about 10 minutes per charge and takes about 5 hours to recharge from empty.
On those, the limit moves from the motor’s heat to the battery bank’s charge.
It steers the bow while you push, let go and push again. A A dock line run forward or aft at an angle rather than straight across. Held against the engine, it pulls one end of the boat in to the dock. It is the cheapest docking aid there is. does the holding.
Two kinds of limit
The first limit belongs to the motor. Most tunnel thrusters are driven by a brushed DC motor drawing hundreds of amps. A motor like that makes heat faster than it can shed it. So the makers rate it for a number of minutes at full power, and a heat switch or the control panel stops it when it gets hot. Let it cool, and it is back.
The second limit belongs to the battery. A self-contained unit carries its own battery pack. It runs until the pack is down, then it charges. DockStar’s is the one this site holds figures for:
- about 10 minutes of running per charge
- about 5 hours to recharge from empty on a 110 V outlet
Both come from the maker’s own spec block, as the DockStar review reports. The figure that matters is the recharge.
Why you cannot rank them against each other. Comparing a motor’s minutes with a battery’s minutes is like comparing a thermometer with a fuel gauge. A tunnel unit that has cooled is full again. A battery unit that has cooled is exactly as empty as it was.
On a day of several dockings, the tunnel unit’s limit never arrives. Each docking takes seconds, and the motor cools between them. The battery unit’s limit arrives when the day’s seconds add up to its charge. On the maker’s figure, that is a long day.
Every maker’s limit, in its own words
Here are nine makers of tunnel, external and jet units, plus the one battery unit above. Each maker’s name links to the review that read the document.
| Maker | How long it runs | What happens then | Where it says so |
|---|---|---|---|
| Sleipner | On the brushed SE, SEP and SR units, 2 to 3 minutes at 20 C (68 F). The E-series runs continuously, limited by the battery. A PRO unit at half power comes close to continuous. | The control panel shuts itself down after about 6 minutes without use. | product pages and the Leisure Product catalog |
| VETUS | On the standard units, 2 to 4 minutes at 12 V, per model (the BOW75 the shortest, the BOW45 and BOW55 the longest). BOW PRO runs 10 minutes, and the RIMDRIVE is unlimited. | The manuals print the figure as an S2 motor rating: that long continuously, or that long in total per hour. | the installation manuals and the webshop |
| Quick | About 5 minutes continuously on the BTQ, set by the control panel. The brushless QSY runs 10 minutes. | The panel interrupts the command and resets itself after a cooling period it computes. It switches off after 6 minutes idle. | the TCD control-panel manual |
| Lewmar | 3 minutes constantly in one direction | The system enters fault mode. A thermal switch stops a hot motor, and the manual says wait 20 minutes for it to cool. The panel powers down after 15 minutes idle (5 on a retractable). | the Gen 2 installation manual |
| Max Power | On the CT100 and CT125, 2 to 3 minutes depending on ambient temperature (S2 3 minutes). The ECO page says "Unlimited runtime (until the battery runs out)". | A thermal switch raises an alarm, then 10 seconds of use before the unit shuts down. It switches itself off after 30 minutes unused (10 on CT100 and CT125 units from serial 83338). | the CT100 and CT125 manual |
| Sideshift | Bursts of 3 to 5 seconds, never more than 20 to 30 (the manual), or 5 to 10 seconds with 10 to cool, never more than 30 (the FAQ) | The FAQ says the unit is not designed to be run continuously, for example holding against a dock. | the Rev 3.1 manual and the FAQ |
| Yacht Thruster | The FAQ says up to 5 minutes continuously and 25 minutes an hour. The Why Us page says 7 to 10 minutes, and the brochure says 10 on the stern models. | An automated shutdown, per the FAQ. | the FAQ |
| ezDrive | Up to 10 minutes continuously | A safety reconfirmation at 3 minutes 15 seconds. | the FAQ |
| Jet Thruster | The manual says pulses of at most 10 seconds. The webshop pages say "1-2 minutes" to "3-4 minutes" continuous. | An overheated motor is left to cool for 20 minutes or more. | the installation manual |
| DockStar | About 10 minutes of running per charge | The pack is empty. It takes about 5 hours to recharge from empty on a 110 V outlet. | the maker’s spec block, via the review |
Three makers disagree with themselves. Each disagreement is covered on the maker’s review.
- Yacht Thruster prints three run times on three pages.
- Max Power’s manual rates the CT100 and CT125 at S2 3 minutes. Its ECO page says “Unlimited runtime (until the battery runs out)”.
- VETUS’s manuals print 10 minutes on BOW PRO. A US press release says “unlimited runtime with patented smart charging technology”.
In the Max Power and VETUS cases, the manual is the document the warranty is tied to.
What the rating means
VETUS and Max Power print the limit as a motor rating: “S2” followed by a number of minutes. VETUS’s manuals add a footnote that decodes it. The motor may run that many minutes continuously, or at most that many minutes in total per hour, at the stated current.
So the figure is a budget as well as a burst. Take VETUS’s shortest rating at 12 V, S2 for 2 minutes. The motor may run that long straight from cold. Or it may run that long in bursts spread over an hour. Then it wants the rest of the hour off.
Our arithmetic. A 5-second burst is a normal push at a dock. VETUS’s shortest rating of 2 minutes holds 24 of them.
Sideshift rates its units in seconds rather than minutes. It tells you to work in bursts of 3 to 5 seconds (the manual) or 5 to 10 (the FAQ), never more than 30 at a time. That is the same discipline, written for a smaller motor. If a docking needs more than a handful of bursts, change the approach before you look for a longer-rated thruster.
The rating rises with voltage and varies with size.
- On every VETUS model sold in both voltages, the 24 V version is rated the same as or longer than the 12 V version (3 longer, 1 the same).
- The VETUS rating does not simply fall with size. At 12 V it is 4 minutes on the BOW45, 4 on the BOW55, 2 on the BOW75, 3 on the BOW95 and 2.5 on the BOW125.
- Max Power says its 48 V units get a 50 percent longer operating cycle than the 24 V equivalent.
- VETUS warns that bigger batteries on shorter cables push the motor harder, so the allowed time comes down.
What happens at the limit
The thruster stops or steps down, and it tells you. Lewmar’s manual is the most specific. Run the thruster constantly in one direction for more than 3 minutes and the system enters fault mode. A heat switch stops the hot motor and the LED flashes red. The manual’s fault page says to wait 20 minutes for the motor to cool and reset.
The other makers say less:
Quick. The control panel interrupts the command after about 5 minutes. It resets itself after a cooling period the panel computes.
Max Power. The heat switch raises an alarm, then allows 10 more seconds of use before the unit shuts down.
Jet Thruster. The fault table says an overheated motor is left to cool for 20 minutes or more, the same figure as Lewmar’s.
VETUS. A single tone with a flashing red LED means the thruster’s own protection has stepped in, for heat, overload or voltage. The panel clears itself once the condition is gone.
Every one of those is the protection doing its job. A thruster that cuts out from cold is a different problem. So is one that has gone weak on a boat where it used to be fine. The troubleshooting page starts there: heat first, then fouling on the propeller, then the cable.
Idle timers are a separate thing. They are the reason a panel goes dark while you are still tied up.
- A Sleipner panel shuts down after about 6 minutes without use.
- A Quick panel shuts down after 6.
- Lewmar’s goes after 15 on a tunnel unit and 5 on a retractable.
- Max Power’s goes after 30, or 10 on its newest CT100 and CT125 units.
Turn the panel on as part of your approach.
What lengthens the run
A controller between the battery and the motor
VETUS rates its BOW PRO A thruster with a controller between the battery and the motor, so the joystick sets how hard it pushes rather than just on or off. The motor and the mounting are the same. Only the control differs. units at 10 minutes, against 2 to 4 on its standard units. Its user manual says why: “The runtime is mainly limited by the capacity of the installed batteries.”
Sleipner rates every E-series unit “Continuous @ 22degC ambient, typically limited by battery capacity”. It says a PRO unit at half power or less gives “close to continuous run time, only limited by your available power supply”. Quick’s brushless QSY reaches 10 minutes.
On all of those, the limit moves from the motor’s heat to the bank’s charge. On an on/off unit a weak battery costs thrust. On a proportional unit it costs run time. The battery page works that through. The proportional page has what the controller costs, model by model.
Less than full power
Sleipner’s half-power figure above is the general rule. A proportional joystick held at half gives the motor half the heat to shed. An on/off unit has no half setting. There, short bursts are the only way to keep the motor cool.
The battery the maker asks for
Every maker’s bank rule is on the battery calculator. The cable that feeds it is on the wiring calculator. A thruster starved of volts runs slower and pushes less. On a proportional unit it also runs shorter.
The one thing no thruster is for
Holding the boat against a dock. Sideshift’s FAQ says its units are not designed to be run continuously, and gives that exact example. Lewmar’s fault mode after 3 minutes in one direction is written for the same misuse.
This site sizes every thruster as a steering control. Its job is to keep steering the bow at docking speed in a breeze while the engines drive the boat. That includes the thruster finder, our free tool that matches a thruster to your boat.
The run limits on this page are the makers saying the same thing in their own way: push, let go, push again. The tool for holding a boat alongside is the A dock line run forward or aft at an angle rather than straight across. Held against the engine, it pulls one end of the boat in to the dock. It is the cheapest docking aid there is., and the low-speed steering page covers it.
About 10 minutes of run time per charge is many dockings. Recharge is about 5 hours from empty on a 110 V outlet, so plan on shore power or an inverter. The figure is the maker’s own, from the spec block the DockStar review reads.
What this means when you dock
If the thruster stops after a long push in one direction, the heat protection has most likely stepped in. On a Lewmar, the manual says wait 20 minutes for it to cool and reset.
If the panel is dark as you come in, an idle timer has switched it off. Turn it on as part of your approach.
If you find yourself holding the bow on with the thruster, rig a spring line and let the thruster go back to steering.
If it cuts out from cold, or has gone weak, heat is not the cause. Start with the troubleshooting page.