SRVP300 PRO™ retract bow/stern thruster

Not necessarily. These systems typically come with a Battery Management System (BMS) that will disconnect the thruster in case of any issue with the battery (for instance, if the thruster draws more current than the BMS allows). Just imagine a sudden cut-out in the middle of a maneuver without any pre-warning.

At Sleipner, we recommend a solution with a simple, separate battery and without a disconnect BMS system (such as the lead acid bank frequently used for starting or similar). The helmsman will then be warned when the battery is getting low and feel that the thrusters are gradually losing power, which is significantly better than losing your thrusters without any pre-warning.

Disclaimer: Ensure battery/energy source is installed according to CE/ISO current rules and regulations and by licensed electricians.

We always recommend that both bow and stern thrusters are mounted in a dry and well-ventilated compartment. Sleipner's thruster motors, electronic components, and wiring harnesses do not perform well when wet or corroded. They are neither water nor corrosion-proof and therefore need to be kept as dry as possible.

We supply ignition proof (IP) thrusters (spark-free) designed for petrol-driven yachts where ignition of petrol fumes is an issue. The IP thrusters can be appropriate for yachts where it is challenging to keep thruster compartments 100% dry. The IP thrusters are tested underwater to handle moisture and a little water shower now and again, but not completely immersed.

(Addition Feb 2023:) The new E-serie thrusters launched in 2022 also features the same characteristisc as IP thrusters, but in a more compact format and might allow installations in small areas where IP models have not previously fit.

Yes – but it needs to be Ignition Protected to avoid risks related to potential gasoline fumes in the engine room.

Yes. Most engineers would tell you that it is not ideal for connecting the bow thrusters to a service bank protected by a Battery Management System. Thrusters are heavy consumers, and they may create sudden peaks in current draw, which again may cause the BMS to disconnect the batteries if the thruster draws more current than allowed. If this happens in the middle of a maneuver, you would be left without thrusters and may lose control of the boat.

Hence, Sleipner recommends that the thrusters be connected to a separate battery bank (that is not lithium) without a Battery Management System that can disconnect the batteries (and consequently the thrusters).

Disclaimer: Ensure battery/energy source is installed according to CE/ISO current rules and regulations and by licensed electricians.

We recommend installing the thruster as deep as possible and at least 3/4x the tunnel diameter below the waterline (eg 300mm x 0,75 = 225mm minimum).

On some boats this might be impossible due to the positioning of other equipment onboard and for the lack of better options, it might only be possible to get the top of the tunnel ½ x the tunnel diameter below the waterline. Notice though that this increase the risk of cavitation.

For some boat types, external or retractable thruster models might be a better solution if it is difficult to place the tunnel deep enough. 

We always recommend to seek the advise of experienced installers for optimal results. 

How much thrust your boat needs generally depends on its size, the thruster's installation point, the surface affected by the wind – and your expectations as to how fast you want the boat to react. 

Sleipner has the world's largest database on expected thruster performance on different boats and has developed proprietary software that can run simulations. Based on this we are giving some general recommendations on our website. You can read more about thruster sizing here. 

For help to right-size a thruster to your boat, we recommend contacting your local Sleipner dealer.

We recommend to replace the anode before every season, or when half the anode has eroded. Always use a sealant or thread glue on the holding screw to ensure that it does not fall off.

If you want to read more about corrosion in general, please see our "Boaters guide to corrosion"

A Lithium or Li-ion battery may maintain a significantly higher voltage and higher current under load than a lead-acid, gel or AGM battery. This will provide significantly more power to the thruster motor and give some undesired side effects:

-      The propeller will rotate significantly faster and with higher power than what they are designed for, increasing the risk of cavitation and following damages in the tunnel and at the thruster.

-      The thruster risks overheating and will have shorter run times. This can cause the thruster to stop in the middle of a maneuver.

-      Over time, the thruster may be damaged and you may have a reduced life expectancy.

Sleipners speed controlled thrusters will not be impacted by Lithium, Li-ion or similar battery times providing a steady high voltage.

Disclaimer: Ensure battery/energy source is installed according to CE/ISO current rules and regulations and by licensed electricians.

This is a unique patented Sleipner safety feature supplied with all standard (on/off) DC electric Sleipner thrusters. The IPC functionality provides two unique features: 

1) It will detect "flapping" of the solenoid (typically caused by badly charged batteries that are subject to a huge current draw and voltage drop when the thruster motor is engaged), and will stop trying to run the thruster, preventing excess solenoid contact tip wear and dramatically reducing the risk for a weld-in situation of the solenoid. A 'weld in' (run away) situation is when a thruster continues operating without a signal from the operator at the control panel. 

2) Even if the solenoid has a weld-in situation, which even with the IPC prevention actions is still possible, as all mechanical switches can weld-in at a point, the unique IPC function will STOP THE THRUSTER, without active action by the operator. This will give the operator time to locate and Select OFF on the thruster system Isolation/Main Switch.

If the tunnel is too short, water will circulate from one side of the tunnel to the other and reduce thrust. The gearleg might also be at risk from water passing through the tunnel at high speeds during driving, turning the propeller(s) at very high speeds. Note that tunnel openings must be rounded and with a deflector to direct water out from the tunnels back wall. Please see installation manuals for proper tunnel installation.

If the tunnel is too long, it creates too much friction and reduce thrust and you might want to increase the thruster size to compensate.

Maximum and minimum tunnel lengths for each thruster can be found in their manuals, which can be downloaded from this website.

Sleipner recommends that the thrusters are connected to a battery bank that is not protected by a Battery Management System (BMS). Typically this means lead-acid, AGM, gel, or similar kinds of batteries. This is important because thrusters draw a lot of currents quickly, and the high amp draw may lead the BMS system to think that there is an issue with the system and consequently disconnect the batteries from the circuit, in which case you would lose maneuverability.

If you have Lithium batteries powering your thrusters, the best advice we can give you is to check the actual voltage measured on the thrusters during operation. Sleipner thrusters are designed to operate within a specific voltage range, and as long as you are within these boundaries, it doesn’t matter for the thruster if the current is delivered by this or that battery pack.

It may also be a very good idea to check the actual current drawn from the battery during full power at the thruster to see that you are not at the limit for the BMS to avoid sudden loss of maneuverability if the BMS disconnects the battery.

With installations where the battery pack is far from the thruster, the higher voltage delivered by LiFePO4 or similar batteries might not be a problem as you will experience a voltage drop through the long cables.

Always make sure you measure your voltage on the thruster to avoid the risk of early thruster wear.

As battery tehcnology is changing rapidly, we always recommend consulting a professional battery supplier. 

Disclaimer: Ensure battery/energy source is installed according to CE/ISO current rules and regulations and by licensed electricians.

The thruster should be positioned as far forward as possible. This is important as the relative distance from the boats pivot point to the thruster installation point will change the actual thrust of the boat. The further away from the pivot point of the boat – the larger the thrust.

The thruster shall be positioned as deep as possible for two reasons;

• So that it does not suck air from the surface, causing cavitation which will significantly reduce thrust and create noise
• To increase the water pressure so that the propeller has a firm substance to work with for maximum performance. We recommend at least ¾ x the tunnel diameter below the surface and more is better. It is never recommended to go less than ½ x the tunnel diameter below the water surface.

In reality it is often a compromise between how far forward you want the thruster to maximise the force arm from the pivot point of the boat – and how deep you can position the thruster.

It is also a good advice on high speed boats to consider that the tunnels can come out of the water at high speed, but as slamming loads can be overcome by working with the tunnel installation to deflect the water.