Sleipner retractable thrusters

A tunnel thruster is a permanent hole through the bow. On a lot of boats that is fine. On a fast planing hull, a performance sailboat or a yacht where the tunnel would end up too close to the waterline, it is a compromise you feel every time you run. A retract thruster solves that by living inside the hull and dropping a propeller pod down only when you need it.

Sleipner has one of the broadest retract ranges around. It is also one of the most confusing to read, because there are three mechanical styles, three control types and two motor technologies.

Three ways to mount it

SR: mold-in. Sleipner says the SR is designed for direct mold-in. That suits new builds, where the base can become part of the hull layup. Listed models are the SR80 and SR100.

SRL: low height. The SRL is flange-mounted and uses bevel gears, which keeps it compact vertically. Sleipner pitches it for boats with limited height space. Listed models run SRL80, SRL100, SRL130 and SRL170.

SRV: vertical. The SRV is also flange-mounted but designed for vertical installation, so it needs more headroom above the hull. In exchange it covers the widest thrust range, from the SRV80 up to the 48V SRV300.

For any of them, measure the space before you fall in love with a model. Height above the hull is usually what decides between SRL and SRV.

Three control types

Each mechanical style comes in versions that mirror Sleipner's tunnel thrusters:

• On/off (SR, SRL, SRV), with the same 2-3 minute duty cycle and thermal shutdown as the SE tunnel thrusters.
• PRO variable speed (SRP, SRLP, SRVP), with power derating instead of shutdown and the bow-and-stern hold function.
• eVision (ERV and ERL), using Sleipner's brushless 6-phase motor with an integrated inverter, rated for continuous running at full thrust at 22°C. eVision retracts are 24V or 48V only.

As with the tunnel range, Sleipner is moving larger PRO units to eVision. On Sleipner's site, the SRVP130, SRVP170, SRVP210, SRVP300 and SRLP170 pages now link to ERV or ERL replacements. Our SEP PRO and eVision review explains the difference in more detail.

Sizing

Retract thrust ratings match the tunnel models of the same number. An SRV80 on 12V is rated 80 kg at 10.5V and 96 kg at 12V, with a 4.4 kW motor drawing about 530 A, the same figures as an SE80. Sleipner's boat-size guidance lines up too:

One sizing advantage retracts have: because the pod drops below the hull, it is not limited by how deep a tunnel can sit. On boats where a tunnel would be shallow and prone to sucking air in a chop, a retract can deliver its rated thrust more consistently.

What the install really involves

Weight

These are heavy units. Sleipner lists the SRL80 at 31 kg, the SRL130 at 101.5 kg, the SRV210 at 112 kg and the SRV300 at 120 kg. For comparison, an SE80 tunnel thruster is listed at 20 kg. Weight right up in the bow affects trim, so it is worth a word with the builder or a naval architect on lighter boats.

The hull opening

You are cutting a large hole in the bottom of the boat and then making the area around it stronger than it was. That means careful glass work, a fair landing for the flange or base, and time for cure. It is not a weekend project. See our retractable thruster installation page for what the job looks like.

Power

Current draw is the same as the matching tunnel thruster, so the same rules apply: dedicated battery near the unit, short heavy cables, correct ANL fuse. For eVision retracts, plan a 24V or 48V bank. The lithium battery page covers why many larger installs go that way.

Controls

Retracts need control logic for deploying and stowing as well as for thrust. Sleipner notes a remote control is a popular accessory, and the units use S-Link CAN, which keeps wiring tidy on boats that also have Sleipner stabilizers or joystick systems.

The weak spots

Complexity. A retract has a deploy mechanism, a closing plate and seals that a tunnel does not. Those parts need checking at haul-out, and marine growth on the pod and its housing is the usual enemy.

Cost. The unit costs more, and the install takes much longer. Get a firm quote before you commit; our bow thruster cost guide gives a sense of how the labor compares.

Space. SRV units in particular need real headroom. On some boats neither style fits without moving tanks or bulkheads.

How it compares

Max Power also offers retract models and is the usual alternative for smaller boats. Vetus offers a different approach with its swing-type retractables, covered in our Vetus retractable and hydraulic review. If you are still deciding between installation types, tunnel vs retractable vs external sets out the trade-offs.

Verdict

Sleipner's retract range covers almost any hull space and size, from an 80-class unit on a mid-30s boat to a 48V 300-class on a large yacht. Choose SR for new builds, SRL when headroom is tight and SRV when it is not. For anything 130 and up, look hard at eVision for the run time and lower current. Before choosing, have the bow space measured, because that measurement usually picks the model for you. Book a survey if you want us to do it.

Questions people ask