Sleipner external stern and pod thrusters

Some boats simply do not have a good place for a tunnel. Twin stern-drive cruisers are the classic example: there is no room for a stern tunnel between the legs, and even if there were, it would blast water straight into the drives. Small boats with thin, curvy bows have the opposite problem. Sleipner's answer to both is to put the thruster on the outside.

The lineup, by the boat it fits

Sleipner's external range splits into three groups that do quite different jobs. It helps to think of them by boat type rather than by model number.

Small boats: SX35 and SX50

The SX35 is the smallest unit Sleipner makes, rated 35-42 kg and suited to boats up to about 32 feet. The SX50 steps up to 50-62 kg for boats to about 37 feet. Both run on 12V. They come as transom-mounted stern units and as pod versions that sit under the hull for bow or stern use. Sleipner says the pod's hydropod cover lets it sit in the water flow on low- and mid-speed boats.

The selling point is installation. Sleipner says no GRP work is needed on hulls up to 50 mm thick, and some variants are listed for hulls up to 150 mm. You drill, mount, seal and wire. Some SX35 and SX50 pages on Sleipner's site now link to versions that ship with a controller unit, so check the part number when ordering.

Twin stern drives: SX80, SX100, SXP and SXE100

This is the group most owners are asking about. The SX80 (80-96 kg) suits boats up to 48 feet with twin stern drives; the SX100 (100-116 kg) goes up to 55 feet. Both come in 12V or 24V. Special cowls redirect the thrust so it flows past the stern drives instead of into them.

Sleipner ships these fully assembled, wired and sealed in a waterproof box. The only hole through the boat is a small one in the transom for power and control cables. Compared with glassing a stern tunnel into a stern-drive boat, that is a much smaller job.

The PRO versions (SXP80, SXP100) add variable speed control and the bow-and-stern hold function. The SXE100 is the newest: the SX100 platform with Sleipner's brushless eVision motor, 24V, rated by Sleipner for continuous running at full thrust at 22°C ambient, limited mainly by battery capacity. If you pair it with an eVision or PRO bow thruster, you get proper proportional control at both ends.

Displacement and semi-planing boats: EX pods

The EX range is for bigger, slower hulls. All three are 24V:

• EX70C: 67 kg, stern only, for displacement and semi-planing boats of about 32-42 feet.
• EX95: 67-95 kg, bow and/or stern, for 35-48 feet.
• EX180: a dual pod with 130-180 kg, bow and/or stern, for roughly 44-59 feet.

These suit trawler-style boats and sailboats where a tunnel would be awkward or where the owner does not want one cut in.

Install notes

Transom real estate

On stern-drive boats, the transom is already busy: drives, trim tabs, transducers, swim platform brackets, sometimes underwater lights. Measure before buying. The cowls have to line up with the drives, and there must be clearance to tilt the legs.

Power

Sleipner lists the SX80 on 12V at 4.4 kW and 530 A, the same as an SE80 tunnel unit, and the SX100 on 12V at 740 A. Battery placement is awkward on many stern-drive boats because the engine room is full. A dedicated thruster battery in the lazarette with a short cable run is usually the cleanest answer. Our AGM battery review covers the basics.

Duty cycle

Sleipner lists the SX80 and SX100 as S2 motors with a 2-3 minute duty cycle at 20°C, the same as the SE tunnel range. The SXE100 is the exception, with its continuous-run rating.

Protection

External hardware lives in the water full-time. Keep it on your antifouling schedule, check anodes at haul-out, and watch it around fuel docks and lifts. If the boat lives on a trailer, check the bunks and rollers clear the unit.

The weak spots

Everything outside the hull is exposed. That means more drag than a tunnel (though usually not enough to notice on a stern-drive cruiser), more surface to foul and more chance of a knock. Power figures hint at the efficiency cost, too: Sleipner lists the SX50 at 2.8 kW for the same 50-62 kg rating the SE50 tunnel unit gets from 2.4 kW. And the EX range is 24V only, which adds a battery bank on a 12V boat.

Controls and pairing with a bow thruster

A stern thruster on its own is useful; paired with a bow thruster it changes how the boat handles. You can walk the boat sideways into a slip instead of working the drives back and forth. For that to feel natural, both ends should behave the same way. An on/off SX80 with an on/off SE bow thruster is fine. If you want the hold function, which presses the boat against the dock with one button, Sleipner says you need PRO or eVision thrusters at both ends, so pair an SXP or SXE100 with a SEP PRO or eVision bow unit.

Alternatives

If there is room for a tunnel, a Sleipner SE or Vetus BOW in a stern tunnel is usually more efficient. If you are torn between the three install types, read tunnel vs retractable vs external. For the bow on a stern-drive boat, a tunnel thruster is still the normal choice.

Verdict

For a twin stern-drive boat that needs a stern thruster, the SX80 or SX100 is one of the cleanest solutions available: assembled, sealed, cowled for the drives, and only a small hole through the transom. Pick the SXP for variable speed or the SXE100 if you have 24V and want the run time. For small boats, the SX35 and SX50 avoid glass work entirely. Send us transom photos and drive model through the contact page and we will tell you which one clears.

Questions people ask