Lewmar Gen 2 TT tunnel thrusters

Lewmar's TT thrusters have been bolted into a lot of production boats, and the Gen 2 range is the current version of that family. It is an on/off electric tunnel thruster with a 5-blade propeller, sealed gear leg, and a new set of control electronics Lewmar calls the "Blue Box." Nothing exotic. That is most of the appeal.

If you own a sailboat or a cruiser in the mid-30s to mid-40s and you want the bow to go where you point it, this is one of the units we end up quoting a lot. It is also one of the easiest to retrofit when an older Lewmar unit dies, since Lewmar says existing mounting holes can be reused.

The lineup, and how the sizes break down

Lewmar's own manual lists the full range in one table, which makes sizing easier than it is with some brands. Thrust figures below come straight from that table.

The smallest three sizes use a composite gearbox and composite propeller hub, so there is no zinc anode to replace on those, according to Lewmar's small-boat page. The 185 mm units move to a stainless gearbox, and the 250 and 300 mm units come in aluminium or bronze. Lewmar markets the 110 to 140 mm units separately as the Small Boat TT for boats up to roughly 28 ft.

The 185 mm tunnel is where most of the decisions happen. Four motor sizes share the same tunnel, which means you can pick thrust by motor rather than by hole size. If you are on the line between two, the extra kilowatt is usually cheaper than wishing you had it on a windy day. Run the numbers through our sizing calculator before settling on one.

What you get for the Gen 2 label

• Same thrust both directions. The 5-blade prop is designed to push equally port and starboard. Some designs are noticeably weaker one way; this one is built not to be.
• Sealed leg, no reservoir. Earlier thrusters from several brands needed an oil header tank. Gen 2 doesn't, which is one less thing to plumb and one less thing to forget.
• Spline-driven prop. Lewmar says the propeller is spline-driven, eliminating drive pins.
• Self-resetting thermal protection and electronics that protect the motor from misuse.
• Ignition-protected option. Lewmar's spec table lists IP versions of the 110, 125, 140 and 185 mm units. The manual is blunt: if the thruster has to live somewhere damp or wet, use the IP version.

The control logic has a few habits worth knowing before you're at the dock. Hold the joystick one way for more than 3 minutes and the system drops into fault mode with a red LED. It also powers itself down after 15 minutes of no use, warns of low battery voltage with an amber LED, and refuses to start if it sees a port or starboard signal at power-up, which guards against a stuck switch or a second joystick being bumped.

Install notes from the manual (and the bilge)

Lewmar's positioning rules are the same physics every brand fights:

• Mount the tunnel as far forward as you can for leverage.
• Keep the tunnel centerline at least one tunnel diameter below the waterline, with 0.75 diameter as the minimum, so it doesn't suck air.
• Minimum suggested tunnel length is two diameters.

The manual also lists tunnel wall thickness for each size: 4 to 6 mm for the 185 mm tunnel, 7.5 mm for the 250, 9 mm for the 300. If you are reusing an old tunnel, measure it. A thin tube that worked with a 3 kW motor is not automatically right for 6 kW.

Power is where installs go wrong. Lewmar wants at least 10V at the motor while it's running on a 12V system and 21V on a 24V system. A 185 mm 6 kW unit on 12V is fused at 500A in Lewmar's table, while the 24V version of the same thruster drops to a 325A fuse. On a boat where the battery bank lives aft and the thruster lives in the forepeak, that difference shows up in cable cost and in how hard the thruster pushes at the end of a long day. Our view: if your boat already has 24V or you are adding a dedicated bow battery anyway, take the 24V version of the bigger 185 mm motors. See how we approach bow thruster installs and the battery options in AGM thruster batteries and lithium thruster batteries.

Lewmar also requires a battery switch that is off when the boat is unoccupied, and an in-line fuse on the main power cables. Neither is optional on our installs either.

Where it falls short

It is on/off. You can feather it with short taps, and plenty of people dock that way for years, but it is not the same as rolling on 30 percent thrust and holding it. If that matters, Lewmar's brushless Proportional Thruster is the in-house answer, and Lewmar says it can retrofit into existing Lewmar installations.

The 3-minute one-direction limit is generous for docking, but if you regularly hold the bow up into a crosswind while crew handle lines, you will meet it eventually. Thermal limits are the reality of every brushed DC thruster, not a Lewmar quirk.

And the 12V 185 mm units are heavy users of current. That is not a flaw so much as arithmetic, but owners are sometimes surprised by the cable size.

How it compares

Against Max Power's CT range, the Gen 2 TT covers a similar span of tunnels with a different philosophy: single props through 185 mm, where Max Power uses twin props on several 125 and 185 mm models. Lewmar's thrust figures and Max Power's are not quoted on identical terms, so read our Lewmar vs Max Power breakdown before comparing numbers. Against Sleipner's SE series and Vetus BOW, the Gen 2 TT is the simpler, plainer package; both of those brands lean harder on proportional options and control networks.

Verdict

The Gen 2 TT is a sensible, unglamorous thruster that does the job, covers 110 to 300 mm tunnels, and is easy to drop in where an older Lewmar used to live. Choose it if you want simple on/off control and solid dealer support. Skip it if you already know you want proportional control. If you're weighing a 12V versus 24V version or a retrofit into an existing tunnel, send us the boat details and we will tell you what the wiring run actually needs.

Questions people ask