Choose a Lewmar thruster by matching thrust output to your boat’s length and displacement: the TT140 (77 lbs thrust, 12V) suits boats up to 30 ft, the TT185 (110 lbs, 12V or 24V) covers 30–40 ft, and the TT250 (160 lbs, 24V) handles 40–55 ft. Beyond size, your hull shape, onboard power system, and whether you want a tunnel or retractable unit determine which model is right for your boat.
Lewmar thrusters at a glance
| Model | Type | Thrust | Voltage | Boat size |
|---|---|---|---|---|
| Lewmar TT 140 | Bow thruster | 77 lbs | 12V | Up to 30 ft |
| Lewmar TT 185 | Bow/stern | 110 lbs | 12V or 24V | 30–40 ft |
| Lewmar TT 250 | Bow/stern | 160 lbs | 24V | 40–55 ft |
| Retractable 185TT | Retractable | 110 lbs | 12V | Performance boats |
What is a thruster and why does it matter?
A thruster is a propulsion device that pushes your boat sideways without any forward motion — exactly what you need for docking, navigating crowded marinas, and holding position against crosswinds. Your main engine and rudder need water flow to steer; a thruster works at zero speed, giving you precision and control right where the engine can’t. Lewmar’s bow and stern thrusters are among the most widely fitted systems on cruising sailboats and powerboats, and a full range of replacement parts keeps them serviceable for the long haul.
How much thrust does my boat need?
Boat length is the starting point, but displacement and windage matter just as much. Heavier boats need more thrust to move the same distance sideways, and a deep-V hull typically demands more thrust than a flatter hull because more of the boat resists lateral motion. As a rule of thumb from Lewmar’s lineup: up to 30 ft, the 77 lb TT140 is adequate; from 30 to 40 ft, step up to the 110 lb TT185; and from 40 to 55 ft, the 160 lb TT250 is the right choice. If your boat sits at the top of a size band, carries a tall superstructure, or docks in windy locations, size up rather than down — an underpowered thruster is the most common sizing mistake.
Should I choose a bow thruster, a stern thruster, or both?
A bow thruster alone transforms docking for most boats — it lets you swing the bow into or away from the dock independently of the engine. The TT185 and TT250 can be installed as either bow or stern units. Adding a stern thruster creates a dual system that lets you walk the boat sideways as one piece, which is a real advantage for larger vessels, single-handed skippers, and tight side-to berths. If your budget covers only one, start with the bow: it is where wind takes charge first and where the rudder gives you the least help.
Tunnel or retractable — which type is right for my boat?
Tunnel thrusters are the most common installation: the unit lives permanently in a transverse tube through the hull, is simpler, and costs less. The trade-off is a small amount of drag from the tunnel openings. Retractable thrusters, like Lewmar’s Retractable 185TT, deploy only when needed and leave the hull fair the rest of the time, which is why they are the choice for performance boats where every fraction of a knot counts. For typical cruising boats, a tunnel thruster is the practical answer; go retractable only if hull drag genuinely matters to how you sail.
What should I know before installing a Lewmar thruster?
Placement and power are the two things that make or break a thruster installation:
- Tunnel position: install the thruster at the correct depth and distance from the bow — too shallow and it ventilates, too far aft and it loses leverage.
- Voltage: choose 12V or 24V to match your boat’s electrical system; the TT250 requires 24V, while the TT185 is available in both.
- Battery capacity: thrusters draw heavy current in short bursts — match battery capacity to the power demand, especially on 24V systems.
- Controls and wiring: use OEM Lewmar control panels, joysticks, and wiring kits so the system is protected and warrantied as designed.
- Test before launch: run the system on the hard and confirm rotation direction and controls to avoid drydock rework.
Frequently asked questions
What size Lewmar thruster do I need for a 35-foot boat?
A 30–40 ft boat is squarely in Lewmar TT185 territory: 110 lbs of thrust, available in 12V or 24V to suit your electrical system.
Can a Lewmar thruster be used as a stern thruster?
Yes — the TT185 and TT250 are designed for bow or stern installation, so the same unit can be fitted at either end of the boat.
Do I need 12V or 24V for a bow thruster?
Match the thruster to your boat’s electrical system. Smaller units like the TT140 run on 12V, while the TT250 requires 24V; the TT185 is offered in both voltages.
Are retractable thrusters worth it?
Only if hull drag matters to you. Retractable units like the 185TT keep the hull fair for performance sailing, but tunnel thrusters are simpler and the better value for most cruising boats.
Does a heavier boat need more thrust?
Yes. Displacement and hull shape drive thrust demand — heavier boats and deep-V hulls need more thrust than lighter, flatter hulls of the same length, so size up when in doubt.
Can I install a bow thruster myself?
Cutting and glassing the tunnel is a significant hull modification best done by a yard, but using OEM Lewmar wiring kits and control panels keeps the electrical side straightforward and safe.
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