Lewmar Thruster Selection Guide (PDF)

SELECTION GUIDE

Size a Lewmar tunnel, retracting or swing thruster by boat length and boat type, and place the tunnel for best performance.

DocumentLewmar Thruster Selection Guide

FormatPDF · 1 page · 0.1 MB

LanguageEnglish

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How to Choose Tunnel Thrusters Retracting & Swing Products

How to Choose the Right Thruster for Your Boat

What sizes a thruster

Performance on a given boat depends on the wind area, the lateral wind draft area and where the tunnel sits in the hull.
From these you get the wind pressure on the boat and its centre point, and from that the thrust needed to counter it at the chosen thruster position.
For full control fit both a bow and a stern thruster, and leave the main engines to drive the boat ahead and astern.

Thruster position

Final position depends on the internal and external construction of the boat.
As far forward as possible to maximise the lever effect (Fig. 1 in the PDF).
1 × Ø below the waterline (0.75 × Ø minimum) so the tunnel does not suck air (Fig. 2). Ø = tunnel diameter.
Minimum suggested tunnel length 2 × Ø. Fig. 2 also marks a minimum of 100 mm (4") at the bottom of the optimum area.

Boat size, type and shape

Each thruster has three bars on the chart, one per boat type: high control / heavy boat, medium control / medium displacement and light control / light displacement.
For the same thruster, the heavy-boat bar covers shorter boats than the light-displacement bar: heavy displacement / high windage boats need more thrust.
Find your boat length in the column for your boat type and read off the thruster on that row.

Tunnel Thrusters – Boat Length Overall

Lewmar tunnel thruster selection chart by boat length and boat type

Lewmar's own selection chart, reproduced from the PDF. 300TT 10.8 and 250TT HYD share one row. The metric scale prints "21 m" at 50 ft (as printed); use the ft scale.