In the Fiberglass Tunnels section, you will find the fiberglass tunnels needed for installing a bow thruster from several manufacturers: Lewmarin's 185x6x1000mm tunnel, MaxPower's 125 and 185 mm tunnels in different lengths (0.75–1 m), Sleipner's 185 mm tunnel, and general-purpose 110–140 mm tunnels.
Why are tunnel diameter and material important choices?
The tunnel is the hull structure through which the bow thruster propeller pushes water sideways – the diameter of the tunnel must be chosen precisely according to the power and propeller size of the bow thruster motor to be installed, as an incorrectly sized tunnel will either limit power or not be suitable for the motor at all.
Fiberglass is a popular material for tunnel construction because it is lightweight, highly resistant to seawater, and does not rust unlike metal structures – this is important because the tunnel is constantly submerged and exposed to water stress throughout the boat's life.
The length of the tunnel depends on the width of the boat's hull at that point - the tunnel should extend completely through the hull on both sides with sufficient margin to allow the installation to be laminated tightly to the hull without the risk of leakage at the joints.
Tunnels from different manufacturers (Lewmar, MaxPower, Sleipner) are designed to be compatible with their own bow thruster engines, so it is worth choosing a tunnel primarily based on the manufacturer of the engine to be installed to ensure compatibility.
Installation is a significant hull penetration that affects the structural durability of the boat – it is always advisable to have this work done by a professional or at least strictly following the manufacturer's instructions, as poorly done installation can cause a serious risk of leakage.
Before ordering, it is a good idea to accurately measure the thickness of your boat's hull and the available space at the installation site so that the selected tunnel fits your boat exactly in terms of both length and diameter without additional adjustments.
The inner surface of the tunnel should be as smooth as possible so that the water flow through the propeller is efficient and unnecessary vortices are not created – a rough or uneven surface can significantly reduce the efficiency of the bow thruster from the value stated by the manufacturer.
Replacing an old tunnel with a new one is a significantly larger project than simply replacing the engine, so it is worth carefully assessing the condition of the tunnel even before the initial purchase of the bow thruster to ensure long-term use.
Always seek installation advice from a certified boat builder or the technical support of the bow thruster manufacturer if you are unsure of the exact tunnel design and installation method required for your particular hull.
Always ensure that the lamination work is done with appropriate materials to ensure long-term water tightness.
