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MOUNTING TYPES – Surface Mount / Thru-Hull / XFM / Weld-In

When choosing underwater lights for a boat, you need to understand the different mounting / fixing type and why each might be used. Different mounting styles determine how the light is installed, how big your hole cut-out will be, and how easy the system will be to maintain over time.

Underwater lights are commonly available in three mounting styles: Surface Mount, Thru-Hull, and XFM (Exchangeable Flush Mount). Each type offers different advantages depending on the boat, the owner’s installation preferences, and the desired lighting performance.

Surface Mount

Surface mount lights are installed directly onto the exterior surface of the hull or transom, typically requiring only a small 12.5mm (half inch) hole for the power cable. The light bezel/body sits on the outer hull surface.

This style is often best for small and medium size boats, anything up to 75ft.

Pros

  • Easiest and fastest installation 

  • Minimal hull cutting required. Just one hole for the cable to pass through

  • Often the most cost-effective option 

  • Ideal for small to medium size boats

Cons

  • Light fixture sits proud of the hull surface 

  • Can be more exposed to impacts

  • Typically offers fewer fixture lumens (less light) than bigger lights

  • Light internals cannot be serviced or changed 

 

Thru-Hull

Thru-hull lights require a relatively small hole drilled through the hull, allowing the shaft of the light body to pass through while the bezel/body sits on the outer hull surface. For example, some OceanLED thru-hull models require a cut-out of 25 mm (1”) while still delivering significant light output and advanced optics. 

Pros 

  • Big fixture lumens figures (very powerful)

  • Strong light penetration and performance 

  • Smaller cut-out sizes compare to XFM 

  • Available with light angling technology for awkward hull angles 

Cons

  • The light internals cannot be serviced or changed 

  • More expensive than surface mount lights 

  • Require external drivers

 

XFM (Exchangeable Flush Mount)

XFM stands for Exchangeable Flush Mount. These lights are designed to sit flush with the hull surface, creating a sleek, integrated appearance. The light cartridge can typically be removed and replaced from inside the vessel, meaning the boat does not need to be hauled out for servicing or upgrades. 

XFM lights often incorporate advanced optics and adjustable angling technology to optimise the light beam in the water. 

Pros

  • Light cartridge can be replaced from inside the boat 

  • Once the mounting tube is in place, you’ll never need to drill another hole 

  • Servicing is easy

  • Massive fixture lumens figures (Very powerful)

  • Advanced optics and high light performance 

  • Completely flush installation for a clean look 

  • Reduced drag and minimal protrusion from the hull 

Cons

  • Larger hull cut-out required compared with surface mount or Thru-Hull 

  • Installation can be complex due to the bigger hole cutouts and 

  • Usually higher cost than surface mounted lights

 

Weld-In 

Weld-In underwater lights are welded directly into the hull itself. These lights use large steel or aluminum cofferdams (housings) that sit into the hull and protrude into the inner void within the yachts hull. Weld-In underwater lights are found predominantly on superyachts due to their size and will always be the most powerful option in terms of their fixture lumen output. 

Pros

  • Excellent serviceability, light cartridges can be replaced from inside the hull

  • No haulout requirement for replacing lights

  • Incredibly powerful 

  • Excellent heat dissipation ability 

  • Advanced underwater optics for extreme performance

Cons

  • Only viable for yachts due to their size and weight 

  • Installation requires specialist welding equipment and experienced installers 

  • Significantly more expensive than Leisure Marine oriented underwater lights

 

Choosing the Right Mounting Type

Each fixing type offers a balance between installation complexity, appearance, price and performance.

  • Surface Mount is ideal for smaller and medium size boats. Anything up to 75ft. 

  • Thru-Hull is for those that want the big light performance, but don’t like the idea of drilling a 4-inch hole in their boat. 

  • XFM provides the most integrated, high-performance solution, often preferred for premium installations or larger boats. It’s the best of all worlds and gives you longer servicing capability, but comes with the premium price tag. 

  • Weld-In is almost exclusively for yachts and super yachts with a metal hull.

Understanding these options helps boat owners choose the best underwater lighting solution for their vessel and installation requirements.

You can learn more about our underwater light range here. 

If you have any questions, ring one of our friendly team on:

UK: +44 1455 637505
USA: +1 (954) 523 2250