How do I install a bilge pump in a fibreglass boat?

Mount the pump low in the bilge on a bonded pad or suitable existing bracket, then run reinforced discharge hose to an outlet positioned above the waterline. Fit a dedicated fused supply, automatic level control and manual override, then test the installation by filling the bilge with clean water.

Choose the pump and position

With the boat afloat at its normal trim, establish where water collects and check that water can reach that point through the limber holes. A pump in the wrong compartment will leave water trapped elsewhere.

Allow access to clean the strainer and operate the float switch. On some yachts, particularly those with deep keel sumps, a remotely mounted diaphragm pump with a suction strainer is easier to maintain than a submerged centrifugal pump.

For a small boat, a 12V centrifugal pump rated at around 500 to 1,100 US gallons per hour is a common starting point. Larger boats usually need more capacity and separate pumping arrangements. Advertised output normally assumes little or no lift, so check the flow curve for your installation. A routine bilge pump cannot be relied upon to cope with a major hull breach.

• Match the pump voltage to the boat's supply.
• Buy compatible automatic control: an integral sensor or a separate float switch.
• Match the hose to the discharge spigot; 19mm and 25mm are common sizes, but larger pumps need larger hose.
• Retain an independent manual bilge pump.

Mount without piercing the hull

Do not drive mounting screws directly into the hull laminate. Bond a mounting pad to sound fibreglass, then screw the removable pump strainer base to the pad. An existing structural mounting platform is another option if you know its construction and thickness.

1. Remove oil and dirt before sanding, then strip paint or bilge coating from the mounting area to expose sound laminate.
2. Prepare an epoxy-encapsulated marine plywood pad, typically 12 to 18mm thick, large enough for the base and its screws.
3. Abrade and clean the bonding surfaces as the epoxy manufacturer specifies, then bed the pad in thickened marine epoxy with a fillet around its edges.
4. Allow a full cure before drilling pilot holes and fitting stainless screws short enough to remain entirely within the pad.

Wear gloves, eye protection and a suitable dust respirator when preparing fibreglass and handling epoxy. Keep the strainer removable. Position a separate float switch where it cannot catch against the hull, wiring or hose.

Prevent back-flooding through the discharge

Use smooth-bore reinforced hose suitable for bilge discharge, with the shortest practical run and broad bends. Avoid reductions, kinks and unnecessary elbows: each reduces delivery.