Bilge Systems: 3D-Printed Strainers, Brackets and Hose Guides

The bilge is the least glamorous compartment on any boat and the one that fails at the worst possible moment. Most bilge problems are not the pump itself: they are a bracket that vibrated loose, a strainer clogged with hair and sawdust, a float switch jammed by a stray cable tie, or a discharge hose that sagged into a loop and siphoned back. All of those are shape problems, and shape problems are exactly what a 3D printer solves cheaply.

This guide covers what is genuinely worth printing for a bilge system, what materials survive down there, and — just as importantly — the parts you should leave to certified marine hardware.

What the bilge actually does to plastic

Before choosing a part, understand the environment. A bilge is warm, permanently damp, and often contaminated with a cocktail of salt water, diesel drips, engine oil, glycol and gearbox lube. It vibrates constantly under way. It sees very little UV, which is one of the few things working in your favour.

• PETG is the sensible default. Good hydrolytic stability, tolerant of salt water, easy to print, and reasonably tough at bilge temperatures.
• ASA is worth using near the engine, where ambient temperatures can climb past 60 °C and PETG starts to soften.
• PLA does not belong in a bilge. It creeps under sustained load in warm, wet conditions and will slowly deform on a bracket that carries any weight.
• Nylon resists fuel and oil well but absorbs moisture and swells — fine for wear parts, poor for anything dimensionally critical.

If you want the full comparison, we went through it in detail in Best Materials for 3D Printing Boat Parts. For anything near the engine, also read up on chemical exposure in Fuel Systems and 3D Prints — a bilge under a diesel is a fuel-contact environment whether you planned it that way or not.

1. Pump mounting plates and brackets

Most submersible bilge pumps ship with a plastic strainer base designed to be screwed to a flat surface. Bilges are rarely flat. The usual bodge — a lump of plywood shimmed with washers — rots, and the pump ends up sitting at an angle that leaves 30 mm of water it can never reach.

A printed mounting plate solves this properly. You model a wedge with the exact angle of your hull section, so the pump base sits horizontal and the intake sits as low as the sump allows. Add:

• Countersunk holes matched to your pump's factory screw pattern.
• A raised lip so the plate cannot slide when bonded down with sealant.
• Drainage channels underneath, so water does not sit trapped between plate and hull.

Print it solid-ish — 4 perimeters and 40% infill — and bond it with a marine adhesive sealant rather than drilling the hull. We covered the adhesive approach in Drill-Free Mounting, and the same logic applies below the sole: fewer holes in a boat is always the better outcome.

2. Strainer baskets and debris screens

Every bilge collects debris. A printed strainer basket that sits around the pump intake is one of the highest-value parts you can make, because it is a pure geometry problem: you need open area, small enough slots to stop the junk, and easy removal for cleaning.

Some rules that make a real difference:

• Slots, not round holes. Vertical slots 3–4 mm wide give far more open area for the same blocking performance, and they self-clear better.
• Open area matters more than you think. Aim for at least four times the pump intake area, or the strainer becomes the restriction and your rated flow collapses.
• Make it removable without tools. A twist-lock or simple snap fit means it actually gets cleaned. A screwed-on basket in a dark bilge never does.
• No horizontal bridges. Print baskets vertically so the slots come out as clean vertical walls rather than sagging bridges.

3. Float switch guards

A float switch fails in two directions, and both are bad. Jammed up, the pump runs dry until it burns out or flattens the battery. Jammed down, the boat fills quietly. Almost every jam is caused by debris or by a hose or wire fouling the float arm.

A printed cage around the switch — open at the bottom, closed on the sides, with generous slots — costs about 40 g of filament and removes the most common failure mode in the whole system. Give the float at least 10 mm of clearance on every side of its swept path, and make sure the cage cannot trap a floating wrapper against the float.

While you are down there, tidy the wiring: printed clips and gland covers stop the very cables that jam the float. There is a full walkthrough in Tidy Boat Wiring.

4. Hose supports and anti-siphon geometry

A bilge discharge hose that sags creates a low point. Water sits in that low point, and on the next pump cycle the pump has to shift it again — or worse, the standing column siphons back into the bilge and the pump short-cycles all night.

Printed hose saddles that clip to a bulkhead and hold the run at a constant rise fix this for pennies. Print the saddle in PETG and line it with a strip of TPU or rubber so the hose is not chafed by a hard plastic edge — the chafe-guard approach from TPU on Board works well here.

You can also print spacers and standoffs that hold the vented loop clear of the hull liner, and labelled collars that identify which hose is which — a small thing at three in the morning with a torch in your teeth.

5. Adapters, reducers and blanking plugs

Bilge plumbing is a museum of mismatched sizes: 19 mm pump outlets into 25 mm hose, a 3/4" BSP skin fitting that meets an imperial hose, a manual pump with a barb nobody stocks any more. Parametric barbed adapters and reducers are ideal here because you can dial the exact two diameters you need instead of buying three wrong parts first.

Two references worth reading before you print one: How to Measure a Hose and Thread for getting the dimensions right the first time, and How to 3D Print Watertight Boat Fittings That Hold Pressure for wall thickness, perimeter count and the sealing details that decide whether a fitting weeps.

Ready-made parametric fittings are in Plumbing & Pumps, and there are free files to test your printer's tolerances in Free Files.

Print settings that hold up down there

Setting	Recommended	Why
Material	PETG (ASA near engine)	Water and temperature tolerance
Perimeters	4 minimum, 5 for pressure parts	Perimeters carry the load and the seal
Infill	40–60% for brackets, 25% for cages	Vibration resistance without waste
Layer height	0.20 mm	Good layer bonding, sensible print time
Orientation	Load across layers, never along them	Layer adhesion is the weak axis

Orientation is the single biggest strength variable in a vibrating environment. There is a longer treatment in Print Orientation and Strength.

What not to print

The bilge is a place to be conservative, because the failure mode is the boat filling with water. Leave these to certified hardware:

• Through-hulls and seacocks. Never. These are the parts that keep the sea out, and they must be certified components in bronze or approved composite.
• The pressurised discharge fitting at the skin. Use the manufacturer's fitting and a double hose clamp.
• The high-water alarm float itself. Print the guard, buy the switch.
• Anything that replaces a hose clamp. Stainless does this job; plastic does not.

A useful rule: print the parts that organise the bilge system, buy the parts that contain water under pressure or below the waterline.

A safety note

3D-printed parts are not certified marine equipment. Nothing in this article should be fitted below the waterline, in a through-hull position, or as part of a safety-critical system such as a high-water alarm or an emergency dewatering path. Always verify that your chosen material is suitable for the fluids, temperatures and loads involved, test the part before you rely on it, and keep a manual backup pump and a bucket aboard regardless of what your bilge system looks like.

Start with one part

If you print one thing from this list, make it the float switch guard. It takes an hour, costs almost nothing, and eliminates the failure that sinks more boats at their moorings than any other bilge problem. The strainer basket is a close second.

Browse the full catalogue at all products, or head straight to Plumbing & Pumps. If you need a bilge part in a size we do not list, write to info@marinelab3d.com — most of our files are parametric, so an unusual dimension is usually a settings change rather than a new model.