Bilge Basics

What is a bilge?

Basic Sailboat Bilge System
The bilge is a chamber at the lowest point of the ship that resides under the waterline. Water that is spilled in the craft, makes it past a through hole fitting, or makes it past the vapor barriers during rain all makes its way into the bilge via engineered channels. This is also often where grey-water ends up, though usually a septic tank is in place to catch water from the head.

All boats take in water and all boats have a bilge to collect said water. The stations and bulkheads often have holes in the bilge area to allow fluid to flow to the lowest point. This is where the primary pump is located. The pump then pushes the water up above the waterline and out an exterior drain through a seacock.

How does a bilge pump work?

Basic Bilge System Components
Modern boats usually have two electric pumps and a manual pump. The bilge pump is a class-A critical system and usually has a second pump as a backup, often running off it's own backup battery. The manual pump is in place as a last resort in an absolute emergency. The pump has a float sensor much like a toilet that detects when the bilge is full enough that the pump can initiate. When this happens the pump begins moving fluid out the outside drain hole and into the water.

Environmental Concerns

Typical Through-Hull Seacock
It is against the law to pump black water or oily discharge into the public waterspace. Cleaning, treating, and segregating fluids that can contaminate the environment are absolutely critical. This concern has driven the development of numerous waste treatment systems to be placed inline to manage bilge contamination. As one could imagine such systems vastly complicate the bilge.

Bilge System Importance

There is NO MORE IMPORTANT SYSTEM than the bilge management system! It is expected for you to maintain redundancies, functional alarms, and backup power to ALL bilge systems! If your bilge monitoring or management system fails you can VERY easily lose your craft to the inky seas.

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