What Is a Dry Bilge System?
- Neptunian Sky
- Mar 7
- 3 min read
A "dry bilge system" refers to a low-volume pump system designed to remove the last few inches of standing water from a boat's bilge, minimizing moisture-related issues like odors, mold, mildew, and corrosion. The primary function of a dry bilge system is to keep a boat's bilge area as dry as possible to reduce or eliminate excess moisture. Almost every bilge has some level of standing water, as even the best designed bilge pump is limited by size and placement and leaves a small amount of water around the intake. While traditional bilge pumps are designed for high-volume water removal in emergencies, dry bilge systems are focused on continuous, low-volume operation to maintain a dry bilge environment.
Water can get trapped in the pockets of stepped hull boats, storage lockers or bilge compartments that don’t drain well, and sections of the bilge with minimal access. This stagnant water can accelerate the growth of mold, mildew and odors, and when the water evaporates it can create an even stronger moisture-rich environment. Dry bilge systems use small, low-volume pumps to continuously remove small amounts of water from the bilge, ensuring the water doesn't accumulate.
There are two types of dry bilge systems: vacuum systems and diaphragm pump systems. Vacuum dry bilge systems include a processor, compressor, and collection chamber which moves air in and out of the chamber. A loss of vacuum keeps the system active, and the system continues to pull water, then air. The bilge pickups are connected to the chamber by thin tubing. This tubing cannot be adjusted in length. For discharge, the air direction is reversed, and vacuum is created in the collection chamber which draws the liquids out through the tubing.
Disadvantages of a vacuum or valve-controlled multi-zone dry bilge systems include:
Failure of the single vacuum pump or valve-controlled diaphragm pump renders the entire system unusable.
Debris, dust and moisture can clog the switching valves and degrade pump performance or require frequent cleaning.
Worn seals, gaskets or valves lead to vacuum leaks and can affect pump performance.
Vacuum pump system constraints and requirements to maintain minimum and maximum length tubing result in installation challenges.
A complicated design of switch, processing and valves.
Vacuum systems are expensive with a difficult repair process.
Diaphragm pump dry bilge systems include: a pump enclosure with one or more small, low-volume diaphragm pumps designed for continuous operation even when dry, remote water pickups which allow the pump to access water from multiple areas of a boat’s bilge, and tubing which connects the pump to the pickups and the pump to an existing overboard drain or tank. A diaphragm pump uses a reciprocating diaphragm made of rubber, thermoplastic, or Teflon, and has valves on either side of the diaphragm to control the flow of fluid. BILGE-B-DRY Dry Bilge System has one to four small diaphragm pumps within the pump enclosure. The enclosure has a 7”x7” footprint and stands 4” tall. The water pickups are attached to the pump enclosure via ¼” PVC tubing and can be placed anywhere in the bilge up to 10-20' or more from the pump unit. Water is drawn from the pickups through the tubing and then pumped through the outlet tube to an existing overboard drain, shower sump, etc. The number of pickups sold with the BILGE-B-DRY pump correlate to the number of diaphragm pumps within the enclosure – one to four. To remove water on a small boat, the single pump unit is adequate. To remove water from multiple areas, like the steps of a twin-stepped monohull, a multi-pump system with two to four pumps is a better choice.
Benefits of a diaphragm pump dry bilge system include:
The diaphragm pumps can run even when a boat’s bilge is dry.
Compared to other dry bilge systems, the cost is much less, especially for a multi-pump unit.
Failure of the system is easily repairable.
The footprint is much smaller and can be installed in any orientation.
The water pickup internal material consists of a sponge and filter and is easily replaceable if clogged or dirty.
BILGE-B-DRY is equipped with multiple ways to activate the system: with its own pre-programmed schedule, the free customizable Mobile App, or connection to a helm switch or water sensor.
Remember, even standing water in small amounts of less than two inches can become the source of boat cabin odor, mold or mildew in fabrics and fiberglass, high humidity below decks, condensation damage on engine room machinery, electronics, and metal components, and hull corrosion or osmosis. Additionally, standing bilge water can prevent a boater from finding the source of a leak or damage, can increase maintenance costs and even reduce a boat’s resale value. Ensuring a clean, dry bilge is helpful to maximize enjoyment of your boat! Learn more about BILGE-B-DRY at www.neptunianskyllc.com or click on one of the best-selling BILGE-B-DRY pumps below:
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