Installing a A Deckwash Pump
By Don Casey
Revised by BoatUS editors in April 2012
Sluicing the cockpit with buckets of water after boating a fish is a poor second to hosing it clean. And bringing a builder's acre of muck aboard when you haul up the anchor is a lot less irritating when you can repatriate it immediately with a powerful water jet. A deckwash pump makes a fine addition to almost any boat, and equipping your boat with one is not difficult.
Choosing a pump
Select either a flexible (or rigid vane) impeller pump or a diaphragm pump. Centrifugal pumps-like the one in your bilge-can move a lot of water, but they are not very good at lifting it, making them a poor choice for deckwash use. Most marine pump manufacturers offer pumps intended for deckwash use. Kits are also available that include the appropriate pump, a check-valve, a pressure switch, and hose adapters.
If you are going to install the pump in an exposed area, choose one that specifies that it is suitable for wet locations.
Mounting the pump
Virtually all deckwash pumps have "feet" with holes through their centers for a screw or bolt. The pump should be securely fastened to some rigid part of the boat, but never install screws directly into the hull. If you do not have an appropriate platform for the pump, you may need to bond one in place. Pumps do not have to be mounted horizontally; they can be fastened vertically to a bulkhead if that is more convenient.
A rigidly-mounted pump can be unacceptably noisy, magnified by the shape of the hull. This is rarely a big concern with a washdown pump, and most come with rubber grommets in the mounting holes to isolate the vibration. Still, you can achieve an even quieter installation, by mounting the pump on rubber hose. Though-bolt the pump to the wall of two short lengths of heavy-duty rubber hose, then screw the hose to the boat.
Electrical connections for a deckwash pump are straightforward-positive (red) to positive (red) and negative (yellow or black) to negative (yellow or black). Resist the temptation to pick up the power for the pump from the nearest pair of wires. A washdown pump can draw 10 amps or more, which can dangerously overload a lighting circuit. The safest course is a dedicated circuit with a new fuse or breaker in the main electrical panel. If your boat doesn't have an electrical panel, connect the pump directly to the battery, with a fuse in the positive side of the circuit. Locate the fuse as close to the battery terminal as possible. In the positive side of the circuit you will also need a conveniently located switch.
If the pump is no more than 15' (wire distance) from the panel (or battery), use 10-gauge wire. For more remote mounting-up to 30'-you'll need 8-gauge. Scrimping on wire size will lower the output and shorten the life of your pump, not to mention the potential fire risk.
Make all wire-to-wire connections with crimp butt connectors, waterproofed with adhesive-lined heat shrink tubing. Use crimp-on ring terminals for screw-terminal connections. Never wrap a bare wire around a screw terminal to make a permanent connection, and do not use wire nuts. Proper crimp terminals are inexpensive and easy to install, and the necessary tool costs less than $10.
Supply the deckwash pump from an existing through-hull fitting, typically either the galley or the head intake. A Y-connector lets the through-hull do double duty. It is not a good idea to use the engine intake because that puts the engine and the washdown pump in competition for the available flow, and because a failure in the washdown pump could cause the engine pump to lose prime. Fitting the pump with an intake hose you can drop over the side when you want to use the pump is another alternative. Double clamp all hose connections below the waterline.
A strainer in the supply line is essential. If the raw-water line already has a strainer, install your Y-connector on its outlet side. Otherwise, you will need to add a strainer between the through-hull and the pump. A small, in-line strainer is adequate.
Pumps push better than they pull, so mount the pump as near the through-hull as practical. A check valve installed in the hose connected to the other side of the Y-connector will prevent prime problems and eliminates the need for manual valves. A second check valve is required on the outlet side of the pump to prevent backflow, but most deckwash pumps are equipped with this valve.
The washdown hose can be connected directly to the outlet on an exposed pump. When the pump is mounted below deck or in an enclosed location, connect it with plastic hose to a conveniently located deck outlet. An unobtrusive male hose connector is normally adequate because flow is controlled with a nozzle on the hose, and the pump is switched off when not in use.
One pump can supply multiple outlets, including a faucet at a fish-cleaning station or a recessed shower for cockpit bathing. In an emergency, it can double as a bilge pump. And with a little ingenuity, it can even get you home when the raw-water pump on your inboard engine fails.