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Cockpit Sump Pump

This article describes the cockpit sump (or "bilge") pump wiring and plumbing commonly used in larger Boston Whaler boats.

Cockpit Sump

Because of their unique construction, Boston Whaler boats do not have the usual hull interior space or bilge. What would normally be the bilge on most boats is filled with foam. Boston Whaler boats do have a cockpit sump area, designed to be the lowest point in the hull where water would collect. On most hulls the sump also has a through-hull drain. In the smaller boats, the drain faces aft and exits through the transom, allowing water to be removed while underway by merely opening the drain. Gravity and suction will evacuate any water in the sump.

On larger Boston Whaler boats with interior hull cavities for fuel tanks, the sump area is generally molded on the starboard side of the boat at the rear of the center cavity. Typically the sump is covered by a small hinged hatch. The hatch was intially made from teak veneer plywood, then later changed to a non-wood material such as King StarBoard®. The drain for this sump normally goes directly down through the hull and is not angled aft through the transom. Since the position of this sump is slightly below the static waterline, this drain is often left plugged when the boat is in the water. If left open water will enter from the sea and fill the sump. Depending on the loading on the boat, the level to which the water will rise will vary. If the boat's static trim makes it sit low in the water and down by the stern, water can accumulate in the sump and overflow onto the cockpit floor, also entering the rigging tunnel and perhaps the central hull cavity. If the boat's static trim is high and not down by the stern, only a small amount of water will enter the sump from the sea, and the drain can be left open. In this state the boat is self-draining and will not accumulate rain water, etc. The entire cockpit area generally drains into this sump, so water that splashes aboard will accumulate in it during normal operation. The capacity of the sump is limited, perhaps only a gallon or so, and once the sump has filled, water can begin to drain forward into the fuel tank cavity and the wiring tunnel to the console. For this reason, it is desirable to prevent water from accumulating and overflowing the sump.

When the boat is underway, if the drain plug is removed, water will drain from the sump to the sea due to the Venturi effect of the open drain on the hull, which is aided by the clamshell covering on the hull bottom.

When boats with bilge sumps described above are stored on trailers or otherwise off the water, the drain for the bilge sump should be removed. If the drain is not removed, any water coming into the cockpit, such as rain water, will fill the sump, flow into the internal tank cavity, flow into the tunnel, and, if the boat is stored fairly level, even flow forward and begin to fill the lockers and compartments in the bow of the boat. The only exit for water accumulating in the cockpit is to rise to the level where it can overflow the engine well bulkhead and escape through the engine well drains. This can mean a large volume and weight of water can be contained in the cockpit if the bilge sump is left plugged. Beside water damage, the weight of a large volume of water can create problems for the hull and its support. This can be avoided simply by leaving the sump drain unplugged during off-water storage.

To remove water from the bilge sump when the boat is in the water and being used, Whaler provided an electric pump as standard equipment on many models, and as an option on others. The pump is typically a RULE centrifugal pump with a capacity of about 1,000-1,500 GPH that permits it to empty the sump in a just a few seconds of operation. The pump is located as deeply as possible in the sump, and may actually be slightly lower than the drain hole, the hole having been intentionally located to create space for the pump at the sump bottom. The pump exhaust is carried on a 1-1/8 inch hose, up through the teak hatch, and to a through-hull fitting located on the starboard hull above the waterline.

Pump Operation

Float Switch

To provide automatic operation of the pump, a float switch is also located in the sump, slightly above and outboard to the pump. By the time the float switch is actuated by rising water, there will be about two inches of water in the sump. The typical float switch is a RULE 15-Amp capacity switch which uses a mercury switch contact.

Location of Float Switch

It is important to note that for the bilge pump system to work properly, the float switch which actuates the pump must be located slightly above the level of the pump intake. If the float switch were to be located below the pump, water could cause the float switch to activate the pump, but the pump would be unable to remove the water. A system configured like this would soon drain the battery, since the pump would be running continually, trying in vain to remove water it could not reach.

The bilge sump area is often a sloping surface (because of the vee-bottom of the hull), and this creates other considerations in the mounting of the float switch. First, the switch should be oriented so that the axis of its pivot is inline with the keel. This will prevent the switch from binding when it tries to float up and actuate. Then, the axis of rotation of the switch should be placed outboard. The switch uses a Mercury liquid switch as the electrical contact, and to orient it the otherway would have the same effect as raising the float lever by an amount equal to the slope of the hull.

Console Controls

A three-position toggle switch and indicator light are mounted on a small escutcheon on the helm console. (You can identify factory installations because the escutcheon plate has a Boston Whaler logo on it.) The switch provides choice of AUTOMATIC, OFF, or MANUAL operation of the pump. The MANUAL position of the switch is a momentary contact, which requires the switch be held in this position by the operator to run the pump. This prevents the pump from inadvertently being left running for long periods of time. (Long operation of the pump might not damage the pump but it would rapidly drain the battery.)

The AUTOMATIC position of the switch allows the pump to be operated by the float switch.

The OFF position of the switch disconnects electrical power to the pump and it cannot operate.

A small indicator lamp illuminates whenever voltage is applied to the pump motor, and it works in either the ON or AUTOMATIC positions of the switch. This provides a visual indication of pump operation.


The factory installed electric bilge pump is wired in a straightforward manner and follows good marine electrical practice. The following is based on the installation in my own Whaler, which I believe to be unaltered from the original configuration as delivered from the dealer, but on further reflection, I am beginning to wonder if it truly is in "stock" condition. More investigating will tell, but in the interrum, here is the description:

The details of the wiring are shown in the diagram below. The wires entering the tunnel are run inside a vinyl sheath. At the exit from the tunnel at the sump, the wires terminate in a three-pin connector. Wiring to the pump and float switch is terminated in a mating connector. This connector is retained by clamps at the top of the bilge sump, but if the sump fills the connector may become submerged. It appears as if the connector is not water-tight, but precautions are taken to prevent entry of water by wrapping it tightly in electrical tape.

The use of a connector at this point is a bit questionable, since there is risk of exposure to water and possibly even total submersion of the connector. The connector does permit the installation or replacement of the float switch and bilge pump as a plug-in assembly. It also avoids having to snake wires through the tunnel when installing or replacing the pump wiring. This may have been part of the motivation for using a connector at this point.

Beyond the connector, there are three splices which accomplish the actual connections to the pump and switch. These are made using butt splices, crimped and soldered, which are then protected by heat-shrink tubing. These connections are not 100% water-tight, but are much more so than the connector mentioned above.

Excess lead length and the splices are folded and retained under the same clamps which retain the connector, again at the top level of the sump.

Also running through the sump area are the fuel lines from the tank, along with engine control wiring and other cables using the tunnel for access to the helm console. It can get crowded in there! These remaining wires and cables are not retained by clamps, but lay in position and are arranged so as not to interfere with the float switch operation.

The Whaler wiring follows recommended marine wiring color codes. The negative lead is WHITE, the pump wiring is BROWN. To differentiate between the ON and AUTOMATIC feeds, a black tracer is added. Leads to the float switch are GRAY. The pump uses BROWN and BLACK.

The location of so much excess wiring associated with the pump and float switch in the sump itself has me wondering if the original installation was made by running the wires under the gunwales. The length of the leads looks about right to permit that. Again, not having owned the boat since new makes it hard to tell. (Update: I have since acquired another Boston Whaler with a factory installed sump pump, and its wiring is run under the gunwales, not through the rigging tunnel. All splices are above the cockpit level, that is, above the waterline.


Schematic Diagram
Whaler Sump Pump Wiring
The negative lead is shown in yellow but is often actually white. Wiring is generally AWG-14 or AWG-16, as appropriate for length of the conductor and load.
Drawing: JWH.


Comments About the Design

Battery power to the bilge sump pump is provided from the main console distribution bus. If the main house circuit breaker or the main battery switch is disconnected, the pump cannot operate. For boats stored on trailers, this may not be a problem. When the boat is not in use the battery is switched off and the sump is drained by opening the plug. In other situations, however, the factory wiring arrangement may be an operational problem.

For example, if the boat is to be left in the water on a mooring and it is desired to have the pump operate automatically, both the main battery switch and the house circuit breaker must be left on. This distributes battery power to the entire boat. This may not be the best practice, both in terms of safety and convenience. If a cabin light is left on or other unintended electrical loads remain connected, the battery will soon be discharged. Also, battery voltage is distributed about the boat, creating greater potential for problems than if it were disconnected.

An alternative would be to provide the float switch with a separate source of battery power, running through a fuse directly to a battery terminal. (Locate the fuse as close as possible to the battery!) By wiring it in this manner, the main disconnect and house circuit breakers could be left off, yet the float switch would still be able to power the pump.

Correct installation of such a direct battery connection would require re-wiring the AUTOMATIC-OFF-ON switch so as to not back feed the entire house distribution panel from the float switch connection. One such arrangement is shown below. This design utlitizes most of the existing wiring.


Schematic Diagram
Whaler Sump Pump Alternate Wiring
This arrangement permits automatic operation of the pump with all other circuits switched off. The negative return to the battery must be common if there is more than one battery, and it must not be interrupted by the circuit breakers or disconnect switches. The negative lead is shown in yellow but is often actually white. Wiring is generally AWG-14 or AWG-16, as appropriate for length of the conductor and load.
Drawing: JWH.


Caution Advised

Wiring of low-voltage/high-current circuits can be hazardous because of the extremely high short circuit current capacity that exists when working with large batteries. All the information provided is believed to be accurate and representative of techniques and practices in common use in the marine applications described. Examine any wiring carefully for proper configuration before applying power. Low-voltage/high-current short circuits can produce extremely rapid heating and can be dangerous. Never wear a ring or metal jewelry when working with high-current sources like storage batteries.

Comments or Questions

If you have a comment or question about this article, please post it in the Whaler Forum.

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Copyright © 1999, 2000, 2018 by James W. Hebert. Unauthorized reproduction prohibited!

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Author: James W. Hebert
This article first appeared February 10, 2001. A revised version appeared February 14, 2001. The HTML was tweaked in May 2018.

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