What's Behind The Panel

Electrical and electronic topics for small boats
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What's Behind The Panel

Postby jimh » Sat Jun 27, 2020 7:53 pm

Most small boats have a helm area with a panel that contains electrical control switches. We look at the panel itself, what will be found on the panel, and what is behind the panel.

Typically an electrical panel on a small boat is fabricated from aluminum sheet made from an alloy like 6061 or 3003. The 3003 alloy is lower in strength and is softer than 6061, and may be easier to work with if making your own panel. Sheet plastic can also be used for panels. Traditionally electrical panels are black.

On an electrical panel one finds electrical switches used to control current to various loads. On small boats, the loads are principally lamps, pumps, or accessory outlets. For many years a pull-switch was common, and in particular brass knob pull switches from Cole-Hersee. A separate article discusses the Cole-Hersee switches. Classic bat-handle toggle switches are also used. Both the Cole-Hersee and the usual bat-handle toggle switch are through-panel mounted from the rear of the panel using a circular hole of appropriate size. More recently-built boats use a rocker switch in the CONTURA series from Carling. The CONTURA switches mount in rectangular holes with precise dimension to hold the switch in a snap-in mount. The CONTURA switches are installed from the front of the panel. The rectangular mounting holes must be made very uniformly, which can be difficult for home-made panel fabricators. Front-installation means a CONTURA switch must installed on the panel before attachment of any wiring behind the panel to the switch.

The CONTURA-series switches are available in many options for configuration, including contact arrangements, number of positions, switch action, illumination, and rocker actuator colors. Some boat builders use specialized configurations of switch contacts, which may not always be available as an off-the-shelf stocked item from electronic distributors. The switch terminals are also available in many options, but a common arrangement is a 1/4-inch push-on terminal intended to mate with a wire terminated in a mating connector, which allows compact and high-density wiring within the footprint of the switch. CONTURA switches are often seen arranged in rows or columns of multiple switches.

Wiring to the switches will usually be done with conductors of 16-AWG or larger. Wire insulation color is an indicator of the circuit function and follows a standard use for marine wiring. A color code for marine wiring and for particular manufacturers, such as Boston Whaler, is given in a separate article.

It is now common for boat builders to fabricate the switch panel, paint and letter it, install the CONTURA switches, and attach a harness containing all the wiring for the switches away from the boat. The finished panel is then moved to the hull for installation. Such panels will be wired to a multi-pole connector or connectors for most of the circuitry. The connector will mate with another connector installed in the boat hull to which all the loads have been pre-wired. Some individual circuits, such as the positive and negative high-current power circuits from a primary power panel may make a home-run to their power sources rather than pass through a connector.

It is common in modern boat building that all electrical conductors will have wire number markings applied to them at each end of their run. Schematic diagrams will indicate the wire number and the wire insulation color, and also the circuit function. A separate article looks at typical schematic diagrams and explains their nomenclature.

The wiring of 12-Volt DC power distribution and control circuits is not particularly complex, and on small boats the number of circuits involved is usually limited. All circuits will be protected by an over-current device, either a fuse or a circuit-breaker. In some installations, a special type circuit breaker that is also rated to be a circuit control switch is used, combining two functions into one device. More common on smaller boats will be a separate over-current protector distinct from the switch.

As mentioned, lamps are often a principal load. Lamps include lamps for navigation lighting, deck and cabin lighting, electrical panel lighting, instrument lighting, compass lighting, and so on.

Electrically operated pumps are another common load. Pumps for lifting water from hull sump areas (often called bilge pumps) are very common. On boats with below deck wells for holding fish there are also pumps to circulate water in the wells. Pumps for onboard freshwater from tanks for washing or bathing are also typical, but usually found only on larger boats.

Switches can also control power to accessory outlets such as USB charging outlets or the old-fashioned standard cigar-lighter socket.

Marine electronic devices may be a load controlled by a switch, but in most cases marine electronic devices have their own power ON-OFF switch and won't be controlled by a helm panel switch. Modern marine electronic devices sometimes have power switches that are not an actual mechanical switch, so the device will not power-on automatically when power is applied to its power leads.

In well-designed boats, the wiring harness for the electrical panel will have been left with enough slack to permit the panel to be unfastened and pulled out six inches or more in order to make working on the panel possible from the front of the helm enclosure rather than from behind the panel.