Motor, electrical and technical equipment in boats

Modern boat building work goes far beyond wood and fibreglass. Engines must be fastened correctly hull penetrations below the waterline must be reliable and electrical installations must work in an environment where moisture and salt water constantly work to break down metal and insulation. Here are some of the technical disciplines that are part of the trade today.

§Motor foundation and motor installation

The motor foundation must transfer the motor's forces to the hull without shifting and at the same time keep the shaft correctly aligned toward the propeller. Good vibration damping in the foundation limits wear on motor, shaft, bearings and hull and reduces the noise and vibrations that would otherwise spread throughout the boat. Access for service is also part of a good installation — a motor no one can reach will not be maintained properly.

§Feedthroughs below waterline

Any opening in the hull below the waterline — for cooling toilet log or other — is a potential weakness. Therefore penetrations are supplied with a shut-off valve so you can quickly stop water ingress if a hose or pump connected to it fails. The material choice matters: brass can dezincify in salt water where the zinc content is leached out and the material becomes porous and weak therefore bronze is preferred for critical penetrations below the waterline.

§Galvanic corrosion

When two different metals are connected in salt water, a galvanic element forms where the least noble metal corrodes faster than it otherwise would. That's why boats have sacrificial anodes—typically of zinc—that are less noble than propeller, shaft, and other metal parts and therefore corrode first and protect the rest. The anodes must be checked and replaced regularly because when they're exhausted, the other parts lose their protection.

§Electrical installations on board.

Most of the boat's electrical consumers run on low-voltage direct current, typically 12 or 24 volts from batteries, because it is more robust and safer in a damp, moving environment than 230 volt alternating current. Equipment placed in or near engine and fuel compartments must be ignition protected according to current standards, so sparks from, for example, a switch cannot ignite flammable vapours. Cable routing, fuses and corrosion-resistant connections are just as important as the components themselves.

§CE marking of pleasure craft

The Recreational Craft Directive (2013/53/EU) covers all recreational vessels with a hull length between 2.5 and 24 meters and sets requirements for, among other things, construction, stability, buoyancy, visibility from the control station and rescue facilities. The Danish Maritime Authority is the notifying authority for the CE marking system in Denmark, while the Safety Authority handles market surveillance. As a craftsperson, you should be aware that major modifications — such as an engine replacement — can affect matters covered by the marking, e.g. weight distribution and buoyancy.

“What you can't see below the waterline is often what determines whether the boat gets home safely.”