Components

The main components of the drive system of any electrically powered boat are similar in all cases, and similar to the options available for any electric vehicle.

Charger

Electric energy will have to be obtained for the battery bank from some source.
Mains charger allows the boat to be charged from a shore-side power point when one is available. This calls into question claims that the boat is 'non-polluting' and uses'renewable energy', but at least it does not directly pollute the water in which it sits as would the use of any petroleum-based motor. Shore-based power stations are subject to much stricter environmental controls than the average marine diesel or outboard motor.

Solar panels can be built into the boat in reasonable areas in the deck, cabin roof or as awnings. Modern solar panels, or photovoltaic arrays, can be flexible enough to fit to slightly curved surfaces and can be ordered in unusual shapes and sizes. It is still true that the heavier, rigid mono-crystalline types are more efficient in terms of energy output per square meter. The efficiency of solar panels rapidly decreases when they are not pointed directly at the sun, so some way of tilting the arrays while under way is very advantageous.

Towed generators are common on long-distance cruising yachts and can generate a lot of power when travelling under sail. If an electric boat is to have sails as well, and will be used in deep water (deeper than about 15 m or 50 ft), then a towed generator will help build up battery charge while sailing (there is no point in trailing such a generator while under electric propulsion as the extra drag from the generator would waste more electricity than it generates). Some electric power systems use the free-wheeling drive propeller to generate charge through the drive motor when sailing, but this system, including the design of the propeller and any gearing, cannot be optimised for both functions. It may be better locked off or feathered while the towed generator's more efficient turbine gathers energy.

Wind turbines are also common on cruising yachts and can be very well suited to electric boats. There are safety considerations regarding the spinning blades, especially in a strong wind. It is important that the boat is big enough that the turbine can be mounted out of the way of all passengers and crew under all circumstances, including when alongside and when coming alongside a dock, a bank or a pier. It is also important that the boat is big enough and stable enough that the top hamper created by the turbine on its pole or mast does not compromise its stability in a strong wind or gale.
If the boat is to have an internal combustion engine anyway, then its alternator will of course provide significant charge when it is running. This does rather defeat the original purpose, however. The weight saving that we would expect by not having this engine and all its associated tanks, pipework and other fittings would help to add to the efficiency that electric propulsion needs.

In all cases, a charge regulator will be needed. This is to ensure that the batteries are charged at the maximum rate that they safely can stand when the power is available. It must also ensure that they are not overcharged when nearing full charge and not overheated when they are discharged and a great deal of charge current becomes available.