Once you’ve worked out your electrical requirements (see the fisrt part of the article here), all that remains to be done is work out how to create it. Having looked at electrical consumption in Part One, here are some ideas on how to reasonably produce electricity on a cruising catamaran.
Uprating your battery bank ?
If you use your catamaran intensively, and even more so if you’re planning to set off long-term cruising, increasing the number of batteries is generally a good first step. Why? Because a battery should never be allowed to drop below 50% of its capacity. So an installation with 200 Ah of batteries will deliver 100 before you have to recharge it.
When to charge?
The engine alternators are the primary means of charging on board. Rather than a single long charge once a day while on passage, it’s preferable to charge in two stages. The first charge in the morning, as it’s generally during night sailing that we consume the most, and another time in the evening, as we can take advantage of the engine to generate hot water. Important so the crew can take a shower!
If necessary, you could always add a third charge in the middle of the night.
A critical look at the alternator :
Alternators never deliver 100 % of their capacity, but only 70 to 80 %, because there are many losses between the engine and the batteries: line loss (length of cables), split chargers, etc.
And be careful not to just measure the voltage on the starter batteries, as they are usually well-charged.
Alternative energy sources:
To limit the use of the motor, alternative energies are obviously a solution… a natural one!
But you may be wondering between wind generators and solar panels.
Wind generators have the disadvantage of making noise, but can be very effective on a fast multihull that creates from good apparent wind, or in a windy anchorage.
The deck area and flybridge of modern catamarans justify fitting solar panels, especially when sailing in sunnier climes. Beware though, even the most efficient (monocrystalline) have fairly low yields, in the order of 50% of their initial power. As they don’t produce at night, they must be combined with a large battery bank, to avoid wasting their output over 24 hours. On the other hand, they’re great for maintaining the batteries at a good level if your boat is laid up for the winter.
Finally, if your program includes serious passage-making, the hydro-generator is a solution worth considering. They are very efficient under way, with really high output as soon as you exceed about 7 knots. However, their installation on the sugarscoop of a catamaran is likely to raise a few issues.
And what about a generator?
Not particularly thirsty, not that noisy, compact, modern generators are an interesting option, even on a catamaran which already has two engines… Their output is higher than the alternator of an engine and they have the advantage of generating AC power directly, which can be useful for many “household” appliances or a laptop computer.
Feel free to let us know your preferences in comments!