Electrical power use on a boat is one of the biggest issues for cruising sailors these days. Talk to any long-term cruising sailor and they will probably bend your ear for hours about the issues and problems in providing the power for their boat. Basically your boat is an independent system when you are away from the dock. Any power you use, and todays gadgets can use a lot, will have to be supplied from the ships systems. Most cruisers find that the gadgets they have draw too much for the boat's original electrical system - and require a substantial redesign.

First steps - to get started it is important to do a basic budget for the 12 Volt electrical system. I covered this in an earlier blog, and came up with 131 amp-hours at anchor, and 198 when we are on passage. Bear in mind this is from our own experience over 20 years of cruising on board Two-Step. Like most cruisers we conserve power when we can, we don't use much water, and we have installed efficient reading lights etc. If you plan a more hedonistic life you might want to budget more ;-)

Next we need to look at how to supply this power. There are two obvious scenarios - at anchor and on passage. On passage boats use more power, depending on autopilot draw it can be a lot more! Luckily the Raymarine pilot is quite good on power. But also on passage you might well find a time during the day when you need to run the engine anyway with light winds. So on those days you will likely get all the power you need from running the engine. The problem is on those wonderful tradewind passages when you are sailing well and don't need to run the engine. Then you must generate the power somehow. On Two-Step we just ran the engine anyway - in neutral. So on an ocean passage we found we had to run the engine twice a day for one hour each. Solar panels helped out somewhat but it is difficult to design a system that will provide the entire power requirements from solar - especially on passage since you use so much.

Power Options

• Solar - For our example of needing 198ah per day - we would need quite a solar farm to provide even half of that. Perhaps 3 large panels would give 100ah. I estimated a solar array would be 5 feet by 7 feet and cost $4000, and generate 100ah per day. And not if its cloudy.
• Wind - Typically these might give 60-12ah per day if there is reasonable wind. Unfortunately many anchorages are protected from the wind and therefore don't produce what the marketing people might claim - even in the windy Caribbean. And a typical Mediterranean summer would not provide enough predictable wind either. They are popular in the Caribbean though - and if you don't mind a constant whirring noise you might consider one. For us the whirring is too annoying.
• Alternator - the mainstay of 12V power generation for most cruisers. We typically used our main engine as a generator by running it one or two hours per day just to make electricity. At anchor if we are careful and its sunny (for the solar panels) then we might just run one hour per day. At sea on passage we needed to run it twice for one hour. On the Southerly we will have a bigger alternator - 80Amps vs 50 on Two-Step. At sea we would need to run it at least 3 hours per day to come up with 198ah. Probably more since an 80Amp alternator is not really going to produce 80 full time for 2.5 hours. Count on maybe 60% of the rated output on a regular basis. So our new 80Amp unit might give us 50 amps - that means 4 hours running at sea and three at anchor.
• Generator - At the risk of oversimplifying - if you have any large power consumers on board you probably should consider a Generator. And I don't mean someone who always leaves the lights on!! A big power consumer would be an air conditioning system, a clothes washer/dryer, a microwave oven, a scuba compressor etc. Most boats have some form of inverter to allow you to run 120V devices from the 12V batteries. This works great for small items, but running anything with real power requirements will need too many batteries to be practical. For example, running a typical small vacuum cleaner for 10 minutes would require 25ah from your batteries. Running a 120V watermaker for 2 hours would take 300-350ah. And if you did have such a big bank of batteries you would still need to put the power back in. Neither the alternator, the solar panels nor the wind generator can produce this much easily. So as you decide on more 120V devices, you are increasingly pointed to a GenSet. We have been considering a generator for a few reasons. First, the genset can easily produce enough 12 volt power to replace 198 amps in roughly 2 hours. It is quieter than the engine since they are usually very well insulated and typically installed with a dry exhaust. Best of all a generator will allow for Sheryl's and my two dream options for the new boat. A washing machine and a scuba compressor!! There are a number of small units meant for sailboats in the 40-foot range.

AC Power Needs
The other part of a complete electrical budget is planning the AC usage. This means anything you will need to run on house current - not 12 volts. For the modern more complicated cruiser (think Steve Dashew not Lin & Larry) this includes a washer or washer/dryer, vacuum cleaner, desalinator, air conditioning etc. And if you have anything in this category that will need to be run away from the dock, then you will need to figure out how to produce the power yourself - basically a generator is the most common solution here.

So for our new boat we had no option but a generator since we will have 2 big power users (washing machine and Scuba compressor) that need house current. Then it was a matter of trying to figure out which one.

Fitting in a Generator
When Northshore did the original drawings for the Southerly 42 they took a genset into consideration. With the raised pilot house/saloon the boat has quite a large area under the saloon floor, that is also positioned nicely in the center of the boat. Many similar modern boats have raised saloon windows but did not raise the saloon seating - so there is no extra space (plus you can't see out either - go figure?!?). But the Southerly is a cunning design that provides space for tanks, generator etc right in the center where it is best to place heavy items like this. You can click on the plans for a larger view. The generator Northshore chose was a Mastervolt. I wasn't familiar with this make but when I looked into them they looked like the perfect solution.

Mastervolt
Mastervolt has a very good reputation worldwide, and best of all they make almost all the components for a boats electrical system. So you can get the whole electrical system from them and the components are designed to work together. This means that the generator is designed to integrate with the charger/inverter. The two can cooperate and add their power output together. For example, if the generator is running but there is a surge of current drawn as the scuba compressor starts up, the inverter adds in the extra needed power. This should allow us to run the compressor - potentially the largest user we will have, on the smaller generator. We will certainly report back as the system progresses.