Empower Your Boat - in a Green Way

by Simon Boyde, Technical Director, Storm Force Marine

I have three times in my life lived on board a boat, once in the UK, and twice in Hong Kong.

In Hong Kong, the first period lasted near five years, the second two: what drove me off the second time was a lack of cool air on those really hot days. The killer here in terms of aquatic living is of course the summers - if you are in a marina or typhoon shelter how are you going to deal with the heat?

First time around here I did it fairly conventionally: a 40' motorboat with a generator and air-conditioner. I was not on a marina mooring and had no access to shore power. insteadit was generator, with all the diesel fumes, every night I wanted the air-conditioner on during the summer.

In those days of course you needed to size the generator for the start up load of the airconditioner, which meant that the generator was not running under a heavy-enough load most of the time, which also meant that the generator had a foreshortened life. I started with a 3.5kw generator to run my 8000btu air-conditioner and the result was not good. The generator was not quite big enough to deal with start up loads or partially blocked inlets for the water pump (for those who have not dealt with this bit of nitty gritty on a boat, marine air-conditioners are water cooled, so you need a pump to move the cooling water). This meant fairly frequent air-conditioner shutdowns overnight while the average load on the genset was not high enough to ensure longevity. The generator was replaced twice in the end over five years. All in all a very expensive experience. Second time around I decided to dispense with air-conditioning. Net result is that I moved back to shore!

The world has moved on of course, I now work in the marine industry and am therefore much more aware of the options available, and of course technology has improved dramatically.

I now own a 42' sailing yacht, and have loads of fun at weekends on it. and I am, once again, very tempted to move back on. The thing which is stopping me is what to do about those worst of the summer nights when you just must get cool! Putting a generator on to run an air-conditioner is possible, but I am straight back to where I was a few years ago - pumping out diesel fumes every night I do this, and at the same time destroying a genset early because not enough load has been put on it. All the while burning precious fossil fuels which are pretty irreplaceable. So, over the last couple of years with Storm Force Marine, I have been thinking about the options:

I have worked out that I am more than happy to NOT run an air-conditioner all night, I just need to run it to get cool - I am quite happy to switch it off at that point. Next, I know from experience with the products we provide, that I can get reliable power off an inverter all night as long as the batteries will take the drain. enough in fact to run a small air-conditioner. Lastly, I know about solar panels, wind generators and alternators which really work.

The basic equation is simple: take a small air-conditioner (I have gone for a 5000btu one) which is enough to cool a sleeping cabin. Add an inverter to run it, a charger to replenish batteries when on shore power, a big alternator to replenish batteries from the engine when not, solar panels to fill them up for free whenever the sun shines, and a wind generator to do the same when a breeze is blowing.

My recipe is as follows:

1 5000btu Webasto marine air-conditioner

2 68W Solara Solar panels

1 Balmar 150A Alternator

4 220AH Victron AGM deep cycle batteries

1 Victron Energy Inverter Charger

1 Ampair 100 100W Wind Generator.

- together of course with ancillary install and monitoring systems.

Now, the details of this system become important - and the brands chosen are not just brands, there are reasons to choose them.

Firstly Webasto air-conditioners: the small ones we can run the cooling water using a DC pump which helps cut our power drain. Next they have specially designed circuitry to enable the air-conditioner to reduce its start up loads considerably from what was available a few years ago. The result is an air-conditioner which is perfectly happy running from an inverter. (By the way, don't even think about DC air-conditioners. They are less efficient, weigh a lot more, and are uncommon and therefore hard to get serviced).

Next the solar panels. Solar power on a sailing boat (especially, but it applies to all boats to greater or lesser extent) is problematic: you need access to all of the deck space on the boat while under way. This normally means removable solar panels in case you step on them or otherwise damage them while sailing.

The Solara panels are what the round the world race people use, and the reason is simple: you glue them to the deck and can walk on them thus removing the issues previously stated. My plan is to have two which on a reasonably sunny day will be able to add 100Ah back into my battery mix. On a bigger boat there is more space so more can be fitted, so it is one of those cases where size can make you greener.

Wind generators have a bad name - basically because they are noisy. While cruising in the Philippines last year we moored close to a boat with a wind generator mounted which was quiet (and on closely questioning the skipper, very reliable). The manufacturer was Ampair and this generator can produce 8A of 12V power in 20 knots of wind. This lets us add charge back to our batteries when the sun is not necessarily shining.

The alternator: add a second alternator to your engine. The Balmar alternators have a neat trick, you can switch them on and off while the engine is running. This means that on a long motoring delivery trip you can turn the high power alternator off to avoid overcharging your batteries (and incidentally saving yourself money on fuel on the way). And when you need the big charge to hit your battery bank you can simply activate it with a simple switch.

The batteries. Victron AGM batteries are good for 8-10 years at a 30-50% discharge. They cost more of course but the hassle and cost of replacing batteries every couple of years, as a lot of owners do, is removed.

Last but by no means least is the Victron Energy Multi Inverter Charger. This is perhaps the ultimate smart charger for your batteries as well as perhaps the only smart inverter on the market. It has two ways of helping your power requirements out. My interest in my little install is their ability to provide for short periods of time around double the output power than they are rated for. This is a great feature, it means you can put a smaller inverter on board because you can size it for peak mean load, as opposed to peak peak load. This means less weight and of course a lot less money. Their second feature is not what I will be using in my little install, but would be of massive interest in the following scenario:

Say that you want to be able to run more air-conditioners than my little system is designed for. This means, if there is no shore power, a genset. There is simply no way round it. But see my previous experience with gensets - having to size them large to deal with air-conditioner startup loads and then having them wear out quickly because of insufficient average load.

The answer is here with the Victron Multis. They have the ability to boost the power of the genset when it is required. Say you put a 3.5KW genset on the boat. That means max current drain you should normally take out of this is 80% of peak power which is 3500/230*80% - a figure of around 12A.

Now, you add air-conditioners to your boat such that their average current draw adds up around 10-12A (from Webasto's figures this would be 2x16000btu air-conditioners).

This means we are happy - we will be loading up the genset enough to ensure longevity and efficient fuel burn while not spending too much money on extra genset capacity which we don't need.

The problem is that, as soon as the second air-conditioner starts up, our little generator, in a conventional setup, is going to stall because we are now trying to pull more power off it than it can provide . Enter Victron's Multis: they have the ability to boost the power available to our AC system from batteries. and as soon as the current draw drops back below generator optimum they will use the difference between the AC system load and the generator's optimum output to re-charge the batteries again. This means that the Victron unit will efficiently keep the generator fully loaded to 80% of capacity, increasing genset life and fuel efficiency, while making sure that you can run AC systems on your boat that at times require double the maximum generator output.

This is good: it saves fuel, it saves money, it extends the life of all your components, it takes up less resources, it weighs less, and the whole thing pumps out less greenhouse gasses. And you stay cool!

Back to my project: I am well on the way. Most of the components are to hand and soon I will happily be able to run my air-conditioner for up to ten hours at a time purely from batteries. I can refill the batteries partly from solar, partly from wind, and partly (when the solar/wind system does not produce enough) from the big alternator. I can hardly wait, life on the water beckons again!

Downloadable pdf of this article.