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Old 12-10-2005, 20:55   #1
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Question A/C, Power, & Refrigeration?

First off, thanks for all the suggestions on catamarans. I've searched the threads here until blue in the face and haven't been able to resolve this next question.
What is the deal with A/C, Power (Electricity), and Refrigeration on boats (catamarans) as far as cruising/live aboard? I understand all this is available hooked up at the marina but once out to sea, cruising or on the hook, do most cats have enough? Those are a few creature comforts it seems worth having.
If you wanted good refrigeration, comfortable A/C, water making capability (hot water too) and electricity for your basic living while on the hook what kinda generators & BTU A/C units are we looking at? Especially if its a prolonged period of time. I also take it that if you have a generator you need an extra supply of fuel. How much is generally needed and how long does it last (in general)?
Can wind or solar units help supplement this? Thanks for any info.

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Old 13-10-2005, 01:57   #2
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Yes you can run a generator onboard, but continuous running will not only be expensive on fuel, but spoil your enjoyment of a tranquil anchorage. It will also not make you any friends amongst your neighbours!

Thus A/C is normally an alongside benefit in all except for large boats (i.e. well beyond my cheque book).

Refrigeration and freezers are a different matter. There are basically three options for long term use:
cool box that you fill with ice from ashore (cheap but not very efficient especially for long passages)
lpg fridge (as in caravans - reasonable price but only suitable for cats and mobos as they dont work when at an angle)
12v fridge driven by a danfoss compressor (expensive, but provided sufficient insulation is used when the fridge is built, it is remarkably efficient.

There are a number of different 12v instalations dependent on how you use the fridge/freezer and the most efficient installation for your vessel, but all the good ones start with some form of the danfoss compressor and either use air or water to exchange heat, and then either use a holding plate (device for making a large lump of ice which provides the cooling) or an evaporator plate (i.e. same as normal home fridge) for the cooling process.

Power can be provided from a number of sources, and normally will be a combination:

running boat engine (or generator) for a while to build up ice on a holding plate and charge boat batteries.
solar panel - cat is great for this cause of the deck space - I have 180w panel, but another forum member has enough to run a small town.
wind generator - some of these can be very noisy, and they dont work very well when boat is following the trade wind routes and wind is from astern.
towed generator - high power output, but dont work too well when boat is at anchor, however most of these can be converted into a wind driven system e.g. duogen.

These power sources can also provide the power required for the water maker - do some searches in these forums and you will find a ot of info on both solar power and water makers.
"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
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Old 13-10-2005, 08:30   #3
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A/C, Power and Refrigeration

I can only address your questions as they pertain to my experience on our Manta 42. Everything on our cat runs on DC except the air conditioning. That includes the watermaker and the fridge/freezer. We have six 75-watt solar panels that literally take care of almost everything most of the time. We are huge fans of solar power - it is safe, quiet and efficient (unlike wind generators). On our previous cat, we mounted the panels over the lifelines with specials rails, and we could adjust them throughout the day to get the most power from them.

Only because of the extremely overcast conditions of the last week have we had to run our generator (5.5kw NexGen) frequently to maintain the batteries for our daily living. Throughout the summer, we had ample sunlight to keep our 10 c.f. fridge/freezer cold (they are very well insulated), as well as the lights, TV, fans, etc. The watermaker takes a fair bit of power, so we tend to run the generator for that as well as the air (which we haven't used much because we spent the summer in New England).
Of course, we can run the watermaker while underway if we happen to be motoring.

As for fuel, our generator takes about a gallon an hour (our 30 h.p. Volvo Penta engines use about 1.5gal/hr). The generator is supplied by the same fuel tank as the engines, and our 120 gal. tank can last us for a couple of months at the most. Naturally, if you do a lot of motoring, or you are in overcast conditions for extended periods, you will use up your fuel much quicker. At least it is the less costlier diesel, not gas.
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Old 13-10-2005, 09:35   #4
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Isn't there another negative to NOT using a generator?

Correct me if I'm wrong here, but from what I have heard, running your diesel(s) solely for charging has two downsides:

1). I have heard that diesels generally don't like to be started/stopped often or run for relatively short periods (I don't know the validity of this comment).

2). Engines in general don't like to be running without their designed load on them. Kind of like revving your car engine constantly while in park. The generator is specifically designed for running on the charging load only.

Does this make sense?


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Old 13-10-2005, 09:56   #5
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Close Bruce

The main problem with diesels idling away without a load is that the cylinders become polished and loose some of their compression, not good.

As for starting and stopping, small diesels, are not too bad with that but the larger ones, like in 18 wheelers, have very large starters and when you start one of them up it pulls a lot of power from the batteries. You may only get 2-3 trys before the batteries are down. There is a lot of metal moving around in there with a lot of resistance (compression).

And some of the really big diesels, like in ships, have smaller diesels just to start the big diesel.
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Old 13-10-2005, 10:34   #6
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Diesel loading-what you're missing

It is a myth that diesel engines "like" to be loaded at rated load. In fact, they will last much longer if operated at lower rpms yet properly loaded for that rpm.

What do you think that variable pitch props were invented for? They allow you to optimally load the engine at any rpm. Well, the new generators, both gas and diesel, operate properly loaded at whatever minimum rpm gives the demanded load. One way that this is done is to drive an alternator that gives a dc output which is utilized by a power inverter. The load demand sense is used to drive a very simple speed control system.

I have been doing such a thing for over twenty years by putting a high-output large frame alternator whose known output power versus rpm and hp requirements are "belted" (correct pulley ratio) to fairly match the hp vs rpm of the diesel. As a result, the engine designed to deliver its rated hp at say 3000 rpm delivers the alternator's "rated" output power at 7 to 7.5 hp and 1200 rpm (of the diesel, not the spindle speed of the alternator). As a result, the engine run at anchor will heat up the oil sufficiently with such a "proper" load in less than 20 minutes. If the batteries do not require much of a charge and I want to heat up the oil to change it I merely put a 1500W heater on the output of my inverter and quickly heat up the oil. Doing it this way at a dock I don't bother anyone behind me with propwash.
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Old 13-10-2005, 11:50   #7
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Correct Rick. It could be looked at this way. Say an Engine has exactly 1 billion revolutions in it's life span and then it's takes it's last gasp. An engine that revs at 10,000 RPM is not going to last as long as one reving at 1,000 RPM. Every stroke the engine makes has a specific amount of wear. It has to, or the cylinder glazes up. That can be said for both fuels by the way. Deisel is less tolerant because of several factors, but the one mainone is that there is 100x more pressure in a cylinder during compression and the power stroke than that in a petrol engine. Fuel is burn't and the efiiciency of that burn is due to that pressure. The load also determins the pressure controlled in that power stroke. So correctly loaded, the engine burns more efficiently, resulting in the least harmful contaminants left in the exhaust during and after burn. ie, excessive unburn't fuel and oil and/or abbrasive carbon particles.

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Old 13-10-2005, 13:07   #8
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Re: A/C, Power and Refrigeration

[QUOTE]Harriet once whispered in the wind:

Only because of the extremely overcast conditions of the last week have we had to run our generator (5.5kw NexGen) frequently to maintain the batteries for our daily living.

So how often is frequently? Is it loud? Sounds like from another post that running a generator could bother others around you. On the flip side I guess this doesn't matter if you're anchored out. So do you just crank'em up during the day so as not to bother anybody at night and that will charge your batteries for electricity and some A/C for a little while?

Other than cost is there any difference to diesal and regular fuel gens?

It sounds like the electricity thing and especially the refrigeration deal are all ok then.

Another question popped into my head. What do you do with waste (not garbage)?
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Old 13-10-2005, 16:00   #9
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Hey Corb, we are almost neighbors. When I am in Raleigh we have a place over in Dutchman Downs. Very close to Penny Road and Killdare Farm. Cary keeps on trying to annex us, we keep fighting it.

You'll find A.C. taking as much as you want to spend pretty much. It depends on how you want to cruise and what you think is comfortable. I am trying to do without A/C at anchor because it necessitates the introduction of a genset, a weight and cost I don't want to incur.

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Old 13-10-2005, 16:38   #10
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Keith, yeah I know where you're at! We live in Lochmere near Tryon. I don't blame you guys for fighting Cary. I despise being in city limits, one reason a boat has caught our attention.

So the genset is a type of generator? Are there different sizes of gensets? I'm sure I need A/C, for myself, wife and kids. Are you happy with your boat?
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Old 14-10-2005, 05:54   #11
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Genset is the generic name for a generator with its own engine. They come in LOTs of different sizes. The most widely used designation is the output of the generator in Watts. Actually they are usually speced in kilo Watts. So you'll hear them talk about a 4.5 Kw generator. This says it puts out up to 4500 watts. Pretty much enough to keep 45 light bulbs burning.

You typically determine what size you need by estimating your consumption. A microwave might consume say 1.8 Kw. A hair drier 1.5 Kw a small 5000 btu portable air conditioner .8kw and so on. Then you determine what kind of fuel you want to use, how heavy it is, how much it noise it makes, will it physically fit in the area you have. Typical size is between 5 and 10 kw. Bigger than that and you're on a boat that is usually 50 feet and longer. Smaller than that and it is typically a portable generator.

A hint here is to try to buy a boat that already has one installed. They are kind of expensive to retrofit.

We love being on the boat. We are doing a LOT of work on it, but we still stop to smell the roses every once and awhile. We meet lots of folks out here cruising and on their boats. They almost have their own community. It gives the kids a way to socialize with others their own age.

What kind of use do you plan to put your boat too? I'd start with that question. You can start making decisions and trade-offs from there.

Good luck.

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Old 14-10-2005, 16:49   #12
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Thanks Keith and the rest of the folks. This puts my mind at ease a little more.
Anyone else "cruising" this thread feel free to leave suggestions or opinions as I'll check back from time to time as the path before me becomes clearer.
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Old 15-10-2005, 18:15   #13
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We have found that solar panels, wind generators and alternators satisfy all of our power needs except for air conditioning. AC is a whole new ball game in power requirements when you "leave the dock." It requires a generator and on a large boat, you need a large, expensive genset running whenever the AC is running. That is too much complication and expense for us so we adjust our temperature by changing latitude. On the other hand, we have some friends who use a 2KW Honda generator ($800 to $1000) to run a small AC unit to air condition their V-berth only. They claim that 1 quart of gasoline lasts 8 hours and they sleep well on sticky nights when the breeze stops. Their set-up is a relatively cheap and simple way to get some AC when you are out on the hook.
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Old 19-10-2005, 10:12   #14
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I plan to use 2 Honda EU 2000i generators as a backup to solar panels and to support extra loads. They are quiet, light and can be operated in parallel with Parallel Cable Kit, giving 3200W rated output (4kW max) at 120V. If load is small, I would start just one gen, saving fuel, for larger loads - e.g. air conditioning unit - I'd start both. Second generator would also serve as backup in case one of them breaks. Redundancy in systems and backups are good things when cruising. 2000i also have 12V/8A output, so they can be used to charge the batteries or power other 12V devices, e.g. watermaker directly without any dependency on boat's 12V electrical system in case it breaks (did I mentioned redundancy is good?). Two 2000i-s are still lighter (93#) - though not quieter - than next larger unit 3000iS (134#) and provide higher output.
Just a thought...
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