Loading Batteries with sunlight

"The main DC generator is connected to the get-home engine.
A second DC alternator, smaller, is connected to the main engine...This is the way, I guess!"

It is A way , although the loads of as 4KW inverter underway will load the smaller alt far too much.

It is good in that with DC, the noisemaker can operate at a speed proper for the load, lowering noise and extending engine life.

With a clean sheet of paper I would choose Hyd instead of electric for many reasons.

FF wrote...

"Marine Air cond is about 15A of 120V , or 150A in 12V.
A wind machine that size would be 30 ft in diameter.
Although there are truck DC air cond that will cool a small cabin."

Certainly you can forget running aircon without significant charging ability, like a full on genset I would think. Air and solar generated power supplementing engine driven charging would not support aircon, other than a very tiny unit as FF says.* But many places don't require aircon, even tho it might be nice for some extreme weather conditions on occasion, and I'm including our area in Queensland in that, although we now have it in the home.


-- Edited by Peter B on Thursday 16th of February 2012 07:13:34 AM

Grumpy O.B said:

Those photos are from the engine room of one of my favourite displacement cruisers.
Watson Bros 48' a magnificent piece of steel work.

U're 100% correct. It is a Watson and it is probably the best Trawler I ever saw. I went aboard one of them in Dubai...Outstanding in all respect!


-- Edited by Portuguese on Thursday 16th of February 2012 12:54:23 PM

For many folks a late PM ritual of buttoning up the boat and using a large deck wash to clean and COOL the deck will suffice for air cond , as the sun goes down and the insolation requirements decrease.

A large whole boat set of covers works even better , but are a pain in thunderstorm areas.

Dometic makes a 12 VDC, 3500 BTU Air Con unit.**They say it draws ~29 amps at 12 Volts and that's for the unit, blower and water pump.* Their recommendation is*AGM or gel cells only, no wet cells.* An interesting unit but I bet it's not cheap.

http://www.dometic.com/4fc9ef64-bd40-404d-b1c0-1a68775ba27a.fodoc

True, but that unit is designed to be run from shore power/charger, or when on the move, as you would need constant and quite high charge output to keep up with it - sort of like the one in your car, really. At anchor, it's use would need to be limited, as 29Amps is a fairly high drain. All the same, if I was to add air to our boat, as we are exclusively 12v, that's the way I would go, but even with the Airbreeze wind turbine charger, as the wind usually drops away at night, you would have to have extra batt capacity and just run it for a few hours to cool the sleeping cabin down.

Actually the Dometic , and their competition is sold mostly to OTR truckers that only wish to cool their sleeper cab , with out paying a gallon an hour to run the engine , or having to listen to a noisemaker.

Their operating for 10+ hours the next day is sufficient to bring the house batts back.

Underway all of these trucks use an engine driven air cond 10,000+ btu, similar to your car.
The heat load thru the windshield is far higher than in a well insulated sleeper.

Amen to the Honda 2000.* Coupled with a good battery charger, it will be your most economical power producer.* While at the Garrison Bight Mooring Field this winter, I ran the Honda 2-3 hours in the evening.* That topped my batteries, operated the TV, powered the hot water heater and a single burner on our electric range.* To keep the batteries up whenever we left the boat for a few days, I purchased an inexpensive little 85 watt solar panel from West Marine.* That provided ample power to offset bilge pump and anchor light draw.* Good luck!