No A/C when motoring? - SailNet Community
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post #1 of 35 Old 07-12-2012 Thread Starter
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No A/C when motoring?

Hi everyone,

I don't own a boat (yet), but we've done a fair amount of chartering on the Nothern Chesapeake Bay. Our last trip was July 6-8 during the extreme heat. The high temperature was well over 100 degrees and the wind was constantly at our back (when there was wind).

Usually, it's fairly comfortable down below when under way becuase the air temps are usually lower on the water and there's generally a pretty good breeze. On this trip however, it was just unbearable.

We had my 2-year-old son with us and it was way too hot for him to take a nap down below, so he ended up being pretty miserable for most of the trip.

Anyway, I was wondering why you can't use the engine to power the A/C like in a car. The boat we had out was a Catalina 350, but as far as I know, most, if not all, sailboats are set up so that the A/C is only operational if plugged into shore power or if you have an onboard generator. Anyone know why? Also, how hard would it be, or is it even possible, to rig something up to allow the A/C to run while the engine is on?

Thanks,

Kevin
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post #2 of 35 Old 07-12-2012
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Re: No A/C when motoring?

The HP required to power AC is fairly high even in very efficient systems. It is possible with a boat that has on-board generation. The propulsion engine can do it HP wise yet it would be running nearly all the time.

Denise, Bristol PA, Oday 30. On Tidal Delaware River, Anchor Yacht Club.
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post #3 of 35 Old 07-12-2012
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Re: No A/C when motoring?

The comparison of a car to a boat is not a good one, for several reasons:

As Denise noted, your typical auxiliary engine in a sailboat is way smaller than the one found in your average minivan -- think about 1/4 or less of the output.

Compounding the issue is that the volume to be cooled inside a boat is probably at least double of that in the minivan.

Certainy not an insurmountable problem, but really expensive to solve.

If you want to run an engine driven system, then you've got to drop in a new larger one that probably won't fit in the space designed for it by the designer. This could also throw off your wieght/balance and cause trim issues. You also would almost never get the engine anywhere near its optimum power curve, unless you're running the a/c constantly. This is not a great thing for a diesel engine.

The more typical solution is to install a genset that can handle the load needed to run the a/c. Only runs when you need it, can also be used on the hook, etc, etc. However, they don't come cheap, and also pose a challenge trying to carve out space for it as well as the weight issues noted above.

Most people find that 12v fans are a good enough alternative.

Last edited by PorFin; 07-12-2012 at 09:08 AM.
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post #4 of 35 Old 07-12-2012
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Re: No A/C when motoring?

Our boat has an engine driven 5kw generator that can run the Mermaid marine reverse cycle AC when motoring.

Tim R.
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post #5 of 35 Old 07-12-2012
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Re: No A/C when motoring?

On extremely nasty days, I've been known to run the Honda EU2000 Generator to run the A/C below while underway.

S/V Jendai
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post #6 of 35 Old 07-12-2012
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Re: No A/C when motoring?

I have an emergency, 8,000-watt generator at home. It's powered by a 5-HP, air cooled engine. When we were without power last summer I was able to run a 10,000 BTU air conditioner, lights and a TV with no problem at all. That 10,000 AC unit cooled 1,450 square feet in no time at all. There, I believe it is quite feasible to utilize an automotive air conditioning system on a sailboat and not consume very much HP from the engine while running. I believe the only reason it has not been done at this point is no one would want to pay for the installation of this type of system that would not likely be used very often.

Now, if the boat only has a 10 to 15 HP diesel engine, 5-HP could constitute a loss of 33 to 50 percent of the boat's available power. Keep in mind, though, that the HP rating of the boat's engine is usually at 2/3 to 3/4 of the engine's maximum RPM (sometimes higher), therefore a 5-HP drop at lower RPM would really be significant.

Boats with larger engines, such as the 55-HP Perkins, 30-HP Atomic-4, etc..., could easily handle a relatively large, automotive air conditioning system and suffer very little power loss. At one time in my life I owned a VW Micro-Bus that had a air conditioner. The van had a 4-cylinder, 36-HP engine. When there were 4 adults in the van, the air conditioner had to be shut down in order to maintain speed when pulling up fairly steep hills. On flat roadways it ran just fine with the AC running full blast. When my 33-Morgan O.I. is underway, the A4 runs at just 1,800 RPM to push it along comfortably at 6-knots. I sincerely believe that the engine would easily handle an automotive AC unit, but I'm too old to undertake the project.

Good Luck,

Gary
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post #7 of 35 Old 07-12-2012
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http://www.ebay.com/itm/1950s-Thermador-Car-Cooler-VINTAGE-Swamp-Cooler-/180919989487?pt=Vintage_Car_Truck_Parts_Accessorie s&vxp=mtr&hash=item2a1fabf4ef#ht_2027wt_689

Not saying this would fit the bill at all but used this in the 50s on VW beetles that were running 20hp motors.

Big downside is that it will add humidity to the cabin up side is that it will drop temp an average of 20 deg and only has a fan to run. Anyway old school thought.
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post #8 of 35 Old 07-12-2012
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Re: No A/C when motoring?

I think the answer to the original question is that most people are much more concerned about A/C when in the slip and thus AC shore power is the way to go. Don't want to have to run the diesel all the time in the slip. A generator is the solution for A/C when away from shore power.
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post #9 of 35 Old 07-12-2012
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Re: No A/C when motoring?

Quote:
Originally Posted by travlineasy View Post
I have an emergency, 8,000-watt generator at home. It's powered by a 5-HP, air cooled engine. When we were without power last summer I was able to run a 10,000 BTU air conditioner, lights and a TV with no problem at all. That 10,000 AC unit cooled 1,450 square feet in no time at all. There, I believe it is quite feasible to utilize an automotive air conditioning system on a sailboat and not consume very much HP from the engine while running. I believe the only reason it has not been done at this point is no one would want to pay for the installation of this type of system that would not likely be used very often.

Now, if the boat only has a 10 to 15 HP diesel engine, 5-HP could constitute a loss of 33 to 50 percent of the boat's available power. Keep in mind, though, that the HP rating of the boat's engine is usually at 2/3 to 3/4 of the engine's maximum RPM (sometimes higher), therefore a 5-HP drop at lower RPM would really be significant.

Boats with larger engines, such as the 55-HP Perkins, 30-HP Atomic-4, etc..., could easily handle a relatively large, automotive air conditioning system and suffer very little power loss. At one time in my life I owned a VW Micro-Bus that had a air conditioner. The van had a 4-cylinder, 36-HP engine. When there were 4 adults in the van, the air conditioner had to be shut down in order to maintain speed when pulling up fairly steep hills. On flat roadways it ran just fine with the AC running full blast. When my 33-Morgan O.I. is underway, the A4 runs at just 1,800 RPM to push it along comfortably at 6-knots. I sincerely believe that the engine would easily handle an automotive AC unit, but I'm too old to undertake the project.

Good Luck,

Gary
Gary the easiest way would be to get a window box. remove the gas, run the comp lines to a engine mounted comp. (with tubing and hoses) and use the condenser or a water cooled condenser. A few tricks with 12 volt relays and a inverter for the blower. it would work.. would look "cobbled" however
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Denise, Bristol PA, Oday 30. On Tidal Delaware River, Anchor Yacht Club.
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post #10 of 35 Old 07-12-2012
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