Lets Talk Air Conditioning - Size Matters

[Mule]

Hey man, you are ready for diesel electric power, just find a hailed out bus to get the motor(s) and wire up your main propulsion, you could certainly have a get home off that genset.

[hellosailor]

As long as you are generating power, try two more effective means of cooling before you fire up the AC units.

Rig a tarp over as much of the deck as you can, at whatever height you can. Reflective cloth or at least, dense cloth. That cuts the solar heating and that reduces the heat load on the AC. Ask anyone who lived in the in 20's if they had AWNINGS on their WINDOWS and they'll tell you how big a different this can make.

Then, get some "misting" nozzles from the irrigation section, and rig a water pump">raw water pump and filter, to spray water mist over the boat. Hull, topsides, trap, whatever is in the sunlight. A fine water mist will be boiled off by that cruel sunlight, taking more BTUs away with it.

Between the tarp and the mist, your AC and fuel bill will both work better. Specs on both? No, just do the best you can.

[Mule]

Your handle reminds me of the come on by Philippino working girls in Olangapo, Hellosailor, you #1. And you were until you spent your last cent.

I thought of the misting idea and I think it would work great, or even better, however, (yeah, here is the however), what about the salt buildup on the boat and tarp? I know it would work great in fresh water, done similar on tin roof marina covered slips, got the water deep and even in Tx in August it was cold. But in salt water?????

[GordMay]

Originally Posted by lorenzo b

... installed a 20k Northern Lights genset for electrical power. I figured hey why not, that's the size all the other boats down here in the oil patch use. So now comes the time to crank up the genset and I get around to reading the instructions and they say I need to load the generator to 75% of its load capacity to break it in and make sure the piston rings seat properly...

I've worked on a couple of boats, where the owner actually had to install resistive load banks on their generators.

I dont'd know how many boats, large & small, that have installed genereators rated TWICE what their shore-power service is rated.
ie: 30A 120V Shore Power & 5000 to 7500W generator

[hellosailor]

Yah, Mule, it might have something to do with that. It also works in Zork. :-)

[ViribusUnitis]

Originally Posted by lorenzo b

so here's a wacky twist to this thread; I've fixing up this 63' steel boat and installed a 20k Northern Lights genset for electrical power. I figured hey why not, that's the size all the other boats down here in the oil patch use. So now comes the time to crank up the genset and I get around to reading the instructions and they say I need to load the generator to 75% of its load capacity to break it in and make sure the piston rings seat properly. Now I sit down to do the math. I'm not making this up.

I always planned to cool off with big open windows which I now have and no insulation on the steel walls, the roof is bright white and partially shaded. Seems like, short of throwing to two leads into the salt water and frying the whole marina, the only thing that will draw anywhere near that kind of power will be the air conditioner from hell, a 5 ton 60,000 BTU behemoth that will draw 35 amps at 240v and even then I'll have to turn on everything else I can find.

Good thing I love the smell of diesel in the morning, noon, and night.

The gen set is welded into the engine room and keel coolers and the hatch I used to install it is welded over. It is not coming out, besides I've become quite fond of it, even though I've never turned it over. It looks really cool. So now I have this air conditioning unit on order and it will be here in a few days.

I'll let you know how it all works out and when I'm coming your way.

Why not go down and buy yourself some resistive electical heaters? A normal heater is around 8-10 amps. Resistive electrical heaters use loughts of amps. You could probably by like 5 of them for like 200 bucks. Plug them in on the boat and that should be enough to do you. At least to get the engine set up. You don't want to install an oversized a/c. That'll lead to other problems with condensation, and short cycleing the a/c down the line. Condensation being expecally bad with a steel boat.

[gulfstar1]

I installed a 16000 BTU mermaid heat pump on our Gulfstar 37 about 3 years ago. I used a formula similar to the one posted earlier to size it. The numbers actually said I needed about 11,800 btu's which would indicate a 12,000 btu unit, but when I considered the age of the boat, insulation, and the climate in Florida the larger unit was the clear choice. It cools and heats great and just as important in this climate, it dehumidifies.

I purchased a Honda portable generator when we were on the hook for about a year after that. I wanted something that could run our battery charger and a/c unit. The main concern is the locked rotor amperage needed to start the a/c unit. Mermaid said to use a factor of 1.8 to figure the LRA. My unit has a running amperage of 12 amps in cooling and 13.5 amps in heating. So 13.5a x 1.8 = 24.3 amps plus 1.5a for the pump when starting the unit. 25.8 x 120 volts = 3096 watts to start. 15 x 120 = 1800 watts to run. I couldn't see the 2000 watt generator starting the unit. I purchased a Honda 3500. It's a little louder than the 2000i I would have liked but wound up costing less at the time. When at anchor we can have A/C or heat and run our battery charger, although I don't turn on the a/c unit until the charger is at a float level. The generator provides 25 amps continuous power at 3000 watts. The nameplate rating ( 3500 watts in this case ) is a max rating and is only good for about 30 minutes runtime. Any longer than that and you will be overloading the generator. You should always size a generator by it's continuous rating.

Hope this helps.

[lorenzo b]

Thanks gulfstar1, that was helpful. I calculated the cubic ft to be cooled/heated at about 8000 times 15 BTUs per gives me 120,000 BTU so a 5 ton 60,000 BTU unit will not be too big. It is supposed to pull 35 amps @ 240v when running or 8400 watts, but will my 20k genset provide enough for the start surge? I've heard talk of something called a surge dampener, have you heard of this? In any case I'll know soon enough. I'll let you know if it all seizes out in a nasty blue cloud of acrid smoke.

[GordMay]

Originally Posted by lorenzo b

I've heard talk of something called a surge dampener, have you heard of this?...

I expect you mean a “Hard Start Capacitor Kit”:

➥ Guide to Installing Air Conditioning Compressor Motor Starter Capacitors - Air Conditioning Compressor & Condenser Replacement or Repair

➥ Kickstart®Hard Start Devices - Contractor FAQ's

➥ Compressor Hard Start Boosters

➥ RV Air Conditioner Hard Start Capacitor | ModMyRV

[lorenzo b]

Thanks dude
most helpful

[Ocean Girl]

Originally Posted by Mule

Also if your unit does not cycle properly the air will not have the moisture wicked out of it and you air will be cold and clammy. What size are you running on your 30CD?

Sorry it took so long to reply, my internet is down (I'm at the library). I have a window unit (5000 btu) in the midship hatch. (pic of awning and ac) I lined the hatch with the 3m bubble wrap insulation, cold air is channeled down into the boat. It looks obnoxious, but can quickly be pulled out to go sailing. Some boaters put the window unit in the companionway but I like this set up better. Not going to install a reverse cycle ac, don't want to use my precious storage for that. Also, next to the ac a good awning is a must. No matter how big the ac, it can't keep up with the peak "heat of the day" in Texas. My boat is ice cold with the little 40 lb 5000 btu unit ( my electric bill averages $30), but the CD interior is smaller then the average 30 footer.
Erika

[Beausoleil]

Lorenzo,

Sounds like you need to temporarily hook up a few 1500W water heaters, and break in the boat with a cruise up to Boothbay, ME in the dead of winter!!!

How's New Iberia? I was just in the area in June (St. Martinville and Lafayette - didn't actually make it to "Da Berry"!).

[lorenzo b]

Maine actually sounds inviting, It's been hot as hell here in New Iberia for the last month or so, although it started raining lately and it's cooled down a bit. My friends in Maine tell me they having a terrible spring and summer and all the gardens are miserable.
I picked up the new AC unit this morning, it's big 48" x 48" x 36" high, and set it on the roof. I went and talked to an electrical contractor to do the hookup and do my basic electrical system on the boat, which relieves me greatly. The more I tried to do that myself and the more I read about it, the more confused I was getting. I've done some residential electrical work before but this stuff is beyond me, and right now I've got my hands full putting together the hydraulic system.
Y'all come down this way again, stop by. I'm at the port of Iberia marina.
OM PADI PADI

[jshukis]

I have a white-hulled 40-foot sailboat with quite a few hatches a cored deck. In San Francisco, which doesn't get very hot or very cold, 12K BTU is just about perfect. In a 90+ degree climate it would be underpowered. For comparison, you can order my same boat with factory AC, one 16,000 BTU unit plus a 12,000 BTU unit for 28,000 BTU total. It's french boat, and so designed for the warm and humid Mediterranean.

[Stillraining]

Hey Erica:

Now this is my kind of air conditioning..Topless..