Wiring A/C for someone who always unplugs the boat

[Kyle Ewing]

I'm considering installing an A/C unit in Donnybrook, my 1990 C34.  I'm always been in the "unplug everything and close all through-hulls when leaving the boat camp."  One of the appeals of the A/C is to keep the boat cool and de-humidified while I'm away, however leaving power on and through-hulls open makes me nervous.

One thought I had is to run a second shore power connection to run only the A/C.  That would allow me to turn off the power to the 25+ year old wiring while running only the A/C all week.  I'd still have one open through-hull, but that's less risk than 5 open through-hulls.

Questions for people with air conditioners:
1.  How long does it take you to cool off the boat?  Think noon Chicago sun, 90+ degrees, high humidity?  I'm leaning toward a 16k BTU unit.
2.  Are there other downsides besides cost and installation effort to having a second shore power cable dedicated only to A/C?  I estimate the only device I couldn't run with a single 30 amp shore power while running the A/C is the water heater.

Thanks in advance for your advice!

Kyle Ewing
Donnybrook #1010 (1990)
Chicago

[KWKloeber]

Kyle.  How then would you run AC when aboard and (presumably) "the  other" shore cord plugged in?   Could you do dual 30-a inlets at your marina?  Or wouldn't that be a situation for how you use her?

A consideration ... is the max draw thru the inlet -- which shouldn't approach 30 a.  First, I would install a smartplug.

Would a solution be, after your main breaker, to simply branch off to the AC breaker, and a switch that cuts power to all other circuits?  If you are leery about the "service entrance" cable, and so want a new one, then you could replace w/ new (10 awg) up to that new switch that will cut power to all the AC circuits.  Maybe define a little better when you would and wouldn't use AC?

ken

[Jim Hardesty]

1.  How long does it take you to cool off the boat?  Think noon Chicago sun, 90+ degrees, high humidity?  I'm leaning toward a 16k BTU unit.

Kyle, 
I think your idea is good. Maybe in the anchor locker.  I've thought that I should have done my AC that way.  Didn't for several reasons some Ken brought up. I'm careful about running the AC and the water heater. 
Back to your question 1.  In Erie Pa, depends on how cold you want it. Shamrock doesn't cool down fast. I have that size AC.   Looking at the temp ,90 deg sunny day, takes a good hour to lower the temp in the boat to 80 deg.  That said it's comfortable in the boat.  Wouldn't want to cook a meal yet, but comfortable.  So, the choices are run the AC 24/7, and/or put up sun shades over the deck.  They really help.
So, my experience is.  The boat cools down slowly.  Is more comfortable fairly quickly.  You need to run the AC all day to keep the boat cold.  Awnings over the deck help.  Also, doors on the companionway are real nice with the AC.

Just  my 2 cents,
Jim

[chuck53]

I've got a 16K unit on my boat and only have 1 - 30 amp plug.  Never had a problem with the AC and water heater running at the same time.  Now if I try to turn on my microwave, yes, the breaker will pop.
There is one problem running a 16k unit....after the sun has set for an hour or two, the compressor doesn't need to run nearly as much.  On my boat, I have to turn the temp way down at night, around 64, otherwise, humidity starts to creep up and becomes uncomfortable.
There are times I wish I had a 12k unit.  If I ever have to replace my unit, that's what I'm getting.

Also, I started using sun shades to keep the deck cool.  Helps A LOT.

[Ekutney]

I installed a 12K unit, had a very experienced AC guy come aboard & he said a 16K would cool the boat too quickly & short cycle not allowing the unit to run in the dehumidify mode.  I ran the unit 24/7 last season in MD & am glad I followed his advise.  The unit is installed in the locker aft of the Nav Station with one vent on the top of the locker with another in the aft berth.  The vent on the top of the Nav Locker has the louvered adjusted so it points to the middle of the salon overhead.  I also run a fan in the salon, one in the Aft berth & one in the V berth on really hot days.  That configuration works just fine even on the hottest days.  All on a single 30amp service with a SmartPlug.  The guy that came aboard said the biggest issue on boats is people tend to use too much ducting to move the air to all over the boat, he suggested pointing the cool air to the middle of the salon then using fans to keep air flowing through the boat works best.  After a summer of really hot humid days last year in MD I must say he was 100% correct.

[chuck53]

Ed, I put mine in that same locker just like you, but I only have one vent, coming thru the louverd door.
When I talked to my AC guy, he wanted the 16k unit and I wanted the 14k unit.  We both felt the 12k unit might be too small.  When he went to order the 14, it had been discontinued, so we both decided to go with the 16.  Wish I had gone with the 12k.  Yes, it would have struggled more on a hot, sunny day, but would have been the better unit to have once the sun went down.  A comfortable, good night's sleep is very important to me.

[J_Sail]

Within constraints, it may be possible to improve the humidity situation on an oversized A/C by reducing the airflow (either smaller fan or partially blocking the airflow). That causes the coils to run colder, improving dehumidification. If overdone, though, you run the risk of the coils freezing. When a unit is oversized, it is also helpful to have the fan stop the moment the compressor stops. That way, any water left clinging to the coils gets a chance to drip into the condensate drain rather than getting evaporated back into your cabin air.

[Jim Hardesty]

A comfortable, good night's sleep is very important to me.

My 16k works very well overnight.  Set it fot 68-70 deg and no problems.  Great sleep.  I bought the big one with the hope that after a long hot sail the boat would cool off quickly.  It is comfortable.  butt  Not as cool as I had hoped.  ie, I would not want to get back from a hot sail sail and turn the AC on and put a lasagna in the oven.  May be I'm not realistic.  I was hoping it would be more like my house.  Seems like once the AC gets behind it takes a long time to really cool the boat down.  Again, it is comfortable.  A nap in the cabin with the AC on after a long hot sail before going out for lasagna is the very best.  Worth the price of the AC.  IMHO

Jim

[Kyle Ewing]

Thanks all for the feedback.  I have two 30 amp plugs at my dock so I can handle two cables, but didn't think about other marinas. 

I'll look into Ken's suggestion of branching the AC at the main breaker.  I've thought about running the A/C all the time to keep the humidity down and eliminate boat smells.

The advice on 12K vs. 16K and dehumidification is invaluable.  We'll be using it while sleeping more than anything.

Kyle Ewing
Donnybrook #1010
Chicago

[KWKloeber]

 Kyle,

I'm really unfamiliar with the C34 panel (various versions) and what you may have behind yours as far as a hot bus. But, it seems pretty straightforward to be able to pick off if there's a buss right after after the main breaker to jump directly to another switch someplace, that would have to handle presumably up to 30a, that would shut down the rest of the 120v panel.   Or, if you have a spare breaker, you could jumper to that and then back to the 120 feed to the other breakers. As I said theoretically though, I just don't have it don't know as a practical matter whether you can be incorporated into the existing panel, or it has to be a separate switch stuck somewhere on the panel. 

D'oh  I was just thinking -- why not simply turn off all the other breakers, and leave the air conditioner breaker on?

ken

[chuck53]

On my 110v breaker panel, I've got 5 switches...
Main, water heater, outlets, battery charger and AC.  As I mentioned, I never have any problem running everything on one 30 amp plug.  Once in a while, we do use our microwave and when we do, we turn off the water heater.  Other than that, 30 amps is plenty.