Air conditioning on a live aboard

[Keithward]

I’m in the process of buying a Pearson 422. Great boat excellent condition but no Air conditioning.
I will be keeping the boat in Florida and plan on cruising the gulf and Caribbean.
I am working from the boat . To not have air-conditioning is not an option.
it seems that for the 300 ft.² that I’m going to be living in I am at 25,000 BTUs or there about’s.
That seems incredible to me.
How big are the units in most 40 ft boats and thinking that Pearson 424s would be a perfect example but other 40 foot boats what do you have for air-conditioning and how effective is it and what are your issues. blessings thank you
Sweating in Florida

[Captain Bill]

You are probably thinking that compared to a house this seems like an awful lot of capacity. The problem is that you are comparing an insulated house sitting in air to an uninsulated boat sitting in hot water. My experience when sitting at a dock in FL is that we can get by on one 15k btu unit to keep our cat cool, but much of our hull is bridge deck and not sitting in hot water. We also don't worry about the aft cabins so much as we are not using them to sleep. If we have guests aboard in the aft cabins we activate the second unit.

[transmitterdan]

For hot days you very well might need 25K BTUs to keep it chilly in the boat. For a boat that size some would install a single 16K BTU unit and survive on the hottest days with it being 80F in the cabin. You can also install two units, one 16K and the other 10K BTUs. Then you can decide when to run the extra AC.

Be sure you have thought out the power situation. To run 26K BTU requires a little over 20A at 125V. That leaves little room for other things on a single 30A plug. And the 30A twist-lock style plug isn’t really going to handle 30A in the hot Florida summers. So consider going with a 50A inlet or the newer Smart-Plug 30A inlet on the boat side of the shore cable.

[skipmac]

Hi Keith,

As you know, I have a 422 as well, also in FL. Don't know about Tampa (a little closer to the ocean cooling) but in N central FL it was over 100 degrees most of last two weeks in May.

I have a 16 kBTU unit and at the dock that has been barely adequate but might be slightly better if installed in a better location. I installed where the PO had his units, in the cabinet in the walk-thru to the aft cabin. The already installed vents are in the bulkhead next to the door into the aft cabin; one facing forward, one into the aft cabin.

The aft cabin gets comfortably cool; definitely not icebox but quite comfortable. The main cabin gets to a level I would call not hot. Part of the problem is the location of the vents sends most of the cool into the aft cabin. If I put a fan in the doorway blowing forward it makes the main cabin a lot cooler. Forepeak, so far I haven't worried about but I think it won't really get much at all.

The PO had dual units with one evaporator/blower unit in the cabinet across from the forward head that blew into the forepeak and the front of the main cabin in addition to the blower in the walk through. That I think would keep the whole boat comfortable.

[svspirited]

I have two units in my 44 footer. One is a 16k BTU for the aft cabin and a 10k in the forward cabin, both have vents into the salon and keep the boat reasonably cool on even the hottest of days. There is a bit of insulation on our boat but it isn't anything like what you would get in a house so the BTU requirements are pretty high compared to a house.

I also have two 30amp shore power connections, one dedicated for the AC as combined they will consume about 20amps, and the other for the house. I can run them both on the 7.6kw generator but it does bog a bit when the compressor first kicks in and if they both kick in at the same time I think I can hear the generator cry out for mercy. I haven't found much need for them away from the dock yet but we haven't spent any time on her in the tropics yet.

[skipmac]

Originally Posted by transmitterdan

For hot days you very well might need 25K BTUs to keep it chilly in the boat. For a boat that size some would install a single 16K BTU unit and survive on the hottest days with it being 80F in the cabin. You can also install two units, one 16K and the other 10K BTUs. Then you can decide when to run the extra AC.

Be sure you have thought out the power situation. To run 26K BTU requires a little over 20A at 125V. That leaves little room for other things on a single 30A plug. And the 30A twist-lock style plug isn’t really going to handle 30A in the hot Florida summers. So consider going with a 50A inlet or the newer Smart-Plug 30A inlet on the boat side of the shore cable.

All excellent points. First I HIGHLY recommend the Smart Plug. Unfortunately can only work on the boat side of the cord since there are no marinas I have ever seen that have them on the dock side but at least it will keep the boat side safer.

I have seen a number of marinas without 50 amp supply on the dock so I would consider installing two 30 amp inlets on the boat and dedicate one just to the air con.

I might say that it could take well over 20 amps to run 26 kBTU when you take into account the starting loads, water pumps and any other incidental AC loads that might be running.

[skipmac]

Originally Posted by svspirited

I haven't found much need for them away from the dock yet but we haven't spent any time on her in the tropics yet.

I did spend a few years living onboard in the tropics and only felt the need for air con at anchor a few times but those few times I would have killed for it. You almost always have some breeze on the water and even without the ocean usually keeps it reasonable cool but once in a while it can get really, really hot even on the water.

The times I wanted air con the most was when anchored in a harbor when the bugs came out. Rarely a problem but the mosquitoes and noseeums can occasionally be a problem, leaving you with the choice of being eaten alive or locking in and dying from heat stroke. Fans and screens help but noseeums can get through any screen I've ever tried.

[Spindrift NH]

We have a Mermaid 16500 btu that works well for us in Charleston. I have three vents, one for each cabin. Not once in the 4 years living on the boat have I wished for more ac. I do have a sunshade for the cabin top forward of the mast and have recently added one from the mast back to the dodger. Those were added not because the ac wasn’t adequate but to cut down on electricity and because the cabin top was 125 degrees in the recent 100 degree weather, I was burning my feet walking on it!

[lancelot9898]

I'll give you my experience of living aboard with and without a/c over the years on a 37 foot Tayana. Decades ago I lived for over 6 months in Fl without air during the summer and it was unbearable so I merely put a window unit in the companionway. It was difficult stepping over but at least it was tolerable. When I moved the boat back up to the Chesapeake I decided to install a built in unit and decided to go with the smallest unit (6K btu/hr) since the 6K window unit down in Fl worked OK and besides the built in unit would be more efficient. That was a wrong choice since it was too small even for the lesser heat load than in Fl. It did however lower the humidity even though the temperature remained high so living with it was tolerable. This past year the old unit was replaced with a 12K unit and I was impressed with the improvement. The heat pump during the winter was very efficient and now that the summer is here so is the a/c. We have yet to have any 100 degree days, but the 90 degree days have been handled well with the 12K unit. I chose to go with 12K rather than 16K since I could reuse the wiring done for the 6K unit previously and thought the installation would be easy. However it was not since additional ducting was needed and piping needed modification to achieve the needed flowrates. My max current draw is 10 amps and if I had gone with the 16K unit it would have been more and additional modification to the electrical circuit would have been needed. I'm happy with the 12K unit on my 37 foot boat, but you may need a larger unit/s considering your insulation and also your location. Good luck.

[sailorboy1]

I'm sitting here in Sarasota and during the day am running my 16k unit in main salon and sometimes shut the doors to other cabins and it's fine. At night I run the 7k unit in the aft berth and turn off the 16k unit.

[redsky49]

I have a comparable sized boat and am also in Florida during much of hurricane season. I have a single 16K unit, and have found that to be adequate.


I use a small awning to shade the forecabin, and an additional one for the aft cabin. This is primarily to reduce the solar heat gain from the two large deck hatches serving these areas. I also use sunbrella covers for the two smaller hatches over the saloon, and have installed some reflective material over a few of the ports.


During the heat spell mentioned above, the boat's interior temperature did rise above the setpoint, reaching 77-78 F around 4:00 pm before returning to setpoint around 6:30 or 7:00 pm. I was still able to achieve 68-70 F for sleeping at night



While interior temps did rise at peak cooling times, it was also far less humid (inside) than exterior conditions and was quite comfortable. Having a single AC unit also allows me to easily support the other electrical devices onboard on a single 30 amp service.


Ideally, I would also have about 24,000 btuh, especially as the sea water temp rises (it's approaching 80 F now, and will rise throughout the summer) here in the marina.


For increasing the efficiency of any HVAC (heat pump) unit, maximizing the condenser water (seawater) flow - reducing/eliminating elbows and fittings, proper hose sizing, etc., and optimizing the airside of the unit - gradual transitions from the fan discharge to the air outlet(s), proper sizing of the supply air grille, ensuring an unobstructed return air path of adequate size, etc. Use a level to ensure the installed unit has sufficient slope to allow the condensate tray (or unit chassis depending on unit) to drain - 1/4" slope per foot will work.



Do not discharge condensate to the bilge. Install a dedicated sump and pump and discharge overboard above the waterline.



To ensure continued peak performance, allow sufficient installed service clearance such that you will be able to vacuum the entering air side of the evaporator coil. Perform this when the coil is dry. Service the seawater strainer regularly and install the largest strainer practical for your installation. Vacuum the discharge grille and the return air grille to remove dust. Do not install additional filters on the return air side.


Good luck with your installation.

[wingssail]

Our experience is a little different (surprise).

We've used 8000btu window units on our boat in Hong Kong, Thailand, the Caribbean, and elsewhere. Currently we are in Puerto Vallarta Mexico. The average high temperature during the summer is around 90F with maximums around 100. The humidity is low 90% range.

We take our air conditioner out of the aft locker around June 1 and place it in the companionway until November 1. It is narrow enough to step past it on one side. When we go sailing we shift it to the dock. We have never used it at anchor or sailing due to insufficient AC power.

Our boat is 43' fiberglass flush deck sloop. The hull is dark blue awlgrip (moderately insulated), deck is white (balsa). We have tall white shade awnings (also for rain catching) which cover the majority of the boat.

We have the forward half of the boat curtained off, leaving the salon, galley, nav area and aft cabin open to the air cond.

Our main salon and aft cabin are tolerable during the heat of the afternoon (78-83) and cool the rest of the day. When we come indoors on a hot afternoon it feels real good. Nights can be chilly with the AC on. At medium to low settings it cycles during the night. It uses about 7 amps running full power.

More cooling capacity would bring the following problems for us:
Where to place it
How to get enough watts to run it
How to pay for it, at $.22 kwh

Keeping with our strategy of a simple, less complex, and lighter, boat, which we can and do sail very often, year around, this is a solution we can live with and afford.

BTW, since we have no place ashore to store it we keep it in a locker onboard all winter and that includes during races, which we nevertheless can quite often win.

[zeehag]

as keel cooling fails in hot water i use a window unit temporarily placed into formosa window in my formosa. some place theirs in overhead hatches with a modification they create for the housing of the unit. .
there was a study which showed the efficiency ratings of window units as compared to others is better. ok. donot know where that is now, but it was a few years ago. so , unless someone has improved the alternatives, i will continue to use 5000 btu window unit in my formosa 41. works well. gets 120 here max, plus humidity, on occasion, so ac is a mandatory life saving piece of kit.
at anchor even in heat, the breezes are such ac is not needed. just place a shade screen over boat and open ports in bow for thru breezes.

[Sand crab]

Keith, the quickest cheapest way to deal with this is to buy one of the many portable household units but this is really only good for dockside or some can be paired with the right genny if at anchor. They have an exhaust tube that you stick out the port or hatch and that's it for installation. Some might have an additional air intake tube. Around $500 and you will be cool today.

https://www.walmart.com/ip/Honeywell...Fb4frQYdKEYCkw

[rbrentp]

Some small adds to others' comments. 35 ft cat, 12,000 btu ducting to main bridge area and sleeping birth. Rear cabins closed off. Made two adjustments: One, made sure cold air was not going to bilges - cold air heavier, etc. They were always cold first. Two, put on a soft start although they are called hard start and easy start, depending. A capacitor that provides the boost for the compressor start dropping amp load a lot.


If the boat gets hot it takes hours to cool down. At night it can freeze you out.


The silver reflective tarp/tent is ugly as hell and everyone hates to look at them except the guy in the boat with the ac running. Temp differential is amazing. Cooling a 95F boat is a lot easier than 125F boat.


I had a full rubberized canvas (18 wheeler type) cover made to fit over mine. It is white, I wish it was silver.