A/C advice please...

Greetings all, I am purchasing a converted shrimp trawler that currently doesn't have A/C. I have looked at units online that are both 'in roof' mounted, similar to RV's as well as ducted units mounted inside a cupboard or similar. Aside from the crappy looks of the roof mounted types, is there a great deal of difference in performance between the systems? The prices appear markedly different....thankyou for your time and wisdom...

Depends on how many amps AC electric available, the total spa e to cool. the temp of tbe water and air temp. Usually the amps avilailible is the limiting factor. I elected to use cheap domestic window AC, four 6000 btu, using 40 amps 120 volts. The main reason I didi not to cut more holes in the hull, and raw water running thru the boat.

There are several alternatives.

A ducted marine unit is basically a water-source heat pump. They're more efficient than an air-source (window) air conditioner. Also they provide a finished, built-in look. And typically they have a reverse cycle, which means you can get heat and AC from the same unit.

If you've heard the hype about "geothermal" systems for your house, and how much more efficient they are, it's the same thing. Geothermal is a misnomer, they really are just ground-source heat pumps. But that's not as catchy, from a marketing standpoint. Boats have it easy, with an unlimited supply of source water just inches away.

The RV rooftop work well and can be had in large BTU capacity and still run from a crappy 15A plug.

Look for "soft start" models and the high efficiency models.

They are RV so if the sea spray regularly douches the unit its life will be shortened.

AS cold sinks a pilot house mount should cool the lower decks as well,a fan may help.

DO not get a unit that is way bigger than you require as it will cycle too frequently and dehumidify very poorly.

You need at least 50% on time to de humidify well.

Since the unit is high and heat rises no extra duct work for required return air is needed.

The required 14x14 RV hole can fit other items like a Fantastic fan set if the unit doesnt work out.

At over 100lbs beware of G loadings on the cabin top.

How big is the trawler? Might help in figuring the air requirments.

The Eagle came with a roof top AC on the pilot house roof so we have 5separate units. We have use the the dirt ones on fan mode to clean circulate the air as the AC is needed only a couple days during the year. I been leaving the plexa glass over the windows all year. By the way the dirt units are mounted inside the boat not out side.

Thankyou for the info Gents, the trawler is 47ft long by 15'6" and I did a quick calculation that the internal cubes are 2100...we will be spending most of our time in the Gulf and when I gain skills, more tropical climes so an A/Cwill most likely be crucial to marital harmony...

more tropical climes so an A/Cwill most likely be crucial to marital harmony.

The std boat units in tropical climes can suffer mightily from ingesting jelly fish or trash into the water side of the units,as will the noisemaker.

IF lots of time will be tropical either keel cooling (BEST) or a screened sea chest for sea water pickup is required.

No fun at all getting out of the sack 3 -5 times a night with a stick to clear sea water intakes to keep the air-cond or noisemaker operating.

I will install these on my boat one day. When I get a large enough battery bank and an inverter one of these units only requires 700w to run, they are ultra quite and they can install (the outside unit) on top of the boat. They have these all over the beach down here in south ms. and the salt air doesn't ruin them as quick as you would think. One outside condensing unit can run up to five inside units independently. Air-conditioning Systems - Products - Room Air Conditioners

AussieCraig said:

Thankyou for the info Gents, the trawler is 47ft long by 15'6" and I did a quick calculation that the internal cubes are 2100...we will be spending most of our time in the Gulf and when I gain skills, more tropical climes so an A/Cwill most likely be crucial to marital harmony...

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A distribution of the lay and where AC is needed will also help. I went with smaller units so the AC could be turned on where needed will ratber than one big unit. I also have each unit on timer. In the morning the master is cool enough so only one state room and salon is needed on low energy mode and at 10 the other two kick on. we keep the boat closed up. one summer ran water down the front deck to cool. most summer have a silver tarp floating over the front deck to reflect the sun. Temp above 70 native PNW start to wilt. Deep down we are wantbe vampires.

swampu said:

I will install these on my boat one day. When I get a large enough battery bank and an inverter one of these units only requires 700w to run, they are ultra quite and they can install (the outside unit) on top of the boat. They have these all over the beach down here in south ms. and the salt air doesn't ruin them as quick as you would think. One outside condensing unit can run up to five inside units independently. Air-conditioning Systems - Products - Room Air Conditioners

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Really ? 700W ? THAT would be a winner indeed, 2-3 indoor heads with one outside condenser...any ideas on price ?

Phil Fill said:

A distribution of the lay and where AC is needed will also help. I went with smaller units so the AC could be turned on where needed will ratber than one big unit. I also have each unit on timer. In the morning the master is cool enough so only one state room and salon is needed on low energy mode and at 10 the other two kick on. we keep the boat closed up. one summer ran water down the front deck to cool. most summer have a silver tarp floating over the front deck to reflect the sun. Temp above 70 native PNW start to wilt. Deep down we are wantbe vampires.

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We too are 'children of the night' however most of society expects us to be up and around during daylight...

The better half does not deal well with heat or humidity despite being a native Texan so I will have to come up with some solid cooling or else...

I don't know about price but it is competitive with house air and heat. Maybe about $2,500 - $4,000 depending on what you want. I am sure the straight air is cheeper. That web site has tons of information. I would have them now but my old trailer style ac keeps on working. 700W could run all night on a batterie set up and then you would only have to run the genset to charge the batteries once or twice a day.

Phil Fill said:

A distribution of the lay and where AC is needed will also help. I went with smaller units so the AC could be turned on where needed will ratber than one big unit. I also have each unit on timer. In the morning the master is cool enough so only one state room and salon is needed on low energy mode and at 10 the other two kick on. we keep the boat closed up. one summer ran water down the front deck to cool. most summer have a silver tarp floating over the front deck to reflect the sun. Temp above 70 native PNW start to wilt. Deep down we are wantbe vampires.

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I surmise (we havent even taken posession of her yet, that happens mid July - YEEHAH) but its a large open salon/galley/helm area and the forward vee berth (to be modded into a queen bed 'stateroom' type deal) that will need to be cooled. So, one main unit in the large area and perhaps a smaller backup unit forward...or a ducted system...I do like the idea of several smaller units so we can be selective as to what is on at any given time...

Oh and I intend to install a fairly large solar array to supplement the 10KW gennie for offshore and the marina has 30 amp shore power so we should be preety OK I think...am I missing anything ?

AussieCraig said:

Oh and I intend to install a fairly large solar array to supplement the 10KW gennie for offshore and the marina has 30 amp shore power so we should be preety OK I think...am I missing anything ?

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AC takes a lot of amps. 30 amps is not much for AC. 30 amps 120 volts AC is equal to 300 amps 12 volts DC which will drain a battery bank in no time and solar will probably not able to produce enough? AC electrcity is usually the limiting factor and the wiring.

You really don't have to speculate, you can go right to any marine store web sites and get prices and specs. The 16,000BTU units are going to cost $1,500 to $1,800 each, plus the pumps, strainers, thru-hulls, hoses and ducts. The one linked below will consume about 11 Amps at 120VAC, but be aware of higher starting current.

Webasto FCF Air Conditioning Unit - Cool with Reverse Cycle Heat

Do the math, but my guess is you will want at least two of those, and maybe one smaller one, depending on how much interior space you want to cool and how the spaces are layed out. You may even get by with one 16K and one 9K.

Not sure what you've got for electrical service. You may want a new breaker panel and shoreside connection.

Dometic does make a rooftop that has been marinized .

No plumbing , no duct work and pretty quiet with the fan off HIGH.

Chop a hole , plug it in , done!

https://www.dometic.com/enus/Americ...ducts-Videos/DuraSea-Rooftop-Air-Conditioner/

FF said:

Dometic does make a rooftop that has been marinized .

No plumbing , no duct work and pretty quiet with the fan off HIGH.

Chop a hole , plug it in , done!

https://www.dometic.com/enus/Americ...ducts-Videos/DuraSea-Rooftop-Air-Conditioner/

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Its a tad exie but I suppose you DO get what you pay for...