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Old 06-02-2019, 03:51 PM   #1
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16k to 24k?

We have two 16k btu units on board. Right now in 90 degree full Texas sun, they can only keep us about 78-79 degrees during the day.

Would kicking them up to 24k but units help? I donít understand BTUís enough to know what the result would be.
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Old 06-02-2019, 04:33 PM   #2
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We have two 16k btu units on board. Right now in 90 degree full Texas sun, they can only keep us about 78-79 degrees during the day.

Would kicking them up to 24k but units help? I donít understand BTUís enough to know what the result would be.

I'll let the AC experts reply, but insulation, thermal windows and shades help. And cool water which you probably won't have at the surface.



Also, be sure the AC units are clean and in good condition.


In the 90d summer sun, I have a similar problem unless all window shades are closed and the covers are on and no one goes in or out.


I'm thinking of adding window tint this summer. I only have a 12 and a 16.
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Old 06-02-2019, 05:01 PM   #3
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When single & not subject to the thermal needs/whims of anyone else, here in NC I kept my home HVAC set at 78 degrees in the heat. That took care of ambient temperature. I used ceiling & other fans to cool myself when active or too warm at leisure. My working theory has always been individual comfort doesn't require that the entire abode be identical to the micro-environmental conditions that I need in proximity to my body, whether active or at rest. It's a tiny bit philosophical & bigly cheaper to function that way (I do the reverse in the cold of winter, with the aid of longjohns & small heating devices, including a toasty bald cat). On board in the tropics for several years sans A/C, the solution was equally simple--lots of canvas shade, a windscoop at anchor & a bevy of 12V fans installed so they could focus on any spot where a body could sit or sleep. My clever skipper modified a couple of the fans to sit in winches & aim at the cockpit seats. As long as we stayed on the boat, we never suffered from the tropical heat (note: we also didn't wear a heck of a lot of clothes unless entertaining). Just remember, ambient temps do not necessarily need to be the same (hot or cold) as the temp in proximity to the bodies in need of heating or cooling. The same goes for lighting. Plan ambient lighting as separate from task lighting for the greatest efficiency.
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Old 06-02-2019, 05:46 PM   #4
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Before you replace, clean the heat exchanger with Barnacle Buster and spray foam the evaporator coil with standard HVAC cleaner. Next, understand that raw water flow through the heat exchanger (condenser) dramatically impacts the cooling capacity (especially when the sea water is in the 80s).

A digital HVAC thermometer is your friend. Less than $20, they will tell you how cold the air is coming out of your AC vents. If both your units run off the same raw water pump, block the flow so that all the water goes through one unit. Take before and after temperature readings at the vent. You may find increased water flow could make a big difference. On my charter boat, replacing the raw water pump with maybe twice the flow, substantially increased the output. Made enough difference in the bunk cabin that the compressor no longer ran continuously as opposed to the cabin being warm.

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Old 06-02-2019, 05:58 PM   #5
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My AC’s are fine, it’s just THAT hot outside. It’s already hard to breathe outside just walking the dog. In fact, I just cleaned strainers and blew the lines out yesterday. And our bow faces afternoon sun. The shallow bay water we are in is also up in temperature.

Would that silver windshield bubble things help on the windows?
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Old 06-02-2019, 06:01 PM   #6
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Weíre on the downhill side, the forward AC just dropped to medium speed fan. But this is what today looked like. We didnít hit these temps until about July last year.
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Old 06-02-2019, 06:31 PM   #7
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Greetings,
Mr. tc. IF you're in the direct sun, almost anything would help on the windows.
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Old 06-02-2019, 08:57 PM   #8
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My 38 has a 12 and 6.5kBtu. In Florida summer and full sunshine, it will not keep it below 80F in the pilot house. But that is fine. Cooler than outside, and rarely are we just sitting in mid day, usually underway with windows open and a good breeze.

The big deal is at night getting good sleeping temps. It is fine then. We often turn off the 12k pilot house unit and just run the 6.5 in the cabin, cools just fine.
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Old 06-02-2019, 09:03 PM   #9
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External shading is more effective than shading inside, like the shiny bubble wrap stuff. Although it helps to reduce some of the infrared transmission, because it's inside the glass, a percentage of the IR is still transmitted through the glass and into the space. External shading stops the IR before it gets inside.
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Old 06-02-2019, 09:03 PM   #10
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I would cover the windows on the outside, put some of the bubble insulation on the inside and do the checks suggested on the A/Cs. I am not sure if there are 24K units that run on 120 or not, havenít checked lately.
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Old 06-03-2019, 06:53 AM   #11
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Quote:
Originally Posted by toocoys View Post
My ACís are fine, itís just THAT hot outside. Itís already hard to breathe outside just walking the dog. In fact, I just cleaned strainers and blew the lines out yesterday. And our bow faces afternoon sun. The shallow bay water we are in is also up in temperature.

Would that silver windshield bubble things help on the windows?
I thought mine was also.

To give you a reference point, my 45' trawler in the avatar, has three 12,000 BTU units and does fine on 90 degree days when the water is in the 80s. How about posting a picture of your AC water flow discharge.

Has either of your units, the water pump or duct work been modified? I find it hard to imagine that the boat manufacturer wouldn't install adequate AC for 90 degree temperatures.

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Old 06-03-2019, 08:17 AM   #12
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We have two 16k btu units on board. Right now in 90 degree full Texas sun, they can only keep us about 78-79 degrees during the day.

Is that the temp being reported at the control unit? Or in the middle of the saloon or berth?

FWIW, our saloon control unit is bulkhead mounted and accuracy is affected by outside temps... so if the control unit says it's 80įF... it's really only about 74įF in the middle of the saloon...

If you have MarineAirrrr Vector Compact ACs -- possibly common from Mainship in that era? -- I've read that the Dometic Vector Turbo units (same btu) are the bee's knees: much better cooling, much quieter, no rust in condensate from the composite drain pan. Said to be an easy drop-in replacement... although that'd be boat-dependent.

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Old 06-04-2019, 06:01 AM   #13
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I thought mine was also.

To give you a reference point, my 45' trawler in the avatar, has three 12,000 BTU units and does fine on 90 degree days when the water is in the 80s. How about posting a picture of your AC water flow discharge.

Has either of your units, the water pump or duct work been modified? I find it hard to imagine that the boat manufacturer wouldn't install adequate AC for 90 degree temperatures.

Ted

Good points. And didn't know that increased water flow would provide better cooling. I've got one pump that runs two AC units I'm going to try to run one and see if that unit runs cooler than if I'm running both units. I could consider adding a pump and having one for each unit, and would provide a backup.


A HUGH thing is the heating thru the windows. A boat like mine with nothing on the window won't cool a bit in 90d temps, even though I'm getting 70d air out of the unit. When I put the exterior covers on, pull the shades and close the blinds it makes a huge difference.



And considering some of the heat reflective window film. Just the simple static cling film which is easy to install or remove makes a difference. And I'm considering the new ceramic film, but a bit more permanent.
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Old 06-04-2019, 08:01 AM   #14
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Good points. And didn't know that increased water flow would provide better cooling. I've got one pump that runs two AC units I'm going to try to run one and see if that unit runs cooler than if I'm running both units. I could consider adding a pump and having one for each unit, and would provide a backup.
If you want to see the difference in real time. Disconnect the raw water inlet to one of your AC units and adapt a dock hose with a flow valve to the AC heat exchanger. With an HVAC thermometer in the vent, start the AC with low water flow. Monitor the vent temperature as you add more flow. You will need to wait a few minutes after each flow adjustment for the AC system to balance to the new flow rate / cooling effect. Water temperature also plays a key factor in cooling. So if dock water temperature is cooler than sea water temperature, that will make a difference also.

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Old 06-04-2019, 08:36 AM   #15
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Originally Posted by O C Diver View Post
I thought mine was also.

To give you a reference point, my 45' trawler in the avatar, has three 12,000 BTU units and does fine on 90 degree days when the water is in the 80s. How about posting a picture of your AC water flow discharge.

Has either of your units, the water pump or duct work been modified? I find it hard to imagine that the boat manufacturer wouldn't install adequate AC for 90 degree temperatures.

Ted

You've convinced me to run Barnacle Buster through my AC water lines. I'm willing to bet they've *never* been cleaned. Mine are marginal on very hot days. I might get a nice bump in output.



Ken
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Old 06-06-2019, 04:32 PM   #16
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So as it turns out, I have a 16k btu in the salon, and an 8k btu in the stateroom.

However I ran barnacle buster today and it made a TREMENDOUS difference in cooling. Waterflow is higher and differential temps are WAY lower.

First pic is before cycle, just water and Barnacle Buster. Second photo is after cycle. The amount of little pink algae that came out is incredible.
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Old 06-13-2019, 01:24 PM   #17
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If you have MarineAirrrr Vector Compact ACs -- possibly common from Mainship in that era? -- I've read that the Dometic Vector Turbo units (same btu) are the bee's knees: much better cooling, much quieter, no rust in condensate from the composite drain pan. Said to be an easy drop-in replacement... although that'd be boat-dependent.

TC, realize you've improved water flow so your issue has improved... but thought I'd close the loop on the Turbo thing.

Our local installers surprised me by showing up a week or two ahead of schedule, and 2 hours later I've got a new Dometic Turbo DTU16 to replace on of the original 2002 Vector Compact ACs... which was working OK but with a really loud (and getting louder?) compressor.

Sure enough, the new unit is quiet; I haven't even closed up the cavity yet and I can't really pick out the compressor sound unless I try. Can't hear the fan motor at all. And that's without the optional sound shiels, that I guess I probably won't need. The loudest sound now is air movement, and the new unit is moving a boatload more air than the older AC did... and the older one had pretty good air flow anyway.

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Old 06-14-2019, 02:04 PM   #18
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Hola' - we live on a 34 Mainship is south FL and installed a new Dometic 12k BTU AC 2 yrs ago. As you can imagine the seawater gets very warm this time of year. We also have internal blinds with custom external window screens that block greater than 50% of the sunrays (I think it may be up to 75% blocked but it's been several years since we had them made so I don't recall exactly). We also configured the A/C water hoses with a valve/pigtail setup for easy periodic flushing with Barnacle Buster. All things combined with frequent checking of water output water flow, strainer cleaning as needed, and flushing every few months keeps the cabin including v-berth cool even during the heat of summer. Sometimes we will also suspend a homemade sun screen over the bow (covering the v-berth) for added shade during the hottest days. Also, checking and cleaning the air filter is a must, plus we sometimes take compressed air and blow out the coils (while running our shop vac next to it to suck in any dust debris and minimize how much floats out of the A/C cabinet). We are very pleased and happy with the performance year round.
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Old 06-15-2019, 09:01 AM   #19
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Another plus-up for the Dometic DTU (turbo) units. I found the OEM 7KBtu Dometic ac unit inadequate in this red boat in 90-degree water on a 98-degree day until about 10 PM, when running at 100% duty cycle, it finally cooled the smallish downeast cabin to 78F. I swore that I would someday replace it with a higher capacity unit. That opportunity came 13 months ago when long term corrosion due to a previously clogged pan drain system ended the life of the OEM unit. I planned to replace it with a standard Dometic 10 KBtu unit, but found it would not physically fit in the small area designated for it. However, the Dometic Turbo 10KBtu unit fit well. Cost was hugely more, though.

The first thing I noticed when I unpacked the DTU was the abundance of shiny copper and the plastic drip pan. The Turbo performed well on what for an air conditioner was a challenging 6-day trip in the Florida heat. It is very quiet, and now that I have a Micro-Air soft starting microprocessor installed, its fairly quiet compressor startup sound as well as the generator loading sounds are simply not heard. I note that this unit is right under the bunk.

The dealer told me that there are a number of firmware subroutines running in the DTU and that it should not be shut down using a breaker (nor should ANY electrical equipment aboard). In support of that, I note that it takes a number of seconds before the CAL pump shuts down after I press the off button on the ac's control panel; so I don't jump to the breaker panel too quickly after shutting the ac down.

I also upgraded the seawater pump from a March to a CAL 900. Don't remember the capacity of the March, but the CAL is somewhat more.

AFAIK, 16 KBtu is as big as you can go in 110 VAC units. Before upgrading the ac unit in a boat, be sure the existing hose sizes in the boat match the new unit and that the water flow capacity is correct and that the breaker is also sized properly.

Glad you got your unit working well with Barnacle Buster. I just solved my generator's overheating issue with a BB flush. Now maybe I will give the ac a wash with it too. Luckily my hardtop ac is air-to-air!
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Old 06-16-2019, 12:41 PM   #20
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We have the same boat as you in the 40' edition. Bought it used with a 16K in the salon and 12K in the forepeak, both original Marine Air. After several summers of never being cool in the salon, I replaced the 16k with a 16k Webasto FCF unit. Much quieter, and could freeze us out. I later replaced the forward 12k with a 6k Webasto, and it is more than adequate, especially considering it is usually only used at night. An added benefit, I can run the forward AC on the inverter if I chose, but must charge the batteries first thing in the morning.
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