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Old 07-11-2015, 03:32 PM   #1
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Marine A/C Question

My bride and I are looking at trawlers and have seen several with either a window unit or a rooftop RV style unit in addition to a typical marine A/C unit. My question is what would be the advantage of having both? Obviously the purchase price of a window unit would be much less than the marine unit, but they are so noisy and not ducted throughout the boat. Am I missing something?

Thanks!
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Old 07-11-2015, 03:58 PM   #2
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They don't pump water through your boat when you are absent...some people including me are nervous about that no matter how well maintained the marine systems are.


I am looking into a trip relay that will cut off the pump when a float switch senses a lot of water in the bilge.
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Old 07-11-2015, 04:01 PM   #3
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The ducting and air distribution throughout a boat is only as good as the installer and space allows.
One problem I see is the return air inlet is not usually high enough to draw hot air off the top of the highest cabin. This is where a rooftop rv unit would work well, also no water pump, lines etc, to clog or winterize. Not quiet but not sure if any air conditioning on a small boat is quiet. Often thought an in wall window unit in the rear of the main cabin above the aft cabin may be the ticket.


I have the traditional 16k btu package marine ac on my 32 foot trawler--works well but not quiet.


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Old 07-11-2015, 04:11 PM   #4
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The ducting and air distribution throughout a boat is only as good as the installer and space allows.
One problem I see is the return air inlet is not usually high enough to draw hot air off the top of the highest cabin. This is where a rooftop rv unit would work well, also no water pump, lines etc, to clog or winterize. Not quiet but not sure if any air conditioning on a small boat is quiet. Often thought an in wall window unit in the rear of the main cabin above the aft cabin may be the ticket.


I have the traditional 16k btu package marine ac on my 32 foot trawler--works well but not quiet.


JohnP
Very good points - thank you for the feedback
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Old 07-11-2015, 04:12 PM   #5
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They don't pump water through your boat when you are absent...some people including me are nervous about that no matter how well maintained the marine systems are.


I am looking into a trip relay that will cut off the pump when a float switch senses a lot of water in the bilge.
I had not thought about the potential water issues. Good points - thank you!
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Old 07-11-2015, 04:24 PM   #6
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A properly set up system will turn off the pump and compressor when water flow ceases. And of course, a properly maintained and plumbed system won't leak to begin with.
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Old 07-11-2015, 04:28 PM   #7
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A properly set up system will turn off the pump and compressor when water flow ceases. And of course, a properly maintained and plumbed system won't leak to begin with.
Multiple A/Cs on one pump?


Guess that would be a good reason to go one pump per A/C.
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Old 07-11-2015, 04:30 PM   #8
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Scott, we have a relay for our ER blowers, I'll find you a part number. Should work for what you need.
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Old 07-11-2015, 04:32 PM   #9
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A properly set up system will turn off the pump and compressor when water flow ceases. And of course, a properly maintained and plumbed system won't leak to begin with.
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Old 07-11-2015, 05:11 PM   #10
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A properly set up system will turn off the pump and compressor when water flow ceases. And of course, a properly maintained and plumbed system won't leak to begin with.
Yes, but a leak in the water hose after it leaves the air conditioner itself will quickly sink the boat.

As for properly maintained systems not leaking, you are putting a lot of faith in your ability to inspect not usually visible plumbing.

Like a salt-water washdown pump, air conditioning is a bit of a loaded gun.
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Old 07-12-2015, 08:07 AM   #11
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The rooftop units are made in far greater numbers , so improvements come years earlier.

Many can be had with low amperage requirements from better components at the same BTU rating.

Soft start is also common so they will work when the dock voltage gets low.

Best of all most are under a boat buck ($1,000) so can simply be tossed when old and broken with no repair specialist required.

They are louder on high than the usual boat ducted system , but in the evening on low , they are great.

They are about 100lbs so the rooftop must be OK.

Compare at
Camping World: RV Supplies, RV Accessories & RV Parts ...

www.campingworld.com/
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Old 07-12-2015, 11:10 AM   #12
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Yes, but a leak in the water hose after it leaves the air conditioner itself will quickly sink the boat.

As for properly maintained systems not leaking, you are putting a lot of faith in your ability to inspect not usually visible plumbing.

Like a salt-water washdown pump, air conditioning is a bit of a loaded gun.
It's really almost a non issue. A/C water leaks are very rarely catastrophic. Nor common. Plus there is very little pressure on the water hoses, fittings, etc.

And besides, you have a good, independently powered high water alarm, right?
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Old 07-12-2015, 01:25 PM   #13
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And besides, you have a good, independently powered high water alarm, right?
That was going to be my point as there are many things that could possibly sink a boat. While one key is having everything in condition that leaks and other issues are highly unlikely, the other key is detection of a problem and immediate attention to it.
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Old 07-12-2015, 01:55 PM   #14
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assuming everything else is perfect and no chance of progressive flooding and you make it back to your boat in a reasonable time...I agree that it's a rare chance..but in my mind much bigger than many threads about hoses and flooding that some seem overly concerned about.


Only a few systems intentionally introduce more water than a dribble within the hull when you aren't present.


Having a cutout circuit for high water seems just as important than many things others but I don't worry about based on my experiences with boats sinking at the dock. Especially with a relay that costs $10 and a float switch for $25-$150 bucks.
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Old 07-12-2015, 05:31 PM   #15
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Yes, but a leak in the water hose after it leaves the air conditioner itself will quickly sink the boat.

As for properly maintained systems not leaking, you are putting a lot of faith in your ability to inspect not usually visible plumbing.

Like a salt-water washdown pump, air conditioning is a bit of a loaded gun.
So let me understand this, it can sink your boat but it is not worth the trouble to make sure it is sound???? Not only that, you're willing to buy a boat where something that you think could sink it is inaccessible? I take it you stimp on bilge pump capacity as well?
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Old 07-12-2015, 05:36 PM   #16
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Multiple A/Cs on one pump?


Guess that would be a good reason to go one pump per A/C.
Huh? If multiple ACs are on one pump a proper pump relay system will shut it down for all. Not that one pump per AC is a bad thing at all... other than the extra strainers and through hulls.
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Old 07-12-2015, 05:49 PM   #17
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Huh? If multiple ACs are on one pump a proper pump relay system will shut it down for all...
Yes, but you'd be surprised how many boats run systems where the pump is on it's own breaker and is turned on when the AC/reverse cycle is on, ie; no trigger box. It's old school but done a lot.
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Old 07-12-2015, 06:30 PM   #18
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I have a relay box made by the manufacturer that triggers when an A/C demands the pump...so I am guessing if 2 A/Cs are running and one trigger stops..the other keeps it running as it doesn't know if the one A/C is just powering down or shutting down for water flow error.


Don't get me wrong about being overly concerned...just I think a simple emergency shutdown is on par with so many other emergency systems aboard.
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Old 07-12-2015, 08:19 PM   #19
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You're guessing about a system that you think could sink your boat? Your bilge pumps would be overwhelmed if this system pumps into the boat rather than the exterior? Why?
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Old 07-12-2015, 08:56 PM   #20
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Believe it or not...I do think...much faster and way beyond many of my posts and the replys.


I understand system failures from many years of aircraft/vessel accident prevention/investigation.


I understand operational risk management pretty well.


Trying to explain my complete position in a couple paragraphs will never happen.


I have followed the "accepted" methods, equipment and proceedures for the system.


Do I trust it???...pretty much yes...100%...well not exactly.


Been in the boat sinking business too long to trust anything 100%.


yes my bilge pump system well exceeds any onboard pump that pumps INTO the boat...yes I used good hose...yes I used double clamped AWAB clamps, yes I have high water alwarm...yes...yes and yes....


Why do other boaters who do the same also have live monitoring of their boat through the internet? Because????


All I'm talking about is a simple pump relay that cuts off the pump if the water in the bilge is far above what it should be.


Probably far less a big deal than the 32 ways people try and figure out their anchor isn't dragging.


Guessing is always part of risk management...then comes..."what can I do about it and is it worth it"....no big deal..just my nature.
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