Location of Self-Contained Marine A/C?

I am in the process of planning a new installation of a self-contained marine A/C unit but have a question about location. I have read numerous product installation manuals and looked at installation diagrams, but cannot find an answer.

My question is, can the unit be placed below the waterline?

Every diagram I have found looks like the attached. i.e. the A/C unit is always above the waterline, with a constant rise on the raw water intake side and a fall on the water output side. But, when reading the installation manuals, it is suggested the units can be placed under a V-Berth. However this to me would most likely be below the waterline.

In my installation I need to cool the an above deck saloon area as well as two below deck cabins, both in the forecastle. I would like to select a single A/C unit with two outputs and place it under the queen berth, with ducting running forward to output under the V-Berth, which would direct cold air backwards. The second outlet would be run into the saloon and output under the settee, directing air forward.

The return air would be underneath the queen berth in the cabin between the V-Berth cabin and the saloon, which I would expect help airflow to circulate and draw air into the queen cabin.

But this would mean the unit is mounted below the waterline.

Is this possible?

If so, how does the water outlet drain when it has to run uphill?

Or, is the key here the seawater pump. i.e. the pump provides enough pressure to push the raw water through the A/C unit and uphill to exit above the waterline?

It should be fine there. The cooling water pump needs to be below the waterline since they aren’t self priming. The intake to the water pump should be a rise from the intake to the pump so it will prime. From the pump to the A/C and on to the discharge isn’t a big deal because the water will be under pressure from the pump. The drain pan needs somewhere to drain to below the unit. If you have a shower sump that is below the unit that would be a good place to run the pan drain to. If no sump then you will need to have somewhere to run the drain from the pan to.

Yes you can do it. You will want to loop the discharge around 18" above the waterline and have the through hull discharge above the waterline. I would also want a siphon break just after the pump. This would be the hose after the pump going above the waterline, teed, and the third leg of the tee well above the waterline or overboard.

Are you or your wife a light sleeper? The blower may switch speeds and the compressor will be intermittent. Something to consider when mounting it under your bed. You really can't noise silence the return air duct without creating problems. Just something to consider.

Ted

Thanks both for your responses. Sounds like I can do what I was planning. I do have a shower sump right opposite the cabin where the unit will be placed. So the drain will be easy to run to the sump.

O C Diver said:

You will want to loop the discharge around 18" above the waterline

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I'm curious why you recommend that. I'm sure mine are nowhere near that high up.

I get that you don't want them too low, where they could take in water, especially on a sailboat which is routinely heeled. But one disadvantage to the higher discharge is louder splashing noise from the outflow. I've seen them just above the waterline for that reason.

CaptTom said:

I'm curious why you recommend that. I'm sure mine are nowhere near that high up.

I get that you don't want them too low, where they could take in water, especially on a sailboat which is routinely heeled. But one disadvantage to the higher discharge is louder splashing noise from the outflow. I've seen them just above the waterline for that reason.

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Sorry if I wasn't clear. The hose loop needs to go well above the waterline. The through hull can be a few inches above the waterline. With the siphon break near the pump and the high loop, you have effectively eliminated siphoning from a leak between the discharge loop peak and the siphon break after the pump.

Best practice also prescribes a similar loop for each bilge pump to eliminate back siphoning.

Ted