I need help with marine a/c....

Recently purchased a 38' Roamer Regal 1971, and the vessel has a self-contained marine a/c unit located under the forward bench seat in the dinette.

The current a/c system is 16,500 BTUs. While this was undoubtedly fine for the boat's original home of Iowa, things are very different down here in Florida where the average day throughout much of the year is well over 90 degrees.

Thus, the boat needs more a/c capacity than it currently has, probably somewhere around 25,000 BTUs total. Though that is only a rough guesstimate, I know it is probably in that range.

My question is how to accomplish this? As you know, these have one shore power plug running 110v. The only single a/c units with enough cooling capacity that I can find run on 220, which is obviously a no-go. So it looks like a second self-contained unit is required.

Will I have to install a second shore-power cable, or can I run two units...say the 16,500 BTU and another 10,000 BTU, on the same cable, or am I going to have to install another shore power inlet?

The genset should be a non-issue, since the maximum power draw at startup for the two a/c units I am looking at is still well under 4kw and the unit has a 6.5kw capacity. So, ideally, I should be able to run both units plus accessories (water heater, stove, etc.).

Any tips? Anyone know what total BTU capacity would be adequate for the boat? What about the second shore-power cable? Advice appreciated!

That's a good suggestion. Can't believe I didn't think of having the existing one serviced instead of putting a new one in.

The installation looks to be 1980s-ish...maybe 1990s-ish at a stretch (still has the old 1980s style 3-knob "AIRRRRRRRRRRR" control panel), and the layer of dust caked on the mechanical unit seems to indicate that it has probably never been serviced at all, let alone to the extent that you are describing.

I guess it was one of those "out of sight, out of mind" things...it just didn't occur to me that it needed service. I figured it was like a house a/c, either it was broken or it was working. I will get the marina to do a service on it and see where that puts me, before installing another one.

Yeah, I too have seen people running a/c units off inverters but I always kinda scratched my head when I saw that. It is certainly possible to do it, and have it work just fine, but when you figure how much battery capacity you'd need to get any decent runtime out of it, it's mind-bogglingly expensive for what you get out of it.

You'd need six or eight series 27 or 31 batteries just to comfortably make it through the night with a 16,000btu unit. Each battery is going to run between $100 and $200, plus figure another $1,500-$2,000 for an inverter capable of running that load for long periods. Even if you are going to wire it yourself, you still end up paying almost as much as you could get a nice used genset for...which you could also install yourself if you're inclined to.

The main argument in favor of inverters seems to be that the inverter setup is silent and safer, compared to a genset. In my case, the decision is already made for me since my boat came equipped with a genset that runs fine.

I figure the $600 I would spend for a sound shield is still far cheaper than the inverter setup would be, and the same goes with buying a couple of CO2 detectors to eliminate the safety risk. To be honest, it's not loud enough to bother me....it's located back with the engines, so you barely hear it at all when you're in the forward cabin. CO2 detectors are currently lacking, though, and those will be addressed before I spend the night onboard with it running.

Anyway, my main concern with the second unit was running it dockside, and whether the single 110 power cord would handle the load of both a/c units. It seems like the consensus is to just install another shore power inlet to run the second unit, so I will go that route if I do end up putting another one in. In the meantime I am going to have the current one serviced and see if that improves things.