How Many BTUs AC on your 50ft(ish) catamaran

[Chotu]

So, I have 30,000 BTUs of air conditioning on my 50 foot catamaran. I’m still doing some fine-tuning and trying to slow the ingress of heat in general. Air conditioning works, but it’s not super cold super fast. It takes a long time to pull it down.

What are you working with on your 50ish foot catamaran?

[rslifkin]

If you're starting out with an already hot boat, I'm not surprised it takes some time to pull the temperature down.



My boat is the same way, but once you get it cooled down, just the 16k BTU unit in my salon and forward stateroom will keep the salon at 74* in 95* weather with full sun. The 10k in the aft stateroom will easily do the same back there, and the 10k up forward is really only for when you want to close that door (or for a faster cooldown on a really hot day).



However, you've got more window surface than I do I think, so it might be a bit harder for you to get things cooled down on the bridgedeck. The hulls should be fairly easy to cool though.

[Chotu]

Thanks for that data point. We do have probably fairly similar interior volumes.

I might have just a tiny bit more. But maybe not.

And yes. I’m talking about going from a boat that is in the high 90s inside to something survivable. LOL

I am just testing out the air conditioning a little bit. I haven’t put all of my reflectix panels up yet, but it got unbearably hot just now so... good time to play with air conditioning. Ha ha.

I’m basically eliminating all those problematic windows with the inserts that you use from the inside. Without these inserts, there is no change in temperature.

[Chotu]

I also have all of my air conditioning on the bridge deck. I am relying on convection to get the hulls.

[CalmSeasQuest]

I have a FP Saba (50', 4 cabin + smaller midship crew cabin) with 60K BTU (3X 12K BTU, 3X 8K BTU Dometics)

It's more than enough to cool the entire boat under any conditions encountered thus far in the Caribbean.

[Chotu]

Originally Posted by CalmSeasQuest

I have a FP Saba (50', 4 cabin + smaller midship crew cabin) with 60K BTU (3X 12K BTU, 3X 8K BTU Dometics)

It's more than enough to cool the entire boat under any conditions encountered thus far in the Caribbean.

Wow. That is incredible. Thank you for that data point.

I am hoping that I am not under cooled. But it sounds like that might be possible.

I may have to take the approach of just cooling areas that we are in. And closing off areas that we are not.

We only have two staterooms. It’s an extreme owners version. The head and shower take up half of one hull. We made everything big. Because it’s just for a couple and may be a guest. That’s why we have a second state room.

So hopefully we can close off some areas if we are a little light on the air conditioning.

[rslifkin]

The big one that'll help is if it's going to be a really hot day and you want the A/C on, get it going in the morning. Keeping the boat cool when it starts out cool is much, much easier than cooling it down from 95* in the late afternoon.

[Chotu]

Originally Posted by rslifkin

The big one that'll help is if it's going to be a really hot day and you want the A/C on, get it going in the morning. Keeping the boat cool when it starts out cool is much, much easier than cooling it down from 95* in the late afternoon.

Ahhh. Ok. I was trying to save fuel.

[rslifkin]

Originally Posted by Chotu

Ahhh. Ok. I was trying to save fuel.

It's a bit of a different equation when out and on generator power. In those situations, I try to avoid A/C as much as possible. When the weather is hot enough that I need the A/C a lot, I'll often hunt for somewhere I can plug in. If in an area where dockage isn't overly expensive, it often makes more sense in my mind to spend a few bucks to plug the boat in, vs the noise, fuel burn and wear of lots of generator runtime.

[Chotu]

Originally Posted by rslifkin

It's a bit of a different equation when out and on generator power. In those situations, I try to avoid A/C as much as possible. When the weather is hot enough that I need the A/C a lot, I'll often hunt for somewhere I can plug in. If in an area where dockage isn't overly expensive, it often makes more sense in my mind to spend a few bucks to plug the boat in, vs the noise, fuel burn and wear of lots of generator runtime.

Well, definitely I’d agree with your strategy.

I’m off grid at my construction dock so it’s all generator all the time here for air conditioning. Usually I am pretty land independent too, so it’ll be generator air conditioning all the time for this thing unless I have the luxury of a dock. Almost never happens. I anchor and travel continuously typically.

I’ll finish my reflectix panels and get them installed then try again.

[rslifkin]

The reflectix panels will definitely help. Plus, once you get the boat finished, you gain the option of moving around in search of cooler weather.

[BillKny]

We don't have the raw solar gain through the kinds of windows that the typical catamaran has, but it still makes a HUGE difference on our boat if we put up our shade cloth awning.

Even a light colored thick balsa core deck transmits a LOT of heat when the sun is vertical. This is not practical if you have a deck covered in solar panels, but when I see people talking about running 60kBTU AC units, holy crap! Five tons of AC! That's way more than most household units. I am guessing that's about 6 or 7 kilowatts?

I am wonder if shading the deck (and loss of any solar) might actually result in lower fuel bills just by cutting the duty cycle of that monster power suck.

We have two AC units on a 50 foot mono, 8000 btu each. We have only ever used them at the dock, although we could out at anchor, just never felt the need.

[Chotu]

Data points so far:

50ft Fountaine Pajot - 60,000 BTUs
38ft Chris Craft - 36,000 BTUs
50ft Mono - 16,000 BTUs

[Coolerking]

If the window covers are not on the outside of the glass, they are useless.
The heat has gotten into the boat.

[Chotu]

Originally Posted by Coolerking

If the window covers are not on the outside of the glass, they are useless.
The heat has gotten into the boat.

Reflectix and XPS panels are being used.


Not looking for this type of information, especially when incorrect.


Looking for BTUs on 50ish foot catamarans or similar, to compare and see how mine stacks up.

Data points so far:

50ft Fountaine Pajot - 60,000 BTUs
38ft Chris Craft - 36,000 BTUs
50ft Mono - 16,000 BTUs