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Tscott8201 · 26-02-2015, 06:52

So I hate being hot and sweaty if I'm just hanging around. Don't mind it when I'm working, but just sitting killing time while I boil with sweat drives me nuts.

So are cats by their open nature cooler in the hot months than a mono? How do you keep a mono or cat cool without air conditioning? Can you divert airflow below decks to help keep it livable while in hotter climates?

Tom

**a64pilot** · 26-02-2015, 07:14

I don't want to make this a Mono or Cat thing as that just seems to get stuff started.

But with big sportfishing boats, one of the very first things that is usually done is those big, beautiful panoramic windows are covered to keep the hot sun out, if you don't it's like a Solar oven.
I'm going to go out on a limb and throw an opinion that a Mono with a boom tent to keep the hull in the shade would be cooler than a Cat, unless of course you can shade it too, if shade is equal, then I think who has the best airflow will feel cooler.

I'm only talking at anchor as that is when it seems hottest.
There are many hatch scoops made to direct air into the hatch, what works best for me is a cheap 20" box fan run off an inverter. Takes power though of course.

Airflow and shade seem to be the best way to keep a boat cool, other than AC of course.

sailorboy1 · 26-02-2015, 07:15

Are Mono's Hotter Than Cats? - yes when they take off clothes

Sorry. I don't believe there is a lot of difference air flow etc between monos and cats in general. I'm sure a given model of either could have a problem.

colemj · 26-02-2015, 07:20

Having owned both, here are my observations.

- catamarans are almost always cored hulls and decks, and this makes them radiantly heat up and cool down slower than solid glass - which are more prevalent in monos.

- catamarans have more deck area, so this works against them radiantly. They also have saloon cabins with big windows - often big slanted windows.

- catamaran hulls are separated (duh) and always have one side of each hull in the shade. If the sun is on one side of the boat, then three hull sides are in the shade. This helps to minimize radiant heat and keep heat localized to a single hull.

-aft cockpit monos are "shotgun shacks", which make it easy to get air flowing through from bow to stern. Center cockpit monos have more issues here. Catamarans are easy to get this airflow in the hulls, but not so easy in the bridgedeck saloon.

- how much air flows through a catamaran saloon is highly dependent on design.

- catamaran cockpits on flying bridge designs can be unbearably hot due to no wind flow. Even bulkhead and outboard bridge designs can be so if they are designed with a tiny gun slit between deck and bimini. Or no opening at all - which seems to be the current design trend.

And lastly, having lived in the tropics for a while now, they both are too hot for me during the heat of the day (and sometimes at night). Cockpit/cabin awnings, windscoops, etc all help tremendously. It is not practical to run AC unless at a dock. A lot of my "hanging around" during the high afternoon sun is in the water.

Mark

JK n Smitty · 26-02-2015, 07:25

I don't think there is any reason to think a mono hull would be hotter than a cat. You could make a quasi-scientific argument either way (monos sit deeper in the water which should act to cool the boat). I also don't think that cats are more open than comparable size mono hulls. Remember a 35 foot cat is comparable to a 45 foot mono or there abouts and typically the mono can carry more weight.

But I hate being hot too. Especially when I am trying to sleep. I also hate the sound of generators running all night and refuse to be one of those guys disturbing a quiet anchorage. So here is what we do, look at Breeze Boosters (Breeze Booster - Breezebooster) and other similar products. They will direct wind down the hatch. If you will be at a marina vs. on anchor or a mooring, look for one that hangs from a spare halyard and can be directed towards the wind. But you will find it is almost always better to be swinging on anchor or a mooring on hot nights. If the wind shifts at night the boat will naturally redirect itself into the wind and you will continue to get the breeze below.

Keep the hatch boards out at night. This will allow for airflow. If you just open the hatch over the berth you will get less airflow and it won't be as effective at cooling the space. If security is a concern, you can get bars made up for the hatch and the main companion way. (Atom Voyages - Improving Your Boat's Companionway) You may also need to look at bug screens depending on where you cruise.

Next add some 12 volt fans. We have 4 of the Hella Jet Fans. They are one speed and a little loud (we like the white noise so that doesn't bother us). We also have one of the Caframo Sirocco 807 Fans. This fan is quiet as long as you keep the blades clean (gets off balance and ticks otherwise). It can move a lot of air and has multiple speeds and a timer built in. Defender Marine has a really good selection. (Defender.com Search Results: fans)

Lastly, and we just began experimenting with this last year so I can't say this is truly affective yet, keep the boat closed during the day with all the shades drawn. The theory here is that you won't heat up the cabin as much during the day so it won't be as hot below. Seemed to work pretty good from our limited experimenting with it.

Good luck and fair winds,

Jesse

2Hulls · 26-02-2015, 07:38

As others have already alluded to, having cruised both in the tropics, I don't think one could classify either a mono or cat as hotter on that aspect alone. Too many other variables not exclusive to one or the other. I don't have AC on my boat and conclude I don't need it in the tropics. But we never stay in a marina. The only place I've craved having AC is on the Chesapeake Bay during the dog days of summer.....

Dave

colemj · 26-02-2015, 07:55

Quote:

Originally Posted by JK n Smitty

Lastly, and we just began experimenting with this last year so I can't say this is truly affective yet, keep the boat closed during the day with all the shades drawn. The theory here is that you won't heat up the cabin as much during the day so it won't be as hot below. Seemed to work pretty good from our limited experimenting with it.

Hoo boy - that certainly doesn't work for us. Better is to make canvas shades over the cabin to block direct sun and leave the air flowing through all day.

Mark

JK n Smitty · 26-02-2015, 08:20

Quote:

Originally Posted by colemj

Hoo boy - that certainly doesn't work for us. Better is to make canvas shades over the cabin to block direct sun and leave the air flowing through all day.

Mark

Funny. I almosted add this. We haven't experimented with this yet but we have been measuring and planning how to make some canvas shades to put up at anchor for when we get to the Caribbean. Most of our experience has been in New England and it usually drops off enough at night to bring the temp down. Shutting everything up during the day helps keep the colder temps in and hotter temps out up here. But when we have chartered in the Caribbean we found this wasn't the case and it just stayed hot and muggy in the boat 24/7.
Good to know we aren't wasting our effort on designing canvas shades.

valhalla360 · 26-02-2015, 08:23

Quote:

Originally Posted by colemj

Hoo boy - that certainly doesn't work for us. Better is to make canvas shades over the cabin to block direct sun and leave the air flowing through all day.

Mark

We find that it works well for an hour or two in the morning when the sun first comes up but then you reach a point where enough heat builds up and you are better off flushing it thru.

To the original point, in general, I would say cats get better airflow but the big windows acting as green houses negate much of the benefits (particulary if the wind dies down).

The problem is "in general" is often superceded by specifics.

**a64pilot** · 26-02-2015, 08:39

Water temp plays a lot into how hot it is in a boat too, I believe. Up North on a hot day, if your in cool water you might be better closed up getting some cooling effect form the cool water, but down South where the water is pi** warm, best thing is to get under some shade with a breeze. I've toyed with the idea of keeping the deck wet with a soaker hose, but have not tried it. Getting yourself wet and wearing a wet T shirt helps too. A wet rag on the neck I learned in the Desert does wonders, cools the blood going to the brain or something.
I put a soaker hose on the ridge pole of a metal building many years ago and you wouldn't believe how much it dropped the temp. Of course metal gets hotter than fiberglass I'm sure.
I think almost all Mono's decks are cored, just some hulls aren't and I assume most of the heat gain is in the deck.

Southern Star · 26-02-2015, 09:15

It surely depends upon the mono and the cat in question. Factors include the location and size of the hatches/opening ports, the amount of core material/insulation in the deck and hulls, the color of the deck/topsides as well as what efforts have been made to provide shading from the intrusion of direct sunlight into the interior. I suspect that the more open the interior design, the better the air flow. Indeed, increased headroom/space should also reduce the 'sweat box' effect of small, enclosed interior spaces. Finally, increased engine room/compartment insulation and isolating the diesel(s)/generator from the interior should also reduce heat intrusion if one is required to run the diesels/generator in order to charge the batteries.

Brad

Tscott8201 · 26-02-2015, 10:18

Sounds like there isn't much of a difference if any. I realize specifics will matter more, but I'm just trying to narrow down my search a bit. I'd love a big open cat but cost wise I may have to settle on a big open mono instead.

Tom

JK n Smitty · 26-02-2015, 12:16

Quote:

Originally Posted by Tscott8201

Sounds like there isn't much of a difference if any. I realize specifics will matter more, but I'm just trying to narrow down my search a bit. I'd love a big open cat but cost wise I may have to settle on a big open mono instead.

Tom

Don't forget to consider the pounds per inch of immersion on the water line in your searching. Cat's are great with all of the space but if you plan to fill it with stuff it will sink down on it's waterline and will have the performance reduced. The same happens with monohulls but in general they will handle added weight better. Not a sole reasons to go with one over the other but something to include when evaluating boats.