Anyone familar with marine A/C units?

[STV_Keith]

I'm considering a marine A/C for the cabin of the Scarab. It would require about 5000btu. I have seen the Marine Air and Mermaid Manufacturing units. Of the two, the Mermaid units look more compact, overall nicer package, etc.

Does anyone have any experience with either of these brands? How about another brand?

Thanks!

[Rocket Man]

I'm not familiar with the Mermaid. The Marine Air is an excellent unit with lots of options ( digital t-stats, etc.) Very popular here in Florida with great Tech support and liberal Warranty Policies. Your Scarab looks like a 34. I would caution you about the water pump placement and keeping it primed. I used to install the units between the bunks under the filler cushion on the 30 and 34 Scarabs. We usually mounted the pumps well aft(aft of the removable fish boxes in the floor) to keep the pickup in the water as much as possible and to facilitate servicing the raw water strainer. Hope this helps. Rick

[STV_Keith]

Thanks Rick. Mine is a 30'er. I'd probably go through the transom with the water pickup, to insure it's always in the water, and put the pump back there. That's where the batteries are anyway. :)

[Mark75H]

Rocketman is right about the water pump placement. Many faster boats have trouble keeping the pump primed even with the best inlet & pump location. Make sure the water piping route goes uphill without dipping down from the inlet thru the pump with a possible priming tee (with valve) up hill after the pump or a cheater vent line tee'd after the pump that automatically vents air thru the pump to automatically prime it after air gets to it to. Did that on some rag boats that thought they were racers and were always heeled over beyond where we could put an inlet.

The pumps are magnetic drive centrifugal circulating type pumps not positive displacement. The pumps are good pushers, but can hardly pull at all. The pump has to be pretty close to the inlet. If the pump gets air bound it doesn't pump, the impellor just spins and can overheat and ruin the pump. After the priming tee or vent, the line can do what ever you need, the water can push out any air that is past the pump.

I'm not familiar with the Mermaid either.

The grandaddy of marine air conditioning is Cruisair

[Mark75H]

You don't want to go thru the transom unless you 100% have to, you'll always have trouble with that because the transom is out of the water when underway. You need an accessible place as close to the bottom of the V and as far back as you can put it for best operation.

You might be able to do a transom mount inlet with a tee/vent line, but I've never tried. It would still have to be low.

[A Fn Noob]

I just looked at the specs for both the Mermaid and the MarineAir 5kbtu units. They both have rotary compressors.. the MarineAir spec sheet boasts cupronickel condenser coil, which is good. The Mermaid doesnt say what their coils are made of, and it looks like they just took off the shelf components and patched it together, whereas the other seems to be more of a purpose-built unit.

Basically its one of these http://www.usamfg.net/ebay/copeland34922.jpg
(That one is $140 on ebay)
and one of these....
http://i2.ebayimg.com/02/i/07/c0/e7/fc_2.JPG
($40 on ebay)

and a water pump.

Those are the same condensing units in say, Taylor Shake machines, reach-in coolers, display cases. They use water cooled when they dont want to add any heat to the kitchen.

If it were me, Id make one that used 410A, a variable speed (ecm) induced draft motor, and give some thought to a way to transfer the heat with a closed-loop somehow. Hell, with 410A the head pressures are high enough that you could do subcooling with the discharge h20 from the motor....probably.

[Mark75H]

These days off the shelf coaxial condensers are usually cupronickel (you'd probably have to really scratch to find an all copper one), boat air conditioners have used varible speed evap fans (without any thing as complicated as an ECM fan) since about 1968. Cruisair made that an option and everyone else copied it.

Your eBay rig doesn't have an evaporator or controls either ... you need a lot more parts.

Keith is probably looking at a single package self contained unit with the compressor, condensor, evaporator, evap fan and controls all on one chassis that he can mount in a locker under the v berth ... probably not much room in the back for a remote condenser type unit, so he'd be too far from the engines to use dump water from them anyway. On top of that - he's probably not going to run the AC at the same time as the engines.

Compressors and condensing units may look the same but there are usually a lot of internal differences. A low temp shake machine compressor doesn't have the correct compression ratio to be used in a high temp AC application - that's why there are so many different compressors.

[A Fn Noob]

>[conditioners have used varible speed evap fans (without any thing as complicated as an ECM fan) since about 1968.

Not multi-speed, variable speed.

>Your eBay rig doesn't have an evaporator or controls either ... you need a lot more parts.

It's not MY ebay rig, I was just making a point that, any product with the word MARINE in it means its gonna cost you.


>Compressors and condensing units may look the same but there are usually a lot of internal differences. A low temp shake machine compressor doesn't have the correct compression ratio to be used in a high temp AC application - that's why there are so many different compressors.

No ****, Sherlock. You dont need to tell me this. Why is it when someone makes a post on this site, a m***** f***** always seems to want to jump in and pick holes in it, without even taking the time to READ the persons post. Some kind of EGO thing? If you ever want to have a big **** contest with respect to refrigeration, or hvac, I would win, hands down.

The guy asked about 2 specific units, and I answered him. Im not trying to sell somebody something, or trying to stand in the way of someone (you?) selling something. I was making a point, that a person could build a superior unit for about 1/3 the cost, if they so wished.

[Mark75H]

Variable speed evap fans (not multi) have been used on boat AC for decades. I'll call you the next time I can't figure something out.

Keith also asked about other brands, maybe you missed that

[A Fn Noob]

Variable speed evap fans (not multi) have been used on boat AC for decades. I'll call you the next time I can't figure something out.

Keith also asked about other brands, maybe you missed that

I took a look at the Crusair stuff, and you're right, they are light years ahead of the others.
The blower motors they are using are PSC motors, which draw a lot of current on startup.. I wasnt referring to the controlling of motor speed, but how that was accomplished. VFD , while not new, has not been around for decades. It will eventually replace the psc motor entirely. It looks like it is available as an option on certain Crusair split-systems. I bet you any amount of money that if looked at their product line 5 years from now, all of the units will have vfd blowers and compressors.

So anyway, I apologize for going off this morning, I promise I was only trying to be helpful.

How much $$ are those 5k Crusair units? :D

[1BadAction]

with respect to refrigeration, or hvac, I would win, hands down.

cool! You do commercial or??

[STV_Keith]

This is the Mermaid unit I was looking at: http://www.mmair.com/marine_division/air_conditioning/6_500_btu_cabin_air_conditioner

http://www.mmair.com/var/mermaid/storage/images/marine_division/air_conditioning/6_500_btu_cabin_air_conditioner/468-9-eng-US/6_500_btu_cabin_air_conditioner_medium.jpg

I only planned to run the unit when stopped, so I think transom mount should be fine.

[A Fn Noob]

Call and ask them what their coils are made of

[STV_Keith]

Call and ask them what their coils are made of

They are cupronickel. 5 yr warranty on everything except the water pump.

[hydroholic]

This is the Mermaid unit I was looking at:http://www.mmair.com/var/mermaid/storage/images/marine_division/air_conditioning/6_500_btu_cabin_air_conditioner/468-9-eng-US/6_500_btu_cabin_air_conditioner_medium.jpg//www.mmair.com/marine_division/air_conditioning/6_500_btu_cabin_air_conditioner
http: (http://www.mmair.com/marine_division/air_conditioning/6_500_btu_cabin_air_conditioner)


I only planned to run the unit when stopped, so I think transom mount should be fine.
If you are only going to be running the unit when sitting still then it really doesnt matter an awfull lot where you put the water inlet.As someone stated above just make sure the pump is as close to the water inlet as possible and going steadily uphill with no low spots in the line.Use a good strainer pickup and an in-line strainer canister so you can clean debris out.As for the durability of the units mentioned above,I have been installing marine A/C systems for quite a few years and the Cruise air and the Marine air are both excellent systems.Have not installed very many Mermaids and have not heard very much on thier durability,pro or con.I can tell you I just installed a 10,000 BTU Marine air unit on my personal 24 FT Wellcraft cabin cruiser and it's great.I opted for it instead of a Cruise air based on price. They are pretty close as far as durability goes and are sold more widely in our area than cruise air(its a standard product for West Marine/Boats US). I only needed about a 6,000 BTU unit but they only had the 6,000 available at the time in a reverse cycle unit for heat also and it was the same price as the standard cycle 10,000 unit for cool only.I didn't need heat so I went with the higher BTU unit.It will freeze you out when its above 100 degrees outside and in Pensacola,it's almost always very humid.I gave less than book price ($1500) with my charter discount and it comes with unit,controlls,all electrical connectors,pump,inline strainer,water line,hose clamps,25 FT duct hose,2 vent registers,the return vent and reuseable filter.Not that bad of a deal.I installed mine under the kitchen sink and the vents come out of the wall above the sink.It is a pretty quite running unit.They are easy to install and takes one person about 3/4 to 1 day to install depending on location to be installed and route of water and electrical lines and duct location.Either way you go I think you will be satisfied. Over figure on your BTU size a little if you live in a hot humid area as the humidity seems to hamper them some.Hydro

[STV_Keith]

It seems that the rule of thumb is 14BTU per cubic foot. My cabin is roughly 7x7x5 or 245 cf-ft thereby requiring 3430BTUs for cooling. I had originally spec'd out the 5000BTU unit, but I can get a 6500BTU unit for less money, so I think that's the way I'm going to go. Should run me about $1100 for everything, not including install, which I will do myself.

Thanks for the info guys!

[A Fn Noob]

Man, they have a bunch of units on ebay, 10000 btu units new 850ish, a used Crusair working with buy-it-now at $200 or so.(I think its ended now), but theres a quite a few.

gl with whatever you decide to do!

[randy 77zt]

if i bring some beer can i check out your a/c?it would be interesting to see how it works at havasu.

[STV_Keith]

Sure Randy. I'm sure I'll have the boat in Havi next year. :)