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Old 26-03-2020, 17:40   #1
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Help deciding on refrigeration.

Bluf: Frigoboat keel cooled or Isotherm Magnum for 6 cf fridge/freezer (50/50 split) spillover system for full time liveaboard sailing the Caribbean.


We're currently doing a refit on our new-to-us boat and we're going to be replacing the refrigeration system. We *think* the previous owner might have put stop-leak in the lines and ruined the current system. We're going to be living on the boat full time soon (cruising Caribbean) and I don't want to be chasing refrigeration issues on a system that is already compromised so we're just going to start from scratch.

Right now the boat has a single Frigoboat keel cooled compressor with a large-ish evaporator (probably 50"x12", though I didn't measure it) in the freezer and the remnants of a spill over system (fan is there, but not hooked to anything). The entire box space is about 6.5 cuft divided nearly in half (3cf freezer, 3.5cf fridge).

Originally, I was just going to replace the Frigoboat with an identical system, which would involve removing/replacing the keel cooler, and we had talked about doing a true split system with separate compressors for each side.

Now that we've started our refit and have begun removing old stuff off the boat, we've ended up with several unused thru-hull fittings. So now I'm considering replacing the Frigoboat keel cooled setup with an Isotherm Magnum watercooled system. This would be a pretty straight forward install on our boat as we already have a thru-hull/seacock with a sea-strainer in place and an overboard drain right next to the compressor location (aft cockpit locker). I should note that the Isotherm SP systems won't work with our layout due to the 3' max distance between the SP thruhull and the compressor.

So I have a few questions. I think I'm going to go ahead and keep the spillover system and get the fan working properly (with thermostat). Does any one have a compelling reason to go with either Frigoboat or Isotherm? Is it worth the extra effort to remove/replace the keel cooler and stick with the frigoboat system? It seems I can get the Isotherm system for a fair amount cheaper than the Frigoboat, and I think the Isotherm would be an easier install. I'm not thrilled about having a retired-in-place keel cooler though (this is just a personal annoyance, I hate retired-in-place stuff, it just adds clutter to the boat).

Also, how do you size for a spillover system? Everything is rated for a refrigerator box of a certain size OR a freezer. Right now I'm looking at the Isotherm Magnum 2507, which is listed as being good for a 4.8 cf freezer or a 14.1 cf fridge. My thoughts are that with my system, the 4.8 cf freezer rating should be enough to keep my 3 cf freezer frozen while the spillover system is drawing off cold air for the fridge side.

This got kind of long winded, so I appreciate it if you read this far and would love to hear your thoughts. Thanks!
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Old 26-03-2020, 21:33   #2
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Re: Help deciding on refrigeration.

There are some big advantages to having a separate system for the fridge and the freezer. Obviously, the biggest disadvantage is cost. The big advantage is that your freezer actually stays frozen, and there's zero "fiddling" with everything. We had a large Grunnert Passagemaker on our boat. Split between the fridge and freezer. We just replaced it with 2 Seafrost systems. One for each. We went with the dual systems - air and water cooled. Great company, great systems.
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Old 26-03-2020, 23:49   #3
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Re: Help deciding on refrigeration.

$pent year$ going through my curve.
Bought a stand alone system so I could have something that was less demanding.
Kept on spending and tweaking. About the time I figured I had things optimal, I also came to appreciate that my stand alone was being far less demanding. That was about 2012. My now perfectly operational, expensive refrigerated, well insulated box has served as a dry foods pantry since then. After all this time, I will be gutting that box and getting a lot more space for dry food storage, and another stand alone Engle to give my wife the freezer that she demands. In addition to being less demanding, it will be easier access than the built in box. I get to choose where it will live.
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Old 27-03-2020, 14:23   #4
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Re: Help deciding on refrigeration.

I do not think a new Frigoboat keel cooler system or a water cooled Isotherm Magnum will provide reliable refrigeration on a live aboard boat in the tropics. Yes they both can handle a divided six cubic foot spillover box in the tropics, but not for an extended period. Compressor oil cooling on both is a major problem when their design envelope is exceeded and a six cu ft box in 90 degree waters is pushing the envelope.

Catastrophic failures of Frigoboat keel cooler systems result from high temperature contamination. Also refrigerant leaks occur as line connector o ring seals age quickly do to high refrigerant temperatures and lack of refrigerant filtering before interring flow control orifice.

Pumped seawater cooling of these small compressor systems will compromise their reliability requiring daily monitoring by someone on board. You can expect in the tropics the Magnum water pump will run at high speed 50% of the time and replacement pumps and controller have a magnum price.

I am sorry but I can not recommend a water cooled single compressor system for your boat other than Two separate Frigoboat BD 50 compressors equipped with keel coolers and Danfoss AEO control modules.

My belief is you would be better off with two Nova Kool $900 air cooled BD 50 systems one with freezer thermostat and the other having a refrigerator thermostat. A live aboard boat needs redundancy in warm climates.
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Old 28-03-2020, 05:30   #5
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Re: Help deciding on refrigeration.

Thanks for the input everyone.

While we didn't go with Nova Kool (stuck with Isotherm due to costs), we did end up going with 2 air cooled units so we'll have some redundancy in the system. I guess I'll just have to live with the retired-in-place keel cooler.
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