In principle I agree with you. In practice on smaller boats it's often a "work point." *grin*
Since I wedge myself into the galley I regularly end up with some interesting bruises from the safety bar in front of gimballed cookers. I am still looking for a more elegant and thermally robust padding solution than a pool noodle.
What I've looked at is amp draw for both built ins and portables to keep a certain temp level, regardless of the thickness of insulation.
You can see insulation quality directly in current draw, measured in amperes (amps, A). Disregarding insulation is ignoring a primary factor.
Again, only considering current is insufficient. Duty cycle, directly affected by insulation and compressor efficiency, is important. Box size is important. Consider an
Engel MT45F-U1. 1.5 cu ft box (pretty tiny) drawing 2 A at 50% duty on a warm summer day. That is 16 Ah/day/cu ft. Compare that to an
Isotherm SP2051 cooling a 4 cu ft box, well insulated, drawing 2.5 A at 20% duty cycle on that same 72F day. 3 Ah/day/cu ft. Clearly a more efficient solution. Even more exciting is that the solution scales. Don't need 4 cu ft? A couple of big insulation blocks in the bottom of your box will decrease duty cycle, increase insulation, and make food easier to reach.
I've not yet found solid info that the built ins are surpassing the latest portables, but that's something to check...and to post about, please.
You haven't looked very hard. Five minutes on Google provided a wealth of specified, tested, and anecdotal data. The two links above are the merest tip of the iceberg.
Keel-cooling is far from new. Frigoboat has been selling keel-cooled refrigeration for about 20 years and Isotherm for at least 15 years.
Without engaging in yet another dissertation, the thermodynamics are quite simple: liquid-to-liquid heat transfer is more efficient than liquid-to-air so any water-cooled refrigeration will be more efficient than an air-cooled one. Consider further that a conventional water-cooled system has the electrical load of the sea water circulation pump that keel-cooled systems do not have and the specified efficiency of keel coolers is apparent. Obviously there is one less noise source as well.
@deniseO30
The numbers with reefers are all suspect. Who is to say that a mass-market boat builder installed a box optimally?
I agree that some skepticism is appropriate, particularly since some production boats don't have the option of factory refrigeration - that makes buyers dependent on whoever the brokerage selects for commissioning.
And of course keel cooling, which would seem to follow the laws of thermodynamics, is so widely panned by so many people.
Some people can be quite vocal without understanding what they are talking about. "I heard" is not a credible footnote.
q; what to do about that ice box lid in the counter top?
a; put a cutting board on it!
Sure. I have a cutting board that drops onto the gimballed cooker which gives me a level cutting service in any conditions. I also have small boards glued to the bottom of the sink covers so I can turn them over and have more prep/cutting space.