Also, and this is just personal experience: I have had at least samples of most of the boat-aged liquors which my friend’s company makes (and have bought and enjoyed several bottles). They are very flavorful and smooth, much moreso than one would imagine for whiskies and bourbons which have only been aged for a relatively short time.
There’s a theory if action which makes sense, but no testing if the theory. I don’t even mean like chemical analysis, anyone taken a 2 barrels with the same mashbill from the same rickhouse, sent one on a boat while leaving the other home, and don’t a double-blind taste test? Chemical analysis?
This has been part of how Norwegian aquavit (caraway-infused grain spirit) has been aged for centuries.
Peculiar to the Norwegian tradition are Linje Aquavits (such as “Løiten Linie” and “Lysholm Linie”). Linje Aquavit is named after the tradition of sending oak barrels of aquavit with ships from Norway to Australia and back again, thereby passing the equator (“linje”) twice before being bottled. The constant movement, high humidity, and fluctuating temperature cause the spirit to extract more flavour and contribute to accelerated maturation.
FWIW, I tried some about 5 years ago and was underwhelmed.
Seems logical that getting sloshed around with wide temp variations for 6 months will have an effect. The question, however, is that effect good or bad on the whiskey???