Regarding shellfish and other gunk in the AC lines, I doubt any charter company regularly (if ever) runs an acid solution through the AC lines to descale the lines. A great product is Barnacle Buster to clean out AC lines as well as Engine and Generator raw water cooling lines and heat exchanger. Pour it in and let it soak for 12-18 hrs. Amazing the dissolved gunk that comes out. AC efficiency improves and you may see your engine operating temperatures drop a few degrees.