I've had a chance to do some playing around with the numbers that I mentioned in the earlier posts, and I do think there are some useful things to be gleaned from them. With all the usual caveats (not truly random samples, reported tonnages may not be correct, the two lists are from 16 years apart, etc.) here's what I found.
Let's start with brigs. Between the two lists there are 27 brigs and 1 snow, which I am listing as a brig for this. The tonnages range from 60 to 350, with the average tonnage being 210.71. While averages can be misleading sometimes, the median and mode for the tonnage numbers are both 200, which would suggest that the distribution here is pretty close to normal. As an interesting aside, the two smallest brigs (60 and 70 tons) were both captured at Isle de France in 1810. Also, two of the larger brigs (300 tons) are probably privateers, since they have the number of guns carried listed and the others do not. They were also both captured at Isle de France in 1810. No information on crew sizes is available, but with merchantmen, going with the absolute minimum needed is a good rule of thumb.
Full rigged ships are a little more complicated. There are 45 ships total on the two lists, or 39 if you don't count the Indiamen (for this, anything of 900+ tons is considered as an East Indiaman). Tonnages here range from 150 to 1,000 or 150 to 800 without the Indiamen. The average tonnage for these is 478.2/405.6 (with/without Indiamen). Because of the larger sample size, the other numbers tend to not be as well definied as the ones for brigs were. The median tonnage here is 400/350, but the mode is 300 both with and without the Indiamen.
So, what do all these numbers mean? It means that for generic merchantmen in these samples, a brig is anywhere between 60 and 350 tons, with an "average" version running about 200 tons. For ship rigged merchantmen (not counting East Indiamen), they can run anywhere between 150 and 800 tons. However, a 300-400 tonner would be the closest to being "average." As for how many cargo boxes they should have, this is still a sort of 'how long is a piece of string' type question. In theory, they should be capable of carrying cargo equal to their tonnage, but that doesn't work in practice.
As mentioned in the earlier message, period documents indicate that cargo weight is determined by tonnage in some cases, and by cubic feet in others. The Shipmaster's Assistant, that I quoted earlier also says (pg. 131) that it is possible for vessels to sometimes carry MORE than their registered tonnage, even after 14 percent was deducted for casks. Just below this, it points out that a vessel will only carry 900 to 1000 pounds of Brazil cotton per registered ton (or, 45-50% of registered tonnage). This seems to be in line with a comment in Sutton's Lords of the East (pg. 39) that says the Nottingham of 1152 tons "brought home almost twice the 712,000 lbs customarily brought home in an 800 ton ship." 712,000 pounds is 356 tons at 2,000 pounds/ton, or 44.5% of 800 tons. The Nottingham brought home almost twice that number, which is 712 tons or 61.8% of tonnage. While this isn't a lot of data to work with, it might be reasonable to let smaller ships with sharp lines (cutters and schooners) carry about 30% of their tonnage as cargo, with brigs and non-Indiamen carrying about 45% and Indiamen carrying about 60%. Admittedly though, the Nottingham got in trouble for violating Company procedures about cargo storage, so a smaller number might be in order as well.
I'd be interested in hearing any comments or other data people might have on this. It seems like much ado about nothing, but when you start looking at the idea of campaigns, then all of this becomes important for a number of reasons.