Worsted spun 5-ply knit on 2 mm needles.
Gauge is 35 stitches per 4" and 50 rows per 4" for ~109 stitches per square inch. It is a nice jersey fabric.
The fabric is about the same weight, hand, and drape as your favorite knit sweat shirt from Nordstrom, but it is wool, so it is warmer in the wet than cotton, and less flammable than polyester. It is long wool, so it is very durable. However, the wool is fine enough to be skin soft. And unlike many of the synthetic fibers, it does not stink.
This is the fabric that I set out to knit 16 years ago, hand knit, but warm enough to keep a fisherman warm on the North Atlantic. It is,in fact, the fabric seen in some of the patterns in Gladys Thompson. This is the yarn and gauge that makes Pattern 1, A Channel Island's Guernsey fit the size given. Moreover, with long needles and a knitting sheath the pattern and the knitting is easy.
It is not easy on circular needles.
To get here, I had to learn about long needles and knitting sheaths that provide the leverage and speed to make such knitting practical. You are not going to knit like this with circular needles. I know, I tried for years and years. I moved to long needles and knitting sheaths only after it was clear that circular needles are not practical for such knitting. I am not saying such knitting cannot be done on circular needles, I am saying circular needles are not practical for such knitting. Think about it, do you know anybody that produces such objects on a regular basis using circular needles?
It is too warm? Not if one is determined to do interesting things in interesting places, regardless of the weather.
It is too much bother to knit? One must be somewhere, while you are there, you can be knitting.
Related fabrics include:
This is based on woolen spun, 2-ply yarn of about the same grist and also knit on 2 mm needles to produce a lovely Guernsey fabric. Again, about 110 spi^2. Knit on finer needles, the surface becomes much smoother and the fabric more water repellent.
These are my answers to the question: "How did the old seamen manage to stay warm?" They used long needles and knitting sheaths to knit the kind fabrics noted above. Given the warmth and durability of the fabric, it was worth the effort, because with long needles and knitting sheaths, it is not really that much effort.
These both happen to be commercial yarns. Am I sorry that I put the effort into learning to spin? Not at all. I had to learn about yarn to become a better knitter.