Boats do roll differently in the same conditions. A monohull
has a natural roll frequency which is inversely related to its moment of intertia. If the frequency of the exciting waves comes near the natural roll frequency, your boat is going to really roll. You can watch boats in a rolly anchorage, or watch as a single
wake moves across a fleet of anchored boats. Some boats are rolling like crazy, while some are not.
As you know, the frequency of wind generated waves also varies--it is a function of how long and how hard the wind has been blowing. Thus, some days, when a short wind chop is generating the waves, it may be your boat which is rolling, while other days, when a long ocean swell is predominant, it may be someone else's.
Generally, a slow roll is more comfortable than a fast one, which is why bigger and heavier boats are more comfortable than small ones. However, roll frequency is related to stability--more stable boats roll faster. If you replace your heavy mast
with a lighter carbon fiber model, you get an increase in stability and sail-carrying power, but you also get an increase in roll frequency and a decrease in comfort level. Carrying to one extreme, if you lose the mast, the roll frequency will probably double and the crew will get seasick. Going the other way, if the roller furling
mast is heavier than a standard mast, it may actually make the boat more comfortable at anchorage.
The other issue is the amount of roll. Wider and flatter hull
shapes (a cat is the exteme) will 'feel' the waves more than a round or narrow hull
, but they also have more damping, so the roll stops quickly. My own observation is that round hull shapes seem to be less comfortable, and this is may be the basis of your feeling that the IP 38 is more rolly than other boats you have experienced.