Fin keel vs bulb keel - any difference in rolling motion side to side?

[SteveSadler]

I agree that deeper fin keels are far better, but they are usually married to a modern hull design which is wider, carries the width to the transom and has harder or hard chines. This is a huge improvement in stability over old, rounder hull shapes.

[HeinSdL]

I think there is another effect which plays an important role in causing roll when at anchor. The water does not actually 'sit still' as a wave passes over. If you were to follow an individual water molecule at say 1m depth then you would observe the following motions:

1. Molecule moves towards an approaching wave,
2. moves up as wave builds,
3. moves with wave as wave passes over,
4. moves back down to more or less end up in same place as wave recedes

or something like that. In any case you would observe a circular motion which regrettably causes a lot of the -rather annoying- role at anchor. If this circular motion did not happen then the bigger surface area of the keel the better to prevent roll. But it does so the keel design has little impact on the amount of roll as indeed seen in anchorages where most mono hulls show pretty similar rolling behaviours.