(semi)Displacement hull vs planing hull at displacement speeds??

[MapisM]

Yep, fast righting movement is indeed connected to the roll period, but "snap back" does describe the concept nicely, I reckon.
And of course, in this respect D hulls are better than SD hulls, but SD hulls are still better than P hulls...

 

[Nick_H]

I haven't been on a D mobo underway, but did a long crossing in a beam sea under motor on a sailing yacht, and that really highlighted the point you make, roll period is every bit as important as roll angle when it comes to comfort and feeling of safety. I guess even the best D mobo can't match a raggie though, with a third of the displacement in the form of lead hung a metre under the hull.

 

[MapisM]

I guess even the best D mobo can't match a raggie though, with a third of the displacement in the form of lead hung a metre under the hull.

Oh yeah, absolutely. When in the other similar thread currently running I said that sailboats are the most logical choice for ocean crossing, I meant it.
Though TBH serious passagemaker mobos, which are obviously fin stabilized, can be VERY close to sailboats in terms of stability, in my experience.
With the added bonus of not having to fight gravity that constantly tries to throw you overboard, either on port on stbd side, depending on which way the wind blows...