Originally Posted by outbound
.... Steering may require dual rudders adding yet more complexity. Many of us think we want a monohull that will take care of us not a multihull we need to take care of in a storm. That being the case many of us choose a high aspect fin with bulb and balance spade rudder of strong construction but don't go to the limits of a Boreal, class 40 or other boats requiring multiple levels of complexities to be sailed "correctly".
There also has been little discussion of the "diagonals" and other features of hull shape on comfort. I been on several boats where the wide stern may have worked under sail but at anchor were noisy, skated around and unpleasant.
A Boreal is very easy to sail and very seaworthy.
Dual rudders come to stay. They did not only make possible the use of much less deep rudders as also provide a bigger safety margin not only because they are smaller (and less deep) and therefore subject to less stress but also because they are two and even without one is possible to sail the boat (slowly) back home. They are not only safer as they also provide better control of the boat, specially in what regards beamy boats. It is a need on those, but even on boats with moderate beam they increase control and directional stability.
Regarding beam and safety it is better not to forget that tank testing showed that there was a relation between the beam of a boat and the breaking wave needed to roll it. That's why multihulls are much more difficult to capsize by a breaking wave than monohulls (and the opposite regarding wind).
The trick with modern boats is to increase the capsize resistance (and the boat power) without diminishing the reserve stability, providing a good AVS and an inverted stability several times smaller than the positive stability. That is, joining the good stability characteristics of multihulls with the good stability characteristics of monohulls (reserve stability and possibility to re-right the boat).
For that beamy boats have to have a very low CG. That's why you have seen on the last years, with the increase of beam a correspondent increase of draft and the proliferation of torpedo keels with all ballast at the bottom of the keel. Draft is also a way of increasing directional stability.
Of course, not all beamy boats are alike and I would suggest that before buying one a good look at the stability curve is a must, to see if the reserve stability, a good AVS and a proportional smaller inverted stability are part of the deal.