First of all, The Motion Comfort Ratio provides no useful information about motion comfort on any boat since the formula does not include the primary factors that truly impact the motion of the boat. Beyond that, Motion Comfort Ratio is especially inaccurate when talking about these more modern designs. Part of the problem is that the Motion Comfort Ratio measures beam at the max beam at the deck. These newer designs are very beamy at the deck, but are comparatively narrow boats at the water plane pretty much at all heel angles. It is deceptive because there is so much boat visible above the water. (You might be able see what I mean about being narrow boats in the water from these images)
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These newer hull forms allow a progressive outboard rotation of the center of buoyancy with heel which develops a lot of initial stability across the normal range of heel, and that helps to dampen roll and helps the boat remain in closer sync with the wave train. Their roll behavior is more like a catamaran than a traditional round bottom cruising boat. In that regard they tend to have a more comfortable motion when it comes to roll rolling through a narrower roll angle at a similar roll rate. .
Similarly, they tend to have a much longer waterline length relative to their length on deck, and that is effective in damping pitch, and so they tend to have a more comfortable pitching motion as well.
Because they have a fairly large water plane, they do tend to heave more than a more traditional design, but the forces involved with heave tend to be large enough that any difference in heave rate should not be readily observable. .
The current trend is towards fuller bows than a decade or so ago. This is a mixed bag. While it does provide more speed when reaching, those fuller bows tend to result in harsher impacts with waves when beating into a chop than the finer bows of the IMS influenced designs. This is not really the same as slamming. Normally slamming is thought to be the impact of water against a relatively flat surface. This is a real concern with the nearly flat bottoms of modern purpose built race boats, and was with many of the IOR era- three-plane bottom profiles. Its less of an issue with the generally rounded forward sections on more modern performance cruising designs.
I will note that while these newer designs are faster when reaching in a breeze than most older designs, they do not seem to have an advantage upwind or in lighter conditions.
Kiting (sailing back and forth with the sails down while anchored) is more a product of the popularization of fractional rig than the hull forms. The center of effort of the sail plan on a fractional rig trends to be further aft than that of a masthead rig. Consequently the keel is also further aft. The result is that these boats balance well under sail. But the masts on a fractional rig tends to be further forward than the mast on a masthead rig. As a result, when the sails are down, the center of effort of the bare poles is quite a bit forward of the center of effort when the sails are up. This effectively is creating a lee helm and so the boat tends to want skew off further to leeward on each swing. Most times the swing is small and inconsequential. (but for example, in a stiff breeze and a long scope, my boat can hit over a knot on each swing,)
I typically use more scope than most folks to reduce the change in the angle of pull on the anchor. In a tighter anchorage or when the swing seems excessive, the work around is to tie a dock line with rolling hitch on the anchor rode, and let that out perhaps 10-15 feet ahead of the bow. I then lead that line aft to a cockpit winch. By tightening that line, it acts as a bridle so that the boat sits slightly skewed to the wind and kiting just about stops.
Modern boat stern slaps are a little more violent when anchored in a choppy anchorage than on some of the prior generation of performance cruisers. That said, it is not as bad as the stern slap on the long overhangs of the 1960's era, CCA boats.
The one thing that I have not seen discussed is that these newer boats tend to throw a lot of spray. I had a change to observe this first hand beating to windward in a smallish chop.
Jeff
