Not very much different, apart from the fact that you would feel any small wave immediately...Wondering what the motion comfort would be if he only plodded along at 5 Knts like most blue water cruisers ?
As Mr. Brewer will tell you, length and beam affect waterline area. On the other hand a full sectioned boat like a Passport 40 and one with finer sections but greater draft can have the same comfort ratio even though their performance is quite different."This is a ratio that I dreamed up, tongue-in-cheek, as a measure of motion comfort but it has been widely accepted and, indeed, does provide a reasonable comparison between yachts of similar type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state.
Beam does enter into it as wider beam increases stability, increases WL area, and generates a faster reaction. The formula takes into account the displacement, the WL area, and adds a beam factor. The intention is to provide a means to compare motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch."
The comfort ratio formula is as follows: Displacement in pounds / (.65 x (0.7 LWL + 0.3 LOA) x B^1.333). Brewer says ratios vary from 5.0 for a light displacement daysailer to the high 60.0's for a super heavy ocean cruiser.
I've always liked Jeff H's dismissal of the utility of the 'Capsize Screening Ratio", by his pointing out that by repositioning a boat's ballast at the top of the mast, will make no difference whatsoever in its resistance to capsize according to the formula...The comfort ratio doesn't even consider weight distribution. There is no consideration of moment of inertia. A boat with dinghy and engine on the back, a full enclosure, packed lazerette, and 400 ft of chain for two big anchors can have the same comfort ratio as one with the dinghy on the foredeck, a dodger, a light load, and 200 ft of chain for one big anchor.
Length to displacement ratio has the same limitations. SA/D - the same, limited by VCE and VCG being ignored. There is some residual value to ratios if you understand their limitations but they cannot be applied across the board in a meaningful way.
While a case can be made that vee shaped sections near the bow can reduce pounding when pitching, vee'd sections do nothing good for motion beyond that. The current thinking is that an elliptic shaped section progressively build buoyancy with heel angle so that there is less of a jerky motion as the boat rolls and the progressive dampening reduces roll speed and heel angle as well. Vee'd sections have no impact on the five other types of motion.What you are saying is very interesting, can you please explain to me the difference underwater profiles makes with regards to motion? I see a lot of posts criticising the 'soap dish' shapes of modern cruisers.
I would like to see more boats with more 'V' shaped underwater profiles but that isn't from understanding of physics, more intuition.
I read about a boat recently called a riptide 55 which I thought was very interesting.
If you are talking the yacht he rode in the Atlantic in 2013, pictured in post #15, that is the RV Ault, a 42' Colvin Gazell.Colin Archer 42
speaking of 42 - Matt and Nicole just posted their weekly report 42 days at sea