Re: The HULL truth and nothing but.
That article does not seem to understand that no matter how the boat may look statically, when you talk about the newer designs, when they are properly designed, the part of the boat that is in the water does have 'balanced ends' relative to the center of gravity of the boat. But that is a very broad generality and does not apply to all of the new designs.
Here is what is not readily apparent to most people looking at the shape of a modern boat is they tend to think of what they see above the water as the shape in the water. But typically these boats are designed to remarkably balanced shapes in the water, which as they heel (up to a point) become even more balanced fore and aft as well as amidships. While it is true that these designs do tend to carry more buoyancy towards the stern than they do forward, and tend to have their centers of buoyancy a little further aft than some more traditional designs, this is offset because they also carry their center of gravity further aft as well. What is not understood is that the actual waterline beam on these boats is surprisingly very narrow, especially when they have a some heel angle. It may actually be narrower than more traditional designs of 20-30 years ago.
Its important to understand that these wider hulls are modeled so that the center of buoyancy moves quickly to leeward with heel angle. Since the center of gravity does not move, they very quickly develop huge amounts of stability without the usual penalties associated with excessively beamy hulls. In order to prevent developing large amounts of weather helm due to the immersed hull shape, the hull shape is carefully modeled so that it results in a comparatively symmetrical immersed hull form (closer in shape to a multihull than a traditional monohull) that is balanced around an axis that starts at the bow but which rotates to leeward at the stern. While this hull form is not parallel to the center line of the hull, it is none the less parallel to the way that water is moving over the hull. (That shifted angle means that the hull in the water is actually pointing slightly upwind and helping to resist leeway)
The article suggests that these boats tend to go bow down when surfing in big waves. While that is true on some of the early broader stern designs and boats like the 6.5 meter Mini TransAt boats, with their huge reaching and running sail plans flown over very short waterline lengths, that has not proven to be the case once these more modern designs get longer and with more normal SA/D's. What is not all that apparent when looking at these boats is that the bow at the deck line is typically a lot fuller then more traditional designs and so while the waterline at the bow might be pretty fine compared to traditional cruising boats. these boats have huge amounts of reserve buoyancy, which occurs further forward of the longitudinal axis of rotation (pitch axis) and therefore has a longer lever arm to dampen pitch angle than more traditional designs. Moving the point of entry of the bow forward allows the boats to experience the impact with waves more progressively and so do not have the sharper impacts that are in more traditional designs of the same displacement. The huge amounts of reserve buoyancy in the stern also helps to damp pitch as well and reduce the likelihood of being pooped. The net result is that these boats tend to pitch through much smaller angles than traditional hull forms and remain closer to parallel to the wave face than more traditional hull forms.
Similarly, they tend to have much greater roll damping as well. The net result is that the non-planning versions of these hull forms generally have a more comfortable motion than something like an IP which transmits much greater wave impacts to the crew and boat, and which tends to pitch and roll through much greater angles.
Designing boats that behave like that takes more care than more traditional designs. The hull shape above and below the waterline needs to be optimized to remain balanced within the intended sailing heel angle. Without computer design and the ability to precisely track hull shape and its effect on trim (all directions) at various heel angles, it would be almost impossible to produce boats that employed versions of these modern hull forms and yet which were still well behaved,
And that gets back to the problem with citing anecdotal evidence. Since these modern designs require more sophisticated design analysis, and not all visually modern boats receive that level of care, its hard to cite any particular design as a case study for the general design principal. This is especially true since many of the production designs that are out there have adopted, "the look" with adopting the science. There is no doubt that these designs neither perform as well nor offer the motion comfort that a more carefully modeled hull will provide. Often 'the look' is employed as a way to cram in some additional accommodations or meet some other design parameter. And, as in many things in life, the pendulum may have swung too far and may need to swing back a little.
As far as the schism between race boats and cruising boats, there is no doubt that race boats have taken a very different route than cruising boats, becoming wildly lighter and more stripped out, living with much greater form stability, and in many cases, employing movable ballast and foils to achieve speeds which would have been inconceivable a few decades ago. From a design standpoint, while they may look like the newer cruising designs above the waterline, they are operating on very different design principles, principals that I do not envision bleeding down into cruising designs unless people are willing to live with huge compromises.
But that is the opposite of the direction that the cruising boats version of the wide body look are going. When I look at the current crop of modern looking 38 footers on the market, they are nearly 5,000 lbs heavier than my four decade old designed 38 foot performance cruiser, and roughly the same weight as a Pacific Seacraft of the same length. Similarly, a Sense 46 is roughly the same displacement as your Outbound. And while the Sense 46 has less ballast, it carries in a larger bulb lower below the canoe body and so probably has more initial stability, and probably a similar angle of positive stability (but with much larger area under both the positive and negative stability curves).
Alright, my lunch is over, I need to get back to work!
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay
Last edited by Jeff_H; 10-01-2018 at 07:32 PM.