Originally Posted by PCP
A First 40 or a J122 will be more stiff than a Catalina 400 simply because they need to be more stiff to carry more sail and going faster. That does not mean that a First 40 will not put a rail in the water faster than a Catalina.
The 400 will get to 8 knots with a heel angle of 7-8 degrees. The First will get to 8 knots with a heel angle of 15-20 degrees. By most any measure the Catalina will be more stiff than a First 40.
Given the Catalina is almost a foot wider, gives it 13% more righting moment for the same weight. However, it is also 3000 pounds heavier adding to the RM. The winged Lead keel is 700 pounds heavier and gains another 400 pounds of effective weight due to the higher density of lead. The keel CG is placed considerably lower in the water as it is attached to a fiberglass skeg that extends almost a foot below the hull. It is doubtful, the CG of the First is lower, so if we assume the CGs to be 1 foot below WL, the Catalina has 3000 ftlbs more mass righting moment. All and all, I expect the Catalina 400 to have about 25% more righting moment.
The reason a light performance hull heels more is because at low heel angles, the hull design focuses on reducing drag rather than creating moment. This can only be acomplished by reducing weight and wetted surface. This creates exactly a hull that is not stiff because the lowest wetted surface is cylindrical rather than flat.
On the other hand, cruisers invariably demand boats that do not heel much. Such boats are much more comfortable, but are slower in light wind because they have more drag.
It is well documented that LESS STIFF
boats require more sail area because the force on the sails goes as the cosine squared of the heel angle. So the First will have only cos(20)^2 or 88% force at a heel angle of 20 degrees. The Catalina 400 will have cos(8)^2 or 98% of the wind force at 8 degrees. The Catalina can get by with 10% less sail area for the same force. The 100% SA is 808 for the Catalina and 848 for the First.
I think this stuff is well known and proven out by Catalina owners.