Hi Mar
Think the benifits of canted hulls outweigh the disadvantages ,but with proper coresponding design applied.
Some would disagree ,it depends on what the design wishes to accomplish and the windspeeds it may be targeting to be sailed in .Some believe cats are already so fast that waves and sea conditions are the limiting factor at top speeds ,so the focus is on better light wind performance .
Some think faster is more fun and would give up some light wind speed for greater top speed or planning capability.
Recall some posts by noted boat builders that stated the canted hull versions of the same designs were faster, though this most likely at higher speeds . Also we see most development classes going to canted hulls in search of more speed,-A class cats per example ,-also the most successfull current design firms using canted hulls is another indicator,-and the Inter line most notabley in production cats having canted hulls. Some of the C Class designs also use canted hulls ,-state of the art designs with solid wingsails. There are advantages and disadvantages to both types of hull design -canted and non canted.The case can be made equally for either type.
Most of the time cats are sailed heeled to leeward ,-hulls never go through the water perfectly level, paralell, or without sail forces acting on them creating heel and bow down forces as well as a high pressure side , just as boards and foils have.
The ideal attitude and fastest a cat is sailed is with one hull just skimming the surface ,this reduces both types of resistance and drag on hulls ,one being form drag {general shape of hull}that causes resistance , the other frictional resistance {surface area} causing drag, frictional resistance the larger factor in light winds .
One hull in the water with crew on the wire, windward hull flying just above the surface waves of course is where both forms of resistance are greatly reduced and the biggest jump in boat speed occurs. Any that have raced in open fleets with monohulls and evan trimarans will notice this is where beach cats come alive and really leave other sailing craft behind.
Evan in light winds the crew should get forward and to leeward which heels the boat and increases boat speed by lifting the windward hull and effecting sails.
Design of catamarans is an intricate mix of practical engineering ,structural considerations, and art.
It is not just a matter of taking existing hulls and canting them . A new set of benifits and problems come into play and trade offs in design with canted hulls.
A simple analysis or view of a hull traveling through water if visualized or seen in a test tank would have much less form drag if more symetrical, this is the goal and benifit of a canted hull design by alligning the hull cant with ideal heel angle that it is sailed .
Another lesser benifit of a canted hull design is how the boat approaches waves when heeled ,-again more symetrically which combined with wider flatter hull shape as is typical of the canted type design, should be less prone to pitchpole with proper design of larger volume bow sections and hydrodynamic lift from flatter lifting hull shape.
Hull allignment becomes more complex with canted hulls that use deeper narrower bow sections which is no problem at higher speeds with one hull up ,but somewhat a problem at lower speeds and in seas downwind with both hulls in the water.
On hull shapes with canted deep high sided narrow bows there is more of a bow down reaction or tendancy from sail forces , this causes a wider underwater dimension from hull to hull as they submerge more. That is the more the bows submerge the greater the misallignment of canted hulls and the greater the form drag of one hull working against the other . Some C Class cat designs in the past with deep narrow bows had a distictive tow in hull allignment appearance ,-The designers averaged out the allignment and designed this in, again hulls never go through water perfectly level but are always heeled or should be ,with a high and low pressure side.
The solution to this problem when designing a canted hull type is to create a hull that reacts to sail forces equally along its length to heeling to negate bow down effects from sail forces,or evan design in a stern down tendancy, many of the trimaran designs desire this in the ama design with much larger volume bows than stern sections .This is similarly accomplished by larger volume bow sections in cat hull design. The Inter designs are one example of this type of large bow area volume hull design ,having a 16 in. width by station 3 or 4 back from the bow, they work well with spin and have less total hull drag at speed , they are however at some disadvantage to non canted hull types in lighter and medium winds ,no trap type conditions particularly in choppy seas where the sharper deeper bows sections cut through waves better and the boats are not heeled as much .
Hull design is generally divided into 10 equal sections from bow to stern and drawn in overlay of each in sequence ,--see the 18 sq post by D Lenke for an example ,-then side profiles added , waterline and top deck views,and sail plan boards rudders hardware bulkheads etc added,
These are generally refined and revised sometimes hundreds of times with different aspects of design considered with each change or revision such as varied amounts of cant in the hulls ,-larger sails, mast rake ,board locations ,hull variations ,- etc etc .
Some do this just as a hobby !!
The larger the beam of a particular design the less degree of cant is required . That is due to the hull lifting clear at less angle on a larger beam cat . The exact angle of cant required for a planning type hull would place the bottom plane of hull between the direct opposition to the forces at work on it and the optimum verticle lift derived from it.
This varies with wave height and seas conditions , also to a lesser extent with varied boat and crew total weight.
Considerabley more cant is required on the planning type than currently used it would seem if drawn in total section view at sailing attitude and heel.
I think the big advantage of canted hulls will be found in the development towards flatter underwater hull bow section shapes and the hydrodynamic lift created , we already see this trend in a number of A cat designs and the Inter designs. In future cat design development this combined with lifting canted foils and larger lifting spin,with greater luff angles on longer spin pole will develop into a planning type cat design that will be potentially much faster than the planning 18 skiffs, yet unlike skiffs still handle waves and surf which is some of the most fun of catsailing ,-surfing down the backs of big waves ,-It would be evan more fun to plane and lift up to surf most of the time.--- hope we see these soon ,--.
