Again from the top of my head (I have the document archieved somewhere but I'm not digging it up)
4% of the Total drag of the Miss Nyles C-class catamaran was attributed to parasitic drag. This EXCLUDES the windage of the crew and the INDUCED AND FORM drag of the sails. Basically it it the windage of the hulls, beams, stays, trampoline, sheet systems and some other fittings.
Your talk of drag coefficient of 0.04 is just confused and totally in error. I only said 4% of the total drag, any aerodynamic coefficients may still be any value, it is just that they don't amount to more then 4% of the total drag.
It would help everyone understand this more if you could quantify the aero drag in terms of lbs or kg.
I don't remember this data from Miss Nylex but I do know that both the 49-er skiffs and F16's have a top speed total drag in the neighbourhood of 75 kg's. Note that this INCLUDES the INDUCED and FORM drag of the sails, a thing you will never "feel" on board. Basically the hulls and daggerboards alone comprise around 50 kg's in total for these 16 footers.
So removing the beams completely as well as the trampoline the stays and other fittings will win you 4% of roughly 75 kg = 3 kg. But at that time you will not have a boat. So the real question is how much can be gained by minimizing the beams etc.
The answer here is that it is often a zero sum game. You can reduce the frontal area of the beams by going for smaller diameters, But as payback you'll also reduce platform stiffness. You can never improve on both simultaniously unless you are willing to accept much heavier beams which many will claim is very slow as well.
Going to thinner stays lowers rig stiffness and sags your spinnaker luff. You think you'll win some windage benefit but throw it out the door with maybe a multiplication factor of ten by having a sagging and unsteable spi luff.
We must see these issue's as an interconnected set of interdependencies. That is why simple rules of thumb like "Thinner stays are always better" are so utterly useless.
It is all about striking the optimal balance.
Now on cabin cruisers and large monoslugs there is plenty of stuff to play with. The "winch behind the cabin" stuff. On beach cats, well, what is still there that isn't truly necessary ? We have already removed stuff like cabins on these boats a long time ago.
On beachcats the choice is between 4 mm 1x19 stays or 3 mm 1x7 dyform stays. Between a 4 mm spi halyard and a 3 mm spi halyard (2 mm halyard really does hurt your hands when a gust slams the spi). This stuff is to small to matter. So you save, what, 0.018 sq mtr on a total frontal area of 0.5 sq. mtr. (=4%) that itself was only associated with 4% of the total drag => 4% times 4% equals 0.16% drag reduction of a total of about 75 kg => 0.12 kg or a quarter lbs.
That is what we are talking about here. Multiplications of several small percentages resulting in negligiable differences.
The only exceptions can be disturbances like the spi halyard running up along the mast as it may negatively influence the reattachment zones of the larger sail behind it and thus leverage its negligiable drag into a much larger loss of drive. But this requires very careful analyses with experimental setups and possibly windtunnels.
Wouter
