Well hello everybody,
I'm glad to see the title change. An engineer is the person who takes all this theory stuff and makes it work in practice.
In 1981 I went over to Brest France to the World Championship Speed Trials for Sailboats. There were mostly sailboards and beach cats there. I was obvisously interested in the beach cats. There were boats there of all sizes, 14ft to 20ft, and descriptions, all the popular classes plus sone one of a kind boats. There were three days of speed runs and every boat was allowed to make as many runs as they wanted to until the clock ran out. The results were calculated by computer and printouts were available every night of every run on every boat that tested that day. I brought those results home with me and studied them and tried to figure out why some boats were faster than others. I knew the old formula, Vmax = 1.4 sqrt LWL. The 1.4 coefficient is called the speed to length ratio. I solved for the speed to length ratios for the fastest boat of each size and then tried to figure out what could be making these ratios or coefficients vary between 4 and 5. I considered hull loading, displacement/length **3, bow wedge angle, work and power of pushing the water aside and many other parameters were considered. What I finally realized was that when I plotted speed to length ratio vs hull fineness ratio the data defined a line that was almost straight. Then I connected it to the 1.4 value for monohulls at a hull fineness ratio of 4 and it too fell on the line. Well now, how about this, we now have a Simple Simon way to estimate beach cat max speed based on boat length and hull fineness ratio for boats in the 14ft to 20 ft length. This I have used in my boat design calculations and it has served me well. I have predicted the Portsmouth Number of the boats I have designed using this equation and many other parameters and ratios and hit the PN of these boats right on the money every time. And for Wouter: This system is not the first law of catamaran boat speed but it is a system that I have come up with and it works very well for me.
Here's another Wouter point that I should respond to. Wouter is bringing forward the position that as boats are built lighter in weight with higher sail area to total sailing weight ratios they can go faster even though they have lower righting moment to sail area ratios. I have a hard time going along with that. I know of no example where that is true. Wouter pointed to the A class cat as an example of success here but I don't go along with that because the A class cat is a development class and many things are improving about that boat as well as the weight going down. I am not willing to give weight reduction total credit for the performance improvement in the A class catamaran. Wouter also pointed out that the Tiapan4.9 was lighter and faster tham the H16 and the Tiapan is the same width and length. Not a fair comparison, Wouter. I think the Tiapan has daggerboards and you can't compare beach boats to board boats on performance. The board boat is faster every time. We do have this comparison: A year or two back they held a trials in Europe to consider a catamaran to replace the Tornado in the Olympics. All the new hot 20 footers took on the Tornado. The Tornado won every heat. WHY??? The Tornado has a higher sail area to weight ratio and it has a higher righting moment to sail area ratio than any of the other boats in the race. Well done basics, fundamentals, will win every time.
Bill
