Thanks to Seahorse Magazine for this excerpt from “Clear the Bench” in the April 2012 issue. Get the CupExperience discount for your subscription or renewal.
“How full do we make the bows? In basic terms the finer the front 30 per cent the faster you go. Unfortunately against that is the tendency of fine bows to dig in and submerge, stopping the boat. At that point momentum takes over and you pitchpole. If you have not seen Torvar Mirsky on YouTube executing a perfect end-over-end in China last year, it is worth a look. Let me put it another way. Cycle down a hill at speed. Now lean forward and lock up the front brake. That same free-flight panic as you go over the handlebars is what every cat sailor lives in fear of.
A fine bow looks like the Extreme 40s where a fuller bow is more like the AC45. In terms of fullness, if the X40 is a one and the AC45 is a 10, then where are we going to put our boat? Personally, I am thinking of a seven or eight. The idea of pitchpoling a 72ft cat scares me too much. Besides, you have to finish to win.
By the way, ever wondered why modern catamaran bows look reversed compared to a monohull bow? The longest part is at the bottom and then the stem tapers back as you move up from the water? Wave piercing. That is also why the top is so fine with no ‘deck’ space as such. When it’s well-designed, you lose less energy by going through the wave than by going over it.
Two things good about wave-piercing bows: there is a lot less drag when the bow is under water and the bow does not get pushed up as much after hitting a wave. That means less pitching moment. A-Class boats have used them for years. I am going to incorporate them on our boat. But I should warn you, wavepiercing bows can lead to a water-management problem.
As far as underwater shape goes there seems to be a pretty good consensus here. Modern racing cats tend to be very straight fore and aft with little rocker and flat bottom sections. I am guessing it is about the lower drag at the higher speeds cats sail at. No need to reinvent the wheel on this one, we’ll just copy current thinking when it comes to profile and cross-section shape.
How close did Rodney March (designer of the only cat used in the Olympics) come to getting it right in 1966? The forward sections of the Tornado are close to line-for-line the same as the AC45… but upside down. Strange but true.”
Any questions? Any comments? Add them below!