The Next Americas Cup Boats

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Bill Roberts
Posts: 487
Joined: November 17th, 2003, 7:13 pm
Location: Stuart, Florida

The Next Americas Cup Boats

Post by Bill Roberts » October 18th, 2017, 4:44 pm

Well, the word is out. The next AC race will be in mono hulls with swing Keels and soft sails. This is going to be quite a step down in boat speed but it will be a sailing contest that will have "trickle down" technology that will help us all.
Boat designers seem to try many many different ways to achieve more righting moment. The catamaran sailboat configuration achieves more righting moment by moving the centers of buoyancy far apart and using boat weight and distance between hulls to achieve a large righting moment and minimum overall boat weight at the same time. Trimarans can do the same thing as long as the the amas are long and low and have enough buoyancy to fly the rest of the boat, main hull and windward ama, like a catamaran.
Now here come the mono hull designers. They want more righting moment also but they go about it in a different way. They add 'weight' to the mono hull and then move that 'weight' around. The weight is moved to windward to increase righting moment which increases sail thrust and therefore boat speed. You could do this by putting a track across the deck and let it extend out some distance beyond the sides of the boat. This track has a large, heavy, weight that runs on the track from side to side. The large weight is positioned along the track to balance the boat and keep the mast straight up. Another way to do this would be to put the large weight on a lever arm 'under the boat' that pivoted about the keel. Then raise the weight UNDERWATER, in general to the windward side of the boat as necessary to balance the boat and keep the mast straight up. The negative of this is all this lever and extra weight make drag underwater. I guess the reason they do it this way is that they don't want anyone to see it. They want to hide it from view. This scheme does make a mono hull go a little faster, but I guess the best part is, it is out of sight. This way they can trick some people because you don't see what they are doing. Ain't that slick.

J Drew
Posts: 103
Joined: September 8th, 2013, 9:39 pm
Boat Make/Model: SC 20
Location: n. florida

Re: The Next Americas Cup Boats

Post by J Drew » December 12th, 2017, 10:33 am

Hey Bill,
Looking at all of the new foil configurations, both with cats and monohulls, I have a question.
Now, we've gone over how to calculate lift, and thus the size of foil. My question is how is lift calculated in a curve? You see many foils that have a rounded V shape. Obviously, depending on the sharpness of the curve, I wonder about lift and how this adds to stability? In some ways it's similar to the tail wing of a V35 beach bonanza, I'm sure there are others like that, but you tell me how this is relevant?
It could go further to wonder about diagonal foils, that appear on some boats that I've seen, and how their lift is calculated?
Anyway, it's been a while, so it's like the golf ball question, I still don't see any smooth golf balls, but now I know why. :D
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