When you see articles on America’s Cup (Open60, etc) yacht design, they always employ scale models in test tanks to test hull shapes, keel configurations, even wave & wake action. In the movie “Wind” they did their testing in a stream.
I suppose today its largely done with software, yet tanks are still used since computers can only gauge so much. Has anyone made a rudimentry test tank (pix pls) or used a real one (or stream) to test a RC yacht?
Thanks, yar
I use a clear plexi test tank quite a bit for ballasting EC-12 and smaller, and a large bathtub type for up to and including the new AC and J Class. I drew up plans for a flow tank but the time and money involved not to mention space make it prohibitive. I doubt that I would get that much more information from using it, but more of a curiosity to see if I could make it work type thing.
Here is the first EC12 in an “Air Flow” tunnel.
The Charlie Morgan test hull later became the basis for the EC12 class.
Here are another couple of interest from my “secret file”
Larry Ludwig, yeah, seams the tank size is prohibitive. And the information gained may not warrant it, as you indicate. One could say, “you already got the finished boat, just sail it for testing”. But it would nice to be beside the hull for reference.
IanHB, that center pic from your “secret files” is interesting. Real water test with computer info overlay? From my file, WTMTOMH*, here’s my design of a portable track and carriage that lays over a swimming pool.
Maybe building a wind tunnel is more practical, the Wright Brothers did so, then test the whole sailing package. Or, Christmas is next week… I’ll ask for a Flotek 1440.
yar
Better still, just get Santa to find you a week off before the next event… and sail your boat every single day, take pics of it… video is good too… sail ALL day, and study images all night. You will place 100% better than you did before.
The first time you sit down and look at pics of your boat, and see problems with the sails, wrinkles here… slack there… you will wonder no more. When you admit that the boomvang isn’t doing what you really need it to do, and when you tighten this much here… that you really get screwed up when the sail goes out there… those are things that the top boats don’t do.
Ounces won’t kill you, but those things will.
A fast boat will NOTwin you races You still have to sail it.
A slow boat WILL lose you races. Even when you make the correct decisions.
:graduate:
Hi Yar
There is a current upsurge in new builds and refurbishments of towing tanks and wind tunnels especially around the world, in order to calibrate the computer models, which aren’t telling the designers everything they thought they would get told… (smile!)
used a real one (or stream) to test a RC yacht
Yup, some of my past students have used the small Lamont tank at the University of Southampton, the larger tank at the Southampton Institute (now Solent University), and the very large tank at QinetiQ, Haslar, Isle of Wight. I haven’t found the resulting data has told me anything a standard textbook didn’t already mention, so don’t show any of these experiments on my pages.
Your swimming pool idea looks very interesting. How do you plan to drive the hull, and how do you plan to measure the various resulting drag forces and vectors?
Your swimming pool idea looks very interesting. How do you plan to drive the hull, and how do you plan to measure the various resulting drag forces and vectors?
The idea was a daydream while thinking of this post and wondering how to “borrow” a body of water. Possibly a electric motor in the housing above/holding the hull, rubber wheels on “lightrail” type track. Pulley? Auger? Cost, simplicity, weight and ingenuity are key, maybe you can provide feedback on the apparatus.
Tiny video cameras (H2Otite housing) for recording flow. Would mini telltales taped all over hull work in water? Like this engineer placed on the helicopter model bolted to the front of this truck (Wind style wind tunnel).
Thanks guys,
yar
I have thought of this while riding my bike home along the river. and that is if you could set up a pully attachment or lever with a fishing scale on it. I do not have a cad progam to draw but what it would do is measure the weight of resistance, then you put new boat on of new appendige and see what that weights in at. I saw somthing similar in Frank Bethweights book " High perfomance sailing" and he is towing a boat behind a small motor boat. Just an Idea.
I agree with Larry. You will learn more about making your boat go faster by sailing it; especailly if you can find a tuning buddy to do side by side sailing, changing only one boat at a time. This will produce far more inprovement in boat speed than trying to get a better hull shape.
IMHO. To improve on the best boats in your class, the difference in boat speed would be measured in 100ths of a knot. To me that would be quite a challenge to measure and repeat such small deltas with a home-made tank setup. The minor differences in resistance would be swamped by inherent forces and resistances in the test rig itself.
Beside, sailing is more fun!
I am always disappointed by my fellow sailors who wag their finger in my face and straighten me out on how I should go about enjoying the sport.
Yar’s post didn’t ask how he might sail faster. He asked about towing tank testing and whether anyone had used model yacht hulls.
Many of us get pleasure from the theoretical side of the sport, and without theoretical input the practical side isn’t going to advance much. It may not be your taste, but I think there is room for other interests.
Sincerely,
To measure very small differences as a proportion, tow two models from the ends of a yoke. Adjust the pivot point of the yoke until the bar is at 90 degrees to the direction of tow. The relative drag is the ratio of the lengths of the two endfs (Ljungstrom, Sweden, c. 1935).
As to the ‘you learn more by sailing it school’. You are probably right. However, the designer who’s design you are trying to extract the maximum from will undoubtedly produce the best result from sophisticated engineering design studies. I remember hearing it said of one of the 12ms that lost the America’s Cup for the NYYC that ‘the only partticular reason for believing that she would be any faster than the previous version was that she was extremely expensive’.