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The Fuller Number |
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Topic: The Fuller Number Posted: 22 Apr 14 at 3:46pm |
PY = 1800 - 144*Length - 37*Sail Area + 1.2*Weight |
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
Post Options Quote Reply Posted: 22 Apr 14 at 3:55pm |
Righting moment?
+ftfy or PY = (1800 - ((144*Length) - (37*Sail Area) + (1.2*Weight))) +ftfy Edited by iGRF - 22 Apr 14 at 4:00pm |
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Post Options Quote Reply Posted: 22 Apr 14 at 4:10pm |
Bless My Dear Aunt Sally
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
Post Options Quote Reply Posted: 22 Apr 14 at 4:30pm |
Please Excuse My Dear Aunt Sally
So now which is it, and what about the righting moment? I'm still waiting for all those who promised me the spreadsheet to ante up. |
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Post Options Quote Reply Posted: 22 Apr 14 at 4:42pm |
Good question about RM. For the 21 boats I looked at there was, suprisingly, no correlation between RM and PY. This might be because all the boats I looked at where kiteless hikers (Laser, Solo, Icon, Streaker etc), and so had similar RM.
I initially had a much more complex formula with things like RM to weight ratios and based the natural log of the PY number, but it did not give a much better fit and was harder to get input numbers for (wetted surface area, sail carrying power etc). So, for boats with no spinnaker, hydrofoil or trapezes: PY = 1800 - (144 x Length) - (37 x Sail Area) + (1.2 x Weight) where Weight is total displacement of boat plus crew |
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
Post Options Quote Reply Posted: 22 Apr 14 at 4:55pm |
It's windsurf race night tonight so I'll be back off the air for a bit, but let me have a go with that and compare it with one I wasted hours on trying to work out myself (Was nothing quite as simple as yours). We definitely need something, I've been away from my club for a week and already I can see some very dispirited chaps not wanting to even bother as a result of the latest PY carnage.
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Post Options Quote Reply Posted: 22 Apr 14 at 5:26pm |
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AlexM
Really should get out more Joined: 10 Jan 06 Online Status: Offline Posts: 857 |
Post Options Quote Reply Posted: 22 Apr 14 at 5:32pm |
Have you just proved the RYA numbers correct?
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iitick
Far too distracted from work Joined: 09 Sep 13 Location: Tunstead Milton Online Status: Offline Posts: 392 |
Post Options Quote Reply Posted: 22 Apr 14 at 5:44pm |
Remarkably close!
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Rupert
Really should get out more Joined: 11 Aug 04 Location: Whitefriars sc Online Status: Offline Posts: 8956 |
Post Options Quote Reply Posted: 22 Apr 14 at 5:50pm |
The formula has been taken from the numbers, so you'd expect it to work for the majority, wouldn't you?
Interesting that according to that, the Europe punches above its weight, which is what I'd expect from a boat a foot shorter than the ones it has a comparable PY to, and that the Pico and Topper, mainly sailed by beginners, have PY's more generous than the formula suggests. Interesting stuff. Now we will see how the Zero and Aero do compared to the theory. I assume it is waterline length we are dealing with? |
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