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Old 02-07-2017, 15:37   #166
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Re: Engineers? Opinions on this please...

Yea, we all get sucked into a little mind-set and it's really hard to see beyond that, when something is just a little beyond our narrow field of experience. Us loud-mouths can create havoc with our dumb comments but sometimes that squeezes good answers from the less dumb/more able that are watching. CF can be a good source to turn to, even though it took 10 pages to get here!
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Old 02-07-2017, 16:32   #167
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Re: Engineers? Opinions on this please...

Quote:
CF can be a good source to turn to, even though it took 10 pages to get here!
Well, it may have taken 10 pages to get the real engineers to agree on things, but post #14 actually seems to have been pretty accurate. This may sound a bit like own horn tooting, but I use it to illustrate the adequacy of observation, experience of real world sailing, and a bit of common sense in solving such problems. Don's instinctive solution may not have been optimal, but it seems that it was adequate for his application.

So, well done Don, and good onya for hanging in there through all the theory!

Jim
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Old 02-07-2017, 19:28   #168
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Re: Engineers? Opinions on this please...

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... post #14 actually seems to have been pretty accurate. ... Jim
Uhu - along with plenty of others but, while we all made guesses and predictions, definitive answers, even quality analysis, were in very short supply.
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Old 02-07-2017, 22:18   #169
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Re: Engineers? Opinions on this please...

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42 1/3 fulrongs/fortnight - For those areas with legalized weed
Thanks all, but the only part I understood in all these 10 pages was that quote!

So I did take her out today, not quite the breeze I had hoped for. I pulled out my new handy dandy hand-held anemometer and it read only 7.5 knots, but I still managed to get more than 10 degrees of heel and 5 knots out of her, close reaching. Not too bad for a dirty bottom.

I had cranked down the rigging a bit more also. If there was movement on the arch it was on the order of ten thousandths of an inch. But really, I think if anything the arch was rigid and the whole boat was flexing. I'll tune the rigging back up and check again when I go out to the islands soon.

Even though the arch seems to work fine, I think this fall I'll probably be getting some solid wood to laminate up a copy using the same template and probably skip the aluminum this time, unless the Flitch beam comes in as the winner.

For everyone who has an older boat, with a deck stepped mast, I think this thread has been very instructive.

Again a big thank you to Eigenvector and all for helping out with this little arch.
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Old 02-07-2017, 22:36   #170
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Re: Engineers? Opinions on this please...

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Uhu - along with plenty of others but, while we all made guesses and predictions, definitive answers, even quality analysis, were in very short supply.
And all of this gives me A LOT more respect for the engineering and strength of the materials that go into boats like the current batch of America's Cup boats.
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Old 02-07-2017, 22:49   #171
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Re: Engineers? Opinions on this please...

Yes, but at an incredible cost in designing those flying machines! There's much to be said for Jim Cate's and others' ability to eyeball these things from past experience but, in this particular case, the strength was just a little bit marginal, so no one could say with absolute certainty. Without FEA, I'd still prefer big factors of safety (though that won't win any AC races for sure).
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Old 05-07-2017, 20:29   #172
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Re: Engineers? Opinions on this please...

So I was out yesterday with the kids and we had a breeze of 10-15 knots and since I was pushing it to windward with the 130 genoa I managed to get her heeled over to 20 degrees and we were banging into a little chop too so the rigging was getting mildly stressed on 2 axes. I put on my high power reading glasses and scrutinized the beam with the reference points I made while my daughter played autopilot. Nothing but that same movement which is actually the deck above the arch flexing a thousandth of an inch or so. So I relaxed and we continued on when suddenly a very loud "WHACK!" Of course I turn to my daughter as suspicious fathers do and say "What was that?!"
"Just the bottom cabinet door falling open when we heeled over."
Not believing her I flew down the steps, grabbed my reading glasses and studied the arch. Nothing. No gaps, no cracks, no bends. My daughter was right. The cabinet door was open on the floor.
If I ever suffer a real knockdown, the first thing I am doing is grabbing my reading glasses!
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Old 06-07-2017, 01:04   #173
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Re: Engineers? Opinions on this please...

good story, Don, and I think good support for the "she'll be right, mate" crowd.

Have fun sailing, and keep those cheaters near to hand... I need 'em too!

Jim
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Old 06-07-2017, 17:31   #174
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Re: Engineers? Opinions on this please...

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If I ever suffer a real knockdown, the first thing I am doing is grabbing my reading glasses!
Brown trousers first! Seriously, that's what those big safety factors are for - anything beyond 'normal'. AC boats expect to fail in anything over 20 kts, so they dispense with the margins.
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