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Old 15-09-2007, 22:46   #1
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Hull flex in heavy weather

An interesting view of hull flex about 20 seconds into this video



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Old 15-09-2007, 22:58   #2
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This okay.

Them big ships are designed and built to do just that.

If they were stiff, they would break.

I spent a few years of my life as a junior crew member on big ships, including super tankers (VLCC) and other big things in the ocean:

In bad weather they behaved like they were built from rubber...Thanks to Allah.

Big airplanes in turbulence shake, twist and bend, but that is what keeps 'em flying. A stiff wing would break.
Check out the video of a Boeing 747 wing being bent to the breaking point in a test stand at the factory: it goes way beyond any Hollywood script or a nightmare thunderstorm before it snaps.....Same with them tankers, they will fail in a 100 year storm, maybe...
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Old 15-09-2007, 23:06   #3
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Interesting stuff though. I was surprised to see the side to side flex. The up and down was expected, but still interesting to see.
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Old 16-09-2007, 10:14   #4
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I was suprised when I sailed offshore to listen to the sound of my Privilege 39 hull flexing. There's a lot of wood trim on the Privilege, and when the hull is working, I can hear the wood creaking. At first, the creaking noise concerned me, but nothing bad ever happened when we were sailing in rough seas. I reckon that just about every boat has some degree of hull flexing.

When I lived in Puerto Rico, I heard of a large charter/cruising yacht that had the rigging go slack in a seaway as the hull did longitudinal banana flexing. The people were not happy with the light construction of their hull by the time they sailed to windward from the USA to Puerto Rico.
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Old 16-09-2007, 13:06   #5
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I heard of a large charter/cruising yacht that had the rigging go slack in a seaway
Yikes, it shouldn't do that. That's the wrong type of bending.
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Old 18-09-2007, 05:46   #6
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When I lived in Puerto Rico, I heard of a large charter/cruising yacht that had the rigging go slack in a seaway as the hull did longitudinal banana flexing. The people were not happy with the light construction of their hull by the time they sailed to windward from the USA to Puerto Rico.

Would'nt have been a Magregor 65 ULDB would it

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Old 18-09-2007, 12:45   #7
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Of course, it does depend on how much slack the rigging was going through. But if it was slackign right off to lose and snapping tight again, that would end in death to the rigging.
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Old 18-09-2007, 17:44   #8
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Multi's with rotating rigs get a lot of slack in them, and use bungee cord attached to the shroud and ran aft to control the "snapping"

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Old 18-09-2007, 18:36   #9
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Multi's with rotating rigs get a lot of slack in them, and use bungee cord attached to the shroud and ran aft to control the "snapping"

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My masts will rotate but won't have ANY slack in the rigging

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Old 18-09-2007, 18:44   #10
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My masts will rotate but won't have ANY slack in the rigging

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Are you doing "free standing" rigs in your's, 1 in each hull??

If so, are these offset from the center line so as to allow access fwd, or do you still have enough room to pass ??

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Old 18-09-2007, 18:50   #11
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Yes one in each hull. They are offset to the outside of the doorway in the most forward connecting bulkhead.
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Old 18-09-2007, 21:05   #12
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About the twin rig. I thought about it, but was worried about possible resale implications. What made up your mind to go that way?
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Old 18-09-2007, 23:37   #13
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Many things contributed such as no standing rigging to corrode and stress.
No stays for the boom to play with, especially in a gybe. or the sails to rub against.
Downwind the booms can go forward of square which puts the CofE ahead of the CLR so it should track like an arrow.
Lower hieght for CofE.
Redundant mast and sail if one gets taken out somehow, maybe lightning.
No furling gear so less to go wrong and no need to go more forward of the mast in rough weather.
And more
Never actually thought about the impact on resale
but then I've never been known to worry about minor details like that.
She'l be right mate.

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Old 19-09-2007, 09:23   #14
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Great video...it really does show the movement well.

Ships not only hog and sag, they also twist (torsion). Imagine taking a long tube and twisting it. Same motion. It's normal thing for ships. There are calculations for it in the Stability and Trim tables.

In fact if a ship is not properly loaded or off loaded it can be broken right at the dock.

At sea you can feel a ships resonance frequency. Every object has a resonance frequency. I have felt ships vibrate a foot or more in heavy seas.

It is a freaky sensation for those unaccustomed to the movement.
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Old 20-09-2007, 14:26   #15
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44 CC
Many things contributed such as no standing rigging to corrode and stress.
No stays for the boom to play with, especially in a gybe. or the sails to rub against.
Downwind the booms can go forward of square which puts the CofE ahead of the CLR so it should track like an arrow.
Lower hieght for CofE.
Redundant mast and sail if one gets taken out somehow, maybe lightning.
No furling gear so less to go wrong and no need to go more forward of the mast in rough weather.
And more
Never actually thought about the impact on resale
but then I've never been known to worry about minor details like that.
She'l be right mate.

Mike
I think a lot of people are put off by anything that doesn't look just how they think it should (some people still buy mono's even with all their disadvantages )

I'll be very interested to see how it works.

Have you sourced your masts yet? There is a guy in Darwin buiding a 44C with a twin rig. He is getting carbon masts built by Rob Denney.
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