Shivering Rigging
Date: August 27, 2000
From: Carol & Bruce McMahon MGHTYM@aol.com
I jave had s/v Cu Mara for about 2 months now, sailed her about 8 times and notices a shiver. This happens primarily when docked but I have noticed it during light wind sailing also. The mast and rigging start shivering when the wind hits a certain speed. It seems to be maximum displacement around the the lower shrouds. I have never had this happen on my other boat (Catalina 25) but this is the first boat I've had with double spreaders. Any ideas? I may just retension the lowers on both sides and see what happens.
Date: August 29, 2000
From: Tom Powers TomPowers@sunnuclear.com
Carol & Bruce,
I believe the phenomenon that you are describing is called "pumping". This is actually fairly common, and I understand that many Endeavours exhibit this characteristic.
Pumping is caused by a low pressure area forming on the leeward side of the mast. It can be alleviated by adjusting the rig tension, but that usually just moves the activation of the pumping to a different wind speed.
I am surprised to hear that you experience the pumping while sailing. Was this just underway or were you under sail?
I can not give you any recommended solution for the problem if it occurs while under sail, but when the sails are down, the solution rests in disrupting the flow of the air around the mast - usually near the point of maximum deflection. An easy way to do this, and I have done it, is to run a small fender up a main halyard with a line attached on other end so it can held tight. The fender should be hoisted to the point of max deflection. This will disrupt the air flow around the mast sufficiently to inhibit the formation of a vacuum. It looks odd, but most people think it is a radar reflector.
I am sure that there are other solutions that you may get from other readers. This solution was suggested to me by Brion Toss, the author of the "Rigger's Apprentice".
I hope this helps, good luck
Date: August 29, 2000
From: Thomas Heckler Ketch4two@aol.com
The "shivering" of any rigid body is caused by vortices. This occurs when a fluid media (air / water) flows past a (typically) smooth and regular object. A vortex (think of this as a mini-tornado) is created on the down-wind (or water) side of the object. These vortices alternate in orientation which can set up vibrations in the object being passed. If these vibrations are significant enough in amplitude, they can not only be annoying, but destructive (fatigue, stress, etc.).
The idea of changing the tension of the shrouds is a valid idea - this will change the shape of the object causing the vortices, and change the resonant frequency. There ARE other methods used in areas other than sailing - but, I think that you would find that if you raised sail when this vibration was occurring, the vibration would cease (interference with the vortex and increasing mass = change of resonant frequency).
Good luck!
P.S. The information above is a simplified explanation of a very complex occurrence - PhD's may send their critique directly. :)
Date: August 29, 2000
From: Carol & Bruce McMahon MGHTYM@aol.com
Hi Paul,
Thanks for putting it out. I did receive five answers and I learned quite a lot. This happens in a relatively low wind-- I would say around 8-10 knots. I have never noticed any leeward deflection of the rig but I will eyeball it this weekend. My lowers are decidely lower tension then the uppers or the fore and aft stays. I think I'll just retension all four lowers very slightly and see what happens.
Date: August 30, 2000
From: Paul Uhl endvr32@endeavourowners.com
I think you've just found your problem. The lowers need to have a tad more tension than the uppers to keep the mast in column. You should read through the rig tension topic on the Endeavour Discussion Forum page to get more specific details. Specific tensions are given for each of the stays. I do mine by feel and tighten the lowers until I 1) have no sag on either tack and 2) the mast remains in column. Sometimes when the wind picks up I add a bit more tension to the backstay to reduce sag in the headsail luff.
Date: September 3, 2000
From: Bill Vance & Julie Roberts Meadolninnn@aol.com
Dear Carol and Bruce:
Hi I am Billy and my friend is Julie, We had the same thing on our E32, and we tightened all the rigging and it corrected it. Good luck, and smooth sailing.
Date: September 8, 2000
From: Carl Hibbard Chgypsy@aol.com
Hello Carol & Bruce,
Your shivering is called mast pumping and you had figured out that it only happens at specific wind speeds and directions. Not much you can do about it. All boats will do this (some more than others) at some point of sail even at the dock. You will find that it can be more consistant at anchor with your bow constantly into the wind.
If you are also getting a wierd noise (at the dock) that accompanies the pumping try loosening up your mainsheet a little, its really the topping lift thrumming. Do check the rigging tension. Good luck
Date: August 16, 2001
From: Robert Lucey bob_lucky@yahoo.com
New guy here reading some old discussions. I lived aboard my E32 for a few years. Many a night I would notice something like the shivering effect described. Finally I tracked it down, and it wasn't the mast. My bimini was shaking when the wind hit it just right. The shaking was felt all the way up in the v-berth. A tightening of the straps cured most of it.
I'm curious if this mast shivering is where the old-time sailors got the term "shiver me timbers." I haven't noticed any shivering on the 122-year-old barque Elissa I volunteer aboard, but perhaps I haven't been aboard in the proper wind conditions for the spars to do the shake.
Also, I'm curious if other E32s have "handles" like mine. They're located at the midway point just aft of the mast attached to the toe-rail and pointed outboard. These are steel handles about six inches long. I use them for tying off my halyards at dock to get them away from my mast where they bang terribly in a breeze (not nice when you're trying to sleep). The handles are also handy for tying off spring lines. I imagine they might be useful in a towing situation, if I ever needed them. Just curious if they are standard equipment or not.
Date: April 24, 2003
From: Paul Uhl endvr32@endeavourowners.com
Mast pumping doesn't always make noise, but can still disturb your peace. Mast pumping at anchor occurs when a boat sits to the current rather than the wind. The cause is a phenomenon called the Karman Effect, and the permanent cure is to attach fins to the mast that detach the airflow. An alternative solution is keeping an empty sail slide in the mast track above the mainsail. Where pumping is a threat, hoisting a line tied to that slide allows you to set up what becomes, in effect, a baby backstay.
