When you tighten the fore stay, back stay, and upper shrouds the mast want to flex out of column, like squeezing a flat tooth pick from its ends. Squeeze too much and snap.
You can see what mast pumping is by squeezing the tooth pick slowly (safety glasses please) in a C-Clamp and then gently try to move the middle back to straight. It will act like an over center spring and want to move to anywhere but straight. Without tensioned lowers the mast acts like the tooth pick and it wants to be anywhere but straight. Add the forces of sailing whether it's the roll of the waves or chop or a sail buffeting and these force at time may move the center of the mast column to ward center where it doesn't want to stay so instead of loading up cleanly it pumps back and forth. Let the pumping continue and it can work harden the aluminum at the flex point leading to failure. The lowers are there to keep the mast in column, although mast tuning for performance may require an intentional bow known as pre-bend. Even when pre-bend is used the center of the column is restrained from moving about so the loads are taken cleanly, without pumping. Higher performance rigs start using quickly adjustable standing rigging known as various types of running stays but each adds to the risk of a demasting, as well as, adding to performance. Your local PHRF authority will penalize you for the modification, if it is allowed at all. Of course it is not allowed at all in one-design racing. The factory added adjustable rear lowers (baby stays) to the Santana 20 design at some point and these appear were accepted by their one-design rules and the change escaped PHRF scrutiny but that's an exception. Phil Agur <http://www.catalina27.org/public_pages/profile270.htm> s/v Wing Tip Secretary, Call Sign WCW3485 IC27/270A MMSI 366901790 <http://www.catalina27.org> www.catalina27.org Vessel Doc# 1039809 -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of iicaptbrad Sent: Sunday, July 06, 2008 10:42 AM To: [email protected] Subject: Re: catalina27-talk: Re: Quick Question on Shroud Hook-up Locations Harvey, I was going to ask a question which you may have touched on in your second paragraph. Mast pumping. When I'm sitting on my boat at the dock while just a moderate breeze blows, the boat occassionally vibrates from the rigging. I was wondering if this is normal and if the rigging might be too tight or loose or out of adjustment. The standing rigging seems tight, all shrouds and stays, and the mast stands straight if not for a slight forward tilt (not noticable unless you hang a plumb bob). I've gazed at the rigging while this vibration is happening on several occassions and noticed, I think, the mast vibrating fore and aft around the spreaders which leads me to believe the lowers are loose, but they are tight like a violin string. Is this what you mean by mast pumping? Brad ----- Original Message ----- From: Harvey <mailto:[EMAIL PROTECTED]> Rosenberg To: [email protected] Sent: Saturday, July 05, 2008 7:58 AM Subject: [Norton AntiSpam] Re: catalina27-talk: Re: Quick Question on Shroud Hook-up Locations Hi Andy, Who is doing the shrouds? Is it George over at Samalot Marine? I can't believe he would do that. He must be thinking of Hunter B&R rigs. Our mast is not a bendable mast. You can adjust shoud tension and rake, but not bending it. It has to stay in column in all four directions. The foreward shrouds supports this. Leading it aft would put more stress on the leading edge of the mast when going upwind. C-27's are known for their mast pumping at dock in high winds and this would certainly aggravate this condition. Take him on a walk over at the South docks and look at the other C-27's. . Where is your boat. I couldn't find it? Regards Harvey Rosenberg C-27TR #6023, 1985 M-18 Harvey Rosenberg C-27TR ------ Original Message ------ Received: Fri, 04 Jul 2008 08:59:07 PM EDT From: [EMAIL PROTECTED] To: [email protected] Subject: catalina27-talk: Re: Quick Question on Shroud Hook-up Locations To List I have a quick question. I am having the shrouds change on my boat (....along with a great deal of other work, Boat fell off its stanchions this past March) and while the marina was setting up the new shrouds, he placed the lower forward shroud at the same spot as the upper shroud. He now had the forward lower and the center upper on the same spot where I thought the upper should be alone, and the stern lower in the correct spot. I questioned him on this and he said that the center was designed to take the forward lower shroud and the center shroud and the stern lower shroud stands alone. I always though that all three had their on spot for hook-up. Am I wrong? The marina guy seemed to be sure of his answer and mentioned that he has done this hook-up on several Catalina 27's before. I hope this explanation makes sense with all the upper and lower words used!!! Thanks Andy Slow "MO" tion #6038 Nyack, NY _____ the world a better place one message at a time. Check <http://www.imtalkathon.com/?source=EML_WLH_Talkathon_BetterPlace> out the i'm Talkathon. = _____ Gas prices getting you down? Search AOL Autos for fuel-efficient used cars <http://autos.aol.com/used?ncid=aolaut00050000000007> .
