Mac 26X Spar Fatigue and Bending

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med
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Mac 26X Spar Fatigue and Bending

Post by med » Sun Feb 15, 2004 7:55 pm

Fatigued Spars

I purchased a new mac26 in April 2003. I sail it approximately once a week for one day so you could say the boat has had a total sailing time of approx 320 hours.
Since starting to sail the boat I have noticed that the spars have, over the period of time, gradually started to bend at the location where the spar exits from the sockets located on the mast. I can say that the rigging has more or less always been at the correct tension but if anything slightly under tensioned. I can send some photos that show the extent of bending and the fatigue if it helps just let me know your email address however the bendin that occurred is equivalent to an offset of 11 deg or over the entire lenght of the spar on offset of 205 mm in the direction of inboard to the original straight position. Ive since shortened the spars by 68 mm to eliminate the fatigued and bent spar sections. Can anyone throw any light on this with a possible cause why the fatigue has occurred to the extent that has caused the spars to fail and bend and can anyone comment on on any possible detrimental effects due the shortening of the spars by 68 mm. Original spar length is 1120 mm they are now 1052 mm long.
Any assistance with resolving this matter would be appreciated.

Bill at BOATS 4 SAIL
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Spars/Spreaders

Post by Bill at BOATS 4 SAIL » Mon Feb 16, 2004 8:55 am

med - Spars is a general term: mast, boom, spreaders, etc.
Check to see if your spreader tips, on the outside end of your spreader tubes, are in the correct spot on the upper shrouds. Your owners manual gives the correct location.

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Chip Hindes
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Post by Chip Hindes » Mon Feb 16, 2004 10:12 am

By the term "fatigue", do you mean actual cracking?

Many people believe that by leaving their rigging loose, the loads will be lower. In fact, although loose rigging does mean static loads are lower, it contributes to higher shock and fatigue loading, which is way more detrimental to rigging health than high static loads. Loose rigging is more likely to cause early failure than tight rigging. If your rigging is at all loose, tighten it.

I'm not sure what you mean by "inboard" bending. Do you mean the tips are moving aft in relation to their original position? I believe such a problem can be caused by too much tension on the upper shrouds, too little on the lower shrouds, and excessive mast bend. Make sure the bend is correct in based on the owners' manual.

I have found, because of the angles of the shrouds and loads placed on the spreaders by the shrouds, over time the spreader tips will tend to slide downward on the shrouds, even if they are initially set correctly. Particularly when the mast is down, when raising, lowering, or trailering, if you happen to catch the spreader on something which pushes it downward toward the base of the mast, the upper part of the shroud is tight and the top will slide down. If you happen to catch it on something that pushes it upward, the lower part of the shroud is slack and it will not slide back up.

If this is a problem as well, you may need to periodically loosen the tips, slide them back up where they belong, again based on the owners' manual as Bill says, and retighten them.

Sailing "only" 320 hours per year may not seem like a lot, but I'm guessing 52 times per year is way more than many of us can hope for. Particulary those of us whose boats are currently covered with snow, as mine is :( You mentioned nothing about the conditions under which you usually sail, which could matter way more than the number of times per year or total hours. Where is the boat while you're not sailing it? One guy has stated he has broken two masts, not while the boat was sailing, but while it was tied to a mooring buoy.

Reducing the spreader length by any amount will reduce the bending stiffness of the mast, and will increase the loads in other parts of the rigging in possibly unexpected ways. The amount you cut off is not large and the differences in loading should be fairly small, as long as you retightened the rest of the rigging to take out the resulting slack. If it were me, I would consider this an emergency repair to keep me sailing, but would replace the cut down spreaders with full length ones at the earliest opportunity.

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craiglaforce
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Post by craiglaforce » Mon Feb 16, 2004 12:50 pm

WHen I bought my boat I was told not to tighten the spreader tips, so that the cable could center itself without bending the spreader tubes "spars".
I don't know if this is right or not, but so far no problems. I keep my rig pretty tight. Someone said they put a broom stick or PVC tube or something inside the aluminum tubes to help strengthen them. Not sure if this helped them or not.

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Post by Billy » Mon Feb 16, 2004 2:30 pm

Was there an earlier post about the socket's inner edge not being completely flush? This would lead to more load on that area of the spreader and eventually wear or bending. The remedy was to grind the inner edge of the socket.

Because I bent my spreaders the first year, I inserted a dowel full length (except for where the spreader tip fits). Really tight fit, but 3 years later no problems.

Frank C

Post by Frank C » Mon Feb 16, 2004 3:48 pm

Billy wrote:Was there an earlier post about the socket's inner edge not being completely flush?
Yes, there's a casting ridge around the inside circumference of the socket, which can score the spreader over time. Also, it's mandatory to tighten the spreader tips to a measured point on the shroud. I recall that it's specified in the owner's manual - wherever that is!

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Timm Miller
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BENT

Post by Timm Miller » Tue Feb 17, 2004 3:04 am

Mine got bent due to Isabel.....the new ones, I placed a 7/8" x 48" Poplar dowel inside and trimmed the excess to fit. Macgregor Parts has SS spars for the Mac......So I guess you could find some SS tube 44" x 1" and make your own.

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Chip Hindes
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Post by Chip Hindes » Tue Feb 17, 2004 4:50 pm

Not sure a stiffer spreader is the way to go. If nothing else, it is likely to change the failure mode from relatively harmless bending of the spreader, to fracture of the cast spreader socket, truly a cruise killer. Hard to argue with success, though. Mine are fine, not bent at all after three years. Most of my sailing is lakes and low to very moderate winds, and until this past fall the mast spent most of its life stowed on the crutch.

I definitely don't need the added weight aloft of SS spreaders.

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Timm Miller
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Valid points

Post by Timm Miller » Wed Feb 18, 2004 4:10 am

I guess it would be cheaper and less troublesome to replace a tube then the base.

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Chip Hindes
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Post by Chip Hindes » Wed Feb 18, 2004 10:43 am

I take back the "relatively harmless" part. I was picturing a nice, moderate "bend". Med sent me pictures of his spreaders and they aren't just nicely bent, they're badly buckled right where they would have exited the sockets.

There are two pictures, but they're substantially different so I can't tell whether I'm looking at one spreader from two different angles, or two different spreaders. Med, it would be interesting to know if this was a progressive type failure or the result of a single incident.

Even as bad as the pictures show, I'm thinking in a pinch you could reverse the spreaders end for end, put the straight end in the socket and the tips in the bent end, and continue to function with two fairly ugly but perfectly serviceable spreaders.

In fact, now that I know (from med) it's possible to operate with the spreaders cut down, I wouldn't hesitate to try straightening the bent part (in a vise, not in the socket :) ) as long as that became the tip end. I believe about the worst that could happen is you'd break them at the bend; then you'd just have to cut that part off.

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norbert
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spreader recycling

Post by norbert » Wed Feb 18, 2004 12:18 pm

hmmm, but imagine the re-bended tip end breaks under heavy load in higher winds, this would make your mast come down! i recommend to replace the spreaders by new ones in the original size. i also am not a friend of cutting the spreaders shorter, this alters the rigg geometry, and it is not so strong built that you want to loose any mechanical advantage.

i sailed my 26x for 6 years now, and the last season has been on the baltic sea with winds up to 8 bft and 6 ft waves. no rigg problems so far. since i bought the boat my spreaders are slightly bent in a gentle bow and did not move since. i recall that it is very important to have the rigg properly tensioned to avoid shock loads.

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Chip Hindes
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Post by Chip Hindes » Wed Feb 18, 2004 7:59 pm

hmmm, but imagine the re-bended tip end breaks under heavy load in higher winds, this would make your mast come down!
No worry there; under any condition of loading, the tips are about as close to "no load" as you can get. All the stress is in the socket ends.
i recommend to replace the spreaders by new ones in the original size. i also am not a friend of cutting the spreaders shorter, this alters the rigg geometry, and it is not so strong built that you want to loose any mechanical advantage.
Agree with you here. My suggestions were intended for temporary or emergency use only, to keep you sailing in case you couldn't get replacement spreaders on short notice.

med
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Mac 26X Spar Fatigue and Bending

Post by med » Thu Feb 19, 2004 2:57 pm

Chip said:
I take back the "relatively harmless" part. I was picturing a nice, moderate "bend". Med sent me pictures of his spreaders and they aren't just nicely bent, they're badly buckled right where they would have exited the sockets.

There are two pictures, but they're substantially different so I can't tell whether I'm looking at one spreader from two different angles, or two different spreaders. Med, it would be interesting to know if this was a progressive type failure or the result of a single incident.

Chip: The two photos I sent you were one shot of port and one shot of the starport spreader. The bending was progressive over about six months. My last sail prior to cutting out the bent sections was, I suppose I could say, in very lumpy seas with short swells to 2.3 mtrs and winds up to 23 knots. It was when I was docking the boat later that I noticed that the bending had gotten considerably worst. This prompted me to cut the damaged section from the spreaders, get rid of the factory supplied chain plates and swap them with turnbuckles (easier to tension the shrouds with the turnbuckles and make any minor adjustments when necessary with retative ease) and tension the rig to achieve the parameters as set out in the Mac handbook. I suspect the cause of the bending was from a loosely tensioned rig coupled with the thumping the boat gets in lumpy seas. I didnt reverse the spreaders after I shortened them as they both looked straight to me and I consider that the fatigued section was discarded. I'm sailing again tomorrow and will see how it goes. I would like to take this opportinity to thank you all for your comments, they have been very helpful in helping me to take the couse of action that I have.

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Newell
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Spreader Fatigue

Post by Newell » Sat Feb 21, 2004 1:40 pm

Coming to this discussion late but have some history to relate.

Two years ago(02) my 96X spreaders both broke from fatigue at the inboard end and fell off the mast, hanging from the shrouds as I lowered the mast at the end of a Lake Mead, NV 3 day sail trip. There were high winds during most of the 3 days and some of the time I was sailing under a reefed main.

The factory replaced them without comment or cost, except the 'wow how could this have happenened' comment from me and I believe Steve K. also called the factory, he was a witness to the problem.

I trailer sail so mast up and down freguently describes my usual routine. I believe the wear and tear and vibration from trailering and snow loads, tarping during the Winter are the biggest contributors to this problem.

I will always wonder how they both could have broke at the same time and yet the compression force held them in place.

When some do the Mac dance to get the spreaders under the lifelines sometimes one will rest on the lifeline and stress the critical area of the spreader where it exits from the socket. That is where they will break.

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Steve K
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Post by Steve K » Mon Feb 23, 2004 8:14 am

Yep,
There was Newell and myself, standing there with our mouths hanging open. I mean, the second he loosed the tension on the rig, to start dropping the mast, the spreaders fell right out of their sockets.

A couple notes;
The spreader sockets are not a cast item (mine aren't anyway) They are a section of ss tubing welded to a ss plate, that is bent to conform to the rounded shape of the mast section. Chances of these ever cracking or breaking would be very slight.

Some of these short sections of tubing, that the spreader fits into, look like they were cut with a pipe cutter. This creates a ridge on the inside of the stainless tubing. Newells problem was that this ridge was not smoothed off during production of the socket. Over the years, this ridge, just inside the end of the socket had caused scoring on the spreader and eventually cut it through.

As soon as I got home with my own boat, after that weekend, I checked my own spreaders. They had the same scoring as Newells and were close to breaking too. Once the ridge wears off the hard anodizing from the spreader tube, a combination of further scoring and corrosion will quickly do the job to cut them through.

And Newells spreaders looked as though they had been cut with a tubing cutter. The break was very clean and straight.

I called Bill @ MacGregor and told him about this, because it was my opinion that the spreader socket could have been finished inside better at the factory. He agreed and checked the sockets on hand that day.

In the meantime, I filed out the ridge, just inside my own spreader sockets. I then cut the spreaders off, right where the score mark was. This shortened the spreader a couple inches (not sure the exact measurement) .
Having one spreader that was slightly bent, I hammered hardwood dowel stock into both spreaders. This dowell piece is about 2/3 the length of the spreader and is flush with the inner end of the spreader (the socket end).
Spreaders are nice and straight now and I like the feeling of comfort I have, knowing the dowel inside the spreader gives a little insurance. The rig also seems to react to adjustment of the uppers more positively.

As far as shortening the spreader goes, there is a limit of anlge you can have for your upper shroud to be effective (sorry, forgot what that angle is exactly, it's 15 or 22 degrees). Shortening the spreader the amount I did kept the shroud well within this limit. I always thought the spreaders on the MacX were too long anyway. They are stiffer that they used to be and the rig doesn't seem to be as sloppy as it used too. JMHO.

In any case, I would HIGHLY recomend that everyone with a 26X pull the spreaders out from the sockets and check them. Feel inside the socket with your finger for this ridge, running around, just inside the socket and look for a deep score mark on the spreader. How you decide to repare them is up to you. I have gotten replacement spreaders for one of my other friends, because he didn't like the idea of shortening them. That's just fine too.

Still don't know how Newell didn't lose his rig that weekend. His gardian angel must have been sittin up there on the mast holding the spreaders in place. :wink:

SK

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