Dismasted this past weekend.

[seahouse]

Hey tlgibson!

I can’t tell from the photos, but examine the break up close and see if it is equally shiny all the way around. I would expect that under good light and a magnifier you will be able to see an area near the holes where the aluminum is not as shiny. Meaning that the area has been fatiguing for a while.

Was the mast curved gently to one side, or was there a fairly sharp bend at the area of the holes? Meaning that the area was already weakening, and probably from lack of proper rig tensioning.

OK, so there’s an echo in here. You get the idea.

The maximum forces on the mast are a function of the righting moment of the boat, assuming proper rigging. And the righting moment of the boat is pre-determined in its design, so the boat simply heels to relieve the stress. Meaning, the way you were handling the boat at the time of the mast failure was not a function of any negligence on your part! The Mac is designed to be very forgiving in that department.

- Brian.

[ualpow]

I made new rigging for my and bought the LOOS gauge that was posted previously. I was very surprised at how tight the shrouds seem at the proper tension. If I was adjusting them without the gauge I wouldn't have even had them close to proper tension.

[seahouse]

Hey ualpow!

Sumner reported that same thing, and after reading his post I went and retensioned my rig tensions up. I had previously tensioned by measuring elongation of the the stays as a percetage of breaking load, but it felt too high so I went a bit lower. I also believe that tensioning is most properly done when the boat is in the water, not on the trailer, but that's a lot less convenient, so it gets done on the trailer.

I did notice that they have relaxed over the season, and will be retensioning again next spring.

When sailing upwind, if the leeward stays are drooping, and not straight, the rigging is too loose. Is that your experience?

- Brian.

On edit, to clarify, I meant "shrouds", not "stays" drooping. My bad.(Thanks Leon, if this is what you are referring to).

[RJG 26S]

I have read of afew "X" masts breaking at the spreader bolt in recent months which makes me wonder why?

The mast will break there (BTDT) primarily for two reasons:

1. It is near the middle of the mast where the bending stresses will be the maximum.
2. The spreader bracket bolt hole creates both a stress concentration and an area with reduced cross sectional area that has to carry the load.

The combination of these will make the remaining material near the bolt hole have the highest stresses. My failure originated on the leeward side spreader bracket hole under tensile stress.

I am pretty certain that the large amount of bend in my mast just prior to breaking was due to the upper shrouds being tighter than the lower shrouds which provided insufficient support to the middle of the mast under heavy wind load.

Don't neglect your shroud tension adjustments! Check them often!!

Bob

[delevi]

Upper shrouds should be tighter than lower shrouds. The loose backstay could have done it. I don't quite understand how the backstay goes slack when sailing upwind. That is actually opposite of what should happen. If you use a loose gauge, static tension on the shrouds should be between 300-450 lbs, depending on your conditions. More tension for heavier air. The forestay, if you have the stock 1/8" should be around 270. These aren't rules of thumb. Many sailors have certain preferences and typical conditions influence how much tension is desired, but the rigging should never be loose. 15% breaking load is what riggers recommend. Exceeding 20% is not recommended. Google "3x19 stainless wire breaking loads if you're interested.

Leon

[tlgibson97]

I think it's pretty clear now that my rigging wasn't anywhere near tight enough. Since I tightened it up some when I got it and the PO had it in a slip for years not being used it likely was loose then too. I tightened the backstay and SB outer shroud by hand with the mast up. There's no way I got it tensioned where it was supposed to be by hand with the mast up. If I used a special tool I probably could have but I didn't.

It sounded like a gunshot when the mast snapped. I looked around the break and couldn't find anything that would indicate cracking. Aluminum is a little harder to see but the break looked consistent all the way across. But with my experience with metal fatigue, it only takes a hairline crack to compromise the whole thing. Sometimes the difference can be between a drilled vs. reamed hole. With pretty much every hole on the boat enlarged by threads rubbing I wouldn't be surprised to find all sorts of cracks if I did a penetrant inspection.But if the rigging was at the correct tension and I had already upgraded the spreaders it could have lasted many more years. Or it could have still failed in the next outing. No way to know.

[RobertB]

Not sure what your plans are but I suggest you look into getting your mast repaired by a welder. Should not be hard for a competant welder and should cost way less than fitting a new mast.

[ualpow]

Hey ualpow!

When sailing upwind, if the leeward stays are drooping, and not straight, the rigging is too loose. Is that your experience?

- Brian.

I am new to sailing and keep forgetting to look at the leeward shrouds until I'm back in the slip. Still trying to convert all my "book knowledge" to "real world" applications and the only translator is experience.

[Divecoz]

I would advise against this.. IMHO and from what I saw my Cert. Wielders do, for many years .. Just a Butt weld followed by fillets will NOT stand the test.. You need a sleeve / over lap etc etc etc.
IIRC they generally referred to things like this as Life Support and the requirements are Very Rigid...They tested my guys as often as every 6 months Bend Test X Ray etc etc... it took several hours to make all the welds and just as many IIRC to test those welds.. My guys ALL had previously worked at one or more of .. Aircraft Manufacturing , Military and Large Commercial Ships and Nuclear Power Plants..

Not sure what your plans are but I suggest you look into getting your mast repaired by a welder. Should not be hard for a competant welder and should cost way less than fitting a new mast.

[RobertB]

When I suggested welding, I did mean by a qualified welder. I consider the welders I worked with to be the type (aircraft welders, F-16 plant in Texas).

[Seapup]

If anyone sees a mast pop up for sale let me know. Would like to get one a bit cheaper than the approx. $1100 it would cost to get one shipped from BWY.

Here is one in atlanta that should work, $200. Take your section with you to compare.

PM MacNcheese on this board, he was putting on a hobie mast a while back.


http://atlanta.craigslist.org/nat/boa/3204200139.html

[Catigale]

Seapup - is there still a Mac dealer in Mayo MD? You could get a mast shipped with a boat for cheap..

If you call them, and they are busy, you can hold the Mayo of course..

[RobertB]

I live in MD and the closest dealer I could find was in northern New Jersey. The guy listed in Maryland two years ago - his business address mapped to a house in a neighborhood.

[seahouse]

One of the reasons I asked if the bend at the holes was sharp before failure was to determine if welding is a possibility, given the $1000 price tag of the alternative. If there is a gradual bend, then welding would have to be accompanied by mast straightening, complicating things considerably.

If the bend were sharp (indicating cracking had already started there), and the rest of the mast is in good condition, then welding is not only a possibility, but it will result in a mast stronger than a new one would be, particularly at that point. A new one subjected to the same conditions would likely just fail again. On the other hand, a welded one would not fail at that point, but, at some time later, at the next weaker point. I assume a proper sleeved welding job, with bosses built up around the holes.

Of course, the variable here, as mentioned, is that you just might get some yokel who might try a butt weld, and, unless you can recognize, or specify a proper job yourself, you might want to explore other courses of action.

- Brian.

[seahouse]

Hey Leon! – it was nice to meet you at Port Credit last month.

Note I edited my use of the word “stays” when I meant “shrouds” in my post above. Sorry for the confusion , it was late , thanks for pointing it out.

As I understand it, because the M has aft swept spreaders, which give a mechanical disadvantage in applying aft-directed pressure, the appropriate shroud tension needs to be higher, up at 20% (or even near 25% when sailing upwind) of breaking tension in order to keep proper forestay tension and prevent it from sagging.

And of course, a sagging forestay is a source of poor pointing ability. The stepped adjustment (sans turnbuckle) of the rigging tension on our Macs either simplifies it, “it’s close enough”, or complicates it “can’t get it right on the money” – depending on how you look at it.

- Brian.