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PostPosted: Sat Jun 23, 2012 7:59 pm 
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Hi,

I have a John Marples 22' trimaran with Hobie 16 rigging. A few months ago I had to replace my mast due to some damage that was not sailing related so I bought a second hand mast from a nearby Hobie sailing club.

I replaced the mast, seemingly without any problems. On my first day of sailing everything seemed to be working perfectly. Then about two hours in, in about 15-18 knot winds there is a loud sound and my sail falls over to the port side. It seems that the mast bent in half about halfway up its length.

I looked on the internet for any similar experiences but could find none. So now I am left wondering, was it a problem with the mast or was it a problem with the installation? One thing about the installation that I remember being different on the new mast as compared to the old was that the forestay was really tight. a couple of us had to pull hard to get it attached.

Here are some pictures of the damaged mast.

http://imgur.com/a/ZqlnY

Any help is greatly appreciated.


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PostPosted: Mon Jun 25, 2012 10:44 am 
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Based on what I could see off an Internet pic for your John Marples trimaran and my experience with a monohull using the same config, I'm going to guess that you may have mounted the spreaders incorrectly. (you do have spreaders, right?) If they are not in the correct position, you end up with an huge amount of downforce which would have caused your failure. Under this premise, the failure occured after you went out because the side-to-side motion eventually allowed the front-to-back flex you could not clearly see to shift to the side where the shape of the mast was not as strong. Think of trying to smash an egg from the ends....you can't do it. Pressing from the sides, it crushes instantly. If you can't check against your original mast, I would suggest seeking another owner to give you the exact measurements. Also, have them give you figures in both directions....maybe you got tricked into buying a mast that was a hair too tall?

FYI, I did something like this a while ago, but it only resulted in a scare. In my situation, the mast bowed out immediately but did not break. I had installed new stays which were tightened down too much.

Good luck!
Blainio


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PostPosted: Mon Jun 25, 2012 4:27 pm 
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There are no spreaders on this mast. That wasn't the problem.

My guess is that the mast was counter-rotated.


Last edited by MBounds on Tue Jun 26, 2012 4:32 am, edited 1 time in total.

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PostPosted: Mon Jun 25, 2012 7:27 pm 
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Hi, thanks for all the advice. There are no spreaders on this mast. Also the old mast worked for years (for the previous owner) in stronger winds without a problem.

MAJBlainio mentions downward force and this is something I was considering as being the possible culprit. As I mentioned, the fore stay was exceptionally tight and I really tightened up the side stays as well. Is it possible to over-tighten these stays to the point where it could cause too much downward force on the mast and result in what I have here? What is a good guideline for the tightening of stays?


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PostPosted: Mon Jun 25, 2012 7:36 pm 
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On my first 16 in 75 I bent a mast because I didn't check that the mast had rotated around after the tack, as soon as the wind caught the main it just bent the mast in the middle, just like your picture.

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PostPosted: Wed Jun 27, 2012 3:08 am 
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I'm almost certain that my mast was not counter rotated as I had been sailing in the same direction for nearly 40 minutes and I feel I would have noticed.


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PostPosted: Wed Jun 27, 2012 8:55 am 
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Ugh that is like a brand new hobie sail.


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PostPosted: Thu Jun 28, 2012 1:53 am 
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Yeah and all of this stuff is so expensive here (philippines). $1000 for the sail, $2000 for a new mast. Thats why I would really like to figure out what's wrong before I put more money into it.


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PostPosted: Thu Jun 28, 2012 5:54 pm 
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Prod wrote:
the fore stay was exceptionally tight and I really tightened up the side stays


I am wondering if very tight standing rigging has prevented the mast from proper rotation?
I think, MBounds is correct -- the issue must be with improper mast rotation. Because of mast tear-drop shape, it has much less strength/stiffness sideways.

Do you recall what course you went? Close reach, run, etc.? How the mast was rotated when mast broke?

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PostPosted: Thu Jun 28, 2012 6:44 pm 
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I was close hauled when it broke and had been so for some time. The mast was actually rotating fine earlier in the trip, though I cannot guarantee it had rotated properly at that time because I didn't take special note of it.

Along the lines of my theory that the stays were too tight, can anyone tell me a general rule of thumb for how tight they should be?


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PostPosted: Fri Jun 29, 2012 5:16 am 
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You can't get the stays tight enough to do that kind of damage - unless they are so tight, they inhibit mast rotation.

When sailing upwind, the leeward shroud is always slack, no matter how tight you think you had the stays beforehand.

This is a classic failure mode of a counter-rotated mast.
It could have happened in a tack, if you didn't ease the sheet to allow for rotation.


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PostPosted: Fri Jun 29, 2012 6:57 am 
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Let's see, you were sailing in 15 to 18mph breeze and had a rig that was designed for a 16 foot, 330lb boat which you were using on a 22 foot trimaran that weighs...how much? I don't think this has anything to do with counter-rotating the mast. You simply overloaded the rig beyond what it was designed to handle. There's a reason that bigger boats have bigger masts and use supporting spreaders/diamond wires.

sm


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PostPosted: Fri Jun 29, 2012 8:13 pm 
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srm wrote:
Let's see, you were sailing in 15 to 18mph breeze and had a rig that was designed for a 16 foot, 330lb boat which you were using on a 22 foot trimaran that weighs...how much? I don't think this has anything to do with counter-rotating the mast. You simply overloaded the rig beyond what it was designed to handle. There's a reason that bigger boats have bigger masts and use supporting spreaders/diamond wires.

sm


Seems like a very logical point. The only thing that makes me wonder is that the boat had sailed fine for years with H16 rigging on it. The boat is 800lbs btw.


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PostPosted: Sat Jun 30, 2012 7:57 am 
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In some cases, catastrophic fracture happen because of not one but a combination of factors.

1. In your case, using smaller boat rigging in much bigger boat, you will always run a risk of breaking your mast. srm is correct here. One factor is boat weight, second is the width, third is draft. There will be a limit your boat can take, -- perhaps it is 18 or 20 knts. If a big gust comes in, H16 leans and spills the wind, and in worst case gets dumped. In your case, this doesn't happen, or not to that extend. All the excessive force goes into bending stress in your mast.
2. Putting an extreme compression on your mast would not break the mast by itself, but could been a factor nevertheless.
Prod wrote:
couple of us had to pull hard to get it attached

This could have resulted with a 300lb of extra compression on the mast and perhaps reduce mast rotation.
3. Last factor would be mast rotation. I still think, the failure should not happen with the mast properly rotated. Perhaps, it got counter rotated, or it was not quite properly rotated on the tack. This may not have been a sole factor to cause a failure, but in combination with #1 and#2, it could have.
4. This is a long shot, but there could have been something wrong with the new (old) mast. Perhaps a small dent in the middle of the mast? Or perhaps, the mast collected salt water and was left like this for a decade or two. This, in theory, could have corroded the aluminum from inside. Again, a long shot, but just to rule it out, you can cut it open and inspect.

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PostPosted: Sat Jun 30, 2012 11:59 am 
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jackB wrote:
2. Putting an extreme compression on your mast would not break the mast by itself, but could been a factor nevertheless.


Actually, excessive compression load is all it takes to snap a mast. Take a plastic straw between your fingers and compress it. As the force increases, eventually it will bend out of column and fold in half. The same thing will happen with an overloaded Hobie mast. Sticking a Hobie 16 rig on a boat that is much larger and heavier means the compressive load on the mast will be much higher. It would be the same if you took a Hobie 16 out in 35 knots with four people on board. Assuming the boat would float, there's a good chance you would break the mast. Everything has a design limit.

If the original poster plans to get another mast and continue to use this rig, I would suggest he installs a pair of spreaders like are used on the H18 to strengthen the mast.

sm


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