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Breaking Masts #65881
01/31/06 12:12 AM
01/31/06 12:12 AM
Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
ncik Offline OP
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I broke my mast on the weekend and was wondering what went wrong.

No stays or diamonds broke, I believed the mast was in good order but old, it was painted (which I believe is very bad for old aluminium masts that aren't necessarily marine grade material) and the mast broke almost exactly in half way.

I'll describe the situation:

It was a little gusty and breezy but probably wasn't above 20 knots. My crew and I (70kg and 65kg) were both on trapeze and we were travelling along well on a tight, two-sail reach, one hull just clear of the waves most of the time. We hadn't sorted out mast rotation or downhaul (only just left shore about 500m behind) but had moved the traveller about half-way down track. The main was slightly luffing, jib was powered up nicely. The main has a square head on it that adds at most 1sqm of sail area. About 30 seconds before it went I noticed that it was certainly flexing more than I'd seen before. When it broke, it bent away from the wind (leeward side of mast) at the centre (reverse of what I would've expected).

I've had the boat pressed much more than this previously without any sign of trouble. My current thinking is that there were a few contributing factors:

1. Mast was old and its time had come.
2. Mast rotation was wrong. (Don't recall what position it was actually in.)
3. Mainsheet tension was pulling on leech and pulling top of mast aft
4. Crew is too heavy...need to ditch the heavy-butt crew and get a light weight girlfriend
5. Diamond tension was all wrong.

Any hints or past experiences would be greatly appreciated before I build a new mast.

I understand the association sells sections, does anyone have a price for these?

I'll purchase a tuning guide from the association soon and maybe that will help.

thanks for reading my rant,
Nick.

-- Have You Seen This? --
Re: Breaking Masts [Re: ncik] #65882
02/01/06 06:25 PM
02/01/06 06:25 PM
Joined: Mar 2003
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East Gippsland, Australia
Tim_Mozzie Offline
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Hi Nick

Does your sail have a lot of luff round? I mean when the sail is flattened, does the mast bend look radical? There were some Cobras in Tassie who experimented with huge luff round on a similar mast a few years ago and they broke several masts.
I think the mast bends so far forward the diamonds can't stop it squirting out to the side.

Or like you said, the mast may have just been very old.

Putting an extra square metre of sail up the top is not insignificant. You may find it a challenge to get enough leech tension without a stiffer mast up top.

Bob Wilson had to run a diamond up the front of his mast, but that is a bit different as he added a metre on to the length.


Tim Shepperd
Mosquito 1775
Karma Cat
Re: Breaking Masts [Re: Tim_Mozzie] #65883
02/01/06 10:04 PM
02/01/06 10:04 PM
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Brisbane, Queensland, Australi...
ncik Offline OP
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Come to think of it, the luff round does seem a little large. What would be a typical luff round measurement? (Measured as an offset from a straight line between head and tack?)

Re: Breaking Masts [Re: Tim_Mozzie] #65884
02/01/06 10:06 PM
02/01/06 10:06 PM
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Posts: 943
East Gippsland, Australia
Tim_Mozzie Offline
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Hi Nick

Do you have any photos of your sail. I would like to know how it compares with this.

I'll get a luff round measurement - it's best done with the battens out.

[Linked Image]

Attached Files
Last edited by Tim_Mozzie; 02/01/06 10:08 PM.

Tim Shepperd
Mosquito 1775
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Re: Breaking Masts [Re: Tim_Mozzie] #65885
02/02/06 05:23 AM
02/02/06 05:23 AM
Joined: Jun 2001
Posts: 9,582
North-West Europe
Wouter Offline
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Quote

Putting an extra square metre of sail up the top is not insignificant. You may find it a challenge to get enough leech tension without a stiffer mast up top.



It is very easy to oversheet a squaretop mainsail, you want to sail a squaretop with noticeable twist in the leech. You'll go faster that way. However, if you still feel that the top of the mast is still to soft (not stiff enough) than the best and easiest solution is to move the hound fitting higher up the mast. The is a 3rd order dependency so only slight movements may produce large effects. The longer section between the hound fitting and mast base can then be stabilized again by the spreaders. And if you feel this is insufficient then longer spreaders arms will correct this. In principle and within reason you can fune-tune the mast to the new mainsail design. It is not a unchangable given, unless the class rules limit were everything may go.

Example : stiffening up the top of the mast. Say a mast is 8 mtr. long and the hound fitting is at 5.75 mtr. The top length is then 8-5.75 = 2.25 mtr. and assume it is too soft in the top in this setup. You want the top to be 20 % stiffer then before. 3rd order dependency => 120 % = 1.2 = (2.25)^3/(new top)^3 therefor (new top) = (old top)/(3rd order root (1.2)) and new hound height = 8 mtr - (new top)

(new top) = (old top)/(3rd order root (1.2))
(new top) = 2.25 mtr/1.0627 = 2.1173 mtr. = say 2.12 mtr. or 130 mm shorter

And new hound height = 8 mtr - (new top) = 8 - 2.12 = 5.88 mtr.

20 % extra stiffness then before is quite alot.

So you can see; 130 mm movement of the hound fitting can be quite alot.

Hope this helps

Wouter




Last edited by Wouter; 02/02/06 05:30 AM.

Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: Breaking Masts [Re: Wouter] #65886
02/02/06 07:53 PM
02/02/06 07:53 PM
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Posts: 943
East Gippsland, Australia
Tim_Mozzie Offline
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Hi Wouter

Nick is out on a limb with his square top sail anyway so the class rules are not that important in this case.

What you said about it being easy to oversheet a square top sail seems to contradict Gary's experience with his Ashby main (square compared to his previous Irwin sail). He thought he was using an enormous amount of mainsheet tension, but Glenn told him he wasn't using enough. He had to find new ways to get more tension on his mainsheet - he may have even added some purchase (Gary?).

It sounds to me like it's very hard to oversheet a square top main (or even sheet it enough sometimes!).


Tim Shepperd
Mosquito 1775
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Re: Breaking Masts [Re: Tim_Mozzie] #65887
02/02/06 09:37 PM
02/02/06 09:37 PM
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Brisbane, Queensland, Australi...
ncik Offline OP
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I was under the impression that roachy mains were used on skiffs so that less leech tension could be used...

Re: Breaking Masts [Re: Tim_Mozzie] #65888
02/02/06 10:38 PM
02/02/06 10:38 PM
Joined: Jan 2006
Posts: 26
Barmera SA
Steve_T Offline
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Barmera SA
Hi Guys
[/quote]
What you said about it being easy to oversheet a square top sail seems to contradict Gary's experience with his Ashby main (square compared to his previous Irwin sail). [/quote]

I'd have to agree here. I've been sailing Dolphins for 30 years, and the last 15 has been with a square topped main, teamed with a wing mast.

I use enormous mainsheet tension to keep the top from laying off. I'd have thought that the mozzie mast would be too soft for a square top, in that it would keep bending whilst more mainsheet is applied. This is where the reverse diamonds up the top would be needed.

Cheers

Steve


Just Do It
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Re: Breaking Masts [Re: Tim_Mozzie] #65889
02/03/06 04:39 AM
02/03/06 04:39 AM

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Hi all,

yes my experience is that the tension I pull on the mainsheet is greater the bigger the head on the sail. However like everything to do with sails, it is not that simple, on my Irwin main my attempts to achieve the leech tension I was looking for where hampered by running out of luff round. Mainsheet tension was bending the mast to the point I was flattening sail before I could get the leech in the head to stand up.

Ashby main has more depth, so I am able to pull on more mainsheet tension before the main flattens to much, keeping the leech standing up longer. However as I have found it over powers earlier, because of greater luff round and bigger head. It is difficult to have everything working the way you want all at once, but the sail is awesomely fast in 5-8 kts. as Tim on Mossie with spin and Chris on the F18 Capricorn saw last weekend.

I am still tinkering with settings and since breaking top batten in capsize last weekend, I am going to try stiffer head batten to see if this keeps head flatter and helps depowering. I haven't added more mainsheet purchases yet,just keep grunting, I hate having to use more mainsheet length than neccesary.

Regards Gary.

Re: Breaking Masts [Re: Steve_T] #65890
02/03/06 05:29 AM
02/03/06 05:29 AM
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Posts: 9,582
North-West Europe
Wouter Offline
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Quote

I use enormous mainsheet tension to keep the top from laying off.



But you want the top the twist off. A straight leech is not what your are looking for.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: Breaking Masts [Re: Wouter] #65891
02/03/06 08:55 AM
02/03/06 08:55 AM
Joined: May 2003
Posts: 4,451
West coast of Norway
Rolf_Nilsen Offline
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I re-read Bethwaites "High performance Sailing" for the umptent time last week, and he said that mast breakages was common if the mast was 15xdiameter out of column. I am sure there are more to it, e.g. compression and dynamic loads, but he has a point.

As for twist and sheeting loads. On sloop rigs we want twist in the top of the main to offset the jibs effect on the wind. Also, at certain windspeeds, we need to trim the top of the main to the different angles of wind at the surface and the mast-top. If owerpowered, we let the top of the main fall off to depower. As long as you are trimming to your telltales, you should be in the ballpark.


I find it hard to determine what twist I sail with unless I go to lie down aft and under the boom to sight up along the leech. I really prefer to follow after the boat or have pictures taken to determine mainsail twist.
What I am wondering about, is what Wouter think is twisted vs. what Gary think is straight?
Do you guys have any numbers for what kind of twist you think is too much or too straight? It depends on conditions of course, so some pictures taken from aft of your boat would be preferable.

Take a look at this picture of Bundy and Forbes for reference: http://tornado.aussailing.com.au/beat.jpg


Gary: Sounds to me like the luff curve of your mainsail doesn't quite fit the mast? No wonder, if Ashby cut it for the A-class mast you have, and you beefed it up to handle the spi (just guessing here really). Next iteration probably will be better, if you have Ashby use what you have learnt

Re: Breaking Masts [Re: Rolf_Nilsen] #65892
02/05/06 11:59 PM
02/05/06 11:59 PM
Joined: Mar 2003
Posts: 943
East Gippsland, Australia
Tim_Mozzie Offline
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Hi Nick

At the weekend I pulled the battens out a foot or so from my Irwin main, stretched the luff out and ran a straight line from the corners. I measured 165 mm at the furthest point from the back of the bolt rope. This wasn't measured under laboratory conditions so allow plus or minus 10-15mm for a sailmaker-quality measurement.

I believe the luff round on this sail is typical of most of the Mosquito sails in use in Aus.

Here's luff round in action on a Goodall radial ----
[Linked Image]

Any hope of a photo of the square top?

Attached Files

Tim Shepperd
Mosquito 1775
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Re: Breaking Masts [Re: Rolf_Nilsen] #65893
02/06/06 05:45 AM
02/06/06 05:45 AM

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Hi all,

I should say that my leech is hopefully always twisted. When I am talking about trying to stop leech twisting, I mean excessive twist, like when you are trying to get on trap looking for maximum power.

I am basing my mainsheet tension on Glenn's advice when he was sailing behind me in 15 kts. telling me to pull on more downhaul to incease twist, but also more mainsheet tension at the same time, idea seems to be to depower sail to the point where you can keep mainsheet in tight. It is improving my upwind speed with this main. By the way Glenn cut this main after sailing Altered and having good look at mast, I think he has it right, it is just different to what I have used before. Irwin main was made without the boat rigged or in the water and was a good result considering.

Regards Gary.

Re: Breaking Masts [Re: Tim_Mozzie] #65894
02/07/06 03:57 PM
02/07/06 03:57 PM
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Brisbane, Queensland, Australi...
ncik Offline OP
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G'day

I measured the luff curve last night and found it to be about 125mm maximum. When comparing against your value, this doesn't appear to be the problem.

I took some photos too and will post these shortly.

Nick.

Re: Breaking Masts [Re: ncik] #65895
02/08/06 02:27 AM
02/08/06 02:27 AM
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OK. photos of broken mast below...photos of main can be found in square head main discussion...

Nick.

Attached Files
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Re: Breaking Masts [Re: ncik] #65896
02/08/06 02:29 AM
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Re: Breaking Masts [Re: ncik] #65897
02/08/06 02:29 AM
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Re: Breaking Masts [Re: ncik] #65898
02/08/06 02:31 AM
02/08/06 02:31 AM
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notice collapsed inner wall

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Re: Breaking Masts [Re: ncik] #65899
02/08/06 02:38 AM
02/08/06 02:38 AM
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Brisbane, Queensland, Australi...
ncik Offline OP
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I haven't really had a chance to investigate the destruction of my mast, but after looking at those photos some more it appears to me that the spreaders may be too low. Raising them up closer to the break should reduce the bending moment around that area.

Does anyone have any measurements for the location of the spreaders above the top of the forward beam?

Re: Breaking Masts [Re: ncik] #65900
02/08/06 05:13 AM
02/08/06 05:13 AM

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Hi Nickb,

mast break looks like most I have seen, in that it looks like compression failure. The damage to what I would call the back of the sail track does seem a little unusual though, usualy most of the compression failure seems to be on the side of the mast. Although only looking at pictures makes it difficult, the angle the back of the track is at could be from tearing after initial side wall failure.

When building Altered, I was asking about failures in carbon wing masts, I was advised compression of the side of mast was usual failure point, so I put timber web crossways inside, to stop it caving in. Seems to have made it bullet proof so far.

Spreader positions I have used is usualy halfway between diamond attachment points. Don't remember anything more technical than that. Top of diamonds is usualy determined by how close you can get to your hounds without fowling stays when rotating mast. Hound point is governed by class rules.

Regards Gary.

Re: Breaking Masts [Re: ] #65901
02/08/06 03:41 PM
02/08/06 03:41 PM
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ncik Offline OP
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I measured the spreader height this morning before work...2.5m above mast base. It has been lowered by a previous owner about 30cm. I think I'll raise it a bit higher, because the distance between hounds and spreaders is about 2.7m.

Nick.

Re: Breaking Masts [Re: ncik] #65902
02/09/06 07:04 AM
02/09/06 07:04 AM
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Posts: 612
Cape Town, South Africa
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Hi Nick,
Just looking at your mast-break reminded me of mine a few years ago, going upwind in about 18-20knots with 170kg on the wire (fat friend ), the mast rotator arm bent suddenly allowing the mast to over-rotate rapidly, and we hit the water with a new two-piece mast. It broke almost in the same place as yours, a little closer to the spreaders in my case. My theory is that the mast rotated to 90deg or even past, with 2 on the wire the spreaders are facing fore-and-aft, no lateral support at all, bang. The other factors you mentioned could also be the cause, I`m just offering a possible explanation if you had not set the mast rotator yet and it was over-rotated.
I don`t believe the squaretop caused the failure, but the additional power may have assisted, although I`m not convinced as you say you had not powered up the main fully yet. There are too many possibilities, only way to know for sure is to get a new mast and try it out again ! (just insure the mast first )

Steve

Re: Breaking Masts [Re: Steve_Kwiksilver] #65903
02/20/06 04:14 AM
02/20/06 04:14 AM
Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
ncik Offline OP
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woot! finally bought a new mast section...it appears as though a calypso 14 mast is the same or very similar to a mosquito section...will let you know how it fairs...

Nick.

Re: Breaking Masts [Re: ncik] #65904
02/21/06 07:38 PM
02/21/06 07:38 PM
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ncik Offline OP
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Does anyone else have preferred spreader heights above the mast base? I'd just like to get a few values to see how my current setup compares.

Nick.

Re: Breaking Masts [Re: ncik] #65905
03/11/06 04:37 AM
03/11/06 04:37 AM
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ncik Offline OP
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Finally got back on the water today. Good 15 knot breeze. Finally had the guts to pull a bit more downhaul on the new mainsail too and it seemed to work like a charm. Now I just have to spend some serious time on the water.

Nick.

Re: Breaking Masts [Re: ncik] #65906
03/20/06 07:53 AM
03/20/06 07:53 AM
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Somers, Westernport Bay, Victo...
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Nick,

What heights did you settle on for the spreaders, diamond wires (upper and lower) and the hound ? I'm gathering info for my next mast. Are you happy with the overall results ?


Mosquito 1814
Macka Mozzie
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