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Mast Repair #72223
04/09/06 02:07 PM
04/09/06 02:07 PM
Joined: Apr 2004
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WA, ID, MT
davefarmer Offline OP
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OK, Wouter has got me thinking seriously about repairing/reinforcing this wingmast. I'd love more input on techniques to use, people who might undertake the work, and more thoughts on why this failed where it did (compression failure?), and whether the design is sound enough to warrant the effort. I'll try to attach a few pics, and would be more than willing to send them to anyone interested in offering advice. Thanks so much!

dave

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Re: Mast Repair [Re: davefarmer] #72224
04/09/06 02:18 PM
04/09/06 02:18 PM
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davefarmer Offline OP
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another pic

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Re: Mast Repair [Re: davefarmer] #72225
04/09/06 02:34 PM
04/09/06 02:34 PM
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WA, ID, MT
davefarmer Offline OP
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one more

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Re: Mast Repair [Re: davefarmer] #72226
04/09/06 06:57 PM
04/09/06 06:57 PM
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toronto, canada
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basket.case Offline
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toronto, canada
build a carbon one. it is easy, and lighter.

Re: Mast Repair [Re: davefarmer] #72227
04/09/06 07:57 PM
04/09/06 07:57 PM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
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How did it break? Describe the conditions, what was happening at the moment, were you in a jibe, tacking, coming off a wave?
Do you have a spinnaker (was it up?)? Any number of things could have caused it to break - it looks like it broke 4' up from the base? Is that correct?


Jake Kohl
Re: Mast Repair [Re: Jake] #72228
04/10/06 12:48 AM
04/10/06 12:48 AM
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WA, ID, MT
davefarmer Offline OP
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Had been sailing for 2 hrs, 10 to 12 knots of wind, gusts 15 absolute max. Flew a hull 6" off the water a couple of time. Boat felt great! Had been upwind and down a couple of times, did run the spin, but did reach with the screacher few times. Checked the diamonds several times, always finding the mast in column.
Mast broke shortly after heading back upwind. The boom has an underside traveller (ala 18 meter square) for the mainsheet between the rear traveller and the boom, so there is zero resistance from the mainsheet to the compressive forces the boom applies to the mast. I could see the boom flexing maybe 3" out of column(10' boom, big squaretop EP main), the mast rotation limiter was on pretty tight because the builder, Malcom Davy, had expressed his concern earlier that the boom was putting a lot of pressure on the mast. The mast is quite well reinforced at the gooseneck, and he feels that the forces were transmitted up the mast to the first weakest point. The break is 6' above the base, 36' mast, hounds 7' from the top of the mast, aft swept spreaders. Malcom said he'd had the boat out in 20 kt conditions before, had flow a hull close to vertical, so he'd put more force to the rig than I did.
What do you think?

Dave

Re: Mast Repair [Re: basket.case] #72229
04/10/06 12:50 AM
04/10/06 12:50 AM
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davefarmer Offline OP
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What do you think a carbon wing mast woud cost? Materials alone?

Dave

Re: Mast Repair [Re: davefarmer] #72230
04/10/06 05:04 AM
04/10/06 05:04 AM
Joined: Jun 2001
Posts: 9,582
North-West Europe
Wouter Offline
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Personally I don't like this comment :

Quote

the mast rotation limiter was on pretty tight because the builder, Malcom Davy, had expressed his concern earlier that the boom was putting a lot of pressure on the mast.



Reducing mast rotation only puts the mast under higher stresses. If you are fearful than more rotation is the better option.

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: Mast Repair [Re: Wouter] #72231
04/10/06 06:49 AM
04/10/06 06:49 AM
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Australia
macca Offline
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What made you tink that a hollow wooden mast would be strong enough in the first place??

I have a carbon wingmast on my taipan and it must be very close to its design strength cause there are times when it looks very ugly up there whan the kite is up. But to build one out of wood is just insane!

use the old wooden one as a plug for a carbon mould, then you will have a good mast


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Re: Mast Repair [Re: macca] #72232
04/10/06 07:27 AM
04/10/06 07:27 AM
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toronto, canada
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Quote
What made you tink that a hollow wooden mast would be strong enough in the first place??

I have a carbon wingmast on my taipan and it must be very close to its design strength cause there are times when it looks very ugly up there whan the kite is up. But to build one out of wood is just insane!

use the old wooden one as a plug for a carbon mould, then you will have a good mast


i had a ply one on my boat for years. replaced it as i came into a bit of cash. heavy but strong and stiff. these things have been about years longer then carbon ones. west has been designing them almost for ever.

Re: Mast Repair [Re: macca] #72233
04/10/06 07:48 AM
04/10/06 07:48 AM
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South Australia
Marcus F16 Offline
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Ply core would be ok for mast construction, but there does not look like there is much glass work included, let alone any carbon.

There needs to be a balance in the composite layup - have you ever seen a multi storey building stand up for long becuase they used more concrete than reinforcing steel??

My observation is not enough glass/carbon to support the ply structure & timber structure.

It looks like the ply webs with fillets may have stopped at this point or did you cut the broken section to make it clearer viewing.

marcus


Marcus Towell

Formula Catamarans Aust Pty Ltd
Re: Mast Repair [Re: davefarmer] #72234
04/10/06 09:09 AM
04/10/06 09:09 AM
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Posts: 371
Michigan, USA
sparky Offline
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I would consult the Gougeon Brother (West System Epoxy) before doing anything with your current mast. They have done many wooden wing masts. They are located in Bay City, Michigan.


Les Gallagher
Re: Mast Repair [Re: sparky] #72235
04/10/06 10:05 AM
04/10/06 10:05 AM
Joined: Jun 2004
Posts: 141
Panama City Beach, FL
steveh Offline
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I don't think that I'd try a repair until the I understood the cause of failure and even then I'm not sure I'd trust a repair done at a point that failed. The big problem that I see is that you can't stagger the scarfs of the wood strips, so now you'd have a two scarf joints at the failure point.

In the first picture, is the dark line running from the leading to trailing edge a couple inches below the end of the web a scarf joint? Also, in picture 3, it looks like there is another dark line running from leading to trailing edge on the upper side just below the break.

"...the forces were transmitted up the mast to the first weakest point."

It doesn't work that way. The vast majority of the boom compressive force is taken up by the mast step. If the force from the boom is 100lbs, the mast is 36ft long and the gooseneck is 1ft above the step, then 97lbs of the load is transmitted to the mast step.

Re: Mast Repair [Re: basket.case] #72236
04/10/06 09:08 PM
04/10/06 09:08 PM
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Posts: 713
WA, ID, MT
davefarmer Offline OP
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This one is a Barlow design, constructed using guidelines gleaned from a article on a similar mast built by the Gougeon Bros, using high quality materials and West System epoxies. Builder said it weighed 85 lbs, which I believe. Only 2 layers of fairly light E glass to sheath the outside. From what I can see, the quality of the construction looks good. The central web has separated from the mast sidewalls some near the break, but it's hard to determine whether it was there before the fracture, or a result of it. Maybe it's too light?

Dave

Re: Mast Repair [Re: Wouter] #72237
04/10/06 09:16 PM
04/10/06 09:16 PM
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Posts: 713
WA, ID, MT
davefarmer Offline OP
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Reducing mast rotation only puts the mast under higher stresses. If you are fearful than more rotation is the better option.

Wouter [/quote]

Wouter, care to expound on this a bit more? I would think that the more the mast was aligned with the centerline of the boat, the stronger it would be. Isn't it stronger fore and aft, than side to side? Mast is 9" x 4.5". Mast was rotated maybe 60 degrees at the time of the break. Thanks!

Dave

Re: Mast Repair [Re: basket.case] #72238
04/10/06 09:20 PM
04/10/06 09:20 PM
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WA, ID, MT
davefarmer Offline OP
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Quote
build a carbon one. it is easy, and lighter.


Tell me more, especially about the easy part. Cost estimate for materials? Designs? Appropriate reading materials? I'm open to everything....

Dave

Re: Mast Repair [Re: Marcus F16] #72239
04/10/06 09:44 PM
04/10/06 09:44 PM
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WA, ID, MT
davefarmer Offline OP
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Quote
Ply core would be ok for mast construction, but there does not look like there is much glass work included, let alone any carbon.


My observation is not enough glass/carbon to support the ply structure & timber structure.

It looks like the ply webs with fillets may have stopped at this point or did you cut the broken section to make it clearer viewing.

marcus


There are 2 layers of fairly light E glass sheathing the outside of the mast, carbon was used at high stress points, tang, gooseneck, base, spreaders and diamond wire attachment points. The ply web with spruce gussets extends the entire length of the mast, it appears to have sheared pretty cleanly at the break. If you look close though to one of the pics of the break, there's a monel staple that appears to be across the plies of the web, which could only be if there was a joint in the web there. Malcom said all the joints in the web (and elsewhere) were scarfed, and the break in the web isn't a machined edge, so the whole thing is mysterious to me.
So a couple of questions come up around the repair. It would be nice to sleeve the inside of the mast somehow, as well as reinforcing the exterior. But not clear how to pull that off. And then there's the issue of how and how much to add to the exterior. I think Wouter is suggesting vertical tapes of unidirectional carbon fiber spaced around the circumference. Additonal layers of E glass or carbon cloth? The builder is suggesting that moving the forward attachment point for the boom off the mast to the main crossbeam will substantially reduce the point load on the mast, and I plan to do that. I need as much advice as you guys can give me!

dave

Re: Mast Repair [Re: steveh] #72240
04/10/06 10:21 PM
04/10/06 10:21 PM
Joined: Apr 2004
Posts: 713
WA, ID, MT
davefarmer Offline OP
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Quote
I don't think that I'd try a repair until the I understood the cause of failure and even then I'm not sure I'd trust a repair done at a point that failed. The big problem that I see is that you can't stagger the scarfs of the wood strips, so now you'd have a two scarf joints at the failure point.
Yeah, that bothers me too. I'm trying to figure out how to cut back the mast wall skin to allow me to get deeper into the mast sections to stagger the scarfs, particularly the leading and trailing edges.

In the first picture, is the dark line running from the leading to trailing edge a couple inches below the end of the web a scarf joint? Also, in picture 3, it looks like there is another dark line running from leading to trailing edge on the upper side just below the break.
You're right. Both of those dark lines are scarf joints in the ply sidewall material. One is 2" below the break, the other is within a 1/2" of the break. The solid wood at the leading and trailing edges have no scarfs within sight. The web, and it's solid wood gussets appear to be broken, but it's not completely clear that there was not a joint there (see note elsewhere about a staple runnung across the grain of the plywood web). The outside of the gussets has a carbon tape running vertically the entire length of the mast, and Malcom said the tricky part of assembling the mast was properly locating the web as the 2 halves were laid together. It's possible that there was an insufficient amount of thickened epoxy between the web and the mast sidewalls in this (and other?) areas. They are separated in this vicinity now, hard to tell if it was prior to the break, or as a result of the break.

"...the forces were transmitted up the mast to the first weakest point."

It doesn't work that way. The vast majority of the boom compressive force is taken up by the mast step. If the force from the boom is 100lbs, the mast is 36ft long and the gooseneck is 1ft above the step, then 97lbs of the load is transmitted to the mast step.

Gooseneck is 18" above the mast step, and the builder said he replaced the original mast step (delrin ball on 1.5" s.s. post) with a stouter version, as a result of the first one bending. That, coupled with my observation of the substantial amount of boom flex, makes me real aware of the amount of force the boom is applying here.
I agree wholeheartedly to the importance of understanding the reason for failure before investing in a repair. I really appreciate all the insight, questions and opinions being offered here. I'm happy to send higher quality pics directly to anyone wishing to help me explore this further. It's a gorgeous mast that I'd love to salvage if it seems feasible and justified.

dave

Re: Mast Repair [Re: davefarmer] #72241
04/11/06 12:33 AM
04/11/06 12:33 AM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
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Wood masts are a bit out of my area of experience...but I do know that if you move the boom to the main beam that you will loose the forward pressure that rotates the mast. You will need to have some sort of positive rotation device (which can be tricky and lead to additional failure if not adjusted properly while tacking). I would think it better to adjust the vertical angle of the mainsheet to control the amount of compression applied to the boom...imagine if you will, if your mainsheet were perfectly vertical, there would be no more compression on the boom and very little induced loading on the mast (although you have the same lack of rotation problem as with a beam mounted boom). There is a happy medium where the mainsheet induces just enough forward pressure to ensure proper mast rotation and you can achieve this by either relocating your traveler or the point at which the mainsheet attaches to the boom.


Jake Kohl
Re: Mast Repair [Re: davefarmer] #72242
04/11/06 03:12 AM
04/11/06 03:12 AM
Joined: Jun 2001
Posts: 9,582
North-West Europe
Wouter Offline
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Quote

That, coupled with my observation of the substantial amount of boom flex, makes me real aware of the amount of force the boom is applying here.


I don't think the boom is excerting much force on the mast at all. How large was the sweptback angle of the mainsheet blocks when the mast broke. If it was almost vertical then the boom axial loads will have been rather small indeed. I think the boom flexing was caused by the mainsheet and clew corner not being in line with eachother. This created a bending laoding on teh end of the boom which bend it over its full length. Was the boom flexing downward ?

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
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