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swchandler



Joined: 08 Nov 1993
Posts: 5881

PostPosted: Mon Dec 10, 2012 3:36 pm    Post subject: Reply with quote

mark,

Regarding making a front end tubing component, it was my thought that it would be relatively easy to create the shape out of polyurethane foam or something similar. Then using carbon tape and slow cure mixture epoxy, I would wet-out the cloth and squeegee it before starting to wrap it around the OD of the shaped foam component. Also, for added strength, I think running the carbon lengthwise in some steps would be appropriate. After a series of steps building up to the final size I would tightly tape off the job to remove any extra epoxy and shape things up. At that stage I would locate the piece in a warm sunny area like on the dashboard of my van to allow everything to fully cure over time. While some final shaping may be needed to ensure a good fit in the boom arms, I would then epoxy everything together. Lastly, I would again use carbon tape and epoxy in a similar fashion to further strengthen the bonded connections. Adding the Maui Sail front end would finish everything off.

Although I've made things sound relatively simple, I realize that getting everything right is the hard part. To best ensure the assembly of everything, it's my thought that some kind of holding fixture would be needed to contain the boom and all its components for bonding. Also, I think that the holding fixture would probably be needed up front to assist in determining the shape and design of the front end tubing component. All and all, it would probably be a very challenging project that would take some time. As far as experience goes, I have been working with polyester and epoxy resins since 1963. While it was never part of my working career, I've made a couple surfboards and I've done a ton of repairs to my surfboards and windsurfing boards over the years. Also, in my home remodel I've done a lot of custom shaped birch plywood panels incorporating carbon and silver Texalium laminations. But as far as tools go, I don't have much in the way of sophisticated tools, just the rudimentary basics like a circular saw, a jig saw, an electric drill, a Dremel tool and some miscellaneous hand tools.

At this juncture, I'm still just toying with the project and have no actual plans to do it any time soon. But I do have all the parts to potentially retrofit three of these old Gulftech booms. Right now I'm still deep in extensive remodeling projects of my home, so that's pretty much my priority for some time into the future. Also, right now I have a pretty solid quiver of carbon booms (Maui Sails Wave, HPL slalom and a still viable old Gulftech).
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mark



Joined: 10 Apr 2000
Posts: 112

PostPosted: Mon Dec 10, 2012 5:42 pm    Post subject: Reply with quote

swchandler,

The form for the front end you describe is a similar approach that I would take. However I would insert the form into the boom ends and build and glass it to the arms in one operation.

Below are a few thoughts for you or anyone else that wants to undertake this project. I may even do it myself if I break any more front ends. If you decide to proceed you can PM me at a later date.

I would make the form diameter so that it fits inside the booms. You can remove the old aluminum parts by using muratic acid. See an earlier post where Thombiz and I describe the removal process.

The form can be made out of either a higher density foam sheet like the old Clark foam, divinycell or from balsa. Draw the outline and cut it to shape. Sand the curve smooth. If you have a router use a 1/2 inch radius bit to radius the edges and the rest can be hand sanded. The important thing is to have it strong enough so it doesn't break or excessively deflect while glassing. You can always wind a layer or two of 2 inch glass tape and let it cure before proceeding with the remaining laminations.

Build a table a slightly wider than the booms and about a foot shorter. A particle board top with a 2 X 4 frame would be fine. Lay the booms on the table with the back end inserted and set the width. Leave about 6 inches of the front part of the tube extending past the table so you can wrap the glass around the form and the front of the booms. Draw the arcs of the booms for reference. Use some U bolts slightly wider than the booms to secure them to the table. So you don't break the foam part you will need to remove one of the arms and the back end so you can insert the foam/wood form into the arms. I would also grind a bevel about 1/2 inch long on the end of the boom arms so you can glass from the form and onto the boom arms without creating a stress concentration. Rough up the first 3 inches of the boom tube with sandpaper and remove any grip.

Clamp the boom arms to the table with the form in place. It should be extending over the table so you can wrap the wetted out tape. Starting with about a 3 inch overlap on the boom wind 2 inch glass tape with a 50% overlap. Build up the layers using strips of carbon or as you mentioned some unidirectional carbon orientated along the form. One you have achieved the desired thickness you can wind another layer or two of glass tape. Finish it with a winding of electrical tape to hold it together while it cures. I would build up the areas where the clamp goes with a bit extra thickness of E or S glass so you can sand it to size where the clamp mounts.

Planning the layup ahead of time will help knowing how may layers you will need. You can get a rough idea by laminating up a few layers of each material on a sheet of mylar or plastic. Measure the thickness once it has cured and you can lift if off the mylar. I would tend to go a bit over kill on the number of layers. I would make the wall thickness at least 4mm thick and a bit more at the curve. I am not sure what the diameter is of the Maui sails end is but the Fiberspar tube has an outside diameter of about 39 mm and a 2.7 mm wall thickness at least where the boom tubes are inserted.
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swchandler



Joined: 08 Nov 1993
Posts: 5881

PostPosted: Mon Dec 10, 2012 6:23 pm    Post subject: Reply with quote

Excellent mark!

Before reading your last post, I was going over in my mind about how I would hold the front end tubing mandrel while laminating it. My thought was that it would be really tough to do. You'd have to build a totally different holding fixture to do it, and the whole effort would take much longer. Your approach to building the front end and attaching it to the arms in a single project is definitely far more sensible, particularly using the idea of projecting the front end overhang of the boom in the fixture. No doubt, a very informative post. I can tell that you have your act together about building things. If I elect to proceed with the Gulftech project, I'll certainly tap your expertise to further discuss the details.
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Brian_S



Joined: 11 Jun 2005
Posts: 149
Location: SE Michigan

PostPosted: Mon Dec 10, 2012 8:56 pm    Post subject: Reply with quote

Mark and swchandler,

I'm going to repair a boom with this carbon sleeve material (below). I've used it before and it's easy to apply a couple/three layers at once. You can pull it like the old 'chinese' finger cuffs, and then bag it or use heat shrink tubing. If you wet it out right and remove some of the excess resin, the heat shrink tubing will actually give you a pretty decent finish, but you must start the heat gun in the middle and work to the ends. The electrical tape takes less skill but leaves a rougher finish.

Slightly taper the ends of the boom arms and overlap the braid onto those arms. The connection to the boom arms will be the weak link. If you have access to a lathe, you can use short pieces of pre-made carbon tubes inserted into the ends of the boom arms to bridge the repair from the inside. Carbon tubes available at same link below.

Boom repairs are always done at risk, of course. YMMV.

http://www.acpsales.com/Carbon-Fiber-Braided-Sleeves.html

Brian
www.miwindsurfing.com
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mark



Joined: 10 Apr 2000
Posts: 112

PostPosted: Mon Dec 10, 2012 9:46 pm    Post subject: Reply with quote

bsangeor,

Thanks for the information. According to the company web site they are in Livermore,CA. I live in the SF bay area so I will have to check them out on one of my windsurfing trips to the Delta. They also have good prices on resin.

Also I noticed that you are a Michigan windsurfer. I grew up sailing and learned to windsurf at Crescent Sail Yacht Club on Lake Saint Claire. Some of the very first carbon fiber windsurf masts were built in my garage in 1980 using a pressure molding process developed by a friend of mine.

At a cloth weight of over 8 oz it wouldn't take too many layers to build a front end similar to what I described previously. I think you could use the same process that I described earlier to make and bond a front end in one operation. You could cantilever the booms further over the edge of the table and have the extra dry layers stacked up on one arm and the shrink tube on the other. The layers could be wet out one at a time and the next dry layer slid over the top and wetted out. It may be a bit tough to pull the shrink tube over the curved front part but you could always resort back to the electrical tape approach. The shrink tube should work fine for your tube repair where the tube is relatively straight.

Thanks again for the information. I will check them out.

Mark
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Brian_S



Joined: 11 Jun 2005
Posts: 149
Location: SE Michigan

PostPosted: Tue Dec 11, 2012 9:23 pm    Post subject: Reply with quote

Mark,
My boom broke right at the rear harness line, during a stupendous catapult when my fin ran aground on a sandbar. The broken rib healed without any carbon fiber or epoxy, but the boom will require additional help.
I turned a piece of carbon tubing that will fit snugly inside the broken section. I will epoxy that in place and let it cure before I add the carbon sock to the outside of the tube. I've done this before, and it will be as strong as the original tube (or stronger).
You're exactly right about the process. You stack the dry layers of carbon sock and heat shrink on the boom next to the area being repaired. I make the first layer of sock shorter than the next layer so that the additional layers overlap more of the boom. You can pull the sock with your fingers to stretch and tighten the layers and remove most of the resin. You can even zip tie them to hold them in place until the heat shrink is in place. You can get the heat shrink anywhere but Soller Composites even sells a 'special' stuff for this purpose.
Brian
(Yeah, I'm in MI. Didn't know anything about the carbon mast production in MI. PM me with your story.)
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U2U2U2



Joined: 06 Jul 2001
Posts: 3077
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Thu Dec 13, 2012 10:10 am    Post subject: Reply with quote

quads have short fins, able to avoid sandbars

can then spend more time making fins


want to see the boom in April Wink

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