Sticky Weekend 2011

[JimC]

there is actually a picture of Atums shroud point being bound on with something, but I am really not sure what this something is.

Unidirectional carbon fibre. Can't find a photo, but its a carbon "cloth" which isn't actually a cloth put just filaments all run parallell to each other.

Basically you cut strips the appropriate length, wet them out with epoxy and wrap them round ring and tube. It seems pretty crude at first but works well. The tricky part is working out how much to put on! You could think of it as lashing the ring on to the spar with carbon fibres...

[Will_Lee]

Hi Ben,

Are you in SW London? This is a job much better done with help. It's not a big job but it is rather important. I would also like to see the failure.

The ring is a seasure one I think. You want a small overall diameter and a big rod thickness. I think it was 20mm od and 4mm rod. Measure the other one.

The ring was bogged on to the rack, and then in a single mix more bog is put over so there are minimal/no hollows. Then individual strands from carbon cloth are wound round and round, having been wet out already. It is not that important to put on loads of fibres because they are very strong, but it is important that they are spread out as they go round the tube. The other thing that is important is that the strength in the art which goes through the rig is good right up to the edge of the strands. If it tapers down then slight flex in the rig can cause the carbon to break one strand at a time.

The individual strands are called 'tow', pronounced "tau" or "toe" variously.

People do use strips of uni, but we used tow. With regard to how much to put on, in section carbon is stronger than steel (which is what the shroud is made from ), so as long as there is more than that in cross section, (taking into account mechanical disadvantages etc), then you'll be fine.

I think we used huge tow from a roll of 'mega-weave' which is quite good for making formula 1 cars, but is too heavy for making cherubs from. There is probably some still around. It was a gift to the class from a formula 1 team and has been used for all kings of funny jobs, like rudder stocks, shroud points, fronting plates, etc.

We can get together to fix this at some point.

[roland_trim]

I am plannig a mass purchase from Wiz. If anyone wants small qunaitites of resin,fibres etc it may be worth asking me to decant some (at cost)...

For those wanting to make rudders/poles/booms this is almost certainly the cheapest way of getting the materials.


I can happily post or bring  some tow - although not sure if I have any of the mega I have a load of slightly smaller diameters (or you can peel some from a sheet of uni and use in the way Will describes). PM an address?

[BenR]

Thanks guys, I am currently in west London but the boat is based in Hampshire at my parents due to not having anywhere to store it yet. It would be great to get some assistance on fixing this but I am not sure when I am going to have time. I will get back to you when I have a better idea.
In the mean time I will order a new loop. What sort of epoxy should I use? I have some sp systems stuff but I would have to check.

[phil_kirk]

When i have attached rings and shackles to things I have used strips of uni as it is a bit quicker and a bit easier to handle. The ring for the kicker on my boom is held on with 3 strips of uni each about a cm wide.

What I have found is that once you have wound all the fibres on round the rack and through the ring as a lashing it helps if you wind some fibres round the lashing between the rack and the ring.  This just holds everything together and appears to stop the fibres pealing from the rack or the ring and thus avoiding chafing of the ring on the lashing.  As will says avoid any voids.

We all use an epoxy resin. SP is fine for smaller jobs such as this but tends to cure quite quickly.  For larger jobs we generally use a slower curing epoxy which delivers the highest mechanical strength. We then usually use this for every job because it is easier to have 1 type of resin.

The important thing is to follow the instructions. Resin is sensitive to temperature, moisture and the ratio of resin to hardener.  The SICOMIN 5550 is a general purpose epoxy and is a bit more temperature tollerant.  The Sicomin 8200 gives higher strength and is easier to use on on larger laminating jobs.  This can be post cured to achive maximum strength. The sicomin resins can be purchased from MCM in bristol.  prices get cheaper the more you buy so I would ask born slippy for a bit of his.

[BenR]

So to summarise the fixing job in newbie terms:
I need to:

• take the old shroud point off
• sand down to the tube
• mix up some filler and epoxy
• stick the new ring to the tube with the mixture
• while it is wet, wind round some 12k tow (or similar) until the cross section of tow is more than that of the steel it is holding
• wet the area thoroughly with more epoxy
• keep the temperature correct while curing (will a beer making element do?)
• have a cup of tea or 2
• sand and fare it
• laquer it (optional i'm sure)
• rig
• sail

I will pm Born Slippy about carbon bits. I need to get a move on with this fix before it gets too cold and also the bonfire night blast sounds like fun 

[roland_trim]

Sounds about right.

As a rough guide the resin we use will set if kept above the temperature you can survive in Shorts and a jumper. But it really is happier if it is hotter (hence BMG use a tea urn and central heating pump).

For the shroud point I'd recommend placing a plastic sheet over the finished job and placing a hairdryer or better still an oil filled electric rad in the bottom for the first couple of hours.

R

[Stuberry]

It can be difficult getting the ring to stay sanding up, the big doesn't hold it very well. I suggest tacking it on with a hot glue gun, then bogging it really well to give the carbon as smooth a path as possible with no voids behind or sharp corners.

[roland_trim]

I'm only too aware of Mr Tinner's previous ring problems.
 5 minute Epoxy and some firm clamping to tack the ring in can have very pleasurable results.

[phil_kirk]

The tow or uni fibres go on better if wet out before being applied.  with the latex gloves on it is easier to do this with a small bit of resin and  fingers.  The fibres will then stick together. Doing the fibres dry will be a night mare.

To squeeze it all together use a strip of cling film and wrap it tightly around the join. If you have some peal ply this is better.

[BenR]

Here is a pic of the damage. I have measured the other ring and it is a 5x30mm one. inspecting the break, it looks as if the weld in the ring did not penetrate to the middle of the metal. I assume that the excess capsizing and probably excess weight of myself, led to the failure.
In order to get the boat back on the water as quickly as possible, I am going to order a ring, and some tow and attempt a fix myself. You will all be able to mock my handiwork at the sticky weekend and I can put it right with some guidance then.

[Will_Lee]

Excellent breakage!

It looks like the carbon is fine (phew!). You might want to send a pic of the break and your analysis to Seasure as some feedback.

Here is my advice to save yourself some hassle.

1) Get the ring out somehow. If it will unthread all the better. If not, then cut down from the top to release it.
2) Sand down all around, but leave the impression of the bottom of the ring so the new ring can it in there and not fall out.
3) Also try to limit your sanding so there are no hollows when you put the new ring in.
4) Lots of tow/uni/both.
5) Go sailing.

[andy_paterson]

Interesting breakage indeed!
I use D-rings for this - the weld is then in the middle of the flat part, and the fibres cam spread out along the flat part, and also you can put more fibre towards the ends.
I would use carbon 'string' that makes up  maybe 1.5 x  the stainless ring diameter.
The flatness means that you can alternatively use strips of ud tape.

[BenR]

I have just checked and they are rated to 1600kg. It must have been stress over the years.
I will see what seasure have to say about it.
The D rings look like they might be a bit easier to hold on straight but I have just bought a circular one so I'll have to make do.

[Phil Alderson]

I started off using D rings but found that they deformed at the top under rig loads. I then started using Triangular rings, which seem more solid, and you can use Uni tape.

The thing about tying rings on is that the load transfer area from the ring to the carbon is small so you need layers where the ring is but can do with less around the tube.

I always put short layers through the ring first and then tie this load transfer patch down to the tube with longer strips that go around the tube.