Rudder surgery part 2

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Rudder surgery part 2

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Iain C
United Kingdom
181 Posts

Posted - 19/11/2011 : 19:11:32
Right then, I've got the rudder shaft back, all welded nicely with 316 grade tangs and s/s welds. Time to put it back together.

Paul advised on the dangers of crevice corrosion on the welds, so I polished them up a bit...

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I decided to strip the two sides of the rudder right back if possible. It would mean I could fair the repair around the "split" better, and also check for any evidence of osmosis(none found). I found a grinder with a 30 grit flexi disc got through the a/f and the 6 layers of VC Tar, anything else just clogged! Going up the grades and finishing with a DA sander I ended up with this...(ignore the prop, it's decking decoration!)


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The shaft was test fitted to the rudder. All seemed OK, however the tangs would have to be sat in some freshly mixed "bog" (colloidal silica/microfibres) so it was time to get the gooey stuff out...

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Here's the gooey stuff, courtesy of East Coast Fibreglass, highly recommended...

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The tangs will be glassed onto the stbd side of the rudder, but it was important to build up some generous fillets to avoid any sharp edges/tight radii. So here is the bog built up, and it will be sanded smooth when cured...

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Last job was to beef up the port side a bit. Compared to the stbd side, the laminate is quite thin, so here's 2 layers of glass cloth (not CSM) laminated in place prior to peel ply being added. You can just see one of the old test holes that had been drilled before. Ultimately, the whole rudder will end up with a layer of this on the outside too when re-assembled as well as the tape/biaxaial on the edges. I don't intend ever taking it apart again, and a bit more strength won't go amiss!


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Next job will be to glass the shaft in place...more soon!

Edited by - Iain C on 19/11/2011 19:16:21
ianfr
United Kingdom
104 Posts

Posted - 21/11/2011 : 09:44:24
Iain

Keep it coming! I am a week or two away from starting the same process so all your info is really useful. How much epoxy did you end up buying and is it going to be enough?

Regards

Ian

Kind Regards

Ian

Iain C
United Kingdom
181 Posts

Posted - 21/11/2011 : 22:00:23
Ian

I bought 3.5kg pack from East Coast Fibreglass but I've used a lot of it doing the bulkhead fillets (different job) so I've just ordered another pack online. I reckon 3.5kg should do it though.

Next installment will be glassing the shaft and tangs onto the rudder. Secret weapon about to come out...vacuum bagging!

ianfr
United Kingdom
104 Posts

Posted - 22/11/2011 : 06:15:29
Iain

Forgive my ignorance, but what is the ply peel actually do?

Thanks

Ian

Kind Regards

Ian

Iain C
United Kingdom
181 Posts

Posted - 22/11/2011 : 11:05:06
In a glass (or carbon, or Kevlar) laminate, there is an optimum ratio of resin to cloth. Excess resin actually weakens the laminate. If you laid up a laminate, let it dry (or nearly dry) and then add more cloth, the laminate will be weakened where a big dollop of resin exists between the layers of cloth.

You put peel ply on top of your laminate and it “sinks” down onto the cloth. When everything dries, you peel off the peel ply and all the resin that is above it, which is doing nothing apart from adding weakness and weight, is ripped off with it. You then have a very nice, flat, uniform and slightly scored surface to laminate on top of should you need to. Adding peel ply also makes it very easy to see any areas that are not sufficiently wet out…this is less of a problem with glass, but it’s quite difficult to see where carbon is, and isn’t, wet out…it tends to look the same in either case.

TBH in this case on the inside of the rudder the peel ply is overkill…it’s just habit really from skiff related boat building, but it does leave a nice uniform surface. However, it will be essential where I vacuum bag the rest of the rudder. I will do this in two places, one where the tangs are glassed in, to ensure that that laminate is well and truly stuck to the inside of the rudder, and also when I tape and sheathe the two halves back together again. The trailing edge is quite sharp and the laminate will need some “persuasion” to go around it properly.

If you ever use peel ply, when you remove it turn the lights out. You actually get a flash of light as the peel ply comes off and the molecular bonds are broken!

Sunfly
United Kingdom
51 Posts

Posted - 22/11/2011 : 11:26:46 Sunfly's Homepage Edit Reply Reply with Quote View user's IP address Delete Reply
Hi Iain

I'm intrigued by the peel ply, haven't come across that before. Can you use with polyester and epoxy resins? I was under the impression that it was a good idea to apply each laminate before the previous one had completely cured, so as to achieve a chemical bond, as opposed to simply adhering the laminates, could you clarify how this works with the peel ply?

Also interested by your reference to building skiffs - I'm something of an oarsman, in fact that's why I haven't done much sailing this year! Was that as a hobby or in a professionjal capacity?

Nothing - absolute nothing half so much worth doing as simply messing about in boats

http://sunflythesabre.wordpress.com

ianfr
United Kingdom
104 Posts

Posted - 22/11/2011 : 11:28:47
Crikey, I thought all you had to do was slop loads of epoxy and fabric on and let it harden

Seems to be a lot more complex than I imagined!!

Do you just lay the peel ply on, or roller it?

Thanks, this is REALLY useful.

Ian

Kind Regards

Ian

Iain C
United Kingdom
181 Posts

Posted - 22/11/2011 : 12:17:48
Sunfly-Yes, you can use peel ply with epoxy or polyester. However I’ve never used polyester for any kind of boat building project unless it was part of the launching trolley! You are quite right, you should ideally laminate the next layer before the existing one has fully cured. However if this is not possible, an epoxy surface that has gone off, and had the peel ply removed will have no amine blush, as well as a great mechanically prepared surface requiring no further preparation. As I mentioned, inside the rudder, the peel ply was more about making sure that everything was wet out properly (dry spots are very obvious through peel ply).

The skiffs I’ve been involved with are not rowing skiffs…they are sailing skiffs. Weight is critical on a dinghy, and excess resin will either add weight, or on a hull surface, add weight and needs much more sanding and fairing! I learnt about boatbuilding in the Cherub class, so it’s purely a hobby. I bought this old knacker for £300…



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…went on a pretty extensive rebuild, involving a whole new front end, foredeck, self tacking jib, bigger rig, new sails, twin wires, new rudder, racks etc etc



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…and ended up with this, which we won the 2006 12’ Skiff National Championships with. Sadly I’ve packed Cherubs in now (a bit too heavy really!) and I now sail a 49er. I sold the Cherub for £2k though so not a bad deal!



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Now back on topic...

Ianfr-You need to make sure that all the layers or glass, resin, and peel ply are as well consolidated (squished together) as possible. In practice, laying it on and using squeegees, brushes, or consolidating rollers will be fine. I’m only going to vac bag mine as I have access to a pump so it seems a shame not to…but in truth it’s probably overkill and not really required. But I want to ensure that any voids are 100% gone if possible.

Pics to follow when I get going on it...next week probably.

ianfr
United Kingdom
104 Posts

Posted - 22/11/2011 : 16:42:46
Iain

What mix did you use in the end for the "Bog" for the tangs to sit in?

Thanks

Ian

Kind Regards

Ian

Iain C
United Kingdom
181 Posts

Posted - 22/11/2011 : 17:16:37
Resin, mainly colloidal silica and some microfibres, to as thick a consistency as possible so it would not sag. The bog is deliberatly over the edges of the tangs, so I can sand down to the tang and get a totally smooth convex radius where tang meets bog, rather than there being any small step/concave area at the edge of the tang if any sag did occur overnight. I suspect it may need a second bit of bog applying anyway once I have sanded down the first lot to make a totally smooth area to glass over. A Dremmel will be handy when smoothing this lot out.

If it had been a dinghy there would have been a lot of glass bubble/microballons in there too to save weight but that's pretty academic on a Sabre rudder!
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