Epoxy and CSM

Laika:
1. If the voids are up to 4cm deep, surely the structural integrity is compromised? You're the man at the job, and should have a sense of this. What do you think?
2. If so, I'd fill, fair and then cover the whole area with a layer of epoxy cloth.
3. If the shapes are heavily compound, biaxial cloth is easiest to work. If not, there is a very good hybrid CSM/woven cloth which isn't too expensive and works well. The CSM is stitched to the woven layer, so no binder to worry about.
4. Epoxy, as said, would make for a lighter repair and goes further than polyester; it also sticks better (if you want to get technical poly only binds at the ends of the molecular chains; epoxy also binds in the middle.)
5. Don't use polythene as a finishing layer on polyester: the styrene makes it expand and wrinkle...and the wrinkles translate to the GRP. Use a proprietory peel layer instead. Or none at all: just fill and fair.
I realise some of this might stretch a limited budget, but I needn't tell you rudders are a bit vital. Good luck.

PS East Coast Fibreglass Supplies are where I usually get GRP gear in the UK. They're excellent. Google finds 'em.
 
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I'm not a professional, however i have a lot of experience in using epoxy with CSM, glass, kevlar and carbon. Projects include major hull and rig construction/conversion work to highly stressed twin trapeze skiffs (Cherubs/12s), and on my Sabre extensive structural repairs to both shroud points/bulkheads, my carbon fibre asymmetric pole, and extensive rudder surgery. Nothing has broken yet, and some of the rudder work is detailed here, have a poke round the Sabre forum for the rest of it. http://www.sabre27.org.uk/forum/topic.asp?TOPIC_ID=327

Firstly, I really wouldn't use polyester. In the grand scheme of things it would not be that much more to use epoxy,and lets be honest, it's a rudder for goodness sake. You can't even keep an eye on it to check that the repair is holding up. Use Epoxy...however whilst i agree that ECF are an excellent company and I buy all my kit from them, I did have a batch of dodgy "own brand" stuff that did not cure, even when mixed to the gram on digital scales. They swapped it for SP for me (great service) but lesson learned on trying to cut costs.

Secondly, I would'nt personally use CSM. Use glass cloth, but TWILL weave, not plain weave. This will go around very tight radii so your rudder really wont be a problem. Its just so much nicer to work with, stronger, and devoid of all binder. Its also a hell of a lot easier to wet out properly.

Thirdly, your rudder needs to be bone dry. I know you want to sail this year but seriously, consider dropping it and splitting it. Otherwise IMHO you are simply papering over the cracks. There could be all kinds of horrors going on inside it, and i would guarantee that the core will be a stinky sludge of broken down foam mush. If you are going as far as you have with the angle grinder, it's not much more of a job to do it right. A rudder failure on a yacht really does leave you pretty much out of options TBH unless you are very practised at rigging jury gear. If you do it now, you can get it dry, and also be able to epoxy in the yard in decent temperatures. As soon as the winter arrives, it becomes a whole lot harder.

Lastly, and I hate to say this but if you are new to composite engineering a yacht rudder is not really the thing to cut your teeth on. There's a lot to go wrong, compounded by the fact that you are talking about large areas, large volumes of mixed product, etc etc etc. I would almost guarantee you that you won't mix your first few batches of bog thick enough, and working on a vertical plane you will have issues with sag (another reason to drop it). Do some smaller projects first, get used to working with the resin, get someone who knows what they are doing to help, and then tackle the big stuff.

No doubt many will say I am being over cautious, and if this was even a non structural hole in your deck I'd say "get stuck in". But to me I think your rudder might have serious issues and you really dont want to be worrying about it on a lee shore at night.

Good luck!
 
Graham_Wright said:
It sounds like that rudder is full of water. Is it worth sucking it out with a (wet and dry) vacuum cleaner? You may be surprised how much appears (don't ask!).
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The spade rudder on my Vivacity ( years ago) had a water problem manifested in the shaft turning but the rudder blade not quite following it.
Splitting it open I found Mild steel tanks welded to the S/S shaft, and the welds were less than optimal after years of use.
appearenty subbing out bits like rudders was common practice , and the quality of workmanship suffered.

With water content like the OP has described that is likely to be the case on his, so splitting it and checking before he does all this work would be prudent.

Spoling the job for 2 weeks sailing seems pointless, go crew for somebody instead, get the rudder out and work on it in decent conditions.
 
JumbleDuck said:
Mind you, it's only a rudder skin, with very low stresses. I'd wodge in a bit of filler and stick a layer or two of cloth and epoxy on top to seal it.
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Iain C said:
your rudder needs to be bone dry.
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That about sums up the two sides to the argument.
If you just want to fill and fair, use polyester. Using epoxy without doing the whole rudder is pointless. Like sticking teak patches to rotten plywood would be.

If you want to do the job properly, take the ruder off and strip it. Dry it (weeks, not days). Then rebuild it using epoxy.
 
Lakesailor said:
take the ruder off and strip it. Dry it (weeks, not days). Then rebuild it using epoxy.
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If there are any osmosis products left in it, drying it isn't simple. These products are hygroscopic: they attract water. So just left to itself it'll never dry.
Instead, and paradoxically, it needs thorough washing and rinsing, then dry, then repeat, several times. As Lakey says, it takes a while.
 
That's about the size of it Lakey. TBH the OP shoukd have probably asked the question before wielding the angle grinder. The advice probably would have been "keep sailing, don't go out in a hoolie, trim the boat properly to minimise rudder load, haul out at the end of the season and drop the rudder whilst she's in the slings".

But with that looking like it does now I think the only option is do it properly. Does the OP have access to a warm garage or similar to do over the autumn? Part of the issue is its not a quick fix...when i rebuilt my rudder it was sometimes 45 mins of work, then come back to it tomorrow when that bit's gone off.
 
Ok, you her back in the water wet or not. This means any time and dosh spent will be lost when the proper repair is made.

A couple of points to note:
The ratio or resin to cloth for epoxy is one to one.
The ratio for standard poly resins and CSM is One CSM to Three of resin. This is because the CSM has a lot more voids between fibres as opposed to to the very small voids in a woven Cloth.

Using CSM with an epoxy will mean more resin and less strength in that layer. This method is used in some structured to provide a bit more flexibility, something you do not want.

Given your situation I would be looking very hard at simply filling the voids to within 5 mm of the level finish and glassing only the cover.

Micro-Fibres are a cheap and very very strong filler well suited to this temporary fix.

Just paint each area with epoxy prior to adding the mix.



By the way, the reason many foam and some ply rudders fail is because they do not use a hard filler (like Micro-fibres) between the tangs and the outer skin. A simple task when building and not expensive at all, but some manufacturers just don't know or don't give a stuff.


Good luck and fair winds. :)
 
Iain C said:
Does the OP have access to a warm garage or similar to do over the autumn? Part of the issue is its not a quick fix...when i rebuilt my rudder it was sometimes 45 mins of work, then come back to it tomorrow when that bit's gone off.
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Thanks for all the replies.

No: no shore base. And not only do I not want to face winter living on the hard, I may have to move the boat to London for work (I'm almost out of cash). I did get advice from the yard before starting on this (which prompted the question :-). I'm aware it's not going to end up perfectly dry. I have drilled a few holes in the bottom to drain water: it was drips for an hour or so rather than a gush (hmm..thereby creating another problem: still wondering how I'm going to fill those again..any ideas?). It's been out of the water since march with ground-out areas having been exposed for the last couple of months drying. Occasionally stood there with a heat gun but I reckon the sun has been more effective. I believe the steel is fine: the rudder was taken off, dried out and professionally rebuilt 3 years ago. Folks in the yard here are blaming the problem on too light a grade of expoxy filler having been used last time: it's mostly those areas I've ground out (as advised). I do have experience of laminating larger areas than these holes with csm and polyester on a vertical surface. I don't claim to be an expert but it turned out OK. Yes I may be delaying the problem but hopefully following a 9 month delay I can accumulate enough cash to pay for it to be done properly
 
Filling the drain holes ...... as they will probably still be dripping I'd use Sikaflex 295 or similar to caulk it. You can then glass over the top. You could also use an underwater setting epoxy putty ...... but they can have a problem actually sticking to the wet surface. If the holes are small enough just put self-tappers in them .....
 
The holes only dripped for a couple of hours and that was 2 months ago. seem dry now. problem is one went up quite a long way (~8cm?). They're about 6mm diameter. Didn't think of sikaflex (why 295 rather than 291?). My fallback was well-thickened epoxy but I was a bit concerned about leaving a little void at the top. Probably least of my worries.

FWIW, if anyone is else is wondering how to tell the difference between emulsion bound and powder bound CSM (with thanks here to AOC composites in manningtree who I tracked down as supplier to the supplier of what I have): Powder bound leaves a powdery residue when you rub it between your fingers, emulsion bound does not. 450gm mat is almost always emulsion bound. Powder bound is more commonly 300gm.
 
If that rudder was "professionally rebuilt" 3 years ago I would be questioning the quality of the work! Epoxy is waterproof with no filler additives, "too light a grade" is simply incorrect.

My bet is its full of water and is going from the inside out...
 
laika said:
The holes only dripped for a couple of hours and that was 2 months ago. seem dry now. problem is one went up quite a long way (~8cm?). They're about 6mm diameter. Didn't think of sikaflex (why 295 rather than 291?). My fallback was well-thickened epoxy but I was a bit concerned about leaving a little void at the top. Probably least of my worries.

FWIW, if anyone is else is wondering how to tell the difference between emulsion bound and powder bound CSM (with thanks here to AOC composites in manningtree who I tracked down as supplier to the supplier of what I have): Powder bound leaves a powdery residue when you rub it between your fingers, emulsion bound does not. 450gm mat is almost always emulsion bound. Powder bound is more commonly 300gm.
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Compressed air in at the top? I would like to remove all the moisture possible form inside. I reiterate - wet and dry vac sealed as well as possible. You may be amazed (and shocked),
 
Having acquired some powder bound csm (it says so on the label) I question the "rub" test I previously mentioned. Might work for someone cleverer than me, but frankly I can't see any apparent powder residue when rubbing it. The wet+dry vac idea sounds brilliant but don't have one. Guessing a dustbuster won't cut it. TBH most of the bits I ground are completely dry and very shallow (1cm or less). There's just one (the big one) that still worries me. Boatwright here says don't worry about it, just heat that area before the first coat of laminate so it goes off quickly to ensure good adhesion and seal in any moisture. As many of you have pointed out, this is probably not ideal, but it should tide me over for a while, and I'll haul the boat again before any big trip. I'll start following the locally advised method this afternoon, maybe leaving the big one for further consideration based on feedback here. I'm conscious that if I get into trouble, I can only really ask for help in the yard if I've followed their advice.

For plugging the drill holes, the guys here apparently have some kind of gloop (I will find out what) for syringing up. I have acquired an ominous looking syringe.
 
I once had a rudder that took water every year, (hair crack where tube entered at the top, almost impossible to seal permanently) I drilled two holes in the bottom and one in the top and left it to drain while ashore, plugged with bodyfiller (isopon) before launching but left a small depression and drilled again at the same place on each lift out. The problem with sealants arises if you need to drill out and seal again.
The eventual cure involved digging a hole under the boat while ashore, dropping the rudder right out, splitting, replacing most of the core foam and web connections to the tangs and gluing together (with epoxy resin and fillers)
 
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