Fibreglass repair in windvane water rudder

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The photos below show cracks in the water vane of a Navik windvane. What type of fibreglass repair should I be looking at to make this as strong as orginally? The longer crack goes about 3/4 of the way through, I thought this needs to be ground out in a V and filled?

The shorter crack from the forward end of the square hole goes all the way through - should this be enlarged before being repaired, or left as it is and filled?

navikcrack1.jpg
navikcrack2.jpg


As usual, thanks for everyone's help.

- W
 
Whats in the core?

Is it dry inside?

If its a hollow core (or foam) I'd say it needs mat to patch it... ...which I suspect will be a bugger to do.

If its solid core then I'd be tempted to try something like a biscuit joint epoxied in?
 
Depends what the core is but you could router a groove at right angles to the crack each side of the rudder & buy a carbon fibre arrow shaft. Cost circa £ 6-00 from a sports shop. Diam 6mm. Length about 900mm. They might have a reject one. You could cut it into 4 pieces & do 4 grooves say 150mm long. Then bed them in west epoxy with filler. Then get some glass mat about 200grm from a car spare shop - woven , not chop strand. & bind the whole section using west epoxy resin . How to do it will be on the internet. Smooth it off & you will have a strong joint. Apply the resin to the mat between 2 sheets of polythene & roll out the resin to ensure you do not get excessive resin before laying in place.
 
webcraft said:
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Wow DDB, sounds amazing but way beyond my skill set. AFAIK the blade is solid fibreglass, no core.

SS, what is a biscuit joint please?

- W
Click to expand...

What they are saying is that you can't just fill the gaps, but need to use some means of physically tying across the gaps. A biscuit is a flat plate, usually wood and you would machine a groove at 90 degrees to the splits and glue it in with epoxy. Then make good the gap. DDB's suggestion achieves a similar effect but is perhaps easier as you can route out grooves on the surface to take the round bits of carbon. Glue them in with epoxy and then make good.

If you don't do a physical tie the splits will only come back and grow.
 
It looks to me like the rudder has had excessive sideways load on the tip of it. So the cracks radiate from the square hole across the chord. As said you need more than just filler for the cracks if you are to have any confidence that the tip won't snap off. It needs some real reinforcement. I would suggest routing grooves at right angles to the cracks ie top to bottom in the area most stressed on both sides and laying in carbon fibre strands. ie pulled from cf cloth or perhaps even better kevlar strands. These should be saturated with epoxy to fill the routed grooves. Then fill the actual cracks fair off the whole thing and paint with 2 pack paint.
An alternative if you don't want to go to exotic fibres is to increase the thickness of the blade in a foil shape ie towards the front 1/3 on both sides with fibreglass cloth. perhaps adding 3mm thickness each side. The reinforcing needs to be from a bit above the pintle to about half way down to tip tapering less as you get near the tip. good luck olewill
 
If you want you can split the arrow shafts after you have cut them to length quite easily with a chisel so they become 3mm * 6mm so the grooves are smaller. They may split when you cut them ( use a fine tooth saw)That might be preferable. If you cannot beg steal or borrow a router you can cut the grooves with a cut off blade in an angle grinder. A grinding disc would give you a wider cut: with a lot of dust so make sure you have a proper face mask. Clamp a piece of wood to the oar as a guide or get someone to hold it or fix it with duct tape or double sided tape The grooves do not have to be exact you just have to clean them out well & use plenty of epoxy to soak in & make sure the carbon is well bonded to the blade. Smooth off the surface afterwards when set. What it looks like is not the issue , it is how strong that matters. You can always paint it
 
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Daydream believer said:
If you want you can split the arrow shafts after you have cut them to length quite easily with a chisel so they become 3mm * 6mm so the grooves are smaller. They may split when you cut them ( use a fine tooth saw)That might be preferable. If you cannot beg steal or borrow a router you can cut the grooves with a cut off blade in an angle grinder. A grinding disc would give you a wider cut: with a lot of dust so make sure you have a proper face mask. Clamp a piece of wood to the oar as a guide or get someone to hold it or fix it with duct tape or double sided tape The grooves do not have to be exact you just have to clean them out well & use plenty of epoxy to soak in & make sure the carbon is well bonded to the blade. Smooth off the surface afterwards when set. What it looks like is not the issue , it is how strong that matters. You can always paint it
Click to expand...

I like it!
Stu
 
Just for curiosity, but could it have been a large load by grounding? There seems to be a crack going 'upwards' from the Fwd side of the hole?
 
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It doesn't extend anywhere near far enough below the waterline to ground, more likely got a line caught round it or similar. I think it has been subject to a twisting force.

I get the idea of a 'biscuit' now and like the idea of the carbon fibre arrow shafts. Just need a router. Do I use just epoxy resin to bond the cf to the fibreglass? Any special things I should know when doing this?

- W
 
Wouldn't the carbon fibre arrow pieces be stressed in the wrong direction? I would guess they are designed to be strong longitudinally but not laterally - carbon fibre spinnaker poles break with lateral loads. I reckon a few wooden biscuits would be better.
 
PeteCooper said:
Wouldn't the carbon fibre arrow pieces be stressed in the wrong direction? I would guess they are designed to be strong longitudinally but not laterally - carbon fibre spinnaker poles break with lateral loads. I reckon a few wooden biscuits would be better.
Click to expand...

No, It is the same system one uses when making model aeroplane wings in EPS foam etc the carbon spars are laid just below the surface & bonded to the foam to act in tension. Bearing in mind how thin the wings are & that the carbon strips are often 1mm thick I think that several short pieces of shaft or 4mm solid rod ( as suggested in my last post) laid at right angles to the crack will be far better than pieces of wood. . They only need to overlap 75mm each side of the crack - 150 would be better though-& provided they are well bonded the strength is excellent. The other suggestion of kevlar threads ( another post) is good & would bond to the epoxy better but harder to obtain . Might be easier to install but not so strong I suspect
Wood would have to go right through the blade & have to fit better & would need to be thicker & need to sacrifice more of the original blade. I suspect that Webbie has limited tools available. Commercial biscuits- if used- would need a biscuit jointer & are limited in length
 
PeteCooper said:
Wouldn't the carbon fibre arrow pieces be stressed in the wrong direction? I would guess they are designed to be strong longitudinally but not laterally - carbon fibre spinnaker poles break with lateral loads. I reckon a few wooden biscuits would be better.
Click to expand...
They do but they bend a lot before they shatter... its going to be epoxied in place so it wont be able to bend to that extent that it will shatter.

The disadvantage of the biscuit it is a porous material. So if the gel cracks the biscuit may soak up water expand and make the whole joint weaker.

Although I suggested the biscuit - I prefer the suggested carbon rod. Not just because it is waterproof even when compromised, but also you can make it as long as you want (a biscuit it typically a couple of inches at most). You also don't have to cut all the way through to insert it so that feels good.
 
Carbon fibre is very stiff ie resistant to bending but is also quite strong compared to glass in tension. Kevlar is not stiff but very flexible but very strong in tension. So using kevlar would be like fitting side stays down each side hence long sections well stuck in with epoxy. Using carbon fibre gives you a bit of both effects of stiffness and "side stay" effect.
Only other point is that epoxy work should be in warm conditions certainly not less than 15 degrees but you could warm the job itself up. olewill
 
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My experience with GRP has been very limited. Let me try to summarise what folk are suggesting and ask a couple of questions:

~ Get some carbon fibre rod (say 4mm diameter)
~ Cut this into pieces say 15cm long
~ Use a router to cut slightly larger than 4mm grooves at right angles to the crack on each side, maybe 4 grooves
~ Mix epoxy resin to the normal proportions (ensuring ambient temp is >15C)
~ Pour epoxy into the grooves and lay carbon fibre rod in the 8 grooves (or do one side at a time?)
~ Leave to harden then sand/tidy up

Some questions:

a) I presume I also fill the crack itself with epoxy? Any special instructions here?

b) Do I do this for the small crack at the back of the square hole as well? I think I could only get one groove/rod each sidein here.

And - will this be as strong as the original if carried out as above?

Failing that, has anyone got a spare Navik paddle?

- W
 
I have repaired a performance dinghy rudder with similar cracks I used carbon fibre weave chopped up into long enough pieces to fill the cracked area which was opened to a deep vee using an oscillating saw .Make sure carbon wetted out well but not an excess of epoxy resin fill cracks proud sand off to flush use mask and goggles,then paint.The repair was done 5+years ago no problems regularly doing 10-12 knots.
 
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