Wind Generator...Shattered Blades

[artemis07]

Has anybody experienced a complete failure of the blades on a wind generator? During the "Vliho micro-burst" in September all the blades on our wind generator shattered. The outer third of each blade disintegrated. We do not know how it was caused because my wife and I were too busy hanging on!

We think it was due to the speed (force) of the wind (100knots), but the manufactures say that is impossible. Other causes could have been contact with the water or flying debris. Water contact is unlikely since that would have destroyed the hub as well, flying debris seems unlikely as well. Each blade showed the same damage with no scratches or marks.
I suspect a complete blade failure. The manufactures say that is impossible, a very arrogant comment in my opinion. They say the blades must have hit the pole (the pole is their product!), the pole shows no evidence of being struck!

Incidentally, the shards tore through the fabric of our dinghy. We were thankful it wasn't our skin. Be warned, high winds and propellers don't mix!

 

[NornaBiron]

sounds dodgy, which wind generator?

 

[Sandyman]

sounds dodgy, which wind generator?

..................and what kind of blades ?

 

[Cloven]

Sorry to hear about your damage.

I have a Aero4gen and that withstood very strong winds when we had the boat on the West Coast of Scotland where winds in the winter regularly reach storm force. Now in France, it also suffered no damage in the big storm last year that severely damaged Les Sables & La Rochelle. OK, we were not in the thick of it but pretty close by. Unit is 10 years old and has only been off the boat for one winter when I was replacing the bearings.

 

[artemis07]

Shattered Blades

The wind Generator is the Rutland 913. It is about 6 years old.

 

[Cloven]

The wind Generator is the Rutland 913. It is about 6 years old.

In our marina there several boast with both Aerogen & Rutland gennies (plus some others of course).I have noticed that the Rutland units spin in the lightest of breezes, long before the Aerogen even thinks of getting going. I have often wondered what would happen to them in very strong winds.

You have already suggested that it may be that with the sudden burst of intense wind, the blades simply spun too fast for the design of the unit. Also, am I right in thinking that the Rutland has a circular surround round the blades? If so, could something have briefly lodged in this slot and caused what appears to be the same damage to each of the blades? This is all supposition and you will probably never know.

I know the replacement Aerogen blades are not too expensive and easy to fit so hopefully the same will apply to your unit. Good luck.

 

[Happydaze]

On a dinghy trip around Vliho the following morning looking for missing gear, we noticed the majority of wind generators had broken or missing blades and at least one had the hub missing. I suspect it was the excessive wind that caused the damage because the generators mounted on mizzen masts were unlikely to have been hit by deck gear and biminis being blown away. It wasn't your average afternoon breeze was it!

 

[silver-fox]

The manufactures say that is impossible, a very arrogant comment in my opinion. They say the blades must have hit the pole (the pole is their product!), the pole shows no evidence of being struck!


The wind Generator is the Rutland 913. It is about 6 years old.

Just for the sake of balance.....

I bought a Rutland 913, a couple of solar panels and voltage regulators from Marlec about 4 years ago and have found their after sales service and support to be admirable - one of my favourite companies in this respect.

I would give them 10/10 for service, technical knowledge, patience etc

 

[catmandoo]

at those speeds if centrifugal force did not shatter the blades then perhaps fatigue caused by vibration at the tip due to uneven air flow across the blades at that speed which is obviously well over design .

If you got eddies at the tip then that would waggle each tip back and forward sideways and result in each blade breaking . . Did the failure at the break look like fatigue ?

 

[RogerG]

My Rutland 913 outputs through Marlecs HSRi controller which has a switch to put the tubine into idle mode which stops it overspeeding in high winds, although according to the Marlec website, the 913 is tested to 10 times the maximum designed rev speed, so should have been able to withstand the sort of wind speed you mentioned.

There is also no ring around the blades on the 913, only on the smaller model, so no chance of damage from that cause.

All I can think of is that one of the blades could have had impact damage or stress at some earlier time, that caused it to shatter in the high winds taking out the other blades.

Roger

 

[GrahamM376]

Some years ago, I supplied an Aerogen4 to a guy based in Holyhead. 3 years later, he complained that it was making a noise so I went to have a look. It was knackered! The shaft bearings were noisy and the swivel bearings were totally shot. Due to the short life and condition, he returned the unit to LVM and they didn't want to know - said it must have been in the water (at the top of a pole 10ft above waterline??) and should have been tied up in high winds.

What's the point of having one if it's supposed to be tied up in case there may be high winds whilst you're away?

 

[mandlmaunder]

Our KISS has a switch as do other makes of wind gen that can in the off position that reduces to almost no movement when not in use, in high winds the revs are extremely low with no power being generated but less chance of damage when left unattended for a period of time.

No help this time but maybe something to think about when purchasing your new or replacement wind gen.

The Superwind is from what I have seen about the best on the market(with a price tag to match) and has self feathering blades so no need to turn it off or remove the blades in a forecast big blow, although I'm not sure I would leave it up in really strong storm force winds myself.

Mark

 

[RogerG]

If I am away from my boat for any length of time, I would expect the batteries to reach a full charge fairly quickly. Certainly with the 913 and controller in a high wind, once voltage nears full charge in the batteries, the controller will govern the speed of the turbine. I often notice mine dropping right down as the wind gets stronger and battery voltage rises.

I should add that I also have solar aswell, so my batteries charge pretty quickly if I am not using power.

Roger

 

[Csail]

Might be a good idea for the makers to come up with a gadged that puts a brake on when wind exceeds say 80mph? Our aero4gen has been fine for 10 yrs exept once losing a blade in very strong winds and mizzen topping lift came loose and hit it.

 

[Tradewinds]

Might be a good idea for the makers to come up with a gadged that puts a brake on when wind exceeds say 80mph? Our aero4gen has been fine for 10 yrs exept once losing a blade in very strong winds and mizzen topping lift came loose and hit it.

When I bought my boat back in '92 it had a Hamilton Ferris (USA) 2-bladed wind gennie mounted on the mizzen.

It had a set of bicycle brakes mounted on the hub which was used to stop it spinning. You applied these as & when using a long cord which was cleated off.

In very high winds the pressure on the blades would overcome the brake pads & it would start spinning - but not as fast due to the resistance of the pads.

 

[Scotty_Tradewind]

Sorry to hear of your problem.

If you had the regulator working correctly it should have 'idled' the generator as already mentioned.

I suspect that rotating at over design speed has set up a resonance/fluttering in the blade tips that they couldn't cope with for long.
Have they quoted for a set of new blades?

In some wind generators other than Rutland/Marlec, this resonance/fluttering of the blade ends causes extra noise even at design speeds and some replacement blades have been designed to stop that.

 

[jimbaerselman]

Agree with Scotty. Probably aero-elastic flutter. Its potential is when the aerodynamic centre of force on the blade (usually about a third from the leading edge) is in front of the torsional axis (usually around the centre of a symmetrical blade). With typical blade stiffness, and moderate wind speeds, there's no problem. But forces on the blades increase with the square of it's rotational speed, so at a certain rpm, the blade is going to start flexing and twisting.

Two things may then happen. It may spring back, and set up a vibration; at some speed this vibration may be in tune with the natural vibration of the blade - then the vibration may increase until the blade breaks. Alternatively, it may just continue diverging til it busts.

A ring connecting the blade tips to prevent them from twisting is one way to postpone the effect. Or stiffer blades. Best is blade design which moves the torsional axis forward - thicker leading edge, thinner trailing edge.

For a slow motion, much larger scale, and very dramatic illustration of the effect, see http://www.youtube.com/watch?v=3mclp9QmCGs

 

[RogerG]

With many thousands of the Rutland 913s having been used by yachtsmen all over the world for many years, I'm quite certain that any problem with the blades at high wind speeds would have come to light a long time ago. Marlec already state on their website that the blades are tested up to 10x the design max speed, so overspeeding and flexing seems unlikely.

As the OP has said that he has been using the generator for some years, I think it more likely that there was already some slight damage to a blade. Even a quite insignificant chip or scrape could make a big balance difference at unusually high wind speed. That could then well lead to the sort of high speed flexing described.

Also replacing the bearings means removing the blades to get the hub apart, so one blade may have been undertightened or not fully snapped into position. Unfortunately it's all speculation and we will never know what actually caused it.

Roger

 

[CharlesSwallow]

Two boats limped back to Gouvia after Vlikho with shattered wind genny blades. Both were those with the black triangular yoke.

Chas

 

[CharlesSwallow]

Some years ago, I supplied an Aerogen4 to a guy based in Holyhead. 3 years later, he complained that it was making a noise so I went to have a look. It was knackered! The shaft bearings were noisy and the swivel bearings were totally shot. Due to the short life and condition, he returned the unit to LVM and they didn't want to know - said it must have been in the water (at the top of a pole 10ft above waterline??) and should have been tied up in high winds.

What's the point of having one if it's supposed to be tied up in case there may be high winds whilst you're away?

I had a quite different experience from LVM. They took my ancient Aerogen3 (now called an Aerogen6) and re-furbished it entirely FOC. The bearings were OK after ten years of service in Poole harbour on a swinging mooring. It had a detached wire from a slip ring. I passed it on to the people who now own that boat and as far as I know, it is still doing good service on a french lake.

Chas