Sailing sloop rig with spinnaker up, crew weight at 145 Kg’s and one on wire what breaks first?
After jibing re-setting the spinnaker and putting the crew out on wire the boat accelerates very quickly with the skipper trying to keep up. On top of that hit by a gust causing a bare away with the boat still accelerating and the spinnaker dumped we heard a loud crack then a tearing noise and no swimming. We had a quick look around and everything seemed fine, the rig was still up, all of the stay points were intact, the hulls were in good shape, rudders and boards were all there, so we continued sailing for the rest of the day. Once on the beach a closer inspection of the boat was carried out and still nothing was obvious. During our next pre race inspection in the shed at home we found a small crack in the top of the port rudder. On closer inspection the rudder had more than a couple of small cracks and the join in the head of the rudder had split and the foam inside was torn. We found our noise. We called Jim to get his opinion and he said he has seen it before on Tiapans. The loads on your rudders when the boats are traveling fast and you have to make large changes of direction can result in broken rudders. He said if your boat is well balanced you might not even know how much load you are putting on things. Next time you are sailing even without a spinnaker and you have to change direction while traveling fast, have a look at your rudders, it will surprise you how far they bend.
Our boat is now sporting a new set of Joey rudders and talking with Joey all the rudders he has and will build for us have the same layup as the Tiapans.
There is a picture of the incident located in the Photo Bucket 2007 Spin States pic 525. The rudder damage pic is attached.
Peter
Peter,
Were they new rudders ? If so is Jim going to replace them ?
It just doesn't seem right that rudders can be designed that fail under normal loading. <img src=
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Deflection testing on production samples should have demonstrated the strength.
Regards,
Peter
It's a pretty weird place to crack them on the very top...
How are they attached and held in place?
Peter, The rudders are three years old and in Jim defence the broken one was also a second. The Mossie rudders Jim has been making have been fine and I don't know of any of Jim’s mossie rudders that have broken in this way.
The problem faced by all boat builders and sailor alike is that light is fast and over building things makes them heavier. So we have a fine balance and in this case the thing that was out of balance is what we were doing, more sail area = more power = more speed = more pressure and the rudder gave up. This rudder is fixable but we chose to replace it instead. The new rudders have the stronger Taipan lay-up and that means my boat will be that bit heavier then my competitions so that puts me at a disadvantage (a couple of hundred grams).
The other contributing factor was the inexperience of the crew with the Kite, our centreboards were down and we should have eased the sheets a little earlier, who knows we are still learning.
The Kit will stay on my boat simply because it put a breath of fresh air into sailing a mossie for me.
Is there going to be sailing at Summers on Boxing day? we are planning to turn up with two sloop rig boats.
Peter
Gero
The attached photo will explain. This is the broken rudder in its locked down position.
Computor three, Peter zip
Ok this one has have the pic's
Hi Peter,
I asked Peter F on another thread about boxing day at Somers. He said he thought there should be 4 or 5 Mozzies out.
I am going over as there is nothing doing at McCrae that day.
See you there.
Cheers
Thanks Simon, See you there
Peter
How are they attached and held in place?
Hi Nick,
the head is actualy a fairly common place for moulded blades to fail from what I have seen. Cracking in the head has happened on some rudders from a few different builders on Mossies and Taipans that I have seen and heard of for many years. With both the older style rectangular rudders in alloy boxes and the newer shapes in carbon boxes and now alloy ones also.
My only guess is the way they are put together in the head, as splitting on the join is usualy the first sign. The ones I have seen appear to just be bogged together with no flange, so the glass just butt joins.
Simon/Peter,
Boxing day is a regatta/trophy race at Somers. Start time is 2:30 pm sharp.
If both of you turn up then there should be at least 8 Mozzies racing.
Sorry I won't be there. <img src=
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/> It would be good to see how you shape up against Brian Gristwood who has re-set the benchmark with a new Goodall mainsail this season.
Regards,
Peter
mmm, a quick sketch of an idealised shear force diagram indicates that the shear forces there are very big.
The only way to stop it is to increase the area connecting the two sides or add material across the area that has better shear properties than resin (ie. almost any resin with a reinforcement.)
peter / mossies at somers
Also Hoping to get over on boxing day make that 9 mozzies sailing
gordon (air Apparent)
Gordon,
Great to see you can make it too. <img src=
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/> It just makes me envious that I have to visit the outlaws <img src=
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/>. Forecast is for 15 knot afternoon sea breeze. Sounds just perfect.
Regards,
Peter