Broken beams of DF920

[a.coppoolse]

This is a small report of what happened with my Dragonfly920 at 3 october 2009.

The accident happened at the IJsselmeer, SW 5-6 moderate waves, close to the shore, 4 miles north of enkhuizen.

Boat-situation before the accident:
waterstays in place, swing-lines were fitted and locked, aluminium blocking bar was in place and locked with pin, the lee-ward backstay was also tightened a bit.
This is the normal situation when you sail.

Within a few seconds the accident happened. loud cracking of beams and the boat was lying at 80 degrees in the water.

At 18 nov mr.J.Quorning was at location to inspect the boat.

First analysis :
- The forward rotation point has metal what was bended upwards.
- The blocking bar (alu) is severly bended and did broke off from the beam and pin. The pin itself is still in place.
- Inside the backwards beam the block connecting the swingwing-line and the wire to the net is bended open (broke).
It was also mounted 180 degrees. It is not a symmetric block and it has a strong side and a weaker(?) side. This was mounted not correctly.
Remark: If you see this block the first time you migth not probably notice this. Im my case, I never had a look at it, it was already in place, done by the prevoius owner, who sailed with it.

Second analysis:
- The braking of the block inside the backwards beam caused the trampoline tension (with its wires)to drop.
- Then the full force came at the blocking bar. This started to bend and finally broke out at the pin-hole and attachment of the beam.
- As soon as the bending of the blocking bar started the front beam (and the whole float) will have moved backwards. This caused release of tension of the waterstay. After this the bending up of the beam started and the breaking of the beam followed. Front beam first and backward beam second.

Root-causes:
1 So the root cause is the failure (braking) of the block inside the backwards beam.
This can be by wrong mounting or by loss of a lock ring or ..?
2 The blocking bar did not function as a backup system.
Mr. Quorning assumes the following:
This might be caused by the previous accidents what happened to this boat. In 2008 in a harbor the front beam hit a pillar and was replaced.
The previous owner had also hit a buoy at sea, after which also a new front beam was installed. These 2 previous hits might have weakened the backward beam at the connecting point of the blocking bar. Causing it to brake through the beam when the full force came on it.

My advice to all Dragonfly owners (and what I will do):
1 Install extra safety wires from the front of the boat to each beam-side.
As is nowadays done on the DF920 extremes.
If these would have been on my boat this accident would not have happened.!
2 Check the blocks inside the backward beams.
3 Replace the aluminium blocking bar if it has oval openings at the lock
position.

Anyway to my great luck I was rescued within 5 minutes after the accident. I only had one wet feet, Nobody was hurt.
Basicly the main hull has hardly any damage, apart from the the electronics which need a refit. Some small polyester repair to the float are needed. And of course two new beams. The mast is rather intact.

This a story what seems to be a reasonable explanation of the accident to me.
From analys point it is difficult to say what happened first and what happened as a chain reaction.

Mr. Quorning said that he himself will come with a statement of the accident. Not necessary on this web-site.

If someone has another analysis of the accident, feel free to send it, but avoid any gossip.








[/b]

[Mika Harju]

Thank you VERY much for this detailed report.

[lercherlsepp]

As a owner of a DF800SW I am a bit worried about this analysis.

Knows anyone the correct mounting of the inner block in the backward beam? I am afraid, nobody does it. Can Quorning give us a detailed description of this important item as a extension of the boatmanual? If possible with fotos.

Is it useful to replace the aluminium-blockbar by a one made of stronger stainless steel?

Should every DF have safetywires at the frontbeams and, if so, in which dimension.

Hope, that Jens give us some advices about that here in that forum.

[Mika Harju]

As a owner of a DF800SW I am a bit worried about this analysis.

Knows anyone the correct mounting of the inner block in the backward beam? I am afraid, nobody does it. Can Quorning give us a detailed description of this important item as a extension of the boatmanual? If possible with fotos.

Is it useful to replace the aluminium-blockbar by a one made of stronger stainless steel?

Should every DF have safetywires at the frontbeams and, if so, in which dimension.

Hope, that Jens give us some advices about that here in that forum.

Here is one simple solution for this problem. The basic idea should fit to all DFs with SwingWing system:
http://dragonfly-trimarans.org/phpBB/vi ... .php?t=296
It is simple to build and also a cheap solution.
Forces are smaller than those in original steel wires inside the rear aka. High quality 8mm Dyneema rope stands for 3800daN (about 3800kg). Of course the block system needs to be strong enough.

[Mal]

Yes, I would like to add my thanks to the owner of the 920 that capsized. Thanks for the information, and I'm sure we are all glad that you and your crew are all OK.

As other contributor stated, we look forward to clarification of what we need to do from Quornings.

I don't quite understand the orientation of the block in the rear beam bit, and note that the back-up tube seemed to break where the pin goes through it at the rear beam attachment. Maybe asking a lot of aluminium to take those sort of loads where already weakened by a couple of holes?

Regards all

Mal

[tpaliwoda]

I see this being the hot topic for the winter!
I really like the method on the 35's, where the cable goes from the bow to the outside pivot point on the amma's.
But let's see what Jen's comes up with ...... we have 5 months till sailing season starts again.
Ted

[jf.brodin]

Than you for this report; I soon have applied the mika haru' system, I think it is very good to prevent accidental folding.

[rudi]

Hello j.f.
Waht is "mika haru' system"
Maybe i woud like to shop your boat. Your change in the construction is important for me, please closer information.
regards Rudi

[jf.brodin]

mika harju's system is described here :
http://www.dragonfly-trimarans.org/phpB ... =1161#1161

[Ipe Piccardt Brouwer]

If I read the report correctly, it was not the aluminium tube that broke. The tube remained intact but it was pushed through the beam. In other words, the back wall of the beam caved in under the pressure of the safety strut. Maybe because of previous collisions, after which only the front beam was replaced.

[Mal]

Ipe;- Report says 'broke out at pinhole'. Suggests to me that aluminium tube failed at pin holes?

Mal

[Ipe Piccardt Brouwer]

Well, yes, you're right. But what to think of 'These 2 previous hits might have weakened the backward beam at the connecting point of the blocking bar. Causing it to brake through the beam when the full force came on it.' ?

Clarification needed!

[buckle.roger]

Hi Ipe
Thank you for posting your report, most helpfull, as I have said in other posts these are complicated boats that I think few of us fully understand.

Jens told me that there are two types of saftey tubes 2mm and 3mm wall thickness, I had the 3mm and was completly unhappy with it, after a 60 mile beat into 25 kns wind the holes were 20 mm long both ends, i have made stainless tubes.

I also have a simple saftey line similar to that shown in the thread but over the trampoline from the lifting point on the froward arm to the 'u' bolt at the end on the rear arm with a 2 to 1 block, as I fold every time I use the boat it is very simple to use, It actualy make opening up much easier, pull by hand on this line and wind the trampolin out haul as it goes slack, I only jam it of slack for normal use but can winch it in on the leward side in big seas.

I have just looked at the blocks in my arms, I can see no difference in the sides of them ? More information please, I have a 2000 number 55 920. BUT I may have a clue to your problem, both my arm blocks are rigged differently!!!!!! and one block is being forced open !
This is difficult to describe, there are 2 pullies in the end of the arms, one is horzontal and one veretical, The end of the outhaul line which is fastened to the block in the arm was on one side in the lower part of the vertical block and on the other side in the top.
with the I belive only by looking that the end of the outhaul be made fast to the block and then go to the lower side of the vertical turning block, This seems to me to give a good run for the rope. the side on my boat that had this line going to the top of the vertical block has opened out the sides of the block???????? So am I right in that the line from the block in the arms should first go out via the lower side of the vertical block?

Good and SAFE sailing

[Steve B.]

The discussion of internal blocks for trampoline tension and unfolding the boat is an important one. I for one, would like to see pictures of what people have found. What has been discussed is disconcerting to say the least.

[Bo Wetzel]

Please find below the report/statement (in .pdf format) issued by Jens Quorning of Quorning Boats, Denmark.

Accident Investigation of DF920-77

[buckle.roger]

Thank you bo and Jens for this prompt report , it is most encourageing and as was to be expected no signs of design problems.

but the correct rigging for this internal arm block is not described.
As in my last post, one arm block in my 920 is being forced open I think by the outhaul line to the becket going into the arm via the top of the vertical block in the arm, this twists the block , It would be nice fro the correct rigging to be known so owners can check for the correct fitting in all respects of this block

[buckle.roger]

I was dumped into the water yesterday because my trampolin boke free when I was standing on it!! On inspection the out haul line had just come un done???? > so While I am looking I have checked the block arrangement as per Jens report, it is simple ( if all are the same as my boat 920 number 55 year 2000) the 6 and 8 mm pins are not easy to check BUT the side plates in the block are much wider at one end, sort of pear shape, the 6mm pin were the outhaul should be fastened is at the narrow end of the block so it is very easy to check without measureing pins.
I also rigged the block with the outhaul first from the top of the vertical turning block in the hinge end of the arm and then from the bottom, From my observations it is MOST important for the outhaul line from the block becket to first go to the low side of the vertical block. When rigged to the top it puts the block out of line and the rope around the pully is pulling at a angle. This has opened, but not broken one of my blocks.
These are only my observations, it would be very nice for Jens to confirm or otherwise my findings please, Also what type of knot is best for the outhaul line to the becket please?
As I sail all year round here in Spain I woiuld be grateful for the detailed answers please

I have NO problems with the design of the boat it is just the most fun of any boat I have had ( 11 in all) but when a boat has had a few owners it is very difficult to know what is right or wrong and my one critisism would be the very poor hand book, Theses issues should be covered in detail in the hand book

[Mal]

I agree with Buckle Roger and others;- a drawing from the factory making clear the rigging of the block inside the rear beam is essential for safety, please. Verbal descriptions are not really working for me.

Secondly, I would like to add to my 920, as suggested in Jens' report, the back-up line rigged from bow to ends of front beam, as per current models. What fitting is required at the bow, and where is it positioned? How is the line or cable attached at the end of the beam? I assume that it is permanently fixed to the bow fitting, but has some kind of snap arrangement for easy attachment and removal at the end of the front beam? Again, factory reply would be nice, but contribution of owners also much appreciated.

[Mika Harju]

Thank you bo and Jens for this prompt report , it is most encourageing and as was to be expected no signs of design problems.

but the correct rigging for this internal arm block is not described.
As in my last post, one arm block in my 920 is being forced open I think by the outhaul line to the becket going into the arm via the top of the vertical block in the arm, this twists the block , It would be nice fro the correct rigging to be known so owners can check for the correct fitting in all respects of this block

I checked the folding system of my DF1000. The block is bigger, but otherwise the system should be similar to DF920 and DF800.
Attached you will find a technical drawing of the system rigging and forces. This explains why the block needs to be installed in right way.

Please click on any of the photos to see them enlarged!

[jf.brodin]

thank you, Mika, for these very good design and photo!

[Double Horizon]

Thank you Mika. Very helpful information.

[tpaliwoda]

Mika,
Nice diagram and picture.
That reminds me of my days in Physics class!
Thanks
Ted

[Bo Wetzel]

Here is a diagram Jens Quorning has sent me showing the swing wing setup for the DF920 Cruising and Racing.
Apparently it's different for the Touring and the Extreme. (Sorry, he didn't sent me images for those.)
Please click on the image to see it enlarged!

[Andrew H]

Above correspondence invaluable and thanks to contributors. I for one with an older boat am going to feel happier with that extra safety wire. As an alternative to "Mika Haru", are there any Extreme owners tuned in that can tell us "cruising owners" please the spec of wires factory fitted on the "extreme" and whether the wires are attatched to the Aka with a simple snap shakle ie relatively slack or made tight using, for example, a Highfield lever as supplied by Seasure. (The latter are pretty expensive and used for inner stays for storm jibs but the only way to put a wire under tension. I did see such an arrangement on an extreme a couple of years ago but do not know if this was factory fitted or an owners mod).Anyone got an answer?

[Slowhand]

I know there is one who knows for sure - Jens Quorning.
8th of december I send him a mail, asking about details on the block in the aft beam and on establishing a safety wire. How to fortify the eye bolt at the bow, what kind of snapshackle to be recommended and dimensions on the wire/dyneema.
Unfortunately I got no answer and can't pass any information on this issue. Deeply frustrating. To me it seems as a very special kind of following up upon their own recommandations.
Quornings communication policy for sure is unique.

[Double Horizon]

Above correspondence invaluable and thanks to contributors. I for one with an older boat am going to feel happier with that extra safety wire. As an alternative to "Mika Haru", are there any Extreme owners tuned in that can tell us "cruising owners" please the spec of wires factory fitted on the "extreme" and whether the wires are attatched to the Aka with a simple snap shakle ie relatively slack or made tight using, for example, a Highfield lever as supplied by Seasure. (The latter are pretty expensive and used for inner stays for storm jibs but the only way to put a wire under tension. I did see such an arrangement on an extreme a couple of years ago but do not know if this was factory fitted or an owners mod).Anyone got an answer?

Of course the following is "handyman engineering" and not blessed by Quorning, but based on experience with these boats these are my thoughts:

First, by adding a bow stay you are adding yet another level of safety. If you add it you are likely to use it, but don't forget inspection and maintenance on all the parts.

6mm 7x19 should work, considering they used 6mm wire on the forward stays of the last 1000 that Quorning built, and they use 6mm 7x19 on the wire securing the nets. (If I was going to replace my forward bow stays today I would seriously consider using Dyneema or Spectra with lashings for fine adjustment.) The stays don't need to be tight (no need for a Highfield lever) but they should fit exactly to prevent further movement in event the primary folding controls let go. A standard turnbuckle for fine adjustment and a standard snap shackle or pelican hook will work well.

The beam ends (near the ama pivot bolts) are solid fiberglass and you should have adequate strength to mount a forward-facing U-bolt with a steel or strong aluminum backing plate, if you don't already have them from the factory. (I think they all come that way for using a mooring bridle). The inspection ports will give you working access.

As for the forward mount, you need a strong location to mount an eye bolt (I would use minimum 10mm hardware) or a U-bolt. The 920 has a large aluminum backing block mounted inside the GRP behind the bow anchor cleat. Careful examination would reveal whether you can put your attachment bolt through that existing backing block without interfering with the cleat. If not, you should mount a substantial backing block further forward and reinforce the fiberglass from the inside of the bow locker, grinding out foam coring replacing with solid GRP layup in the area behind the mounting bolt. (I would not mount it in a foam-cored material or even solid fiberglass unless it is fairly thick).

When you are anchored or docked you won't need the backup bow stay, so the easy way out for the bow attachment would be to use the anchor cleat, and rig a removable stay from the beam end to a loop of 8mm Amsteel or Dyneema that is spliced to the bow cleat. If you do use synthetic line, don't forget to replace it every 4 or 5 years due to UV exposure.

[Mal]

Diagram from Quornings as posted by Bo is taken from Owners Manual. It really doesn't show the block threading in sufficient detail for such an important safety matter. Any chance of Quornings taking half an hour or so to do a decent diagram for us owners, please? (The drawings probably already exist, anyway). Come on, this isn't detailing the fixing of a bunk or something, but the main system that keeps the boat the right way up! Anything more important?

Also, printed on that drawing is shown 10mm Dyneema for the main winched line, but someone has scribbled in 8mm. Which is it to be?

Contributions of users and their suggestions re forward safety wires much appreciated, but it would only take a few minutes of Quornings' time to stick a few of their factory drawings and specifications on this site so that we can do a proper job.

Come on Quornings;- you build quality exciting boats, yet seem to treat your customers/boat owners almost with contempt. Happy owners go on to buy more Dragonflys!

[Bo Wetzel]

Mal you're absolutely right. It's the page from the manual which I've received from Jens after asking him for detailed drawings of the block fitting etc concerning the problems in this thread.
Since the beginning of this forum, many sailing seasons ago, I've begged Jens to contribute to important issues in this forum. Every time I get the same answer. He does not want to get involved in this forum.
I've tried on many occasion to explain to him that one answer in the forum avoids having to answer the same question over and over again to customers who contact the shipyard. He doesn't see it the same way. His latest reply to one of my requests was, if people really want to know something they will find him.

Maybe, if every concerned owner contacts him with the same question at the same time, maybe, just maybe he will get the point and see the benefit of contributing to the DF User Forum.

So, anybody out their who wants to give us the first question to ask Jens? And we all could send it to him.

P.S. One reason, why Jens has refused me the permission to publish current boat owner manuals in this forum is that he fears "industrial espionage".

P.P.S. However, I'm grateful to Jens for sponsoring this forum.

A happy festive season to all and good sailing in 2010!

[Mal]

Bo;- thanks for your post.

There are 3 questions that I would like answered;- two in my last post;-
1. Decent diagram of rear beam block line threading
2. Should the winching line by 10mm or 8mm
3. A previous series of unresolved postings about correct method of tensioning water stays on 920;- lots of different ideas, but Quornings should be able to give us a definitive method. An in water and out of water method would be nice, but anything would be better than our current gueswork.

Anyone agree?

Mal

[a.coppoolse]

To all who had quastion about the mounting of the block:

Enclosed you will see 1 photo of the block bended open after the accident
with my DF920.
The block is asymmetric and the rope was mounted at the wrong side.
(something I didnot know).
In the sketch I made you can see the correct way of mounting.
The wire is then connected to the strongest part and the rope with have more space to run through.

Of course a solution to avoid this problem is to use a symmetrical block of the right strength and enough space for the rope.

Please click on any of the photos to see them enlarged!

[jf.brodin]

curious!
it seems not to be the block itself wich is broken, only the ring is gone, and then the block opened?

[Double Horizon]

curious!
it seems not to be the block itself wich is broken, only the ring is gone, and then the block opened?

Interesting. Was there a ring there originally?

I have seen other situations where a ring snagged on a rope and was pulled open, then it could come out by itself if turned from vibration or handling.

For that reason I prefer cotter pins to rings. It's unlikely a properly bent cotter pin would straighten enough to come out on its own, but for a ring to come out it just has to be deformed enough to create a gap in the overlapped portions.

If you have retaining rings holding the clevis pins on your nets (including the aft outboard corner block) they should be replaced by cotter pins, in my opinion. This also applies to the lower connection of the top shrouds (stays) which have sheets running past.

[Steve B.]

curious!
it seems not to be the block itself wich is broken, only the ring is gone, and then the block opened?

When you analyze the loads on the block it becomes clear that when properly oriented, the load on the wire end equals the total load of the three "rope" ends. One entering the block, one exiting the other side of the block, and the terminated end on the (now bent) pin. The block was designed to provide load bearing with minimum weight when properly installed.

The block carrier is obviously meant to take the full load on the right side end, while distributing the load to the left side between the becket (failed pin) and both sides of the block.

Taken in that light, I suspect that the block is not at fault, nor did the ring fail. In fact, with the becket pin bent like it was, the retainer ring may very well have been cut or otherwise destroyed due to the outward forces of the carrier sides as the pin was bent. The remains of it may still be inside the aka.

The block was simply overloaded by improper installation by (who?)

IMHO, someone took a 50/50 guess at orientation and got it backwards.

Steve B.

[Mika Harju]

Steve B.[/quote]
I agree. Steve is right.

[Bo Wetzel]

To all owners:

Please check your block has been correctly installed!

[LouieNum]

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